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The kidney's role in homeostasis (Regulatory (Regulation of …
The kidney's role in homeostasis
Regulatory
Regulation of acid-base balance
The kideney's main role in acid-base balance is through the excretion of acid in the form of hydrogen ions
To keep constant of hydrogen ions concentration is important for the constancy of the pH of body fluids through bicarbonate buffering system
Regulation of electrolyte balance
Potassium
An increase potassium in extracellular fluids stimulates more aldosterone secretion from the adrenal cortex to affect the distal tube of the nephron to secret potassium into the urine
The release of aldosterone stimulated by rises in extracellular potassium is controlled by a negative feedback system
Aldosterone is only hormone involved in control of Potassium content in the body
Phosphate
Phosphate is important in buffer system to maintain the pH of plasm and exists in equilibrium with calcium
Phosphate is reabsorbed in early proximal tubule if it is low in plasm. If there a rise in plasm, it is secreted from distal tubule into urine
Calcium
Small amounts of calcium in extracellular fluids are important to control nerves and muscle
Calcium reabsorbtion in distal tubule depends on the level of circulating PTH
Magnesium
Parathyroid hormone(PTH) increases tubular reabsorption of magnesium.
Magnesium is important intracellular cation involved in energy storage and production
Regulation of extracellular fluid volume and osmolality
Antidiuretic hormone (ADH) is secreted from posterior pituitary gland ADH receptors are in the collecting ducts of kidney tubule ADH is triggered by extracellular osmolality
When an rise in plasm osmolality is detected osmoreceptors, water is reabsorbed into blood
The fall in plasm osmolality leads to a slowing-down of ADH
secretion by negative feedback
Atrial natriuretic peptide is released from cardiac atrial cells
inhibition of aldoserone secretion
reduction of renin release
reduction of ADH
vasodilation
natriuresis amd diuresis
Aldosterone is secreted from the adrenal cortex. It effects on the
distal tubule of the nephron. The more aldosterone is secreted,
the more sodium is reabsorbed. However, it is regulated
angiotensin II.
Sodium is the main extracellular cation and is intimately related to extracellular volume. Therefore, an increase sodium content in body could lead to an increase in extracellular fluids volume and a decrease sodium content in body could lead to an decrease in extracellular fluids volume
Regulation of blood pressure
Metabolic
Activation of Vitamin D
Kidney in main sit for 25-hydroxyvitaminD
(25D) to circulating calcitriol
Vitamin D has a significant role in calcium homeostasis and metabolism
Production of erythropoietin (EPO)
EPO is produced by EPO cells of the kidney to maintain red cells count at normal levels.
EPO production is stimulated by hypoxia under negative feedback control
Production of renin
Renin is secreted by Juxtaglomerular cells which are located in the endothelium of the aterioles when macula densa in the distal tubule wall stimulate those cells
The macula densa and renin-releasing cells are collectively called the juxtaglomerular apparatus to remain constant blood flow through the glomerulus through tubule feedback mechanism
Renin acts via the renin-angiotensin system to produce both local vasoconstrction of efferent arteriole and peripheral vasoconstriction to increasarterial blood pressure, to regulate the secretion of aldosterone which is called renin-angiotensin-aldosterone system
Excretory
Excretion of wastes and toxins
Excess ions in urine: sodium, potassium, : calcium, magnesium, chloride, bicarbonate, phosphate ,ammonium
Metabolic wastes in urine:urea, uric acid and creatnine
Excretion of drugs and drug metabolites
Drugs are polarized and water-soluble(most of them detoxified in liver first) in urine
Excretion of other products of metabolism
hCG in urine is an example of Hormone metabolities for a diagnostic aid
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