The Circulatory System
The main structures of the cardiovascular system are the heart, arteries, capillaries and veins. The function of the heart is to pump blood through the arteries to the organs of the body. The arteries branch out into a network of capillaries that carry blood with nutrients to the cells and remove their waste products. The capillaries merge to form the veins that circulate the blood back to the heart.
The pulmonary artery carries blood from the heart to the lungs. The function of the lungs is to exchange gases. The carbon dioxide produced from carbohydrate and fat metabolism is carried in the bloodstream to the lungs where it is released to the atmosphere, and oxygen from the air is absorbed and stored in the hemoglobin of the red blood cells.
The aorta, which is the largest artery in the body, branches from the heart into the mesenteric and renal arteries that carry blood to the intestines and the kidneys, respectively. The blood in the capillaries of the intestines absorbs carbohydrates, proteins, and fats from the foods processed by the digestive system. Blood from the intestines goes to the liver via the hepatic portal vein. The liver removes toxins from the blood. In the liver, the ammonia produced from protein metabolism is combined with carbon dioxide to create urea. The blood from the liver flows back to the heart via the hepatic vein and the inferior vena cava. The kidneys remove nitrogen waste products from the blood. Uric acid from nucleic acid metabolism and urea from protein metabolism are filtered out by the kidneys and excreted in the urine. Blood from the kidneys goes through the renal vein, then to the inferior vena cava, and finally recirculates back to the heart.
Cardiovascular diseases, such as arterial plaque and hardening of the arteries, may result in heart attacks and strokes that are some of the leading causes of death. Proper diet and exercise can help to prevent cardiovascular diseases.
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