Explain the autoregulatory mechanism of GFR.
The kidneys have built-in mechanisms for the regulation of glomerular filtration rate (GFR). One such efficient mechanism is carried out by the Juxta Glomerular Apparatus (JGA), a special sensitive region formed by cellular modifications in the distal convoluted tubule and afferent arteriole at their contact location.
A fall in GFR can activate the JG cells to release renin, which converts angiotensinogen in blood to angiotensin I and further to angiotensin II. Angiotensin II acts as a powerful vasoconstrictor, increasing the glomerular blood pressure and thereby restoring GFR to normal.
Additionally, angiotensin II activates the adrenal cortex to release Aldosterone, which causes reabsorption of Na⁺ and water from the distal parts of the tubule. This also leads to an increase in blood pressure and GFR. This complex mechanism is known as the Renin-Angiotensin mechanism.
Explanation
The answer covers the complete autoregulatory mechanism of GFR as described in the NCERT textbook. It includes: (1) the role of JGA as the regulatory apparatus, (2) the renin-angiotensin cascade explaining how fall in GFR triggers renin release leading to angiotensin II formation, (3) the vasoconstrictor effect of angiotensin II increasing blood pressure and GFR, and (4) the role of aldosterone in Na⁺ and water reabsorption. The answer is within the 80-120 word limit appropriate for a 3-mark question.