11th Class Biology Excretory Products and their Elimination Hormonal Control Of Renal Function

Hormonal controls of the kidney function by negative feedback circuits can be identified :

(1) 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.

(2) Control by Juxtaglomerular apparatus (JGA) : (Low Blood pressure triggers the Reninangiotension pathway) JGA operates a multihormonal 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 hormone, 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 increases blood pressure by causing arterioles to constrict. It also increases blood volume in two ways - firstly, by signaling 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.

(3) Parathormone : The hormone increases blood \[C{{a}^{++}}\] (Hypercalcium) and decreases \[P{{O}_{4}}\] accordingly, it increases absorption of \[C{{a}^{+}},\]increases excretion of \[P{{O}_{4}}.\]

(4) Thyrocalcitonin : It increases excretion of \[C{{a}^{++}}\] in the kidney.

(5) Prostaglandin : The renal pyramids produce fatty acids of prostaglandins (P.G.) which participates in blood pressure regulation.

(6) Erythropoeitin : It is secreted by juxtaglomerular apparatus and plays an important role in erythropoeisis (blood production).

Differences between Rennin and Renin