Medical Laboratory Scientist (MLS) ASCP Practice Exam

What is the primary mechanism responsible for glomerular filtration?

1. Osmotic pressure in the Bowman’s capsule

2. Hydrostatic differential in glomerular tufts

3. Active transport of substances through the renal tubules

4. Selective permeability of the glomerular membrane

The correct answer is: Hydrostatic differential in glomerular tufts

The primary mechanism responsible for glomerular filtration is the hydrostatic pressure differential found in the glomerular tufts. This pressure gradient forces water and solutes from the blood in the glomeruli into the Bowman’s capsule, initiating the filtration process. The glomerular capillaries are designed with a high hydrostatic pressure due to the unique arterial connection and the narrow efferent arterioles, which enhances the filtration of plasma. While factors such as osmotic pressure and selective permeability of the glomerular membrane play significant roles in the overall process of renal function, they do not primarily initiate glomerular filtration. Osmotic pressure in Bowman’s capsule counters filtration by creating a force opposing the hydrostatic pressure, which helps regulate the final composition of urine, but it isn’t responsible for the filtration itself. Active transport through renal tubules occurs later in the nephron, after filtration has taken place, to reclaim essential substances and maintain homeostasis, making it unrelated to the mechanism of glomerular filtration itself.