How do nephrons maintain osmotic balance in the body?

Nephrons maintain osmotic balance in the body by filtering blood and regulating water and electrolyte concentrations.

Nephrons, the functional units of the kidneys, play a crucial role in maintaining osmotic balance in the body. They achieve this through a complex process involving filtration, reabsorption, secretion, and excretion. The process begins when blood enters the nephron via the afferent arteriole and is filtered in the glomerulus, a network of tiny blood vessels. This filtration process separates waste products and excess substances from the blood, while retaining essential nutrients and electrolytes.

The filtered fluid, known as filtrate, then moves into the renal tubule, where reabsorption occurs. Here, useful substances such as glucose, amino acids, and a large amount of water are reabsorbed back into the bloodstream. This reabsorption process is selective and is regulated by hormones such as antidiuretic hormone (ADH) and aldosterone, which control the permeability of the renal tubule and the reabsorption of water and sodium respectively.

The next step is secretion, where certain substances such as hydrogen ions, potassium ions, and certain drugs are actively secreted from the blood into the renal tubule. This process helps to maintain the pH balance of the blood and to eliminate substances that are not filtered out in the glomerulus.

Finally, the remaining fluid, now called urine, is excreted from the body. This fluid contains waste products, excess water, and electrolytes, and its composition reflects the body's state of hydration and electrolyte balance.

In summary, nephrons maintain osmotic balance by filtering the blood, selectively reabsorbing water and essential substances, secreting certain substances, and excreting the remaining fluid as urine. This process is finely regulated by hormones and ensures that the body's internal environment remains stable, despite changes in the external environment or in the body's metabolic activities.