Circulation in man

Arteries take blood rich in oxygen (oxygenated blood) to the capillary network, which intern feeds the cells in the body. Deoxygenated blood (blood with very little oxygen) is taken back to the heart through veins. It then goes to the lungs where gas exchange occurs so the carbon dioxide can exit the body. There are however exceptions to this, as the hepatic portal vein transport blood rich in nutrients from the small intestine to the liver. A portal vein is a special type of vein which links capillary networks.

Another exception to this role is the pulmonary artery. Arteries generally transport blood rich in oxygen away from the heart, however the pulmonary artery transport deoxygenated blood from the heart to the lungs where it is oxygenated and returned to the heart through the pulmonary vein.

The heart

The human heart has four chambers:  right atrium, right ventricle, left atrium and the left ventricle. The heart is made of a special type of muscle called the cardiac muscle. This is the only muscle in the body that does not experience fatigue and for good reason! Can you imagine if your heart got tired and couldn’t beat?

-The right ventricle is separated from the right atrium by the tricuspid valve, while the left ventricle is separated from the left atrium by the bicuspid valve.

-Blood from the lower and upper part of the body enter the heart at the right atrium through the posterior (also called inferior) and anterior (also called superior) vena cava respectively.

-The aorta is the largest artery. Oxygenated blood from the left ventricle is sent to this artery where it then sub-divides sending blood around the entire body.

If we look at the heart we will see there are two upper chambers and two lower chambers. The two upper chambers are called the left and right atrium. The two lower chambers are called the left and right ventricles. The left and right side of the heart are separated by what is known as a septum.

The right side of the heart contains deoxygenated blood and the left side of the heart contains oxygenated blood. This is because the blood from the body enters the right atrium and is sent to the right ventricle where it is pumped to the lungs through the pulmonary artery. Oxygenated blood from the lungs then enters the left atrium and is pumped to the rest of the body by the right ventricle. The pumping mechanism is discussed in the next section of these notes.