Final answer:
Bowman's capsule oncotic pressure approaches zero because there are no proteins in Bowman's space to create an oncotic pressure. The other pressures, like glomerular oncotic and hydrostatic pressures, are significant and influence the net filtration pressure that drives kidney filtration.
Step-by-step explanation:
Within the glomerulus, the pressure that approaches zero is Bowman's capsule oncotic pressure. Oncotic pressure, also known as osmotic pressure caused by proteins, tends to pull water into the circulatory system. However, since there are no proteins in Bowman's capsule, its oncotic pressure is effectively zero.
The other pressures, such as glomerular capillary hydrostatic pressure and glomerular oncotic pressure, are significant and contribute to the movement of fluid through the nephron. The net filtration pressure (NFP), which is critical for the process of glomerular filtration, is determined by the hydrostatic pressures and colloid osmotic pressures on either side of the glomerular capillaries.
It is helpful to understand that the filtration barrier restricts the movement of cells and larger proteins, therefore, the colloid oncotic pressure in the glomerular capillaries is maintained whereas the Bowman's capsule does not contain these proteins and their associated oncotic pressure.