tag:theconversation.com,2011:/us/topics/blood-vessels-54402/articlesBlood vessels – The Conversation2023-08-28T12:00:44Ztag:theconversation.com,2011:article/2047262023-08-28T12:00:44Z2023-08-28T12:00:44ZWhy do fingers get wrinkly after a long bath or swim? A biomedical engineer explains<figure><img src="https://images.theconversation.com/files/539371/original/file-20230725-23-csjiht.jpg?ixlib=rb-1.1.0&rect=41%2C143%2C3700%2C2682&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Those puckered prints show up after a while in the water.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/human-hand-wrinkled-and-shriveled-due-to-the-long-royalty-free-image/1010765076?adppopup=true">MarijaRadovic/iStock via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<p><strong>Why do fingers and toes get wrinkly and change color after a dip in a pool or a bath? – Raymond Y., age 12, Bothell, Washington</strong></p>
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<p>Skin is an awesome and weird organ. As the body’s biggest organ, it does a lot to look after you, protecting you from the outside world of sunlight, harsh chemicals, nasty germs and severe cold. And it does all this while keeping water inside your body and enabling the sense of touch. </p>
<p><a href="https://scholar.google.com/citations?user=PFa8F_oAAAAJ&hl=en&oi=ao">I’m a biomedical engineer</a>. <a href="https://sites.google.com/a/binghamton.edu/bbsmm/?pli=1">My research team and I</a> try to better understand the mechanics and function of soft biological tissues.</p>
<p>We know skin wrinkles as you get older or when you pinch it between two fingers. But it’s been somewhat of a mystery why skin gets wrinkly and even sometimes changes color after you take a leisurely bath or spend too long in the swimming pool. </p>
<p>Often people assume that these wrinkles form because the skin absorbs water, which makes it swell up and buckle. To be honest, I did too for a long time. </p>
<p>But researchers back in the 1930s discovered that in people with nerve damage in their fingers, the <a href="https://doi.org/10.1371/journal.pone.0084949">post-bath wrinkles didn’t form</a>. Wrinkly fingers can’t just be due to water absorption then, or this would be a universal phenomenon, no matter how well your nerves are or aren’t working.</p>
<p>So, if it isn’t swelling due to water, then what is behind pruny fingers and toes after a long swim? Scientists have recently discovered what they think is the answer. </p>
<h2>A nerve signal for narrower blood vessels</h2>
<p>To explain what is happening, first you need to know a bit about the <a href="https://www.britannica.com/science/autonomic-nervous-system">autonomic nervous system</a> – the involuntary part of how your body works. Functions like breathing, blinking, your heart pumping or your pupils constricting in the sun all happen without your needing to consciously control them, thanks to the autonomic nervous system. </p>
<p>It also automatically controls the expansion and contraction of your blood vessels. Typically, temperature, medications or what you eat or drink can cause your blood vessels to expand or contract. Think of how your skin may flush of its own accord when you go out into a hot day, exercise or even blush.</p>
<p>This contraction of your blood vessels is also what causes the skin to wrinkle after a lengthy swim.</p>
<p>When your hands and feet come into contact with water for more than a few minutes, the sweat ducts in your skin open, allowing water to flow into the skin tissue. This added water decreases the proportion of salt inside the skin. Nerve fibers send a message about lower salt levels to your brain, and the autonomic nervous system responds by constricting the blood vessels.</p>
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<a href="https://images.theconversation.com/files/539637/original/file-20230726-29-ifl1n1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="artist's rendering of a cross section of skin, showing network of blood vessels under the surface" src="https://images.theconversation.com/files/539637/original/file-20230726-29-ifl1n1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539637/original/file-20230726-29-ifl1n1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=445&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539637/original/file-20230726-29-ifl1n1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=445&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539637/original/file-20230726-29-ifl1n1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=445&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539637/original/file-20230726-29-ifl1n1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=559&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539637/original/file-20230726-29-ifl1n1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=559&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539637/original/file-20230726-29-ifl1n1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=559&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">When tiny blood vessels inside the skin contract, they pull the skin’s surface down, forming the wrinkles you see after a long bath.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/human-skin-anatomy-computer-artwork-royalty-free-illustration/536228590">Shubhangi Ganeshrao Kene/Science Photo Library via Getty Images</a></span>
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<p>The narrowing of the blood vessels causes the overall volume of skin to reduce, puckering the skin into these distinct wrinkle patterns. It’s like how a dried-out grape becomes a wrinkled raisin – it’s lost more volume than surface area.</p>
<p>This constriction of blood vessels also causes the skin to become paler – it’s the opposite of what happens when your skin gets redder when you get into a really hot bath, due to your blood vessels dilating. The color change is a little more obvious in people with lighter complexions.</p>
<p>With nerve damage, this constriction doesn’t occur. The blood vessels never get a message to narrow, so the wrinkles never happen even if you stay in the bath for a really long time.</p>
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<a href="https://images.theconversation.com/files/539639/original/file-20230726-15-trfob2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="bare feet walking over mossy stones in a river" src="https://images.theconversation.com/files/539639/original/file-20230726-15-trfob2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539639/original/file-20230726-15-trfob2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539639/original/file-20230726-15-trfob2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539639/original/file-20230726-15-trfob2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539639/original/file-20230726-15-trfob2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539639/original/file-20230726-15-trfob2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539639/original/file-20230726-15-trfob2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Wrinkled wet toes may provide an advantage in a slippery environment.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/austria-salzkammergut-mondsee-feet-of-teenage-girl-royalty-free-image/486483031">Westend61 via Getty Images</a></span>
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<h2>An advantage to wrinkled fingers or toes</h2>
<p>But does this skin wrinkling-when-wet serve any purpose?</p>
<p>Researchers have found that wrinkled skin has <a href="https://www.science.org/content/article/wrinkles-help-fingers-get-grip">added grip underwater</a> in comparison to unwrinkled skin. Better grip lets you grasp objects more firmly. It makes walking along an underwater surface easier, with less likelihood of slipping. I think this is a fantastic feature to have evolved over time.</p>
<p>My research team and I have performed studies to look at changes in skin structure and function with prolonged immersion in water, but not to study wrinkles. We’re interested in skin analyses that can be done to help forensic investigators after a crime or disaster. We also want to <a href="https://doi.org/10.1016/j.eml.2020.101017">learn more about immersion foot syndromes</a> – skin injuries caused by working in wet environments for long periods. They tend to affect military personal, or farmers whose crops grow in flooded fields, such as rice paddies.</p>
<p>Prolonged immersion in water makes skin more likely to break, but this weakening can take weeks to occur. Just don’t stay in the swimming pool too long and your pruny digits will go back to normal once you’ve dried off.</p>
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<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
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<p class="fine-print"><em><span>Guy German receives funding from the National Science Foundation. </span></em></p>Recent research suggests blood vessels are the key to why fingers and toes turn pruny and pale after being submerged for a while.Guy German, Associate Professor of Biomedical Engineering, Binghamton University, State University of New YorkLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2011492023-03-29T12:28:19Z2023-03-29T12:28:19ZBrains also have supply chain issues – blood flows where it can, and neurons must make do with what they get<figure><img src="https://images.theconversation.com/files/516713/original/file-20230321-20-at1818.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1921%2C1561&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Blood carries oxygen and vital nutrients to the brain.
