An adult kidney is about 12 cm (5 inches) long, 6 cm (2.5 inches) wide, and 3 cm (1 inch) thick, about the size of a large bar of soap. Because it is crowded by the liver, the right kidney is positioned slightly lower than the left. These small, dark red organs with a kidney-bean shape lie against the dorsal body wall in a retroperitoneal position (beneath the parietal peritoneum) in the superior lumbar region they extend from the T12 to the 元 vertebra, thus they receive protection from the lower part of the rib cage. The kidneys, which maintain the purity and constancy of our internal fluids, are perfect examples of homeostatic organs. The kidneys alone perform the functions just described and manufacture urine in the process, while the other organs of the urinary system provide temporary storage reservoirs for urine or serve as transportation channels to carry it from one body region to another. The urinary system consists of two kidneys, two ureters, a urinary bladder, and a urethra. Kidney cells also convert vitamin D to its active form. By producing the enzyme renin, they help regulate blood pressure, and their hormone erythropoietin stimulates red blood cell production in the bone marrow. The kidneys also regulate the blood’s volume and chemical makeup so that the proper balance between water and salts and between acids and bases is maintained. Although the lungs and the skin also play roles in excretion, the kidneys bear the major responsibility for eliminating nitrogenous wastes, toxins, and drugs from the body. The kidneys then process this filtrate, allowing wastes and excess ions to leave the body in urine while returning needed substances to the blood in just the right proportions. Every day, the kidneys filter gallons of fluid from the bloodstream.
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The function of the kidneys are as follows: Practice Quiz: Urinary System Anatomy and Physiology.
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