Which part of the kidney is reabsorption dependent upon needs at time and regulated by hormones?

The proximal convoluted tubule (PCT) is the part of the kidney where reabsorption is dependent upon needs at the time and regulated by hormones. The PCT is the first part of the nephron, and it is responsible for reabsorbing a large amount of water, sodium, and other nutrients from the filtrate. The reabsorption of these substances is regulated by a number of hormones, including aldosterone, antidiuretic hormone (ADH), and parathyroid hormone (PTH).

Aldosterone is a hormone that is produced by the adrenal glands. It is responsible for regulating the reabsorption of sodium and potassium in the PCT. When the body needs to retain sodium, aldosterone is released, and it causes the PCT to reabsorb more sodium and less potassium. This helps to maintain the body's fluid balance and blood pressure.

ADH is a hormone that is produced by the pituitary gland. It is responsible for regulating the reabsorption of water in the PCT. When the body needs to conserve water, ADH is released, and it causes the PCT to reabsorb more water. This helps to prevent dehydration.

PTH is a hormone that is produced by the parathyroid glands. It is responsible for regulating the reabsorption of calcium and phosphate in the PCT. When the body needs to increase its calcium levels, PTH is released, and it causes the PCT to reabsorb more calcium and less phosphate. This helps to maintain the body's calcium balance and bone health.

The reabsorption of substances in the PCT is a complex process that is regulated by a number of hormones. These hormones work together to maintain the body's fluid balance, blood pressure, and mineral levels.