Biology: Structure of the Human Heart

Terrific breakdown of the structure of the huma...

10/21/2009

~ Michelle11

s with all of Mr. Wolfe's lessons he explains things in easily understood terms. I frquently use his videos to supplement the Anatomy and Physiology course I teach!

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One of the problems with being multicellular is that you're thick. You have many, many layers of cells; and the problem is, as we evolved from thin, two-cell layer thick creatures to multicellular creatures that were very thick, along had to come transport systems. At the heart of the transport system is the heart, and that's what I want to talk to you about right now. I want to go through the plumbing of the transport system, the plumbing of the circulatory system, and how it works in our body, and just the kinds of things it does.
Now here's the thing: You know that the purpose of blood - blood has several purposes - but the purposes we're concentrating on so far is oxygen exchange. It's got to get oxygen from the lung to the cells, and it's got to get carbon dioxide from the cells to the lungs. And in order to do that, you have to have blood that goes to every single cell in your body. Think of that, the trillions of cells in your body - all of them - have to somehow be in touch with your blood. Well, that's quite a feat. Not only that, the blood has to be brought to them. And that's what I want to talk about now. How do you bring blood to that so you can get rid of oxygen, so you can get oxygen to the cells, get rid of it out of the hemoglobin, so you can get CO[2] and get rid of that out of the cells and into the lungs? Wastes, like nitrogenous wastes, nutrients - everything that has to be carried to the body - and for that we have something called the heart.
I want to start with this picture, but we'll jump out of here in a second and really get into heart structures back and forth here. But, literally, you have a two-pump system. Now I want to talk to you about misconceptions first. What color is the blood in your veins? How many of you guys had teachers once - I can't imagine a teacher doing this - had friends once - that told you that the blood in your veins is blue? Come on, tell the truth, yeah, I know. It's not. Blood is red, period. Have you ever given blood, and they sucked blood out of a vein? And people say, "Oh, it's because it touches oxygen." Well, where's the oxygen in that syringe? There's no oxygen in that syringe, and when they pull blood out of your vein, it's red. Blood is red.
Now, I'll grant you this: Blood is red, and there's different shades of red - there's dark red and bright red, depending on how much oxygen is in the blood - but that's it. So why have we colored these charts blue and red? Because, I want to show you the difference. So this is what textbooks do; and sadly, we make a mistake, because it sets you up for - don't think it's blue and red. I've got to color them blue and red, because we need to be able to tell the difference between one side of the heart and the other. Don't tell me blood is blue.
So let's go to the blue side. This is the right side of the heart, and this is the left side of the heart. I said that the heart has a two-sided pump, and it is. And it turns out that the right side is going to pump blood that is deoxygenated. Oop, there goes that same thing I'm trying to show you not to think about, but the right side pumps deoxygenated blood, and the left side pumps oxygenated blood.
There are a couple of things you need to know, and once you know them, the heart and the circulatory system's easy. Memorize this: right, deoxygenated blood; left, oxygenated blood. That's the first thing to memorize. Second thing to memorize: Where do you send the oxygenated blood? You need oxygen; where are you going to send it? To the lungs. Where are you going to send the oxygenated blood? To the body. So, therefore, the right side is going to pump to the lungs; the left side is going to pump to the body - easy.
So let's trace the path of a blood cell as it enters these chambers, and let's talk about the names of the chambers. First of all, those of you who know Latin know that the name for hallway or receiving room is the atrium of the house; and, indeed, the heart has atria. We're going to start at the right atrium, and we're going to progress through. We start at this chamber right here, where we've got a blood cell coming in, and let's just say it was in your brain. And that blood cell is going to come out into your brain from a vein. So, first thing you want to remember is veins carry blood to the heart. This particular vein is called the "cavernous vein," or the "vena cava," because it's a big vein. This particular vein is a big vein, and that's a vena cava. And since this one is coming from the head, we call it the "superior vena cava"; and since this one is coming from the "not head," or everything below your heart, it's called the "inferior vena cava."
So here comes the blood; this little deoxygenated blood cell is coming in from someplace, and it's lacking oxygen, and there are a lot of them. Then the heart - the atrium squeezes; and when the atrium squeeze, the blood is going to shoot through, and it's going to pass through these two doorways, like swinging doorways. These swinging doorways are called the "valves," and they are called the "atrioventricular valves." These particular valves separate the atrium and the ventricle. So this particular blood cell's going to go here, and it's going to go to the ventricle.
Now, the ventricle is going to fill up; and as the ventricle fills up - because the atrium squeezes - now the ventricle gets its load of blood, and - here's a blood cell, and that's called a ventricle. So we have, this is the right ventricle, this is the right atrium - and the ventricle squeezes, and two things happen simultaneously. When it squeezes, there's a back pressure, and these doors slam shut - boom - so that blood cannot go back that way. So blood only has one pathway it can go in, and that's up in that direction. And in going up in that direction, it will open this valve, this kind of a halfmoon valve called the semilunar valves.
We're running out of room to write, so we'll get rid of this, and we'll see what we can do, and we'll do the semilunar valves. Now it is now going to go where? Well, let's see, it's the right side - it's got to go to the lungs, right? Well, we have a name for anything connected to the lungs, and it's called pulmonary - pulmonary emphysema, pulmonary arteries - the blood is going to go into these two structures here, which are carrying blood away. Now notice it's deoxygenated blood, but it's carrying blood away. So now we're going into pulmonary arteries, and once we leave the pulmonary arteries, where are we going to go? We're going to go to the lungs. So we're going to go to the lungs, right, away from the heart, and then we're going to come back, and we're going to come back into the other side, nice and full of oxygen. And it's going to come in like this, and in like this, and in from the other lung in that direction.
Let me show you that on a whole systemic diagram - look at this. On this diagram of all the systems, we can see what's happening. It's going to come through here, and there, and it's going to fork to each of the lungs. We've set up our capillary beds in the lungs so that we're showing that the blood goes from blue to red, right? No, it does not; it goes from deoxygenated to oxygenated. And now it's going to come back into this side of the heart, right there, the left side. And now we're almost done, because now we have this nice charged up, oxygenated blood cell, and what's it going to do? Well, once again, at the same time, both of these atria are pumping - it's going bloop bloop bloop bloop bloop bloop - lub-dub - we'll talk about that later.
So the blood is going to go down into here from the left atrium to the left ventricle. The left atrium squeezes, the blood goes down. The right ventricle - the left ventricle squeezes, the doors slam shut, and the blood has to go out this way. And now we come to this gigantic blood vessel called the aorta. I wrote up here "to the body." It is, and it's called the "aorta," and the aorta is going to carry blood to the body, where it will once again lose its oxygen.
So let's watch that. So here it comes, it comes in here, goes up, it might go to the brain, or it might go down to the system. We call that "systemic circulation" instead of "pulmonary circulation." So it's going to go to the systems, as in the brain and the kidney and the liver and things like that. So that's the way the blood circulates. I have one more thing. Everybody always asks me this, my students ask me this all the time, "So what's heartbeat? What's that sound you hear, `lub-dub, lub-dub, lub-dub'?" Believe it or not, it's these valves slamming. The "lub" is the valves slamming; when the ventricle is squeezing, and you're keeping everything from going backwards, that's the "lub." And then later, when the atrium is squeezing, and the semilunar valves close, that's the "dub." So it goes lub-dub - no, let's see - lub - lub-dub, lub-dub, lub-dub. Let's show it on the bigger one - lub-dub, lub-dub. That's the way the heart beats. This is great stuff. Wait till you see what happens next, when we get into arteries, capillaries, and veins - good stuff.
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