Regulation of Kidney Function

REGULATION OF KIDNEY FUNCTION

Control by Antidiuretic Hormone (ADH):

ADH, produced in the hypothalamus of the brain and released into the blood stream from the pituitary gland, enhances fluid retention by making the kidneys reabsorb more water.

The release of ADH is triggered when osmoreceptors in the hypothalamus detect an increase in the osmolarity of the blood above a set point of 300 mosm L^–1.

In this situation, the osmoreceptor cells also promote thirst.

Drinking reduces the osmolarity of the blood, which inhibits the secretion of ADH, thereby completing the feedback circuit.

Control by Juxtaglomerular Apparatus (JGA):

Juxtamedullary nephrons help in retaining Na⁺ ions in high concentration in the interstitial fluid between the nephrons.

JGA operates a multi hormonal Renin-Angiotensin­ Aldosterone System (RAAS).

The JGA responds to a decrease in blood pressure or blood volume in the afferent arteriole of the glomerulus and releases an enzyme, renin, into the blood stream in the blood, renin initiates chemical reactions that convert a plasma protein, called angiotensinogen, to a peptide, called angiotensin II, which works as a hormone.

Angiotensin II is powerful constrictor of arterioles; one of the most potent vasopressor substances known.

Angiotensin II increases blood pressure by causing efferent arterioles to constrict.

It also increases blood volume in two ways : firstly, by signalling the proximal convoluted tubules to reabsorb more NaCl and water, and secondly, by stimulating the adrenal gland to release aldosterone, a hormone that induces the distal convoluted tubule to reabsorb more Na⁺ and water.

This leads to an increase in blood volume and pressure, completing the feedback circuit by supporting the release of renin.

Atrial Natriuretic Factor (ANF), opposes the regulation by RAAS. (Renin -Angiotensin -Aldosterone System).

The wall of the atria of the heart release ANF in response to an increase in blood volume and pressure.

ANF inhibits the release of renin from JGA. This inhibits the reabsorption of Na⁺ by the collecting duct and reduces release of aldosterone from adrenal gland.

It also increases excretion of Na+ in urine.