The following are considered functions of the Urinary System, EXCEPT:
A. Vitamin D synthesis
B. Regulation of red blood cell synthesis
C. Excretion
D. Absorption of digested molecules
E. Regulation of blood volume and pressure
Correct Answer: D. Absorption of digested molecules
This is a function of the digestive system. The small molecules that result from digestion are absorbed through the walls of the intestine for use in the body. Digestion is the process of mechanically and enzymatically breaking down food into substances for absorption into the bloodstream.
Option A: This is a function of the urinary system. The kidneys play an important role in controlling blood levels of Ca2+ by regulating the synthesis of vitamin D. The kidneys have an important role in making vitamin D useful to the body. The kidneys convert vitamin D from supplements or the sun to the active form of vitamin D that is needed by the body. With chronic kidney disease, low vitamin D levels can be found, sometimes even severely low levels.
Option B: This is a function of the urinary system. The kidneys secrete a hormone, erythropoietin, which regulates the synthesis of red blood cells in the bone marrow. The kidney produces 85 percent of circulating erythropoietin; the liver, the remainder. If you move to a higher altitude, the partial pressure of oxygen is lower, meaning there is less pressure to push oxygen across the alveolar membrane and into the red blood cell.
Option C: This is a function of the urinary system. The kidneys are the major excretory organs of the body. They remove waste products, many of which are toxic, from the blood. The urinary system includes the kidneys, ureters, bladder and urethra. This system filters the blood, removing waste and excess water. This waste becomes urine.
Option E: This is a function of the urinary system. The kidneys play a major role in controlling the extracellular fluid volume in the body by producing either a large volume of dilute urine or a small volume of concentrated urine. Due to osmosis, water follows where Na+ leads. Much of the water the kidneys recover from the forming urine follows the reabsorption of Na+. Antidiuretic hormone stimulation of aquaporin channels allows for regulation of water recovery in the collecting ducts. It is through these means that blood volume and osmolarity are regulated by the kidneys.