. A by-product of protein catabolism is called__________.

A. Estrogen is a hormone involved in the regulation of the menstrual cycle and pregnancy, but it is not the hormone detected by pregnancy tests.

B. Luteinizing hormone (LH) surges just before ovulation but is not the hormone detected by pregnancy tests.

C. Progesterone supports pregnancy by maintaining the uterine lining, but it is not the hormone detected by pregnancy tests.

D. Human chorionic gonadotropin (hCG) is the hormone produced by the placenta shortly after implantation, and it is the hormone detected by pregnancy tests.

A. Diuretics increase urine output by inhibiting the reabsorption of water and sodium in the kidneys, which leads to increased water loss. This action is opposite to water conservation, making this the correct answer.

B. The counter current exchange system in the kidneys helps conserve water by maintaining a high osmolarity in the medulla, which facilitates the reabsorption of water in the collecting ducts. This system contributes to water conservation.

C. The collecting duct plays a crucial role in water reabsorption. Antidiuretic hormone (ADH) increases the permeability of the collecting duct to water, allowing more water to be reabsorbed back into the bloodstream, contributing to water conservation.

D. The counter current multiplier is a mechanism in the loop of Henle that creates a concentration gradient in the kidney medulla, which is essential for water reabsorption in the collecting ducts. It contributes to water conservation.