Final answer:
The nephron of the kidney filters blood via the glomerulus, reabsorbs vital substances like Na, glucose, water, and bicarb in the renal tubule, and secretes waste products, ultimately forming urine.
Step-by-step explanation:
Kidney Function and Nephron Anatomy
The kidney serves a crucial role in filtering blood, maintaining homeostasis, and forming urine. Its basic functional unit is the nephron, which performs three primary processes: filtration, reabsorption, and secretion.
Filtration
Filtration takes place in the glomerulus, where blood pressure pushes water and solutes out of the blood and into Bowman's capsule. The result is a fluid called filtrate, which then enters the renal tubule.
Reabsorption
Reabsorption occurs predominantly in the proximal convoluted tubule (PCT), where substances like Na, glucose, water, and bicarb are transported from the filtrate back into the blood. Na is actively reabsorbed, creating an electrochemical gradient that facilitates the reabsorption of glucose and bicarb. Water is reabsorbed by osmosis following the solutes' concentration gradient.
Secretion
Substances such as certain ions and urea are secreted into the filtrate, removing them from the blood. Secretion primarily occurs in the distal convoluted tubule (DCT) and collecting duct.
The loop of Henle and the collecting duct are also involved in water reabsorption, aided by the countercurrent multiplication mechanism, which helps concentrate urine. The filtrate, now termed urine, exits the nephron and enters the collecting duct before being expelled from the kidney.