Question

Removal of proximal convoluted tubule from the nephron will result in
A. No change in quality and quantity of urine
B. No urine formation
C. More diluted urine
D. More concentrated urine

Answer 1

The proximal tubule efficiently regulates the pH of the filtrate by exchanging hydrogen ions in the interstitium for bicarbonate ions in the filtrate; it is also responsible for secreting organic acids, such as creatinine and other bases, into the filtrate.

Complete answer: The proximal convoluted tubule(PCT) is involved in the active and passive absorption of solutes like sodium, potassium, bicarbonate, amino acids, etc. present in the filtrate and passing it into the capillaries. Due to the solute absorption, water potential is lowered in the capillaries and so, the water from the filtrate also moves across the proximal convoluted tubule into the capillaries. Therefore, the removal of the proximal convoluted tubule (PCT) will result in the formation of highly dilute(more water) urine. The PCT secretes organic acids and bases such as bile salts, oxalate, and catecholamines (waste products of metabolism). Hydrogen ions- important in maintaining acid/base balance in the body. H+ secretion allows reabsorption of bicarbonate via the use of the enzyme carbonic anhydrase. PCT absorbs some of the solutes completely and others partially; i.e., there is a separation of substances that must be retained from those due for rejection. Subsequently, the loop of Henle, distal convoluted tubule(DCT), and collecting ducts are mainly concerned with the conc. of urine to provide control of water and electrolyte balance.
So, the correct answer is D.

Note: The 1st part is called the proximal convoluted tubule (PCT) due to its proximity to the glomerulus. The second part is called the loop of Henle, or nephritic loop because it forms a loop with descending and ascending limbs that goes from the renal medulla.