Summary
Highlights
The circulatory system, also known as the cardiovascular system, is an organ system comprising the heart, blood vessels, and blood. Its primary function is to transport substances like oxygen, nutrients, and waste products throughout the body. The heart pumps the blood, and blood vessels direct its flow.
Mammals have a double circulatory system, meaning it consists of two separate circuits. The pulmonary circuit carries blood from the heart to the lungs and back. The systemic circuit transports blood from the heart to all body tissues (muscles, brain, liver, etc.) and then back to the heart.
The heart is a muscular pump with four chambers: two Atria at the top and two ventricles at the bottom. Atrioventricular valves between the Atria and ventricles ensure one-way blood flow. When labeling a heart diagram, remember that the 'left' and 'right' refer to the perspective of the body the heart belongs to, not the viewer's left and right.
The left ventricle has a thicker muscular wall than the right ventricle because it needs to pump blood throughout the entire body, whereas the right ventricle only pumps blood to the lungs, which are much closer.
Deoxygenated blood enters the right atrium from the body via the vena cava. It then moves to the right ventricle, which pumps it into the pulmonary artery to the lungs for oxygenation. Oxygenated blood returns from the lungs to the left atrium via the pulmonary vein, then goes to the left ventricle, and finally is pumped into the aorta, which distributes it to the rest of the body.
The heart muscle itself requires a constant supply of oxygenated blood. This is provided by the coronary arteries, which branch off the aorta and encircle the heart. Blockages in these arteries can lead to coronary artery disease or a heart attack.