What physiological response occurs in normal kidneys of a hypo-perfused patient?

In a hypo-perfused state, the kidneys respond primarily by conserving resources to maintain blood volume and pressure. The physiological response of reabsorbing sodium and water is crucial because it helps to combat the effects of decreased perfusion and ensures that the body can maintain adequate blood pressure and circulate blood effectively to vital organs.

When renal perfusion decreases, the kidneys activate several mechanisms, including the renin-angiotensin-aldosterone system (RAAS). Aldosterone promotes sodium reabsorption in the renal tubules, which not only helps retain sodium but also leads to water reabsorption due to osmosis. This reabsorption process is essential for restoring intravascular volume and alleviating the risks inherent in hypoperfusion, such as hypotension and ischemia.

The other physiological responses, such as excretion of excess sodium, increased filtration at the glomerulus, and increased renal blood flow, do not align with the kidney's natural protective mechanisms in a hypo-perfused state. Instead, they would typically occur in the presence of adequate or increased blood flow and pressure. Thus, the correct response reflecting the physiological adaptation of the kidneys in a hypo-perfused patient is the conservation of sodium and water.