WEBVTT - Why is Blood Red?

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<v Speaker 1>Welcome to brain stuff from how stuff works. Hey, brain stuff,

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<v Speaker 1>it's Christian saga. Do you remember in the movie Carry

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<v Speaker 1>where they dumped pig blood on that girl at her prom? Well?

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<v Speaker 1>The Annals of Human Biology actually published an article in

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<v Speaker 1>two thousand twelve showing that humans are excellent detectors of

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<v Speaker 1>pig blood, but we are far less developed at detecting

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<v Speaker 1>human blood. They concluded that human blood has no specific

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<v Speaker 1>smell or appearance that triggers immediate recognition. So blood is

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<v Speaker 1>always red, right, But why does it have to be read?

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<v Speaker 1>Contrary to popular belief, it's not blue when it's in

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<v Speaker 1>our bodies, even when it's deoxygenated. But oxygen is part

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<v Speaker 1>of the color, along with the protein molecule hemoglobin that

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<v Speaker 1>attaches to oxygen. It carries from the lungs two muscles

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<v Speaker 1>as blood gets pumped through the human body. And while

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<v Speaker 1>blood is always red, its shade depends on how much

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<v Speaker 1>oxygen it's carrying. For instance, when you cut a person's

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<v Speaker 1>arteries open, they bleed this really bright red blood because

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<v Speaker 1>of the complex formed between hemoglobin, iron and lots of oxygen.

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<v Speaker 1>But if you look deeper into the circulatory system and

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<v Speaker 1>peered into a vein that was delivering all of its oxygen,

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<v Speaker 1>you would see that the blood is a deeper maroon color,

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<v Speaker 1>So veins they look blue or green mainly because of

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<v Speaker 1>skin and skin pigmentation plays a big role. Since everyone's

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<v Speaker 1>skin is a different color, our veins look different, especially

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<v Speaker 1>because the tissue above our veins scatters red light, but

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<v Speaker 1>let's blue light right on through. Even though veins are

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<v Speaker 1>a reddish brown, they appear to be blue from the outside.

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<v Speaker 1>So is the way human beings perceive color and other

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<v Speaker 1>factor here as well. Yes, researchers have shown that it

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<v Speaker 1>is partially an optical illusion. So light colored skin reflects

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<v Speaker 1>most light and blood absorbs most light, particularly dark deoxygenated blood.

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<v Speaker 1>It reflects a little blue and some red, But since

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<v Speaker 1>the skin surrounding the veins scatters and reflects a lot

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<v Speaker 1>of red light, the veins look way bluer in comparison.

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<v Speaker 1>The ratio is so skewed that it tricks the eye.

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<v Speaker 1>In fact, some animals actually bleed other colors, like slugs

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<v Speaker 1>and molluscs, they bleed blue. Check out the brain stuff

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<v Speaker 1>channel on YouTube, and for more on this and thousands

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<v Speaker 1>of other topics, visit how stuff works dot com,