Final answer:
In the proximal convoluted tubule of mammals, sodium reabsorption is coupled with the reabsorption of glucose and protons. This process involves the exchange of sodium and hydrogen ions, and the co-transport of sodium and glucose, which helps maintain blood pH levels and nutrient balance.
Step-by-step explanation:
In the mammalian proximal convoluted tubule, sodium reabsorption is coupled primarily with the reabsorption of glucose and to a lesser extent, with the exchange of protons. Thus, the correct answer to the question is d. glucose and protons. Sodium ions are primarily reabsorbed through an antiport mechanism in the apical membrane of cells lining the renal tubule, which allows for the exchange of sodium ions from the filtrate with hydrogen ions (H+). This is essential for balancing pH levels in the blood. Additionally, sodium-glucose transport proteins (SGLT) facilitate the co-transport of sodium and glucose back into the blood stream.
The reabsorption and secretion activities that define the function of the proximal convoluted tubule are crucial as this site reabsorbs ions, water, and nutrients, which include glucose, and adjusts filtrate pH by removing toxins. This fine-tuning of reabsorption ensures that necessary substances are returned to the bloodstream while waste products are excreted in urine.