How do nephrons respond to antidiuretic hormone (ADH)?

Nephrons respond to antidiuretic hormone (ADH) by increasing water reabsorption in the collecting ducts.

ADH, also known as vasopressin, is a hormone produced in the hypothalamus and stored in the posterior pituitary gland. It plays a crucial role in maintaining the body's water balance. When the body is dehydrated, ADH is released into the bloodstream. The hormone then travels to the kidneys, where it acts on the nephrons, the functional units of the kidney.

Nephrons are composed of a glomerulus and a tubule. The glomerulus filters the blood, and the tubule processes the filtrate to form urine. The last part of the tubule, the collecting duct, is where ADH exerts its effect. ADH makes the walls of the collecting ducts more permeable to water. This means that more water is reabsorbed from the urine back into the bloodstream, reducing urine volume and helping to concentrate the urine. This process helps to conserve water and maintain the body's fluid balance.

The action of ADH on the nephrons is a fine example of the body's homeostatic mechanisms. When the body is dehydrated, the blood becomes more concentrated, a condition known as hyperosmolarity. This is detected by osmoreceptors in the hypothalamus, which trigger the release of ADH. The increased reabsorption of water in the nephrons dilutes the blood, bringing it back to its normal osmolarity. If the body is well-hydrated, less ADH is released, resulting in less water reabsorption and more dilute urine.

In summary, the nephrons respond to ADH by increasing water reabsorption in the collecting ducts, a process that is crucial for maintaining the body's fluid balance and preventing dehydration.