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The Kidney's role in homeostasis - Coggle Diagram
The Kidney's role in homeostasis
Fluid volume balance
Atrial natriuretic peptide (ANP)- is released from cardiac atrial cells in response to stretch in atrium from fluid overload.
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ADH- is secreted by the posterior pituitary gland and ADH receptors are found in collecting ducts of kidney tubules.
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Aldosterone- is a steroid hormone secreted from the adrenal cortex of the kidney and effects the distal tubule of the nephron. Secretion of aldosterone is regulated by peptide, angiotensin II.
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pH balance
The rise in hydrogen ion concentrattion (acidosis) is corrected by kidneys by secreting the excess hydrogen ion into the urine and in the process generation futher bicarbonate for reabsorption into the plasma. Fall in hydrogen ion concentration (alkalosis) in the body fluids is corrected by kidney by reducing the amount of hydrogen ion secretion in the urine.
pH scale that measures the concentration of free hydrogen ions in a fluid. The scale is reciprocal, when pH is low, hydrogen ions is high. Normal pH is between 7.35-7.45.
Kidney controls the acid base balance by controlling the bicarbonates ions concentration in the body.
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Electrolytes balance
Postassium-Aldosterone is the only hormone involved in the control of potassium content in the body.
When the aldosterone level falls, the reverse occurs and less potassium is secreted and is controlled by negative feedback system.
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.
Calcium- is important in the extracellular fluid in controlling nerve and muscle conduction
Calcium reabsorption occurs depending on the level of circulation parathyroid hormone (PTH).
Phosphate- is important in buffer systems to maintain the plasma pH and exists in equilibrium with calcium.
When plasma phosphate level is low, the filtered phosphate is reabsorbed in the early proximal tubule and if it is high, it is excreted in the urine.
Magnesium- also an important intracellura caption involved in energy storage and procution
Similar to calcium, increase in PTH, increase tubular reabsorption of magnesium.
Waste excretion in urine
Metabolites-most of hormone-for example human chorionic gonadotrophin in the urine in early pregnancies.
Excess ions-sodium, potassium, calcium, magnesium, chloride, bicarbonate, phosphate and ammonium.
Drug metabolites-most pharmacological agents are detoxified in liver and then excreted through the kidney.
Metabolic wastes-urea, creatinine, uric acid, nitrogenous waste.
Erythropoietin production
This hormone is produced by erythropoietin-producing cells of the kidney to maintain normal red cell count and prevention of anemia.
Erythropoietin production is stimulated by hypoxia and stopped when hypoxia is corrected, thus, its production is controlled by the negative-feedback principle.
Blood pressure control
Macular densa in the wall of distal tubule make contact with cells in the endothelium of the arterioles which relase a hormone called renin, this is called juxtaglomerular apparatus which maintains a constant blood flow through the glomerulus through tubule feedback mechanism.
Renin acts via the renin angiotensin system to produce both local vasconstriction of the efferent arteriole increasing GFR ad also peripheral vasoconstriction to increase arterial blood pressure.
For example: when there is dehydration, sodium deficiency or haemorrhage, there will be decrease in blood volume and blood pressure
This will stimulate kidney to produce renin which produce angiotensin I which is converted to angiotensin II.
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