Circulatory system - Function, Definition & Anatomy - Human Anatomy | Kenhub
Hello everyone! It’s Matt from Kenhub, and this tutorial will provide a general overview of the function, definition, and anatomy of the circulatory system or the cardiovascular system. The circulatory system is comprised of the heart, the blood vessels, and the blood. It consists of 2 circuits that carry blood around. The smaller being the pulmonary circuit which runs between the heart and the lungs, and the larger being the systemic circuit which runs between the heart and the peripheral tissues.
The cardiac circulatory system functions by providing the tissues of the body with oxygen and nutrients which are transported in the blood. The pulmonary circuit carries the deoxygenated blood into the lungs where the exchange of oxygen and carbon dioxide that the body has produced occurs before the blood returns back to the heart. The heart then pumps the newly oxygenated blood around the systemic circuit of the body and delivers the oxygenated blood to the tissues before collecting the deoxygenated blood and sending it back to the heart with unused nutrients and metabolic waste products. These extra substances within the blood filter into the liver for processing.
The heart is a muscle that acts as a pump. Through electrostimulation, it beats and pushes the blood around the entire body through the circulatory system. The heart is comprised of 4 chambers that consist of 2 pairs on the left and right sides of the heart. The atria collect blood returning to the heart while the ventricles pump blood out of the heart.
The valves in the heart prevent the backflow of blood into the chambers of the heart. The muscular septum divides up the 2 sections of the heart creating a left and right side each containing one atrium and one ventricle. The right side of the heart pumps deoxygenated blood and the left side pumps oxygenated blood.
The amount of blood in liters that is pumped out of the heart per minute is known as the cardiac output, which is around 5.6 liters in males and 4.9 liters in females. It can be calculated by multiplying the heart rate which is the number of beats per minute by the stroke volume which is the amount of blood that collects in the ventricles when they are at full capacity and about to contract. The cardiac output varies depending on whether the person is exercising or resting.
There are 3 major classes of blood vessels namely arteries, veins, and capillaries and they are categorized according to their histological structure. Arteries transport blood between the tissues and away from the heart and have thick muscular walls with small internal lumina or passageways that can withstand blood under high pressure. Veins carry blood away from the tissues and towards the heart and have thin walls. Their internal lumen is larger than that of the arteries due to the fact that they contain blood under low pressure. They also have valves that prevent the blood from flowing backwards.
Lastly, the capillaries, which are found in the muscles and the lungs, are microscopic and have a one-cell layer thick endothelial lining. In other words, the walls of the capillaries have the width of one single epithelial cell. They can only tolerate blood under very low pressure due to the fact that it will move slower and gas exchange has a chance to take place. This is also where the exchange of gases, water, nutrients, and waste products takes place because the capillary walls are thin and fenestrated. After this, the capillaries collect into venules which are the equivalent to arterioles and fenestrated. Capillaries connect arterioles and venules.
The blood is made up of 4 major components. The plasma is the fluid that surrounds the blood cells and helps transport carbon dioxide, hormones, and the metabolic waste products. Red blood cells which are also known as erythrocytes are formed in the bone marrow and function mainly as oxygen carriers. White blood cells or leukocytes make up the body’s immune system by producing antibodies and helping destroy harmful microorganisms. These cells are also created in the bone marrow. Lastly, platelets are cells that clump together to form blood clots and help protect the body by preventing bleeding.
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