Circulatory Notes

The Anatomy of the Heart There are four chambers in the heart - two atria and two ventricles. The atria are responsible for receiving blood from the veins leading to the heart. When they contract, they pump blood into the ventricles. It is the ventricles that are the real workhorses, for they must force the blood away from the heart with sufficient power to push the blood all the way back to the heart.

The muscle in the walls of the ventricles is much thicker than the atria. The walls of the heart are really several spirally wrapped muscle layers. This spiral arrangement results in the blood being forced out of the ventricles during contraction. Between the atria and the ventricles are valves, overlapping layers of tissue that allow blood to flow only in one direction. Valves are also present between the ventricles and the vessels leading from it.

The Blood Vessels There are three types of vessels: 1. Arteries - a muscular blood vessel that carries blood away from the heart. 2. Veins - a blood vessel that carries blood to the heart. 3. Capillaries – Small blood vessels, the walls are so thin that oxygen and glucose can pass through them and enter the cells. Waste products, such as carbon dioxide, pass back into the bloodstream via the capillaries to be carried away and expelled from the body.

Flow of blood Blood from the body flows: to the Superior and Inferior Vena Cava, then to the Right Atrium through the Tricuspid Valve to the Right Ventricle through the Pulmonary Valve to the Pulmonary Artery to the Lungs

The blood picks up oxygen in the lungs, and then flows from the lungs: to the Pulmonary Veins to the Left Atrium through the Mitral valve to the Left Ventricle through the Aortic Valve to the Aorta to the body

Circulatory Problems Atherosclerosis is a degenerative disease that results in narrowing of the coronary arteries. Coronary arteries can become clogged or occluded, leading to damage to the heart muscle supplied by the artery. Valvular regurgitation occurs when the valves become so worn that they cannot close completely, and blood flows back into the atria or the ventricles.

Stained cross sections through coronary artery (left) and a coronary artery with lipid deposits in its walls (right).

Name the numbered parts of the heart Using arrows, show the path of blood moving through the heart Color the pathways of deoxygenated blood blue and oxygenated blood pathways red.

Question Why is the human heart called a “double loop”?