Question

2) Answer each of the following:

a) Describe the purpose and mechanism of action for aldosterone.

b) Describe how changes in osmolarity and blood pressure and volume are regulated by angiotensin and atrial natiuretic peptide.

c) Describe how pH is maintained in the proximal and distal tubules of the kidneys.

Thank you

Answer 1

Please find the answer as below.

Ans no 1) Aldosterone is the hormone produced by adrenal glands which have major role in regulation of blood pressure through its action on kidney excretory process .it causes reabsorption of water along with sodium and thereby increases blood volume and blood pressure

Mechanism of action is through renin-angiotensin-aldosterone system .Activation of this system occurs when the blood volume and pressure is low .in this reaction the enzyme renin result in production of angiotensin which in turn stimulate aldosterone release . Aldosterone causes renal tubules to reabsorb sodium and water from urine .

Ans no 2) atrial natriuretic peptide is a hormone secreted by the heart which have major role in reducing the amount of extracellular fluid in the body. ANP increases renal extraction of water and sodium and thereby reduces the blood pressure and volume and decreases osmolarity . aldosterone function is to increase the blood pressure that is against the ANP. ANP receive impulse from the volume receptors of atrial valve due to increase arterial blood volume . Angiotensin is hormone that causes vasoconstriction and increase the blood pressure .it acts on central nervous system to regulate the renal sympathetic nerve activity . angiotensinogen is produced from liver ,this is broken up by renin to form angiotensin I . it increase the sensation of thirst ,desire for salt and encourage release of other hormone that are involved in fluid retention .

In proximal convoluted tubule of kidney angiotensin II act to increase Na-H exchange increasing sodium reabsorption. Increase level of sodium in body will increase the osmolarity of blood . this increases blood pressure .

Ans no 3)In proximal renal tubule, following events happen to maintain blood pH.

a) secrete acid in to tubule lumen, thereby reabsorbing almost 80% of filtered HCO3- as well as generating new HCO3- for regulating blood pH.

b) Carbon dioxide entry through epical membrane and gas channel and it acidifies the cell .

c) Epical H+ secretion via Na-H exchange and H+ pumping .

d) Basolateral exit of HCO3- via electrogenic Na/HCO3 co transport

e) Regulation of overall HCO3- reabsorption by CO2 and HCO3- sensors at the membrane .

In distal convoluted tubule sodium reabsorption is mediated by aldosterone . DCT is responsible for maintaining potassium sodium and calcium level in blood . It regulates pH by absorbing bicarbonate and secret H+ into the filtrate or by absorbing H+ and secret bicarbonate into filtrate.