</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/cerebral-angiography-image-from-fluoroscopy-in-royalty-free-image/1473413961">Mr. Suphachai Praserdumrongchai/iStock via Getty Images</a></span></figcaption></figure><p><a href="https://doi.org/10.3389/fnint.2022.818685">Neuroscientists have long assumed</a> that neurons are greedy, hungry units that demand more energy when they become more active, and the circulatory system complies by providing as much blood as they require to fuel their activity. Indeed, as neuronal activity increases in response to a task, blood flow to that part of the brain increases even more than its rate of energy use, leading to a surplus. This increase is the basis of common <a href="https://doi.org/10.3389/fnint.2022.818685">functional imaging technology</a> that generates colored maps of brain activity.</p>
<p>Scientists used to interpret this apparent mismatch in blood flow and energy demand as evidence that there is no shortage of blood supply to the brain. The idea of a nonlimited supply was based on the observation that <a href="https://doi.org/10.1038%2Fjcbfm.2013.181">only about 40% of the oxygen</a> delivered to each part of the brain is used – and this percentage actually drops as parts of the brain become more active. It seemed to make evolutionary sense: The brain would have evolved this faster-than-needed increase in blood flow as a safety feature that guarantees sufficient oxygen delivery at all times.</p>
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<figcaption><span class="caption">Functional magnetic resonance imaging is one of several ways to measure the brain.</span></figcaption>
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<p>But does blood distribution in the brain actually support a demand-based system? <a href="https://scholar.google.com.br/citations?user=cldyZo8AAAAJ&hl=en">As a neuroscientist myself</a>, I had previously examined a number of other assumptions about the most basic facts about brains and found that they didn’t pan out. To name a few: Human brains <a href="https://doi.org/10.1002/cne.21974">don’t have 100 billion neurons</a>, though they do <a href="https://doi.org/10.3389/fnana.2014.00046">have the most cortical neurons</a> of any species; the <a href="https://doi.org/10.1126/science.aaa9101">degree of folding of the cerebral cortex</a> does not indicate how many neurons are present; and it’s not larger animals that live longer, but <a href="https://doi.org/10.1002/cne.24564">those with more neurons in their cortex</a>.</p>
<p>I believe that figuring out what determines blood supply to the brain is essential to understanding how brains work in health and disease. It’s like how cities need to figure out whether the current electrical grid will be enough to support a future population increase. Brains, like cities, only work if they have enough energy supplied.</p>
<h2>Resources as highways or rivers</h2>
<p>But how could I test whether blood flow to the brain is truly demand-based? My freezers were stocked with preserved, dead brains. How do you study energy use in a brain that is not using energy anymore?</p>
<p>Luckily, the brain leaves behind evidence of its energy use through the pattern of the vessels that distribute blood throughout it. I figured I could look at the <a href="https://doi.org/10.3389/fnint.2022.760887">density of capillaries</a> – the thin, one-cell-wide vessels that transfer gases, glucose and metabolites between brain and blood. These capillary networks would be preserved in the brains in my freezers.</p>
<p>A demand-based brain should be comparable to a road system. If arteries and veins are the major highways that carry goods to the town of specific parts of the brain, capillaries are akin to the neighborhood streets that actually deliver goods to their final users: individual neurons and the cells that work with them. Streets and highways are built on demand, and a road map shows what a demand-based system looks like: Roads are often concentrated in parts of the country where there are more people – the energy-guzzling units of society.</p>
<p>In contrast, a supply-limited brain should look like the river beds of a country, which couldn’t care less about where people are located. Water will flow where it can, and cities just have to adjust and make do with what they can get. Chances are, cities will form in the vicinity of the main arteries – but absent major, purposeful remodeling, their growth and activities are limited by how much water is available.</p>
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<a href="https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Microscopy image of astrocytes contacting a capillary" src="https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">This image shows astrocytes, a type of brain cell, contacting a ravinelike capillary.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/astrocyte-in-the-brain-touching-a-capillary-250x-royalty-free-image/152883277">Ed Reschke/Stone via Getty Images</a></span>
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<p>Would I find that capillaries are concentrated in parts of the brain with more neurons and supposedly require more energy, like streets and highways built in a demand-based manner? Or would I find that they are more like creeks and streams that permeate the land where they can, oblivious to where the most people are, in a supply-driven manner?</p>
<p>What I found was clear evidence for the latter. For <a href="https://doi.org/10.3389/fnint.2022.760887">both mice</a> <a href="https://doi.org/10.3389/fnint.2022.821850">and rats</a>, capillary density makes up a meager 2% to 4% of brain volume, regardless of how many neurons or synapses are present. Blood flows in the brain like water down rivers: where it can, not where it is needed.</p>
<p>If blood flows regardless of need, this implies that the brain actually uses blood as it is supplied. We found that the tiny variations in capillary density across different parts of dead rat brains matched perfectly with the rates of blood flow and energy use in the same parts of other living rat brains that researchers measured 15 years prior. </p>
<h2>Resolving blood flow and energy demand</h2>
<p>Could the specific density of capillaries in each part of the brain be so limiting that it dictates how much energy that part uses? And would that apply to the brain as a whole?</p>
<p>I partnered with my colleague <a href="https://scholar.google.com/citations?user=18-0e2EAAAAJ&hl=en">Doug Rothman</a> to answer these questions. Together, we discovered that not only do both human and rat brains do what they can with what blood they get and typically work at about 85% capacity, but overall brain activity is indeed <a href="https://doi.org/10.3389/fnint.2022.818685">dictated by capillary density</a>, all else being equal. </p>
<p>The reason why only 40% of the oxygen supplied to the brain actually gets used is because this is the maximum amount that can be exchanged as blood flows by – like workers trying to pick up items on an assembly line going too fast. Local arteries can deliver more blood to neurons if they start using slightly more oxygen, but this comes at the cost of diverting blood away from other parts of the brain. Since gas exchange was already near full capacity to begin with, the fraction of oxygen extraction seems to even drop with a slight increase in delivery.</p>
<p>From afar, energy use in the brain may look demand-based – but it really is supply-limited.</p>
<h2>Blood supply influences brain activity</h2>
<p>So why does any of this matter?</p>
<p>Our findings offer a possible explanation for why the brain can’t truly multitask – only quickly alternate between focuses. Because blood flow to the entire brain is tightly regulated and remains essentially constant throughout the day as you alternate between activities, our research suggests that any part of the brain that experiences an increase in activity – because you start doing math or playing a song, for example – can only get slightly more blood flow at the expense of diverting blood flow from other parts of the brain. Thus, the <a href="https://doi.org/10.1126/science.1183614">inability to do two things at the same time</a> might have its origins in blood flow to the brain being supply-limited, not demand-based. </p>
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<a href="https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="MRI brain scan images" src="https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=727&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=727&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=727&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=914&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=914&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=914&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A better understanding of how the brain works could offer insights into human behavior and disease.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/brain-scan-close-up-royalty-free-image/sb10069835m-001">Peter Dazeley/The Image Bank via Getty Images</a></span>
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<p>Our findings also offer insight into aging. If neurons must make do with what energy they can get from a mostly constant blood supply, then the parts of the brain with the highest densities of neurons will be the first to be affected when there is a shortage – just like the largest cities feel the pain of a drought before smaller ones. </p>
<p>In the cortex, the parts with the <a href="https://doi.org/10.3389/fnint.2022.821850">highest neuron densities</a> are the hippocampus and entorhinal cortex. These areas are involved in short-term memory and the <a href="https://doi.org/10.1212%2F01.wnl.0000106462.72282.90">first to suffer in aging</a>. More research is needed to test whether the parts of the brain most vulnerable to aging and disease are the ones with the greatest number of neurons packed together and competing for a limited blood supply. </p>
<p>If it’s true that capillaries, like neurons, <a href="https://doi.org/10.1016/j.cmet.2019.05.010">last a lifetime</a> in humans as they do in lab mice, then they may play a bigger role in brain health than expected. To make sure your brain neurons remain healthy in old age, taking care of the capillaries that keep them supplied with blood may be a good bet. The good news is that there are two proven ways to do this: a <a href="https://doi.org/10.1001/archneurol.2011.548">healthy diet</a> and <a href="https://doi.org/10.18632/aging.103046">exercise</a>, which are never too late to begin.</p><img src="https://counter.theconversation.com/content/201149/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suzana Herculano-Houzel does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Neuroscientists have typically thought of energy supply to the brain as demand-based. A supply-limited view offers another perspective toward aging and why multitasking can be difficult.Suzana Herculano-Houzel, Associate Professor of Psychology, Vanderbilt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2022262023-03-24T12:36:40Z2023-03-24T12:36:40Z3D-printing the brain’s blood vessels with silicone could improve and personalize neurosurgery – new technique shows how<figure><img src="https://images.theconversation.com/files/517257/original/file-20230323-28-w03xh4.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1864%2C1604&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">3D printers can lay down more than just layers of melted plastic.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/realistic-3d-paper-cut-human-brain-royalty-free-illustration/1391832014">Dedraw Studio/iStock via Getty Images Plus</a></span></figcaption></figure><p>A new 3D-printing technique using silicone can make accurate models of the blood vessels in your brain, enabling neurosurgeons to train with more realistic simulations before they operate, according to our <a href="https://doi.org/10.1126/science.ade4441">recently published research</a>.</p>
