The _____________ regulates the flow of contents from the stomach to the duodenum.

The slow block is a mechanism that prevents polyspermy, which is the fertilization of an egg by more than one sperm. It does not prevent fertilization of another egg when one is already pregnant. The slow block involves changes in the egg's membrane after a sperm has entered, making it impermeable to other sperm. Therefore, this statement is false.

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.