What is the function of the nephron loop? The collecting duct? Antidiuretic hormone?

The nephron loop, also known as the loop of Henle, is a crucial part of a nephron, which is the basic functional and structural unit of the kidneys. It plays a major role in the reabsorption of water and ions (sodium and chloride) from the filtrate, and it helps in concentrating the urine and maintaining the proper balance of electrolytes in the body. The nephron loop is divided into two parts: the descending limb, which mainly reabsorbs water, and the ascending limb, which mainly reabsorbs sodium and chloride ions. This creates a concentration gradient in the medulla of the kidney, which aids in the conservation of water and maintenance of the body's osmolarity.

The collecting duct is a part of the nephron that receives filtrate from several nephrons and carries it down to the renal pelvis, where it eventually forms urine. The main function of the collecting duct is to fine-tune the reabsorption of water and sodium ions, as well as the secretion of potassium and hydrogen ions. The permeability of the collecting duct to water and ions is regulated by hormones like antidiuretic hormone (ADH) and aldosterone. By adjusting the amount of water and ions reabsorbed or secreted, the collecting duct helps maintain the body's electrolyte and acid-base balance, as well as its overall fluid balance.

Antidiuretic hormone (ADH), also known as vasopressin, is a hormone produced by the hypothalamus and released by the posterior pituitary gland. It plays a critical role in regulating the body's water balance by controlling the amount of water reabsorbed by the kidney's collecting ducts. When the body is dehydrated, or when there is an increase in the blood's osmolarity, the hypothalamus releases more ADH. This hormone then acts on the collecting ducts, making them more permeable to water and increasing water reabsorption. As a result, the body conserves water, and the urine becomes more concentrated. On the other hand, low levels of ADH result in less water reabsorption, leading to the production of dilute urine and water excretion.