What is the function of the glomerulus in the kidneys?

The glomerulus serves a critical role in the kidneys by filtering blood to form urine. As a network of tiny capillaries located at the beginning of the nephron, the glomerulus allows for the passage of water, electrolytes, and small molecules from the blood into the Bowman’s capsule, a part of the nephron. This process is known as glomerular filtration and is essential for the formation of urine.

In this filtering process, larger molecules such as proteins and blood cells are generally retained in the bloodstream due to their size, while waste products and excess substances are filtered out. This initial filtration is crucial for maintaining the body's homeostasis, as it allows for the excretion of waste while preserving necessary nutrients in circulation.

While other structures in the nephron are concerned with reabsorption and secretion, the specific function of the glomerulus is distinctly centered on the filtration of blood. Thus, the primary function of the glomerulus is accurately described by the correct answer.