Anatomy and Physiology II Practice Test

Where does urine formation begin?

1. Secretion

2. Reabsorption

3. Filtration

4. Excretion

The correct answer is: Filtration

Urine formation begins with filtration, which occurs in the renal corpuscles of the nephron. During this initial process, blood enters the glomerulus, where water and small solutes are filtered out of the blood plasma into Bowman's capsule. This filtration step is crucial because it dictates the composition of the renal filtrate, which will undergo further processing in the renal tubules. In this phase, substances such as ions, glucose, urea, and water are filtered based on size and charge, allowing for the selective removal of waste products and excess substances from the bloodstream while retaining larger molecules like proteins and blood cells within the circulatory system. The filtrate then moves through the nephron, where reabsorption and secretion processes modify its composition before the final product, urine, is formed and excreted from the body.