<p>Many neurosurgeons practice each surgery before they get into the operating room <a href="https://doi.org/10.3390%2Fbioengineering7010007">based on models</a> of what they know about the patient’s brain. But the current models neurosurgeons use for training <a href="https://doi.org/10.1093/neuros/nyaa217">don’t mimic real blood vessels well</a>. They provide unrealistic tactile feedback, lack small but important structural details and often exclude entire anatomical components that determine how each procedure will be performed. Realistic and personalized replicas of patient brains during pre-surgery simulations could reduce error in real surgical procedures. </p>
<p>3D printing, however, could make replicas with the soft feel and the structural accuracy surgeons need.</p>
<p>3D printing is typically thought of as a process that involves laying down layer after layer of melted plastic that solidifies as a self-supporting structure is built. Unfortunately, many soft materials do not melt and re-solidify the way the plastic filament that 3D printers typically employ do. Users only get one shot with soft materials like silicone – they have to be printed while in a liquid state and then irreversibly solidified.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/uHbn7wLN_3k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Researchers are exploring 3D-printing organs using living cells.</span></figcaption>
</figure>
<h2>Shaping liquids in 3D</h2>
<p>How do you make a complex 3D shape out of a liquid without ending up with a puddle or a slumping blob?</p>
<p>Researchers developed a broad approach called <a href="https://doi.org/10.1002/adma.201004625">embedded 3D printing</a> for this purpose. With this technique, the “ink” is deposited inside a bath of a second supporting material designed to flow around the printing nozzle and trap the ink in the place right after the nozzle moves away. This allows users to create complex shapes out of liquids by holding them trapped in three-dimensional space until the time comes to solidify the printed structure. Embedded 3D printing has been effective for structuring <a href="https://doi.org/10.1126/sciadv.1500655">a variety of soft materials</a> like hydrogels, microparticles and even living cells. </p>
<p>However, printing with silicone has remained challenging. Liquid silicone is an oil, while most support materials are water-based. Oil and water have a high <a href="https://doi.org/10.1039/D0SM01971B">interfacial tension</a>, which is the driving force behind why oil droplets take on circular shapes in water. This force also causes 3D-printed silicone structures to deform, even in a support medium.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/517272/original/file-20230323-26-beetje.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up of oil droplets on water" src="https://images.theconversation.com/files/517272/original/file-20230323-26-beetje.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517272/original/file-20230323-26-beetje.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517272/original/file-20230323-26-beetje.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517272/original/file-20230323-26-beetje.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517272/original/file-20230323-26-beetje.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517272/original/file-20230323-26-beetje.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517272/original/file-20230323-26-beetje.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Interfacial tension is what causes oil droplets to form on water and silicone to deform.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/abstract-art-oil-in-water-royalty-free-image/1251006239">Baac3nes/Moment via Getty Images</a></span>
</figcaption>
</figure>
<p>Even worse, these interfacial forces drive small-diameter silicone features to break into droplets as they are being printed. A lot of research has gone into making silicone materials that can be printed <a href="https://doi.org/10.1016/j.addma.2018.10.002">without a support</a>, but these heavy modifications also modify the properties that users care about, like how soft and stretchy the silicone is.</p>
<h2>3D-printing silicone with AMULIT</h2>
<p>As researchers working at the interface of <a href="https://scholar.google.com/citations?user=PYnyFvsAAAAJ&hl=en">soft matter physics, mechanical engineering</a> and <a href="https://scholar.google.com/citations?user=rVFU5coAAAAJ&hl=en">materials science</a>, we decided to tackle the problem of interfacial tension by developing a <a href="https://doi.org/10.1126/science.ade4441">support material made from silicone oil</a>.</p>
<p>We reasoned that most silicone inks would be chemically similar to our silicone support material, thus dramatically reducing interfacial tension, but also different enough to remain separated when put together for 3D printing. We created many candidate support materials but found that the best approach was to make a dense emulsion of silicone oil and water. One can think about it like crystal clear mayonnaise, made from packed microdroplets of water in a continuum of silicone oil. We call this method <a href="https://doi.org/10.1126/science.ade4441">additive manufacturing at ultra-low interfacial tension, or AMULIT</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/517288/original/file-20230323-22-p3hiok.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram of AMULIT technique printing the bronchi of a lung model within a bath of supporting material, with a close-up of the needle depositing layers of silicone to make the tissue." src="https://images.theconversation.com/files/517288/original/file-20230323-22-p3hiok.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517288/original/file-20230323-22-p3hiok.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=380&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517288/original/file-20230323-22-p3hiok.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=380&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517288/original/file-20230323-22-p3hiok.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=380&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517288/original/file-20230323-22-p3hiok.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=478&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517288/original/file-20230323-22-p3hiok.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=478&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517288/original/file-20230323-22-p3hiok.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=478&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This diagram shows the AMULIT technique printing the bronchi of a lung model within a bath of supporting material. At right is a close-up of the needle depositing layers of silicone to make the tissue.</span>
<span class="attribution"><a class="source" href="https://www.science.org/doi/10.1126/science.ade4441">Senthilkumar Duraivel/Angelini Lab</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>With our AMULIT support medium, we were able to print off-the-shelf silicone at high resolution, creating features as small as 8 micrometers (around 0.0003 inches) in diameter. The printed structures are as stretchy and durable as their traditionally molded counterparts. </p>
<p>These capabilities enabled us to 3D-print accurate models of a patient’s brain blood vessels based on a 3D scan as well as a functioning heart valve model based on average human anatomy.</p>
<h2>3D silicone printing in health care</h2>
<p>Silicone is a <a href="https://doi.org/10.1002/14356007.a24_057">critical component of innumerable products</a>, from everyday consumer goods like cookware and toys to advanced technologies in the electronics, aerospace and health care industries. </p>
<p>Silicone products are typically made by pouring or injecting liquid silicone into a mold and removing the cast after solidification. The expense and difficulty of manufacturing high-precision molds limits manufacturers to products with only a few predetermined sizes, shapes and designs. Removing delicate silicone structures from molds without damage is an additional barrier, and manufacturing defects increase when molding highly intricate structures. </p>
<p>Overcoming these challenges could allow for the development of advanced silicone-based technologies in the health care industry, where personalized implants or patient-specific mimics of physiological structures could transform care.</p><img src="https://counter.theconversation.com/content/202226/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Organ models that more accurately capture finer details could reduce surgical error and lead to personalized implants.Senthilkumar Duraivel, Ph.D. Candidate in Materials Science and Engineering, University of FloridaThomas Angelini, Associate Professor of Mechanical and Aerospace Engineering, University of FloridaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1960162022-12-13T22:56:16Z2022-12-13T22:56:16ZWhy does the Alzheimer’s brain become insulin-resistant?<figure><img src="https://images.theconversation.com/files/499100/original/file-20221205-26-1etuem.jpg?ixlib=rb-1.1.0&rect=7%2C7%2C988%2C555&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Type 2 diabetes, characterised in its advanced stages by insulin resistance, is an important risk factor for Alzheimer's disease.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>As the population ages, the number of people with <a href="https://braininstitute.ca/research-data-sharing/neurodegenerative-disorders">neurodegenerative diseases</a>, such as <a href="https://alzheimer.ca/en/about-dementia/what-alzheimers-disease">Alzheimer’s disease</a>, increases. Approximately <a href="https://www.canada.ca/en/public-health/services/publications/diseases-conditions/dementia-highlights-canadian-chronic-disease-surveillance.html">75,000 Canadians</a> are diagnosed with Alzheimer’s disease each year and experience a decline in their cognitive abilities. The ordeal usually lasts for several years while their family members watch helplessly.</p>
<p>Neurodegenerative diseases are characterized by <a href="https://www.sciencedirect.com/science/article/abs/pii/S0924977X13001107">proteinopathies</a> — abnormal accumulations of proteins in the brain that impair the functioning of <a href="https://cancer.ca/en/cancer-information/resources/glossary/n/neuron">neurons</a>. The most widely studied therapeutic approach to developing drugs for Alzheimer’s is to try to reduce the aggregation of <a href="https://canjhealthtechnol.ca/index.php/cjht/article/view/eh0103/683">amyloid-beta peptide</a> and <a href="https://nouvelles.umontreal.ca/en/article/2022/10/20/unlocking-the-mysteries-of-tauopathies-a-protein-that-gives-hope/">tau protein</a> in neurons.</p>
<p>However, in order to reach their targets, the drugs must first cross the <a href="https://www.theglobeandmail.com/canada/article-toronto-researchers-look-at-new-approach-for-treating-alzheimers/">blood-brain barrier</a> (BBB) from the blood to the brain. This is because <a href="https://www.biorxiv.org/content/10.1101/2020.12.10.419598v1.full">endothelial cells</a>, cells that line the tiniest blood vessels in the brain, regulate the exchange between blood and the brain. They maintain a balance that allows access to essential molecules such as glucose, but restrict the passage of <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3494002/">most pharmaceuticals</a>, including the new and <a href="https://www.ft.com/content/32478dbf-7270-4eb6-a576-663a47a3603e">much-hyped</a> drug <a href="https://www.nejm.org/doi/full/10.1056/NEJMoa2212948">lecanemab</a>.</p>
<p>When these brain endothelial cells become diseased, the balance is upset. The brain struggles to get the substances it needs back into the circulation and rejects those that might harm it.</p>
<p>The brain and the other organs of the body are thus in constant communication, while in health or in disease.</p>
<p>As experts in neurodegenerative diseases and the BBB, we have conducted a study on insulin receptor dysfunction in Alzheimer’s disease.</p>
