AAMC FL Practice Exam

What is the sequence of the filtration pathway in the mammalian kidney?

1. Distal tubule, glomerulus, collecting duct

2. Proximal tubule, loop of henle, distal tubule, collecting duct

3. Glomerulus, proximal tubule, loop of henle, distal tubule, collecting duct

4. Collecting duct, distal tubule, proximal tubule

The correct answer is: Glomerulus, proximal tubule, loop of henle, distal tubule, collecting duct

The process of filtration in the mammalian kidney follows a specific sequence, beginning with the glomerulus, which is a network of capillaries housed within the Bowman’s capsule. Here, blood is filtered, allowing water, ions, and small molecules to pass through while retaining larger molecules and cells. This is the initial step of forming urine. After filtration at the glomerulus, the filtrate moves into the proximal tubule. In this section, a significant amount of reabsorption occurs, including nutrients, water, and ions back into the bloodstream. The next segment in the sequence is the loop of Henle, which has a descending and ascending limb that is crucial for establishing a concentration gradient in the medulla, contributing to water reabsorption. Following the loop of Henle, the filtrate enters the distal tubule, where further regulation of electrolytes and fluids occurs. Finally, the filtrate is collected in the collecting duct. This duct is important for the final adjustment of water reabsorption, influenced by hormones such as ADH (antidiuretic hormone). Thus, the correct sequence captures the entire journey of filtrate as it is processed through various nephron segments, ultimately leading to urine formation. This understanding is crucial