Which processes are involved in urine formation in nephron units?

Urine formation in the nephron, the functional unit of the kidney, involves three key processes: filtration, reabsorption, and secretion.

Filtration occurs in the glomerulus, where blood pressure forces water, ions, and small molecules from the blood into the Bowman's capsule, forming a filtrate. This process effectively removes waste products and excess substances while retaining larger molecules like proteins and blood cells.

Reabsorption takes place primarily in the proximal convoluted tubule and involves the selective movement of substances from the filtrate back into the bloodstream. This process allows the body to reclaim essential nutrients and water, preventing their loss and maintaining homeostasis.

Secretion occurs when additional substances, such as certain ions and metabolic waste products, are actively transported from the blood into the tubular fluid. This helps regulate electrolyte balance and eliminate toxins that were not filtered during the initial filtration process.

Together, these processes ensure that urine contains waste products while retaining important substances for bodily functions, highlighting the nephron's critical role in maintaining fluid and electrolyte balance.