<h2>Insulin and the brain</h2>
<p><a href="https://www.healthlinkbc.ca/health-topics/types-insulin">Insulin</a> is an essential hormone for life. It is best known for its effect on the regulation of <a href="https://www.diabetescarecommunity.ca/living-well-with-diabetes-articles/blood-sugar-levels-in-canada/?gclid=Cj0KCQiAyracBhDoARIsACGFcS4fee8N8dfBJj9HKxpUiGlNO6RANNF9BiZN52dsd6oxqgLCW7Od_WsaArF9EALw_wcB">blood sugar</a> and remains an essential part of the pharmaceutical treatment of <a href="https://www.healthlinkbc.ca/health-topics/types-insulin">diabetes</a>. In recent decades, researchers have noted vascular and metabolic abnormalities <a href="https://pubmed.ncbi.nlm.nih.gov/30022099/">in a high proportion of patients with dementia</a>.</p>
<p>Indeed, Type 2 diabetes, characterized in the later stages by <a href="http://www.diabetesclinic.ca/en/diab/1basics/insulin_resistance.htm">insulin resistance</a>, is a major risk factor for Alzheimer’s disease. There is some evidence to suggest that the <a href="https://pubmed.ncbi.nlm.nih.gov/29377010/">Alzheimer’s brain is less responsive to insulin</a>. Conversely, studies have shown that insulin can <a href="https://pubmed.ncbi.nlm.nih.gov/32730766/">improve memory</a>, prompting the development of clinical trials on the effect of insulin on Alzheimer’s disease.</p>
<p>Yet we still don’t know what cell types and mechanisms are involved in the action — and loss of action — of insulin in the brain. The vast majority of insulin is produced by the <a href="https://pancreaticcancercanada.ca/the-pancreas/">pancreas</a> and secreted into the bloodstream. Therefore, to affect the brain, insulin must first interact with the BBB and its endothelial cells, which are in contact with the blood and can take up insulin through <a href="https://pubmed.ncbi.nlm.nih.gov/36280236/">receptors</a>.</p>
<h2>Alzheimer’s and the insulin receptor</h2>
<p>In order to measure the amount of these insulin receptors in the brain, <a href="https://doi.org/10.1093/brain/awac309">we performed analyses directly in human tissues</a>. These samples came from a <a href="https://www.rushu.rush.edu/research/departmental-research/religious-orders-study">cohort</a> of over a thousand people who agreed to donate their brains after death. We have access to them through a partnership with researchers at Rush University in Chicago.</p>
<p>We found that the <a href="https://healthenews.mcgill.ca/new-insights-into-how-insulin-interacts-with-its-receptor/">insulin-binding receptor</a> is predominantly located in the microvessels, so, within the BBB itself. Moreover, the abundance of this receptor is decreased in Alzheimer’s patients. This decrease could lead to the loss of insulin response in the Alzheimer brain.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/499093/original/file-20221205-15238-9izujo.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="schematic" src="https://images.theconversation.com/files/499093/original/file-20221205-15238-9izujo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/499093/original/file-20221205-15238-9izujo.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=781&fit=crop&dpr=1 600w, https://images.theconversation.com/files/499093/original/file-20221205-15238-9izujo.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=781&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/499093/original/file-20221205-15238-9izujo.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=781&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/499093/original/file-20221205-15238-9izujo.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=982&fit=crop&dpr=1 754w, https://images.theconversation.com/files/499093/original/file-20221205-15238-9izujo.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=982&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/499093/original/file-20221205-15238-9izujo.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=982&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The brain insulin receptor is located mainly at the BBB, and its ability to respond to blood insulin is diminished in Alzheimer’s disease.</span>
<span class="attribution"><span class="source">(Manon Leclerc)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Insulin receptor dysfunction</h2>
<p>In order to better control the experimental variables and measure the response of the insulin receptor, we then tested our hypotheses in mice. The <em>in situ</em> cerebral perfusion technique consists of injecting insulin directly into the carotid artery (an artery located in the neck) so that it reaches the brain in its entirety. We have shown that circulating insulin mainly activates receptors located on the cerebral microvessels.</p>
<p>Although it was generally accepted that insulin crosses the BBB to reach cells such as neurons deeper in the brain tissue, our results show that the proportion of insulin that crosses the BBB is low.</p>
<p>These two observations thus confirm that the majority of insulin must interact with cells in the BBB before it can exert an action on the brain.</p>
<p>We then applied the same method to <a href="https://www.criver.com/products-services/research-models-services/genetically-engineered-model-services/transgenic-mouse-rat-model-creation/transgenic-mice?region=3601">transgenic mice</a>, which were genetically modified to model Alzheimer’s disease. We found that the response to insulin at the BBB was dysfunctional, with no activation of the insulin receptor in these diseased mice.</p>
<p>Thus, in both humans and rodents, the brain insulin receptor is located primarily at the BBB, and its ability to respond to blood insulin is impaired in Alzheimer’s disease.</p>
<h2>A significant breakthrough</h2>
<p>In sum, our results suggest that alterations in the number, structure and function of insulin receptors at the level of BBB endothelial cells may contribute to the cerebral insulin resistance observed in Alzheimer’s disease.</p>
<p>Alzheimer’s research efforts are currently focused on drugs that, in order to reach their therapeutic target, the neurons, must first cross the BBB, which severely restricts their passage. By targeting the metabolic dysfunction of the brain instead, we propose a research alternative that has two major advantages.</p>
<p>The first is that we can use treatments that do not have to cross the BBB barrier, since it is the endothelial cells themselves that become the therapeutic target. The second involves <a href="https://www.nature.com/articles/nrd.2018.168">“drug repurposing,”</a> which consists of taking advantage of the phenomenal therapeutic arsenal already approved to fight diabetes and obesity, but using this in the context of Alzheimer’s.</p>
<p>It should be remembered that the few drugs available to us provide only a modest improvement in symptoms. Combating insulin resistance in the brain would make it possible to break the vicious circle between neuropathology (disease that affects the brain) and diabetes, and in theory slow down the progression of the disease.</p>
<h2>The work is not finished</h2>
<p>On the basic research side, we will continue to study the mechanisms downstream from the microvessels to understand the action of insulin on the deep layers of the brain.</p>
<p>We hope that clinical research will follow suit with human studies to repurpose drugs that target certain metabolic diseases, such as diabetes, towards fighting Alzheimer’s.</p>
<p>In the meantime, while waiting for pharmaceutical solutions, each of us would do well to adopt the preventive cocktail that we all know well: a healthy diet combined with frequent physical and mental exercise.</p><img src="https://counter.theconversation.com/content/196016/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Frederic Calon has received funding from: Canadian Institutes of Health Research (CIHR), Natural Sciences and Engineering Research Council of Canada (NSERC), Fonds de la recherche du Québec en santé (FRQS), Alzheimer Society of Canada.</span></em></p><p class="fine-print"><em><span>Manon Leclerc has received scholarships from the Fondation du CHU de Québec and the Fonds de Recherche du Québec - Santé (FRQS).</span></em></p><p class="fine-print"><em><span>Vincent Emond ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>Impaired insulin receptors in the blood vessels between the blood and the brain may contribute to the insulin resistance observed in Alzheimer’s disease.Frederic Calon, Professeur, Université LavalManon Leclerc, PhD student, Université LavalVincent Emond, Professionnel de recherche, Université LavalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1500162020-11-18T16:26:24Z2020-11-18T16:26:24ZFour reasons you might always feel cold<figure><img src="https://images.theconversation.com/files/370072/original/file-20201118-15-e1n699.jpg?ixlib=rb-1.1.0&rect=8%2C0%2C5742%2C3837&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Some people need to bundle up all year round.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/beautiful-thoughtful-young-woman-coveted-coverlet-400520170">Dean Drobot/ Shutterstock</a></span></figcaption></figure><p>Almost all of us will complain of being cold at some point, especially as lower temperatures arrive. But some people feel cold no matter the weather – and there are a number of reasons why this might be case.</p>
<p>The average <a href="https://www.bmj.com/content/359/bmj.j5468">normal body temperature</a> is 36.6°C, but variations are common with differences of up to 0.5°C. A person’s <a href="https://journals.physiology.org/doi/full/10.1152/ajpregu.1998.275.5.R1478">resting temperature changes</a> throughout a 24-hour period, peaking around 6pm and dropping to its lowest around 4am. <a href="https://elifesciences.org/articles/49555">Average body temperature</a> has also decreased by up to 0.03°C per birth decade since it was first established in the 19th century.</p>
<p>Different parts of our body have <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6456186/">different temperatures</a>, with the rectum being the warmest (37°C), followed by the ears, urine and the mouth. The armpit (35.9°C) is the coldest part of our body that is usually measured.</p>
<p>Here are four other factors that affect our body temperature – and may be the reason behind why some people always feel cold.</p>
<h2>Anatomy</h2>
<p>Men and women actually create different amounts of heat to keep the body warm. Men have a higher average <a href="https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2009.162">resting basal metabolic rate</a> (of energy burned at rest) due to their <a href="https://journals.physiology.org/doi/full/10.1152/jappl.2000.89.1.81">higher muscle mass</a>. This means men naturally create higher amounts of heat to keep them warm.</p>
<p>Similarly, the layers of fat, which are designed to insulate and keep the body warm, are distributed differently in men and women. Women have an almost <a href="https://pubmed.ncbi.nlm.nih.gov/11706283/">two-times thicker</a> layer of fat underneath the skin in the arms and legs, so the heat from any underlying muscles finds it more difficult – and takes longer – to get to the temperature receptors in the <a href="https://www.softwareadvice.com/resources/improve-employee-productivity-with-climate-control/">skin</a>, which may be why some women may complain of feeling cold more often. It’s not clear whether, once at a comfortable temperature, this difference in fat distribution keeps women warmer for longer. </p>
<h2>Hormones</h2>
<p>Women have a <a href="https://www.nature.com/articles/s41746-019-0152-7">cyclic change</a> in their base body temperature which is influenced by various hormones involved in the <a href="https://www.ncbi.nlm.nih.gov/books/NBK546686/">menstrual cycle</a>. Before ovulation, temperatures average 35.9°C, then peak at 36.7°C a few days after. </p>
