Question

The maximum amount of electrolytes and water (70 - 80%) from the glomerular filtrate is reabsorbed in which part of the nephron?
A. Ascending limb of loop of Henle
B. Distal convoluted tubule
C. Proximal convoluted tubule
D. Descending limb of loop of Henle

Answer 1

The first step in the process of urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration. The capillary blood pressure inside glomerulus causes filtration of blood.

Complete answer:
Ascending loop of Henle: In the ascending limb of the Henle loop, the reabsorption takes place which is minimal. Moreover, it also plays a vital role in the maintenance of high osmolarity of medullary interstitial fluid. Water is impermeable but the transport of electrolytes is allowed actively or passively in the ascending limb of the Henle. Therefore, due to the passage of electrolytes to the medullary fluid, the concentrated filtrate gets diluted as it passes upward. Hence, ‘option A’ is incorrect.
Distal Convoluted Tubule (DCT): Reabsorption of $N{a^ + }$ and water takes place in DCT. DCT is the site of the reabsorption of $HC{O_3}^ -$ and at the same time, selective secretion of hydrogen, ${K^ + }$ and $N{H_3}$ takes place. This whole process occurs to maintain the pH and sodium-potassium balance in the blood. Hence, ‘option B’ is incorrect.
Proximal Convoluted Tubule (PCT): Around 70% - 80% of electrolytes from the glomerular filtrate, nearly all of the nutrients and water are reabsorbed by PCT. It also helps in the maintenance of the pH and ionic balance of the body fluids. It is achieved by selective secretion of ${H^ + }$ , $N{H_3}$ and ${K^ + }$ into the filtrate and by absorption of $HC{O_3}^ -$ from it.
Descending loop of Henle: Water is permeable in the descending limb of the loop of Henle whereas it is impermeable to electrolytes. As it moves down, the filtrate becomes concentrated. Hence, ‘option D’ is incorrect.

Hence, the correct answer is option (C).

Note: Nephrons are the structural and functional units of the excretory system. The glomerulus is a network of capillaries formed by the afferent arteriole. Blood comes out through the efferent arteriole from the glomerulus. Bowman’s capsule encloses the glomerulus and together is called the malpighian body or renal corpuscle.