The adrenal cortex also produces sex hor-
mones, some with male characteristics (AN-
DROGENS), others with female characteristics
(ESTROGENS). These hormones appear in dif-
ferent concentrations in both men and women.
The adrenal medulla secretes EPINEPHRINE
(ADRENALIN) in the presence of emotional
crises, hypoglycemia (low blood sugar), or low
Epinephrine constricts the
peripheral vascular system and dilates the blood
vessels to the skeletal muscles. Heart rate, respira-
tion rate and depth, blood pressure, blood sugar
levels, and metabolism are all increased by
epinephrine. It also stimulates the production of
other adrenal cortical hormones.
NOREPINEPHRINE is also produced in the
adrenal medulla. It is a chemical precursor to
epinephrine. Its effects are similar to those of
epinephrine, but its action differs.
Despite these marked influences, the
medullary tissue of the adrenal gland is not essen-
tial to life, because its various functions can be
assumed by other regulatory mechanisms.
The male gonads secrete the hormone
TESTOSTERONE, which influences the develop-
ment and maintenance of the accessory organs
and the secondary sex characteristics of the male.
The female gonads, the OVARIES, produce
ESTROGEN and PROGESTERONE. Estrogen
influences the development and maintenance of
the female accessory organs and the secondary sex
characteristics and promotes changes in the
mucous lining of the uterus (endometrium) dur-
ing the menstrual cycle. Progesterone prepares the
uterus for the reception and development of the
fertilized ovum and maintains the lining during
pregnancy. It is used in many birth control pills.
The islands of Langerhans in the pancreas
contain two types of endocrine cells, alpha and
beta. The alpha cells secrete glucagon, which
causes a temporary rise in blood sugar levels. The
beta cells secrete insulin, which is essential for car-
bohydrate metabolism. Insulin lowers blood sugar
levels by increasing tissue utilization of glucose
and stimulating the formation and storage of
Figure 3-52.The digestive system.
glycogen in the liver. Together, glucagon and in-
sulin act to regulate sugar metabolism in the body.
When the islet cells are destroyed or stop func-
tioning, the sugar absorbed from the intestine re-
mains in the blood and is excreted by the kidneys
into the urine. It is not used by the body or stored.
This condition is called diabetes mellitus, or sugar
diabetes. Insulin is given to patients having this
disease as part of their ongoing treatment.
THE DIGESTIVE SYSTEM
The digestive system (fig. 3-52) consists of the
alimentary tractmouth, pharynx, esophagus,
stomach, intestines, and certain accessory organs
of digestion. As food passes through the 9-meter-
long alimentary tract, digestion and absorption
occur, and eventually waste material is eliminated.
Secretions of the accessory organs assist in prepar-
ing food for absorption and use by the tissues of
the body (table 3-2).
Digestion is both mechanical and chemical.
Mechanical digestion occurs when food is chewed,
swallowed, and churned by peristalsis. Waste is
evacuated when the bowels move. Chemical diges-
tion consists of changing the various foods, with