<p>A number of sex hormones interact with the system that <a href="https://pubmed.ncbi.nlm.nih.gov/26674572/">regulates our temperature</a>. For example, oestrogen increases vasodilation, a widening of blood vessels, which helps reduce body temperature – whereas progesterone tends to cause warmer body temperatures. Studies show synthetic <a href="https://pubmed.ncbi.nlm.nih.gov/11512029/">progesterone</a>, found in oral contraceptives, causes a prolonged elevation of body temperature.</p>
<p>While higher testosterone levels in men don’t appear to change the temperature of the body, it appears it may cause men to feel the cold less by <a href="https://www.jneurosci.org/content/36/45/11435.long">desensitising</a> one of the receptors that detects cold.</p>
<h2>Health conditions</h2>
<p>Some illnesses and conditions are associated with a reduced tolerance or increased sense of cold.</p>
<p><a href="https://www.nhs.uk/conditions/raynauds/">Raynaud’s disease</a> is a condition which causes some areas of the body, especially the fingers and toes (though it can also affect the <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3275138/">ears</a>, nose and <a href="https://www.bmj.com/content/314/7081/644">nipples</a>) to go cold and numb in response to low temperatures or stress. Typically, the whole body doesn’t feel cold, but the severity of the affected areas can be incredibly painful. </p>
<p>It’s caused by the rapid narrowing of small blood vessels in these areas. Women are more likely to suffer from Raynaud’s, as are those who live in colder climates. Treatment primarily focuses on avoiding the cold, stress triggers, drugs (some cold medications) that can cause blood vessels to narrow, and some lifestyle changes. </p>
<p><a href="https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/">Hypothyroidism</a> is another condition which can make someone feel cold. It affects the thyroid gland in your neck, stopping it <a href="https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/triiodothyronine">producing enough</a> of <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3822221/">the hormones</a> involved in maintaining energy levels, hair, skin, weight and internal temperature. However, hypothyroidism can be treated with <a href="https://www.ncbi.nlm.nih.gov/books/NBK539808/">synthetic hormones</a>. </p>
<h2>Blood vessel problems</h2>
<p>Arteriosclerosis is the narrowing of blood vessels due to a build-up of plaque – the same material that can cause heart attacks. There are different types of this condition, but the one that most commonly causes a cold feeling is <a href="https://pubmed.ncbi.nlm.nih.gov/29540326/">peripheral artery disease</a>, where arteries supplying blood to your limbs are narrowed. </p>
<p>The blood maintains our limbs’ tissues by providing them with nutrients that enable them to continue functioning and generating heat – which is why people with the condition may constantly feel cold. If untreated, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4232437/">symptoms</a> can progress to limb ischaemia, where blood is totally cut off, causing gangrene, the need for amputation and potentially death.</p>
<figure class="align-center ">
<img alt="Fingers turned red by frostbite." src="https://images.theconversation.com/files/370075/original/file-20201118-15-1tqscdb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/370075/original/file-20201118-15-1tqscdb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/370075/original/file-20201118-15-1tqscdb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/370075/original/file-20201118-15-1tqscdb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/370075/original/file-20201118-15-1tqscdb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/370075/original/file-20201118-15-1tqscdb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/370075/original/file-20201118-15-1tqscdb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Frostbite also reduces blood flow to help organs stay warm.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/frostbite-652785946">tome213/ Shutterstock</a></span>
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</figure>
<p>Frostbite can also cause continued or prolonged sensitivity to cold, even after the visible injury has healed. Frostbite typically starts when the body, particularly exposed skin, is subject to temperatures below freezing. The body’s response is to <a href="https://www.ncbi.nlm.nih.gov/books/NBK536914/">reduce blood flow</a> to these skin areas to <a href="https://www.ncbi.nlm.nih.gov/books/NBK232852/">prevent heat loss</a> and maintain the warmth of vital internal organs. </p>
<p>Damage comes from ice crystals forming in and ripping apart body tissues. In the worst-case scenario, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2615432">fingers</a> and <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2827043/">limbs</a> can be lost.</p>
<h2>When cold is hot</h2>
<p>On the opposite end of the spectrum is a type of food poisoning, called <a href="https://theconversation.com/explainer-what-is-ciguatera-fish-poisoning-21835">ciguatera</a>, which makes cold things feel hot (and vice versa). This type of reef-fish poisoning – which affects approximately 50,00-500,000 people every year – comes from consuming <a href="https://pubmed.ncbi.nlm.nih.gov/23778293/">ciguatoxin</a>, which is found in plankton species called <em>Gambierdiscus toxicus</em> and accumulates as it makes its way up the food chain to us through some fish.</p>
<p>The toxin cannot be destroyed by cooking and, when consumed by humans, causes gastrointestinal symptoms and sensitivity to hot and cold, <a href="https://www.nature.com/articles/s41598-018-21373-2/">hypothermia</a> and even <a href="https://www.sciencedirect.com/science/article/abs/pii/0041010194903123">death</a>. The sensitivity is made all the more alarming as the senses are <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5224948/">reversed</a> – so hand-washing in cold water causes a <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4078439/">burning feeling</a> on the hands. There’s no <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3463840/#b19">treatment</a> and symptoms can take months or even years to disappear.</p>
<p>As the cold months approach it’s normal to reach for the thermostat or a blanket. But bear in mind that any prolonged or abnormal sensation of cold should be checked by a doctor.</p><img src="https://counter.theconversation.com/content/150016/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Taylor is affiliated with The Anatomical Society. </span></em></p>Everything from hormones to certain heath conditions can affect how we feel.Adam Taylor, Professor and Director of the Clinical Anatomy Learning Centre, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1416622020-06-30T13:40:17Z2020-06-30T13:40:17ZRepurposing Alzheimer’s drugs could prevent blood vessel damage caused by type 2 diabetes and obesity – new research<figure><img src="https://images.theconversation.com/files/344793/original/file-20200630-103653-txyqj7.jpg?ixlib=rb-1.1.0&rect=28%2C0%2C9556%2C5389&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Beta amyloid causes damage to the blood vessels.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/3d-illustration-constricted-narrowed-artery-blood-1254693310">Christoph Burgstedt/ Shutterstock</a></span></figcaption></figure><p>People who suffer from a combination of type 2 diabetes, high blood pressure, high cholesterol, and obesity have a condition known as “<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5393930/">metabolic syndrome</a>”. This condition causes the blood vessels to stiffen. When the arteries are stiff or become blocked, there’s a reduced flow of oxygenated blood that’s able to reach the body’s tissues and vital organs. This puts a person at increased risk of heart attack or stroke. But in order to prevent further harm to patients with metabolic syndrome, it’s key to understand what causes damage to the blood vessels – and how this can be treated.</p>
<p>Our <a href="https://www.jci.org/articles/view/122237">latest research</a> has identified a previously unknown mechanism by which metabolic syndrome is able to cause blood vessel damage. But, we also found a way to reverse this damage. Our study looked at both mice and human tissue samples. In both groups, we found that if a subject was obese and had type 2 diabetes, their blood vessels overproduced an enzyme called BACE1. This triggers a biochemical reaction that creates a protein called <a href="https://www.sciencedirect.com/science/article/pii/S1044743199908114?via%3Dihub">beta amyloid</a>. Levels of <a href="https://www.nature.com/articles/s41467-018-03755-2">BACE1 are increased</a> by excessive blood lipids (fats) and glucose (sugar), which are characteristic of the metabolic syndrome.</p>
<p>In humans, raised levels of beta amyloid are associated with <a href="https://www.sciencedirect.com/science/article/pii/S0006899397003831?via%3Dihub">damage to the surface lining</a> (endothelium) of blood vessels. Damage to the endothelium disrupts the normal functioning of the blood vessels, leading to high blood pressure and atherosclerosis – the build up of plaque along the walls of the blood vessels. This build up of plaque can harden over time, narrowing the arteries and making it harder for oxygenated blood to move through the arteries. This can lead to severe complications, including heart attack, stroke or death.</p>
<p>Our research also showed that beta amyloid <a href="https://www.jci.org/articles/view/122237">alters the chemical environment</a> inside the blood vessels, causing them to stiffen. Importantly we showed this process was also found in obese people with type 2 diabetes. They had more BACE1 in their blood vessels and higher levels of beta amyloid in their blood, compared to lean people without diabetes.</p>
<p>This work builds on <a href="https://portlandpress.com/biochemj/article/441/1/285/47542/Reduction-in-BACE1-decreases-body-weight-protects">our previous findings</a> that showed raised levels of the BACE1 enzyme is linked with <a href="https://www.nature.com/articles/s41598-017-18388-6">obesity and type 2 diabetes</a>. But perhaps the most promising finding from our latest study was that this process could be targeted by drugs.</p>
<h2>Repurposing drugs</h2>
<p>The pharmaceutical industry and researchers have been interested in BACE1 for a number of years because of the role it plays in the development of another major illness. As BACE1 generates beta amyloid, these aggregate together and form amyloid plaques in the brain, which are <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4888851/">characteristic of Alzheimer’s disease</a>. </p>
<p>Drug companies have developed a number of <a href="https://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=2330">candidate drugs</a> to inhibit the activity of BACE1. But those trials have so far failed to produce any evidence that these interventions would halt or slow the onset of Alzheimer’s disease. </p>
<p>Intriguingly, <a href="https://www.jci.org/articles/view/122237">our study suggests</a> these drugs could potentially be repurposed in order to target the over-activity of BACE1 – and beta amyloid production – in the blood vessels of people with obesity and type 2 diabetes. </p>
<p>Current treatments for vascular complications are aimed at improving the underlying components of the metabolic syndrome. Statins, insulin sensitisers, and anti-obesity drugs all have beneficial effects, but unfortunately they don’t work for everyone and adherence of these drugs are low. Currently this leaves <a href="https://link.springer.com/article/10.1007/s11154-016-9345-4">invasive surgery</a> as the only option remaining.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/344795/original/file-20200630-103673-fxrlwv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/344795/original/file-20200630-103673-fxrlwv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=351&fit=crop&dpr=1 600w, https://images.theconversation.com/files/344795/original/file-20200630-103673-fxrlwv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=351&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/344795/original/file-20200630-103673-fxrlwv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=351&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/344795/original/file-20200630-103673-fxrlwv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=441&fit=crop&dpr=1 754w, https://images.theconversation.com/files/344795/original/file-20200630-103673-fxrlwv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=441&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/344795/original/file-20200630-103673-fxrlwv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=441&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Mice with obesity and type 2 diabetes were given a compound that stopped beta amyloid production.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/genetic-obese-mouse-black-healthy-control-716011576">Janson George/ Shutterstock</a></span>
