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The kidney is surrounded by tough fibrous tissue, the renal capsule, which is itself surrounded by perirenal fat, renal fascia, and pararenal fat. The anterior (front) surface of these tissues is the peritoneum, while the posterior (rear) surface is the transversalis fascia. The superior pole of the right kidney is adjacent to the liver.
The first step in urine formation is the filtration of blood in the kidneys. In a healthy human, the kidney receives between 12 and 30% of cardiac output, but it averages about 20% or about 1.25 L/min. The basic structural and functional unit of the kidney is the nephron.
This illustration demonstrates the normal kidney physiology, including the Proximal Convoluted Tubule (PCT), Loop of Henle, and Distal Convoluted Tubule (DCT). It also includes illustrations showing where some types of diuretics act, and what they do. Renal physiology (Latin renes, "kidneys") is the study of the physiology of the kidney.
The kidneys are a pair of organs of the excretory system in vertebrates, which maintain the balance of water and electrolytes in the body (osmoregulation), filter the blood, remove metabolic waste products, and, in many vertebrates, also produce hormones (in particular, renin) and maintain blood pressure.
The unipapillary kidney with a single renal pyramid is the simplest type of kidney in mammals, from which the more structurally complex kidneys are believed to have evolved. [17] [6] [18] Differences in kidney structure are the result of adaptations during evolution to variations in body mass and habitats (in particular, aridity) between species.
The venous drainage of the kidney large mirrors its arterial supply, except that there are no segmental veins. [4] The stellate veins arise from the capillaries, then drain successively through interlobular veins and interlobar veins until these converge from across the kidney to form the renal vein for that kidney.
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Oxygen-deprived blood from the superior and inferior vena cava enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle, from which it is then pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs.