Press "Read More" to see the answers.
The correct answer is b. The kidney is part of the body’s excretory, or urinary, system. Its functional unit, the nephron, works to regulate the concentration of water in the blood. The nephron is a long tube-like structure that has multiple parts necessary for the regulation of ions, water, amino acids, and other molecules in the blood. When the blood enters the nephron through the afferent arteriole, it is passes through a network of capillaries (known as the glomerulus) and leaves through the efferent arteriole. The Bowman’s capsule filters out certain components of the blood, such as urea, water, and sodium chloride. This filtrate will then pass through the tubules, where it will end up in the collecting duct and exit as urine. When the filtrate travels through the Loop of Henle, two important things occur. In the descending limb of the Loop, water is reabsorbed by the blood, however sodium is not permitted to leave. In the ascending limb of the Loop, sodium is reabsorbed by the blood, however water is not permitted to leave. This creates a salty environment in the medulla of the kidney. Therefore, in the collecting duct, water gladly diffuses back out into the blood, thus created more concentrated urine (four times more concentrated, to be specific). ADH is a hormone synthesized by the hypothalamus and secreted by the posterior pituitary when the levels of water in the blood are too low (or when there is an increase in osmolarity). ADH increases the activity of aquaporins, allowing more water to be reabsorbed by the blood.
Most of these questions come from our tutors, who are always looking for ways to get students more interested in the subject.