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<p>During our study, we treated mice that were obese and had type 2 diabetes with an experimental compound, named M-3. This compound is a potent small molecule inhibitor that was able to <a href="http://jpet.aspetjournals.org/content/324/3/957.long">stop BACE1 from producing beta amyloid</a>. While this compound is not suitable for use as a drug in humans, its method of action to stop BACE1 activity is the same as more clinical relevant drugs.</p>
<p>The effects of reducing beta amyloid were dramatic. Not only did it prevent further damage to the blood vessels, but the reduction of beta amyloid reversed the damage that had already been caused. </p>
<p>These findings suggest that drugs that inhibit BACE1 could potentially be used as a therapy to restore blood vessel health in people with metabolic syndrome. It could also open up the possibility of using drugs that have already been through phase one trails for Alzheimer’s disease to reverse vessel damage found in people with metabolic syndrome. </p>
<p>Though the existing drugs will need to be trialled in humans for this type of treatment, our functional studies in mice and human samples suggest that these findings will also be seen in patients. Being able to repurpose an already existing therapy will allow for an easy, cost-effective way to give people living with diabetes a therapy that will enable them to live longer, healthier lives.</p><img src="https://counter.theconversation.com/content/141662/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>This research was performed at the University's of Dundee and Leeds and funded by grants from the British Heart Foundation, Diabetes UK, the Medical Research Council, the Diabetes Research and Wellness Foundation, and the Innovative Medicines Initiative (SUMMIT).</span></em></p>In mice, we found that drugs developed to treat Alzheimer’s Disease could be re-purposed to prevent, or even reverse, the blood vessel damage caused by obesity and type 2 diabetes.Paul Meakin, BHF Intermediate Basic Science Research Fellow and University Academic Fellow, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1351662020-04-23T12:12:09Z2020-04-23T12:12:09ZWhat is a brain freeze?<figure><img src="https://images.theconversation.com/files/329186/original/file-20200420-152581-pm3o7v.jpg?ixlib=rb-1.1.0&rect=74%2C27%2C4456%2C3029&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Cold and sweet in the heat.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/children-enjoy-icecream-during-the-hot-afternoon-on-june-7-news-photo/450223408?adppopup=true">Raj K Raj/Hindustan Times via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What is a brain freeze?</strong></p>
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<hr>
<p>Has this ever happened to you? You’re eating a delicious ice cream cone or frozen lemonade, so cold and sweet and suddenly, bam, brain freeze! What happened?</p>
<p>A brain freeze is a short, intense pain behind the forehead and temples that occurs after eating something cold too fast. If you get one, don’t worry – your brain isn’t actually freezing. The sensation feels like it’s happening inside your skull, but it really has to do with what’s going on in your mouth.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/327044/original/file-20200409-38906-1b1qvqf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/327044/original/file-20200409-38906-1b1qvqf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=439&fit=crop&dpr=1 600w, https://images.theconversation.com/files/327044/original/file-20200409-38906-1b1qvqf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=439&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/327044/original/file-20200409-38906-1b1qvqf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=439&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/327044/original/file-20200409-38906-1b1qvqf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=552&fit=crop&dpr=1 754w, https://images.theconversation.com/files/327044/original/file-20200409-38906-1b1qvqf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=552&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/327044/original/file-20200409-38906-1b1qvqf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=552&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Mmmmmm. Brrrrrrrr. Ouch!</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/DEU-BW-Wetter-Speiseeis/135fdca280524c04a0a4e9a65078965f/211/0">AP Photo/Daniel Maurer</a></span>
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<p>Brain freeze isn’t as common as you might expect. Many studies report that less than half of their participants get them. Scientists still don’t understand why.</p>
<h2>What makes a brain freeze hurt?</h2>
<p>There’s a lot we know about how a brain freeze works. There’s also a lot we don’t know.</p>
<p>Just beneath the skin on your face is a network of blood vessels that supply the face and brain with blood. Blood contains many nutrients <a href="https://kidshealth.org/en/kids/blood.html">like oxygen</a>, which is essential for your brain to function. Tangled up in this network of vessels are tiny nerve endings connected to one another and the brain through the <a href="https://www.healthline.com/human-body-maps/trigeminal-nerve">trigeminal nerve</a>. This nerve makes it possible for you to feel sensations in your face, including pain.</p>
<p>Scientists believe the blood vessels in the throat and mouth and the trigeminal nerve are central to what makes a brain freeze hurt. But they don’t quite agree on which is more responsible for causing the pain.</p>
<p>Most agree that eating or drinking something cold, too quickly, rapidly <a href="https://www.sciencedaily.com/releases/2013/05/130522095335.htm">lowers the temperature</a> at the back of your throat and roof of your mouth. Many also agree this causes the tiny blood vessels in these areas to shrink, allowing less blood to pass through them. This reduces their ability to supply your brain with necessary oxygen in the blood. What happens next is a little blurry.</p>
<h2>Pain in the brain means stop!</h2>
<p>Some scientists believe the trigeminal nerve responds to these events in your throat and mouth by sending a pain signal to the front of your brain. Whether the nerve is specifically responding to the cold or a sudden reduction of blood and oxygen supply to the brain – or both – is unclear. </p>
<p>Other scientists believe the pain is caused by a rush of blood to the front of your head. Shortly after the vessels in your throat and mouth shrink from the cold, these same vessels immediately expand. By expanding, additional blood and oxygen <a href="https://www.medicalnewstoday.com/articles/244458">flood these areas</a>. Although this blood rush might provide your brain with desperately needed blood and oxygen, it also might increase the amount of pressure in your head, causing pain.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/X3bn6pmpLEw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The mystery of a brain freeze.</span></figcaption>
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<h2>Is a brain freeze dangerous?</h2>
<p>A brain freeze may seem like a bad thing at first, but the pain could actually be good. By forcing you to stop eating that delicious but cold treat, the pain from a brain freeze may protect your brain from losing its continuous supply of blood and oxygen.</p>
<p>If you’re worried about a brain freeze, try slowing down. It may be hard with something as delicious as a Bomb Pop on a hot summer day, but at least it will last longer.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
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<p class="fine-print"><em><span>Tyler Daniel Anderson-Sieg does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Have you ever felt a piercing pain in your head when you eat something cold?Tyler Daniel Anderson-Sieg, Doctoral Student in Biomedical Sciences, University of South CarolinaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1177272019-07-05T12:22:07Z2019-07-05T12:22:07ZSo far cultured meat has been burgers – the next big challenge is animal-free steaks<figure><img src="https://images.theconversation.com/files/282365/original/file-20190702-126382-pchbd2.jpg?ixlib=rb-1.1.0&rect=479%2C455%2C4501%2C3038&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Meat of the future might be quite different from meat of the past.</span> <span class="attribution"><a class="source" href="https://www.loc.gov/pictures/item/2004671592/">Stanley Kubrick, photographer, LOOK Magazine Photograph Collection, Library of Congress, Prints & Photographs Division, LC-USZ6-2352.</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>The meat you eat, if you’re a carnivore, comes from animal muscles. But animals are composed of a lot more than just muscle. They have organs and bones that most Americans do not consume. They require food, water, space and social connections. They produce waste.</p>
<p>Farmers spend a lot of energy and resources to grow complex organisms, creating waste in the process, only to focus on the profitable cuts of meat they can harvest.</p>
<p>It would be easier, more humane, less wasteful, to <a href="https://vimeo.com/78403188">produce just the parts people want</a>. And with cell biology and tissue engineering, it is possible to grow just muscle and fat tissue. It’s called cultured meat. Scientists provide cells with the same inputs they need to grow, just outside an animal: nutrients, oxygen, moisture and molecular signals from their cell neighbors.</p>
<p>So far researchers have <a href="https://youtu.be/slslQLZL2EI">cultivated bunches of cells</a> that can be turned into processed meat like a burger or a sausage. This cultured meat technology is still in the early phases of research and development, as prototypes are scaled-up and fine-tuned to prepare for the challenges of commercialization. But already bioengineers are taking on the next tougher challenge: growing structured cuts of meat like a steak or a chicken cutlet.</p>
<h2>What meat’s made of</h2>
<p>If you look at a piece of raw meat under the microscope, you can see what you’re eating on the cellular level. Each bite is a matrix of muscle and fat cells, interlaced with blood vessels and enrobed by connective tissue.</p>
<p>The muscle cells are full of proteins and nutrients and the fat cells are full of, well, fats. These two cell types contribute to most of the taste and mouth-feel a carnivore experiences when biting into a burger or steak. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/279615/original/file-20190614-158945-158jkci.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/279615/original/file-20190614-158945-158jkci.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/279615/original/file-20190614-158945-158jkci.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=677&fit=crop&dpr=1 600w, https://images.theconversation.com/files/279615/original/file-20190614-158945-158jkci.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=677&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/279615/original/file-20190614-158945-158jkci.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=677&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/279615/original/file-20190614-158945-158jkci.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=850&fit=crop&dpr=1 754w, https://images.theconversation.com/files/279615/original/file-20190614-158945-158jkci.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=850&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/279615/original/file-20190614-158945-158jkci.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=850&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Section of turkey stained to show cellular-level organization skeletal muscle tissue – also known as meat.</span>
