Question

In the kidney, macula densa is present in
(a) Proximal convoluted tubule
(b) Loop of Henle
(c) Distal convoluted tubule
(d) Bowman’s capsule

Answer 1

Hint: The macula densa cells are part of the juxtaglomerular apparatus. Their function is to regulate the functioning of kidneys by observing the conditions of the blood pressure to maintain homeostasis in the body.

Complete Step by Step Answer:
The macula densa is found at the place where the distal convoluted tubule touches the afferent arteriole of the glomerulus. There is a thick lining of these cells present on the lining of DCT at this junction. The function of macula densa is that they act as salt checkers. They detect when there is a change in the sodium levels in the blood and release chemicals that allow the body to reabsorb or release sodium to bring back its level to normal.

So, the correct option is ‘Distal convoluted tubule’.

Additional information: Let us discuss the functioning of the juxtaglomerular apparatus in detail. A fall in the glomerular filtration rate GFR activates the JG cells to release renin which converts angiotensinogen in the blood to angiotensin I. This is further converted into angiotensin II which is a powerful vasoconstrictor, increases the blood pressure thus increasing GFR. Angiotensin II also stimulates aldosterone secretion which causes reabsorption of sodium and water from the distal parts of the nephron.

Note:
- There are receptors in the hypothalamus that detect a change in osmotic concentration and stimulate the release of the antidiuretic hormone ADH or vasopressin to regulate the kidney’s function.
- The atrial wall of the heart also releases atrial natriuretic factor ANF and acts as a check on the renin- angiotensin mechanism.