Hey everybody, welcome back to explain like I'm fine. I'll talk about what we take the questions you always want to ask and talk about them in a way that's easy to understand. You're your host, I'm Tim. Hey everyone, I'm Kevin.
So Kevin today we're talking about blood. Awesome, what about blood? Well, there's lots to learn about blood, including blood types and where they all came from, but how about this question to start? How does blood circulate through your body if you've had an amputation?
You know, there are arteries in your system which supply the blood and veins which take it away. And in between those two is this massive spiderweb of smaller capillaries which get that good blood to kind of every cell in the body and then take it away once the cell gets what they need. So even though you have had an amputation, there are still thousands of connections between your arteries and veins. In one remains of that kind of amputated limb.
And this redundancy in the system is also really important in situations other than amputation. For example, if one blood vessel is blocked by an embolus, basically like a blood clot or an air bubble or even fat, there's often another route that the blood can take. Obviously some blood vessels are more important than others, for example coronary arteries which supply the heart. And if these become blocked, then you can have some real problems like a heart attack.
Why is it that when you try to wipe away drops of blood off of a surface, it leaves behind this ring around wherever the drop of blood was? You know what I'm talking about? I do know what you're talking about. And that's because the blood at the edges of those drops, it dries more quickly.
So when a drop of blood hits the surface, it obviously tries to stay together. It will obviously spread out into a circle and the innermost part of the blood will kind of be more dense and have more blood in the outside, right? Due to just intermolecular forces. So since the outer part has less blood, it tends to dry more quickly, leaving dry residue behind when it's wiped away.
Okay, another one. Why does blood stick to, say, or stain things like cloves really badly? But when it's on say human skin, it just wipes off really easily, unlike say a permanent marker. Yeah, you know, your skin is fairly smooth and it's waterproof.
So when you draw your arm in marker, the ink is carried from the tip to your skin by solvent. And the solvent is a water so it penetrates more deeply into that layer of skin. It marks the skin. This leaves the ink on the top of your skin and it will get inside your skin.
For blood, it can't really get inside your skin so it just kind of dries on the surface. It's also water soluble, so it's easier to get off. The color is also from red blood cells and they're much larger than ink molecules. Very helpful.
Now, how about fabric that differs from skin? So ink will stain the fabric just as easy as blood. And it's because the solvent, you know, spreads the ink into the fabric through something called capillary action. And that's why when you draw on a white shirt with a marker, you get that, bleed where you aren't really marking it.
It's just because ink is traveling down the threads. And blood interacts with the threads in a similar way. Cotton will absorb water, so blood will absorb onto the threads just like ink. It will go into all the little nooks and crannies of the thread, and while red blood cells are bigger than the ink, they're small enough still to get to the very inside of the threads, you know?
And then, you know, when you try to wash the blood out, the red blood cells are inside that thread. They're trapped now. They're flow away, but can't really flow out. When you wash it, the red blood cells pop, leaving the red color behind, which is still trapped, stuck to, you know, like individual confibres now.
So that's why you can wash out some of the blood is the blood on the surface of the threads. But you can't really wash the blood that's on the inside of the threads. It's really hard. Now to the meat of this episode and the question everyone's always asking, which is not all blood is the same, why do humans have different types of blood?
Yeah, yeah, you know, blood types are way more complicated than those people realize. Blood types are basically a way to describe what proteins are present on the surface of your red blood cells, and blood types predict whether a series reaction will occur in a blood transfusion. So this reaction is called a hemolytic reaction, and it may destroy red blood cells and cause real failure. Shock is likely to occur, and death is also a possibility, so you need to understand blood types very well.
Okay, so the types you've got A, B, A, B, and O, right? Yeah, yep, you got them. There are a number of human blood group systems of these systems, the A, B and O blood group system, and the recess blood group system are actually the most important to know. In the system, the presence or absence of the A antigen, the B antigen, and the RHD antigen are determined.
So another way to think about this is that somebody with type A blood cells has a type A protein on their red blood cells, and a person with type B blood has this protein B under red blood cells, and a person with type AB has both, and a person with type O blood has neither proteins. And your ABO type determines who you can give blood to and who you can take blood from, right? Exactly, that's why it's so important. Those with blood type O can give it to everyone.
While those with type ABs can receive from everyone, and A and Bs are kind of in between. So they can take from O's and themselves and give to ABs, and you're kind of trying to map it out in a diagram, you can find online. But the ABO system is not the only blood type like you're saying, right? That's right.
So the RHD factor, RHD or meaning recess, is a feature of the second most common blood group system in human blood transfusion. RHD proteins are usually designated either a positive or a negative after your kind of ABO typing, and the RHD typing actually describes the activity of 50 different proteins that are considered as a whole in determining if you're RHD positive or RHD negative. There's also the HH and SCS-C typing, but we don't have time in this episode to go over that over. Just tell us how many blood groups there are in total then.
Okay, there are over 30 different blood groups covering hundreds of different proteins in addition to ABO, although not all of them are as critical when determining things like transfusion. So finally, this is a real ELI 5 question. It came from my nearly 5 year old, and it is this, if the blood in your veins looks blue, why is it that you never see blue blood whenever you get a cut? That is a really good question.
And something I thought of myself when I was younger. So for humans, the blood in your arteries and capillaries are bright red, as oxygen actually imparts a very strong red color to kind of the hemogroup. But deoxygenated blood is a darker shade of red. This is kind of present in your veins, and can be seen during things like blood donation and when venous blood samples are taken.
And veins close to the surface of the skin appear blue for a variety of reasons. However, the factors that contribute to this alteration of color perception are related actually to the light scattering properties of the skin, and the processing of visual input by your visual cortex, rather than actually the color of the blood itself. Well now we know we can explain that to our 5 year olds. Did you learn something new?
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