Glucose and amino acids are reabsorbed from the glomerular filtrate by

A. enhanced sodium ion loss in urine: Increasing the excretion of sodium would not address the underlying hydrogen ion excess or bicarbonate deficit. In fact, the kidneys typically attempt to retain sodium to maintain blood volume during the fluid loss associated with diarrhea. Electrolyte loss is a consequence of the illness rather than a corrective compensatory mechanism for pH.

B. increased respiratory rate and depth: The body compensates for metabolic acidosis by stimulating peripheral chemoreceptors to increase alveolar ventilation. This process, known as Kussmaul breathing, enhances the elimination of carbon dioxide from the blood. Reducing partial pressure of carbon dioxide shifts the carbonic acid-bicarbonate buffer equation to decrease the concentration of free hydrogen ions.

C. increased renin secretion: Renin secretion is a response to decreased blood pressure and volume resulting from fluid loss in diarrhea. While the subsequent production of aldosterone helps regulate electrolytes and blood pressure, it is not the primary mechanism for correcting systemic pH. Renin serves a hemodynamic rather than an immediate acid-base compensatory function.

D. hypoventilation: Decreasing the rate and depth of breathing would cause the retention of carbon dioxide, leading to an increase in carbonic acid. This would result in respiratory acidosis, which would exacerbate the existing metabolic acidosis instead of correcting it. Hypoventilation is a compensatory response for metabolic alkalosis, not acidosis.

A. protein-regulated diffusion. Large plasma proteins like albumin are too big to pass through the filtration membrane and remain in the capillaries. They actually create a colloid osmotic pressure that pulls water back into the blood, opposing filtration. Diffusion is a passive movement of solutes, not the primary mechanical force driving the high-volume ultrafiltration of plasma.

B. glomerular hydrostatic pressure (glomerular blood pressure). This is the blood pressure within the glomerular capillaries, which is typically much higher than in other capillary beds due to the high-resistance efferent arteriole. It serves as the dominant outward force that physically pushes water and small solutes through the filtration slits. It is the fundamental driver of the glomerular filtration rate.

C. the size of the pores in the basement membrane of the capillaries. The fenestrations and filtration slits determine the permeability and selectivity of the filter, essentially acting as a sieve. While these pores permit the passage of substances, they do not provide the energy or force to move them. They represent a physical constraint on what can pass rather than a driving force.

D. the ionic electrochemical gradient. Electrochemical gradients primarily drive the movement of specific ions across tubular epithelial cells during reabsorption and secretion. Glomerular filtration is a non-selective, bulk-flow process driven by mechanical pressure rather than individual ion concentrations. The process is governed by hydrostatic and osmotic pressures according to Starling's law.