Here we have a diagram of the heart. The heart has four chambers. You’ve got two atria and two ventricles. The two upper chambers of the heart are called atrium (and the plural is atria) and you’ve got two lower chambers which are called ventricles.
The function of the heart is obviously to pump blood around the body. The blood contains lots of things – oxygen, nutrients, various gases, hormones, that kind of thing.
Blood first enters the heart and it enters into the atrium on either side. It’s useful to think of the heart as a dual pump. You’ve got two pumps. One pump pumps blood to the lungs and one side of the heart pumps blood to the rest of the body. The right heart pumps blood to the lungs and the left side of the heart pumps blood to the rest of the body.
Blood is received into the atrium. The atrium then contracts and pumps blood to the lower chambers, the ventricles. They pass through these valves here. On the right side, you’ve got the tricuspid valve and on the left side, you’ve got the mitral valve.
Blood is pumped into the ventricles after the atria contract. And when the ventricles contract, they pump blood either to the lungs or to the rest of the body.
One of the primary functions of the heart and the circulatory system is to deliver oxygen to the tissues of the body. When you breathe in, you breathe air into your lungs and air contains oxygen. In the lungs, oxygen diffuses across the alveoli, which are little sacs in the lungs and it enters into the blood stream. You breathe oxygenated air, it enters into your lungs and then it diffuses into the blood.
On this diagram, the red vessels, the red color demonstrates that the blood is carrying oxygen and the blue color demonstrates that the blood is deoxygenated, so it has no oxygen.
When blood enters into the lungs and it diffuses across the alveoli into the blood stream, it is then carried to the heart. It’s carried to the left side of the heart because the left side of the heart pumps blood to the rest of the body and the body needs oxygenated blood so it can function.
Oxygen diffuses into the blood stream through the lungs and it enters into the left side of the heart into the atrium. The left atrium contracts and sends blood into the ventricles, the left ventricle. The left ventricle contracts and sends blood to the rest of the body. It sends blood up to the head and to the rest of the body.
The body then uses up all these oxygen through muscular contractions and various other things – respiration. And then once the cells and tissues of the body are done with the oxygen with the blood, it is returned back to the heart. Blood returns back to the right side of the heart. This is blood that has been used up, depleted of oxygen. Deoxygenated blood returns to the right side of the heart.
It enters into the right atrium. The atrium contracts, sends blood into the right ventricle and the right ventricle shoots blood out here and sends it to both lungs to receive oxygen again. And the process continues. Blood is returned back to the left side, it’s oxygenated in the lungs, returned to the heart and the heart contracts and sends blood back up to the head and the rest of the body.
This happens simultaneously. The left side and the right side contracts simultaneously. You’ve got this pump to the lungs and this pump to the rest of the body. The pump to the lungs is often known as the pulmonary circulation and the pump that sends blood to the rest of the body is known as the systemic circulation because it provides blood to the systems of the body.
Just to quickly recap before I switch back to the 3D model, the heart consists of four chambers. You’ve got two upper chambers called atria (singular is atrium), one atrium on either side and you’ve got two ventricles.
The atrium is smaller chambers where the blood is first received. The atrium contract and send blood to the ventricles. The ventricles are more powerful and muscular and send blood to the lungs and to the rest of the body.
The right side of the heart receives deoxygenated blood and it sends this deoxygenated blood to the lungs to receive oxygen. The left side of the heart oxygenated blood from the lungs and it pumps it out to the rest of the body and to the head.
Think of the heart as a dual pump. It’s got one pump that sends blood to the rest of the body and one pump that sends blood to the lungs to receive oxygen.
I’ve just flicked back to the 3D model of the heart. Obviously, it doesn’t look as clear as in the diagram, but I’ll talk you through the structure of the heart. I’ll just switch to another view of the heart just isolating the heart.
Remember in the diagram you saw the left and right atrium. These were the upper chambers of the heart and this is where blood is received from the rest of the body on the right side and from the lungs on the left side.
This is the right atrium here. You can see its receiving blood from a vessel up here and a vessel down here. The vessels which immediately lead to the heart to bring blood to the heart and take blood away from the heart are known as the four great vessels.
On the right side of the heart, which is this side, you’ve got the right atrium. The blood vessels leading to the right atrium are called the vena cava. You’ve got a superior vena cava and an inferior vena cava. Leading away from the heart – so if you remember the right heart pumps blood to the lungs and is called the pulmonary circulation, you’ve got the pulmonary trunk. This comes from the right ventricle. This area here is the right ventricle.
It’s not as clear as it is on the diagram, but this is the right side of the heart and this is the right ventricle. The right ventricle pumps blood to the lungs via the pulmonary trunk. The pulmonary trunk is another one of the great vessels.
The final great vessel is the aorta and it forms this arch here. This pumps blood up to the head and to the rest of the body. If I just rotate this model around so we can look at the back of the heart, you can see these four vessels entering into this chamber. This is the left chamber of the heart. It’s the left atrium. You’ve got the right atrium here and the left atrium here. You’ve got these vessels which are leading into this chamber. These are the pulmonary veins. You’ve got the pulmonary veins leading into the left atrium carrying oxygenated blood. The left atrium contracts and shoots blood out of the aorta. The aorta then sends blood up to the head and to the rest of the body.
Blood is then used up, depleted of oxygen and returned to the heart via the inferior and superior vena cava, which return blood into the right side of the heart, the right atrium. The right atrium contracts, sends blood into the RIGHT ventricle, which contracts and shoots blood up through the pulmonary trunk. This sends blood to the lungs, which oxygenates the blood and returns it via the pulmonary veins to the left side of the heart. And the cycle continues.