In the context of nephron function, what pressure pulls blood into the capillary?

The correct answer is osmotic pressure. In the context of nephron function, particularly within the glomerulus, osmotic pressure plays a vital role in the processes of filtration and reabsorption. Outside of the capillaries, the plasma proteins create an osmotic gradient that tends to draw water into the capillaries.

Osmotic pressure arises primarily from the presence of solutes, such as proteins, that cannot easily cross the capillary membrane. In the kidneys, this pressure is crucial because it helps to retain water in the blood and contributes to the regulation of blood volume and pressure.

While hydrostatic pressure is also significant in the context of blood flow and filtration, it primarily refers to the pressure exerted by fluids within the capillaries that push liquid out into the surrounding tissue. Conversely, arterial and venous pressure relate to the overall pressure gradients created by the heart’s contraction and vascular resistance but are not specifically responsible for the osmotic effects at the renal capillaries during filtration.