Role of kidney in homeostasis
Waste excretion in Urine
Electrolytes Balance
pH balance
Blood pressure control
Erythropoietin production.
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Fluid volume balance.
Erythropoietin is a hormone produced by the kidney and released in response to hypoxia and decreased renal blood flow.
Erythropoietin stimulates the production of RBCs in the bone marrow. A deficency of erythropoietin in renal failure leads to anemia.
macular densa in the wall of distal tubule make contact with cells in the endothelium of the arterioles which release a hormone called renin, this is called juxtaglomerullar apparatus which maintains a constant blood flow through the glomerulus through tubule feedback mechanism. For example: when there is dehydration, sodium deficency, or blood loss, there will be decrease in blood volume and blood pressure.
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Renin acts via the renin angiotensin system to produce both local vasoconstriction of rthe efferent arteriole increasing GFR and also peripheral vasoconstriction to increase artereial blood pressure.
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This will stimulate kidney to produce renin which produce angiotensinogen 1 which is converted to angiotensinogen II.
Release of angiotensinogen II stimulates adrenal cortex to produce aldosterone which reabsorbed more sodium and water and eliminates potassium which increase blood volume and blood pressure.
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Excess ions- sodium, pottassium, calcium, magnesium, chloride, bicarbonate, phosphate and ammonium.
Metabolic waste - urea, creatinine, uric acid and nitrogenous waste product.
Drug metabolites - most pharmacological agents are detoxified in liver and then excreted through the kidney.
Hormone metabolic waste like human chorionic gonadotrophin in the urine early pregnancies.
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Potassium - Aldosterone is the only hormone involved in the control of potassium content in the body.
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Calcium- is important in the extracellular fluid in controlling nerve and muscle conduction.
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Small increase of extracellular potassium directly stimulates adrenal cortex to produce aldosterone which affects the distal tubule of the nephron to secrete potassium into the urine. when the aldosterone level falls, the reverse occurs and less potassium is secreted and is controlled by negative feedback system.
Calcium reabsorption occurs depending on the level of circulating parathyroid hormone.
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