<span class="attribution"><span class="source">Natalie Rubio</span></span>
</figcaption>
</figure>
<p>The blood vessels supply an animal’s tissue with nutrients and oxygen while it’s alive; after slaughter, the blood adds a unique, metallic, umami nuance to the meat.</p>
<p>The connective tissue, composed of proteins like collagen and elastin, organizes the muscle fibers into aligned bundles, oriented in the direction of contraction. This connective tissue changes during cooking and adds texture – and gristle – to meat.</p>
<p>The challenge for cellular agriculture researchers is to emulate this complexity of meat from the bottom up. We can grow muscle and fat cells in a petri dish – but blood vessels and connective tissue don’t spontaneously generate as they do in an animal. How can we engineer biomaterials and bioreactors to provide nutrient diffusion and induce organization so we end up with a thick, structured cut of meat?</p>
<h2>Cultured-meat burgers are the first step</h2>
<p>To create any cultured meat, researchers take small – think marble-sized – amounts of tissue from a cow, pig or chicken and isolate individual cells. Then, bioengineers like me put the cells in plastic flasks and give them nutrients, oxygen and moisture while housing them at body temperature. The cells are happy and can divide exponentially, creating more and more cells. </p>
<p>When grown on plastic, the cells will continue to divide until they exist on all of the available surface area. This results in a crowded layer that’s one cell thick. Once the cells stop dividing, they start to mature. Muscle cells fuse together to create long muscle fibers and fat cells begin to produce lipids. Researchers can combine a bunch of these cells together to create processed meat products, like burgers, hot dogs and sausages.</p>
<p>Animal cells alone can replicate most of the meat experience. But without blood vessels and connective tissue, you don’t end up with an organized, three-dimensional tissue – and that’s what you need for structured cuts of meat, like steak, chicken breast and bacon. </p>
<p>To overcome this challenge, scientists can use biomaterials to replicate the structure and function of blood vessels (for nutrient and oxygen transfer) and connective tissue (for organization and texture). This area of research is called <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/scaffolds-for-tissue-engineering">scaffold development</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/282551/original/file-20190703-126400-8iv3fh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/282551/original/file-20190703-126400-8iv3fh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/282551/original/file-20190703-126400-8iv3fh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=473&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282551/original/file-20190703-126400-8iv3fh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=473&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282551/original/file-20190703-126400-8iv3fh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=473&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282551/original/file-20190703-126400-8iv3fh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=594&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282551/original/file-20190703-126400-8iv3fh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=594&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282551/original/file-20190703-126400-8iv3fh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=594&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Providing some structure for cells to grow on will get cultured meat from hamburger to steaks.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/high-angle-rear-view-female-butcher-242663623">Tyler Olson/Shutterstock.com</a></span>
</figcaption>
</figure>
<h2>Scaffolds are the secret ingredient for steaks</h2>
<p>The concept of scaffolds originates in the field of <a href="https://doi.org/10.1016/B978-008045154-1.50021-6">tissue engineering for medical applications</a>. Scientists combine cells and scaffolds to produce functional biomaterials for research, toxicology screening or <a href="https://www.sciencedaily.com/releases/2019/06/190607193705.htm">implants</a>.</p>
<p>These biomaterials can take different forms – films, gels, sponges – depending on what properties are desired in the resulting tissue. For example, you could <a href="https://technobleak.com/regenerative-artificial-skin-new-technology-booming-worldwide/">grow skin cells on a flat collagen film</a> to create a skin graft to help burn victims or <a href="https://www.sciencedaily.com/releases/2019/05/190516155338.htm">bone cells in a hydroxyapatite sponge</a> for bone regeneration.</p>
<p>For medical applications, scaffolds generally need to be safe for implantation, must not induce a response from the body’s immune system, be degradable and capable of supporting cell growth. </p>
<p>For food applications, the design considerations of scaffolds are different. They should still support cell growth, but it’s also important that they are inexpensive, edible and environmentally friendly to produce. Some common biomaterials for food applications include cellulose from plants, a carbohydrate called chitosan from mushrooms and a carbohydrate called alginate from algae.</p>
<p>Here’s one “recipe” for cultured meat that I’ve worked on in the lab. First, create an appropriate scaffold. Isolate chitosan from mushrooms and dissolve it in water to create a viscous gel. Put the gel in a tube and expose one end to a cold substance, like dry ice or liquid nitrogen. The whole tube of gel will slowly freeze, starting at the cold end. The frozen gel can then be freeze-dried by a vacuum pulling on the gel at very low temperatures, ultimately creating a dry sponge-like material. The <a href="https://doi.org/10.1021/acsbiomaterials.8b01261">directional freezing process creates a sponge</a> with small, long, aligned pores resembling a bundle of straws – and also muscle tissue.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/282536/original/file-20190703-126400-19y7moh.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/282536/original/file-20190703-126400-19y7moh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/282536/original/file-20190703-126400-19y7moh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=116&fit=crop&dpr=1 600w, https://images.theconversation.com/files/282536/original/file-20190703-126400-19y7moh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=116&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/282536/original/file-20190703-126400-19y7moh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=116&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/282536/original/file-20190703-126400-19y7moh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=146&fit=crop&dpr=1 754w, https://images.theconversation.com/files/282536/original/file-20190703-126400-19y7moh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=146&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/282536/original/file-20190703-126400-19y7moh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=146&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The simplified process for creating a chitosan sponge with aligned pores.</span>
<span class="attribution"><span class="source">Natalie Rubio</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Then, instead of growing meat on flat plastic, you can transfer the cells to this three-dimensional sponge to provide more surface area for growing thicker tissue. The pores can also help distribute nutrients and oxygen throughout the tissue. So far with this technique, my lab has been able to produce small bits of meat less than a centimeter square – a little small for a cookout but a strong start.</p>
<p>Other scaffold possibilities include growing cells within alginate-based fibers, gels or sponges. Or technicians can rinse plant cells off of plants in a process called decellularization and <a href="https://medium.com/neodotlife/meat-on-a-leaf-glenn-gaudette-9b2765a861f0">repopulate the cellulose framework that’s left behind with animal cells</a>.</p>
<p>Once researchers find materials and methods that work really well, we’ll work on creating larger batches. At that point, it’ll be a game of scaling up the process and bringing down the cost so cultured meat products can be cost-competitive with farmed meat products.</p>
<p>It’s always exciting to see startup companies debut their cultured meatballs, sausages and burgers. But I’m looking ahead to what’s next. With a bit more research, time, funding and luck, the cultured meat menu 2.0 will include the steak and pork chops many carnivores know and love.</p><img src="https://counter.theconversation.com/content/117727/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Natalie R. Rubio is funded by New Harvest and is an advisor for Bond Pet Foods.</span></em></p>It’s relatively easy to grow a bunch of animal cells to turn into a burger. But to grow a steak made of cultured meat is a trickier task. Bioengineers must create organized, three-dimensional tissues.Natalie R. Rubio, Cellular Agriculture PhD Candidate, Tufts UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/971832018-07-09T02:50:00Z2018-07-09T02:50:00ZHealth Check: what causes chilblains and how can I prevent them?<figure><img src="https://images.theconversation.com/files/225839/original/file-20180703-116123-1sjqrdz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Red, itchy and dry spots on your fingers and toes are caused by cold, but should resolve on their own. </span> <span class="attribution"><span class="source">from www.shutterstock.com</span></span></figcaption></figure><p>While some of us love the winter chill, this winter others will notice itchy or tender red lumps on their fingers and toes.</p>
<p>These small bumps are called chilblains (also known as pernio) and they occur with exposure to cold. While children and the elderly are most commonly affected, other age groups are not immune to this problem.</p>
<p>Several hours after exposure to cold, damp weather, the blood vessels in the fingers and toes tighten up and get smaller (called vasoconstriction) to keep the warm blood as far away from the skin as possible, as this is where heat is lost.</p>
<p>When returning to a warm environment from the cold, these blood vessels expand again, but can get inflamed (called vasculitis) if this happens too quickly.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/health-check-do-cold-showers-cool-you-down-71004">Health Check: do cold showers cool you down?</a>
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<p>This causes itch and burning in the affected area. Small reddish lumps can appear on the skin, which may become painful or blistered. In those with <a href="https://www.chromaderm.com.au/services/skin-of-colour/">skin of colour</a>, chilblains may look purple-ish or even present as a brown patch of skin. The most commonly affected areas include the fingers, toes, ears and nose.</p>
<p>If they’re untreated, chilblains can swell and form blisters, with a risk of ulcers, scarring and infection. But usually, if extremities are warmed, they will get better on their own in a few weeks.</p>
