kidney - KIDNEYS The kidneys are organs that have numerous...

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KIDNEYS The kidneys are organs that have numerous biological roles: 1. Their primary role is to maintain the homeostatic balance of bodily fluids by filtering and secreting metabolites (such as urea) and minerals from the blood and excreting them, along with water, as urine. 2. The kidneys are poised to sense plasma concentrations of ions such as sodium, potassium, hydrogen, and compounds such as amino acids, creatinine, bicarbonate, and glucose, 3. They are important regulators of blood pressure, glucose metabolism, maintenance of acid- base balance and they are produced erythropoietin and vitamin D. The kidneys receive unfiltered blood directly from the heart through the abdominal aorta which then branches to the left and right renal arteries. Filtered blood then returns by the left and right renal veins to the inferior vena cava and then the heart. Renal blood flow accounts for 20-25% of the cardiac output. Renal physiology The nephron is the functional unit of the kidney. It consist with renal corpuscle (glomerulus and a Bowman's capsule), proximal tubule, loop of Henle, distal tubule This encompasses all functions of the kidney, including reabsorption of glucose, acids, and other small molecules; regulation of sodium, potassium, and other electrolytes; regulation of fluid balance and blood pressure; maintenance of acid-base balance; and the production of various hormones including erythropoietin and vitamin D. Much of renal physiology is studied at the level of the nephron, the smallest functional unit of the kidney. Each nephron begins with a filtration component that filters blood entering the kidney. This filtrate then flows along the length of the nephron, which is a tubular structure lined by a single layer of specialized cells and surrounded by capillaries. The major functions of these lining cells are the reabsorption of water and small molecules from the filtrate into the blood, and the secretion of wastes from the blood into the urine. Proper function of the kidney requires that it receives and adequately filters blood. This is performed at the microscopic level by many hundreds of thousands of filtration units 1
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called renal corpuscles, each of which is composed of a glomerulus and a Bowman's capsule. A global assessment of renal function is often ascertained by estimating the rate of filtration, called the glomerular filtration rate (GFR). Functions of the kidney The functions of the kidney can be divided into two groups: 1. secretion of hormones, 2. and extracellular homeostasis Secretion of hormones Secretion of erythropoietin ( regulates red blood cell production in the bone marrow). Secretion of renin , which is a key part of the renin-angiotensin-aldosterone system. Secretion of the active form of vitamin D ( calcitriol ) , and prostaglandins .
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