AAMC FL Practice Exam

What type of molecules freely pass into Bowman's Capsule during filtration in the kidneys?

1. Large proteins

2. Cells and platelets

3. Small molecules such as glucose and water

4. Only ions

The correct answer is: Small molecules such as glucose and water

In the context of renal physiology, Bowman's Capsule is part of the nephron, the functional unit of the kidney. During the process of glomerular filtration, the glomerulus allows certain substances to pass into Bowman's Capsule while restricting others based on size and charge. Small molecules such as glucose and water can easily pass through the pores in the glomerular filtration barrier because of their size and the relatively non-selective nature of the filtration membrane. The filtration barrier is designed to allow substances that are below a certain size threshold to move into the renal tubule, facilitating their subsequent reabsorption or excretion depending on the body's needs. Larger molecules, like proteins, and cellular components, such as cells and platelets, are generally too large to pass through the filtration slits and are retained in the bloodstream, which helps maintain appropriate concentrations and functions of these molecules. Additionally, while ions can pass through, the emphasis of the question on molecules implies a broader range of small solutes, including glucose and water, making these small molecules the best representative option.