AAMC FL Practice Exam

During the initial filtration step in the kidneys, what components are excluded from Bowman's Capsule?

1. Water and salts

2. Cells and large proteins

3. Amino acids and glucose

4. Only nutrients

The correct answer is: Cells and large proteins

The initial filtration step in the kidneys occurs in Bowman's Capsule, part of the nephron, where blood is filtered to form urine. This process relies on the size and charge of various components present in the blood. During this filtration process, large molecules, particularly cells (such as red and white blood cells) and large proteins (like albumin), are excluded from passing into the Bowman's Capsule. This is due to the structure of the glomerular filtration membrane, which contains slits that are too small for these larger entities to pass through. The filtration mechanism is designed to retain these larger components within the bloodstream while allowing smaller substances, such as water, ions, glucose, and amino acids, to filter through into the renal tubule. The rationale behind this selective filtration is to ensure that essential components that the body needs, such as nutrients and proteins, remain in circulation, while waste products and excess substances can be excreted. The presence of cells and large proteins in the filtrate would indicate a pathological condition, as under normal circumstances, they should not be found in the urine. Therefore, the correct answer emphasizes the exclusion of cells and large proteins from Bowman's Capsule during filtration, which is a critical aspect of kidney function