it curves back into the short (2.5 to 4 cm) anal
canal. The ANUS is the external opening at the
lower end of the digestive system. Except during
bowel movement (defecation), it is kept closed by
a strong muscular ring, the ANAL SPHINCTER.
ACCESSORY ORGANS OF DIGESTION
The PANCREAS is a large, elongated gland
lying posteriorly to the stomach. Its digestive
juices amylase, proteinase, and lipase are secreted
through the pancreatic duct into the duodenum
and act on all types of food. The pancreas con-
tains a special group of cells called the islands of
Langerhans, which secrete the hormone insulin
needed for use of sugar by the body.
The LIVER is the largest gland in the body.
It is located in the upper abdomen on the right
side, just under the diaphragm and superior to
the duodenum and pylorus.
Of its many functions, the following are im-
portant to remember:
Metabolism of carbohydrates, fats, and
proteins preparatory to their use or
Formation and excretion of bile salts and
pigment from bilirubin, a waste product
of red blood cell destruction.
Storage of blood and water and the pro-
ducts of carbohydrate, protein, and fat
Detoxification of end products of protein
digestion and drugs.
Production of antibodies and essential
elements of the blood-clotting mechanism.
Production of heat and formation of
vitamin A from carotin.
The GALLBLADDER is a pear-shaped sac,
usually stained dark green by the bile it contains.
It is located in a hollow on the underside of the
liver. Its duct, the cystic duct, joins the hepatic
duct from the liver to form the common bile duct,
which enters the duodenum. The gallbladder
receives bile from the liver and then concentrates
and stores it. It secretes bile when the small in-
testine is stimulated by the entrance of fats.
THE URINARY SYSTEM
The urinary system is the primary filtering
system of the body. It consists of two glands, the
kidneys, which produce urine; two tubes, the
ureters, which drain the urine from the kidneys;
a large reservoir, the bladder, where the urine is
temporarily stored before it is excreted from the
body; and a tube, the urethra, which carries the
urine from the bladder to the outside of the body.
All these parts, except the length of the urethra,
are the same in both sexes.
The importance of the kidney can be realized
only when its structure and function are
understood. It is the only part of the urinary
system in which any changes occur. The bladder,
ureters, and urethra store and pass only the prod-
ucts of the kidneys.
The kidneys are two large, bean-shaped organs
designed to filter waste materials from the blood
(fig. 3-53). They are located in the upper posterior
part of the abdominal cavity, outside the
peritoneal sac, one on each side of the spinal col-
umn. The upper end of each kidney reaches above
the level of the 12th rib. The suprarenal (adrenal)
gland sits like a cap on top of each kidney. Each
Figure 3-53.Cross section of the kidney.