Which hormone regulates urine concentration through reabsorption?

The regulation of urine concentration is primarily influenced by antidiuretic hormone (ADH), also known as vasopressin. ADH is secreted by the posterior pituitary gland in response to changes in osmotic pressure within the blood. When the body senses that hydration levels are low or that the blood is too concentrated, ADH is released into the bloodstream.

Once in the kidneys, ADH acts on the collecting ducts, making them more permeable to water. This increased permeability allows for more water to be reabsorbed back into the bloodstream rather than being excreted as urine. As a result, urine becomes more concentrated, which helps the body retain water and maintain appropriate fluid balance. Thus, ADH plays a crucial role in osmoregulation and the concentration of urine.

The other choices are associated with different functions in the body. Parathyroid hormone (PTH) primarily regulates calcium levels in the blood rather than urine concentration. Atrial natriuretic peptide (ANP) is involved in the reduction of blood volume and pressure by promoting the excretion of sodium and water, leading to increased urine output rather than concentration. Glomerular filtration rate (GFR) indicates the rate at which the kidneys filter