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# CIRCULATORY SYSTEM Animals are complex multicellular organisms that require a mechanism for transporting nutrients and removing wastes throughout the body. The human circulatory system has a complex network of vessels (arteries, veins, and capillaries) that reach all parts of the body. This exte...

# CIRCULATORY SYSTEM Animals are complex multicellular organisms that require a mechanism for transporting nutrients and removing wastes throughout the body. The human circulatory system has a complex network of vessels (arteries, veins, and capillaries) that reach all parts of the body. This extensive network supplies cells, tissues, and organs with oxygen and nutrients, while removing carbon dioxide and waste compounds. This is a closed-loop system where blood is largely separated from the interstitial fluid. The circulatory and respiratory system work together to exchange oxygen and carbon dioxide. ## I. The Heart ### I.1. Anatomy The diagram shows the heart with its major components labelled: * **Aorta:** Major artery * **Superior vena cava:** Major vein * **Inferior vena cava:** Major vein * **Right atrium:** Part of the heart * **Left atrium:** Part of the heart * **Tricuspid valve:** Heart valve * **Right ventricle:** Part of the heart * **Left ventricle:** Part of the heart * **Pulmonary trunk:** Major artery * **Pulmonary valve:** Heart valve * **Bicuspid (Mitchell) valve:** Heart valve * **Aortic valve:** Heart valve * **Ventricular septum:** Wall dividing the two ventricles ### I.2. The Blood Flow The heart has two pumps: one for pulmonary circulation to the lungs, and the other for systemic circulation to the rest of the body. The right side of the heart receives deoxygenated blood from the body: 1. **Deoxygenated blood** returns through the: * Superior vena cava * Inferior vena cava 2. This blood passes into the right ventricle. 3. From the right ventricle blood moves to the lungs through the pulmonary trunk and the pulmonary arteries. The left side of the heart receives oxygenated blood from the lungs (in pulmonary circulation). This oxygen-rich blood then moves into the left ventricle, then to the body. The heart is about the size of a clenched fist and is divided into four chambers: * Two atria * Two ventricles Each side of the heart (right and left) contains one atrium and one ventricle. The text also highlights that the left side of the heart is slightly larger than the right side. This is due to different sizes of the pulmonary and systemic circuits. Valves prevent the backflow of blood.