Question

Proximal convoluted tubule of nephron is responsible for
A)Filtration of blood
B)Maintenance of Glomerular Filtration Rate
C)Selective reabsorption of glucose, amino acid, NaCl and water
D)Reabsorption of salts only

Answer 1

In essence, the function of the proximal tubule is filtrate reabsorption in compliance with homeostasis (equilibrium) requirements, while the distal portion of the nephron and the collecting duct is primarily concerned with the thorough control of the balance of water, electrolytes and hydrogen-ion.

Complete answer:
The proximal tubule is the nephron portion of the kidneys that starts at the beginning of Henle's loop from the renal pole of the Bowman's capsule. The proximal convoluted tubule (PCT) and the proximal straight tubule may be further categorized into (PST).
The proximal convoluted tubule is active in the selective reabsorption into the peritubular capillary network of oxygen, amino acids, salt and water. Whilst water reabsorption is a passive process, glucose, amino acids and salts are actively reabsorbed. Glomerular blood filtration and glomerular filtration rate maintenance are the functions of the afferent arteriole and glomerulus.

By exchanging hydrogen ions in the interstitium for bicarbonate ions in the filtrate, the proximal tubule effectively controls the pH of the filtrate; it is also responsible for secreting amino acids such as creatinine and other bases into the filtrate.
The peritubular capillaries are reabsorbed by fluid in the filtrate that joins the proximal convoluted tubule. This is powered by the Na+/K+ ATPase in the basolateral membrane of the epithelial cells via sodium transfer from the lumen into the blood.

Hence, the correct answer is option (C)

Note: In the proximal tubule, much of the ammonium excreted in the urine is formed by the degradation of glutamine into alpha-ketoglutarate. This happens in two steps, both of which release an ammonium anion: glutamine to glutamate conversion and glutamate to alpha-ketoglutarate conversion.