Describe the hormonal regulation of water and electrolyte reabsorption in the ki

Question

Describe the hormonal regulation of water and electrolyte reabsorption in the kidneys. In your answer, make sure to address the following questions: (17 marks total)

a) Where is antidiuretic hormone (ADH) synthesized and where is it secreted? What is the primary stimulus for the secretion of ADH? Where does this hormone act? What effect does ADH have on the osmolarity of the renal filtrate? What is the specific mechanism responsible for producing this effect (Be specific)? (6 marks)

b) Describe the renin-angiotensin-aldosterone system (RAAS). What is the primary stimulus for the production of renin and where is renin secreted from? What are the specific steps involved in the RAAS pathway? Make sure to include the names of all of the enzymes and hormones involved, as well as their specific actions. Where does aldosterone act and what effect does it have? (8 marks)

c) Where is atrial natriuretic peptide (ANP) produced in the body? What stimulates the production of this hormone? What effect does it have on the kidneys? (3 marks)

Explanation / Answer

Ans.

(a). Antidiuretic hormone is synthesised in hypothalamus and secreted by Posterior pituitary gland.

Low blood volume, Low blood pressure, dehydration, high electrolytes concentration in blood, low levels of sodium in blood, nausea, Vomiting, pain and thirst stimulates secretion of ADH from pituitary gland into blood stream.

On release into blood stream this hormone acts on Renal tubules in the kidney and enhances reabsorption of water and sodium ion from the renal tubules back into the blood stream there by increasing the blood volume and blood pressure. It mainly acts on the late distal tubule and collecting duct of nephron in the kidney.

Regulation of urine osmolarity is key aspect of total ECF osmoregulation. When ECF osmolarity rises then kidney produces concentrated urine by returning water to ECF causing ECF dilution and when ECF osmolarity falls then kidney produces diluted urine thus removing water from ECF there by increasing the concentration of ECF.

The specific mechanism to produce this effect is by negative feedback mechanism and osmoregulation.

(b). RAAS is renin angiotensin aldosterone system. RAAS system controls systemic blood pressure and glomerulus filtration rate in kidney. When systemic blood pressure falls the baroreceptors in blood vessels sense this change which leads to secretion of renin from juxtaglomerular cells of kidney. On release, renin which is an enzyme converts angiotensinogen to angiotensin I hormone.This angiotensin I hormone is then converted to angiotensin II hormone in the presence of angiotensinogen converting enzyme(ACE). Angiotensin II when produced increases systemic blood pressure by constricting blood vessels, increases Renal perfusion pressure and increases glomerulus filtration rate. Angiotensin II acts to cause the release of aldosterone. Aldosterone acts on distal convulated tubule and collecting duct of nephron of kidney and helps in reabsorption of water in systemic circulation there by increasing systemic blood volume and blood pressure.

(c). ANP is synthesised and secreted by cardiac muscle cells in the wall of atria of heart. They contain volume receptors which respond to increase stretching of atrial wall due to increase atrial blood volume. ANP hormone reduces high ECF volume by increasing Renal sodium excretion there by increasing Renal water excretion and then reducing the ECF volume.

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