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A fall in glomerular filtration rate (GFR) activates -
(a) Juxtaglomerular cells to release renin
(b) Adrenal cortex to release aldosterone
(c) Adrenal medulla to release adrenaline
(d) Posterior pituitary to release vasopressin

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Last updated date: 16th Jun 2024
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Answer
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Hint: The glomerulus is a highly important component of the kidney that is responsible for the filtration of blood. Any damage to it results in damage to filtration, leading to the buildup of toxic substances in the blood. The rate of filtration is thus maintained by various cells that release a particular hormone that normalizes the filtration rate.

Complete step by step answer:
- The Glomerular Filtration Rate or the (GFR) is a test that estimates how much blood is flowing through the glomeruli every minute. It is an efficient test to determine how well the kidneys are working.
- Kidneys have built-in regulatory mechanisms to maintain the GFR.
- Glomerular filtration occurs due to the pressure gradient in the glomerulus. The increase in GFR will be due to the increased blood pressure and blood volume.
-Construction of afferent arterioles going into the glomerulus and dilation of different arterioles coming out of the glomerulus will decrease GFR.
- The juxtaglomerular apparatus is formed by cellular modification at the location of the contact of the distal convoluted tubule and the afferent arteriole forming a special sensitive region.
- Low GFR activates the renin-angiotensin feedback system that senses the low GFR by increasing the blood volume.
- When the rate of GFR lowers it then activates the juxtaglomerular cells that in turn release the renin hormone whose function is to stimulate the glomerular blood flow and thereby normalizes the GFR level.
So, the correct answer is ‘Juxtaglomerular cells to release renin’.

Additional Information:
- The GFR is estimated by a medical professional from a blood creatinine test.
-The normal GFR number in the case of adults is more than 90 and decreases as the age increases, even in people without kidney disease.
- Hydrostatic pressure in Bowman’s capsule is necessary to decrease GFR. The osmotic pressure in the Bowman’s space is zero, but becomes present and decreases the GFR if the glomerulus becomes leaky.

Note:
- GFR is also known as eGFR or estimated glomerular filtration rate.
- Other tests to determine the functioning of the kidney include the simple urine analysis, creatinine clearance test, imaging tests like CT, kidney biopsy, and others.
- The juxtaglomerular apparatus is formed by the combination of juxtaglomerular cells and the macula densa.