<p>This reaction is <a href="https://www.mayoclinic.org/diseases-conditions/chilblains/symptoms-causes/syc-20351097">more common</a> in people who have a family history of chilblains and those who have problems with their <a href="https://www.webmd.com/dvt/ss/slideshow-dvt-improve-circulation">blood circulation</a>. Smoking, diabetes and high cholesterol can lead to poorer blood circulation. People who are underweight or have diseases that affect connective tissue (such as <a href="https://theconversation.com/explainer-what-is-lupus-and-how-is-stress-implicated-92699">lupus</a>) are also at <a href="https://www.mayoclinic.org/diseases-conditions/chilblains/symptoms-causes/syc-20351097">increased risk</a> of chilblains.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/225840/original/file-20180703-116120-1tdtzkb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/225840/original/file-20180703-116120-1tdtzkb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/225840/original/file-20180703-116120-1tdtzkb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/225840/original/file-20180703-116120-1tdtzkb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/225840/original/file-20180703-116120-1tdtzkb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/225840/original/file-20180703-116120-1tdtzkb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/225840/original/file-20180703-116120-1tdtzkb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/225840/original/file-20180703-116120-1tdtzkb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Keep your extremities covered, and warm them up slowly if they get cold.</span>
<span class="attribution"><span class="source">from www.shutterstock.com</span></span>
</figcaption>
</figure>
<p>The diagnosis is usually straightforward and no extra tests are needed. But occasionally other conditions need to be excluded, such as lupus and <a href="https://www.mayoclinic.org/diseases-conditions/raynauds-disease/symptoms-causes/syc-20363571">Raynaud’s disease</a> (where small arteries narrow, limiting blood circulation). For this, your doctor might need to do some blood tests or even take a small piece of skin (skin biopsy) to confirm the diagnosis.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/forget-heatwaves-our-cold-houses-are-much-more-likely-to-kill-us-83030">Forget heatwaves, our cold houses are much more likely to kill us</a>
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<p>If the weather gets the better of you and chilblains do appear, your doctor is likely to suggest topical steroid creams to help with itch and inflammation. For more severe cases, medications that open (dilate) blood vessels, such as nifedipine and diltiazem, can be used.</p>
<p>But we all know prevention is better than cure, so here are some tips to avoid chilblains:</p>
<ul>
<li><p>clothing: keep your extremities warm with covered shoes, gloves and ear muffs</p></li>
<li><p>temperature control: keep your skin dry and warm, and when you’re rewarming your skin, do it slowly and gently</p></li>
<li><p>get active: staying active and keeping fit with physical activity improves circulation so will decrease the risk of developing chilblains</p></li>
<li><p>avoid smoking and eat well to optimise the health of your blood vessels.</p></li>
</ul><img src="https://counter.theconversation.com/content/97183/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michelle Rodrigues does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A “how to” on avoiding and resolving chilblains this winter.Michelle Rodrigues, Consultant Dermatologist, St Vincent's Hospital MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/970642018-06-01T10:40:45Z2018-06-01T10:40:45ZBlood in your veins is not blue – here’s why it’s always red<figure><img src="https://images.theconversation.com/files/221065/original/file-20180530-120514-1u71tcq.jpg?ixlib=rb-1.1.0&rect=477%2C72%2C5457%2C3737&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Is it always the same?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/lab-assistant-testing-blood-samples-hospital-1099719305">Elnur/Shutterstock.com</a></span></figcaption></figure><p>Whenever you see blood outside your body, it looks red. Why?</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/220819/original/file-20180529-80650-rav3a8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/220819/original/file-20180529-80650-rav3a8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/220819/original/file-20180529-80650-rav3a8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=483&fit=crop&dpr=1 600w, https://images.theconversation.com/files/220819/original/file-20180529-80650-rav3a8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=483&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/220819/original/file-20180529-80650-rav3a8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=483&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/220819/original/file-20180529-80650-rav3a8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=606&fit=crop&dpr=1 754w, https://images.theconversation.com/files/220819/original/file-20180529-80650-rav3a8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=606&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/220819/original/file-20180529-80650-rav3a8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=606&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Heme is the part of the hemoglobin molecule that latches onto oxygen and then releases it to tissues around the body.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Heme2.jpg">Waikwanlai</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Human blood is red because of the protein hemoglobin, which contains a red-colored compound called heme that’s crucial for carrying oxygen through your bloodstream. <a href="https://store.macmillanlearning.com/us/product/Biochemistry-A-Short-Course/p/1464126135">Heme contains an iron atom which binds to oxygen</a>; it’s this molecule that transports oxygen from your lungs to other parts of the body.</p>
<p>Chemicals appear particular colors to our eyes based on the wavelengths of light they reflect. Hemoglobin bound to oxygen absorbs blue-green light, which means that it <a href="https://doi.org/10.1016/j.forsciint.2011.07.027">reflects red-orange light</a> into our eyes, appearing red. That’s why blood turns bright cherry red when oxygen binds to its iron. Without oxygen connected, blood is a <a href="https://www.acs.org/content/dam/acsorg/education/resources/highschool/chemmatters/issues/best-of-chemmatters/sample-lesson-plan-the-many-colors-of-blood.pdf">darker red color</a>. </p>
<p>Carbon monoxide, a potentially deadly gas, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1281520/pdf/0940270.pdf">can also bind to heme</a>, with a bond around 200 times stronger than that of oxygen. With carbon monoxide in place, oxygen can’t bind to hemoglobin, which can lead to death. Because the <a href="https://doi.org/10.1383/medc.31.10.41.27810">carbon monoxide doesn’t let go of the heme</a>, your blood stays cherry red, sometimes making a victim of carbon monoxide poisoning appear rosy-cheeked even in death.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/220822/original/file-20180529-80658-1hpl23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/220822/original/file-20180529-80658-1hpl23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/220822/original/file-20180529-80658-1hpl23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/220822/original/file-20180529-80658-1hpl23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/220822/original/file-20180529-80658-1hpl23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/220822/original/file-20180529-80658-1hpl23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/220822/original/file-20180529-80658-1hpl23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/220822/original/file-20180529-80658-1hpl23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">People with pale skin may think their blood is blue inside the body.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/eltpics/12522139305/">eltpics</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Sometimes blood can look <a href="https://doi.org/10.1364/AO.35.001151">blue through our skin</a>. Maybe you’ve heard that blood is blue in our veins because when headed back to the lungs, it lacks oxygen. But this is wrong; human blood is never blue. The bluish color of veins is only an optical illusion. Blue light does not penetrate as far into tissue as red light. If the blood vessel is sufficiently deep, your eyes see more blue than red reflected light due to the blood’s partial absorption of red wavelengths.</p>
<p>But blue blood does exist elsewhere in the animal world. It’s common in animals such as squid and horseshoe crabs, whose blood relies on a chemical called hemocyanin, which <a href="https://www.acs.org/content/dam/acsorg/education/resources/highschool/chemmatters/issues/best-of-chemmatters/sample-lesson-plan-the-many-colors-of-blood.pdf">contains a copper atom</a>, to carry oxygen. Green, clear and even purple blood are <a href="https://news.nationalgeographic.com/2015/03/150312-blood-antarctica-octopus-animals-science-colors/">seen in other animals</a>. Each of these different blood types uses a different molecule to carry oxygen rather than the hemoglobin we use. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/221066/original/file-20180530-120493-1kkxnr2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/221066/original/file-20180530-120493-1kkxnr2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221066/original/file-20180530-120493-1kkxnr2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=423&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221066/original/file-20180530-120493-1kkxnr2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=423&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221066/original/file-20180530-120493-1kkxnr2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=423&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221066/original/file-20180530-120493-1kkxnr2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221066/original/file-20180530-120493-1kkxnr2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221066/original/file-20180530-120493-1kkxnr2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Horseshoe crabs’ blue blood has become an important raw material for the pharmaceutical industry.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Associated-Press-Domestic-News-Virginia-United-/12f7334962e5da11af9f0014c2589dfb/3/0">AP Photo/Steve Helber</a></span>
</figcaption>
</figure>
<p>Despite exceptions, the majority of blood from animals is red. But that doesn’t mean it’s exactly the same as what courses through our veins. There are many variations of hemoglobin present in different species, which allows scientists to <a href="https://doi.org/10.1016/j.forsciint.2017.11.033">distinguish blood samples</a> from various animals.</p>
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<p>Over time, spilled blood that starts out red turns darker and darker as it dries and its hemoglobin breaks down into a compound called methemoglobin. As time passes, dried blood continues to change, growing even darker thanks to another compound called hemichrome. This continual chemical and color change <a href="https://doi.org/10.1016/j.forc.2017.05.002">allows forensic scientists to determine the time</a> a blood drop was left at a crime scene.</p>
<p><a href="https://sites.google.com/site/lednevlab/">In our lab</a>, we’re developing methods that look at the ratio of the different compounds that hemoglobin breaks down into. Then using computer modeling we can <a href="https://doi.org/10.1007/s00216-016-9486-z">estimate the time since the blood was deposited</a> to help investigators determine if a blood stain is relevant to a crime. If the blood is a year old, it might not be important to a crime committed yesterday.</p><img src="https://counter.theconversation.com/content/97064/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Your blood is red;
it’s never blue.
Because of hemoglobin;
and the view through tissue.Marisia Fikiet, Ph.D. Student in Chemistry, University at Albany, State University of New YorkIgor Lednev, Professor of Chemistry, University at Albany, State University of New YorkLicensed as Creative Commons – attribution, no derivatives.