3-12. FUNCTIONS OF THE ACCESSORY ORGANS OF DIGESTION AND THE
The liver, the gallbladder, the pancreas, and the small intestine play closely
interrelated roles in the digestion and absorption of food.
a. The liver secretes about 650 milliliters of bile per day. The hepatic duct
carries the bile (between meals) to the gallbladder. There, the bile is concentrated (by
removal of water) so that each 10 milliliters of bile secreted by the liver is reduced to
about 1 milliliter. When chyme containing fats enters the duodenum, the gallbladder
contracts and the bile is emptied into the duodenum by way of the cystic and common
bile ducts. Pancreatic juice (which contains several enzymes that facilitate the break
down of undigested proteins, carbohydrates, and fats) enters the duodenum
simultaneously with the bile. Bile emulsifies fats and the pancreatic lipase splits them
into fatty acids and glycerol.
b. In the jejunum and ileum, the intestinal juice completes the hydrolysis of
carbohydrates to simple sugars and of proteolytic products to amino acids. Sugar
metabolism provides muscular energy and the amino acids are chiefly rebuilt into
proteins for the maintenance of cells. Neutral fat is absorbed and stored until needed.
c. In addition to excreting bile, the liver assists in removing disintegration
products of hemoglobin (bile pigments) from the plasma. The liver also receives the
products of digestion after absorption and converts them into other substances. It
converts glucose to glycogen, which it stores; removes nitrogen from amino acids; and
forms fibrinogen and heparin, which function in the clotting of the blood.
d. The pancreas contains cells that make insulin, which is secreted directly into
the bloodstream. Insulin is a hormone essential for glucose metabolism.
Section II. THE UROGENITAL SYSTEM
The urogenital system (figures 3-8 and 3-9) consists of the urinary organs for the
production and elimination of urine and the genital organs, which are concerned with
reproduction. The urinary system removes waste products of metabolism from the
blood. In the average man, the kidneys clear about 1,300 milliliters of blood per minute;
therefore, in approximately 5 minutes, all of the blood is circulated through the kidneys.
In addition to filtering the waste products from the bloodstream, the kidneys also help to
maintain the alkaline and acid balance of the blood and the required level of body fluids.