endocrine portion of the pancreas consists of cells
arranged in groups, called islands (islets) of
The islands (islets) of Langerhans
contain three types of endocrine cells: alpha, beta, and
delta. The alpha cells secrete the hormone glucagon.
Glucagon causes a temporary rise in blood sugar
levels. The beta cells secrete insulin, which is essential
for carbohydrate metabolism. Insulin lowers blood
sugar levels by increasing tissue utilization of glucose
and stimulating the formation and storage of glycogen
in the liver. Together, glucagon and insulin act to
regulate sugar metabolism in the body. Delta cells
produce the hormone somatostatin. Somatostatin
helps regulate carbohydrates by inhibiting the
secretion of glucagon.
When the islet cells are destroyed or stop
functioning, the sugar absorbed from the intestine
remains in the blood and excess sugar is excreted by
the kidneys into the urine. This condition is called
diabetes mellitus, or sugar diabetes. Insulin, a
synthetic hormone, is given to patients having this
disease as part of their ongoing treatment.
GONADS (TESTES AND OVARIES)
The term gonads refers to the primary sex organs
of the reproductive system (male and female).
The male gonad is the testis (pl. testes), and the
existence of the testes is the primary male sex
characteristic (fig. 1-47). The testes produce and
secrete the male hormone testosterone, which
influences the development and maintenance of the
male accessory sex organs and the secondary sex
characteristics of the male. The male accessory sex
organs include two groups of organs: the internal sex
organs and the external sex organs. See section titled
Male Reproductive System for more information on
the male accessory sex organs.
Male Secondary Sex Characteristics
Male secondary sex characteristics influenced by
the hormone testosterone are as follows:
Increased growth of hair, particularly in the areas
of the face, chest, axilla, and pubic region.
Enlargement of the larynx (Adam's apple) and
thickening of the vocal cords, which produces a
Thickening of the skin.
Increased muscle growth, broadening of the
shoulder and narrowing of the waist.
Thickening and strengthening of the bones.
The female gonads, the ovaries, produce the
hormones estrogen and progesterone (fig. 1-47).
E s t r o g e n i n f l u e n c e s t h e d e v e l o p m e n t a n d
maintenance of the female accessory sex organs
a n d t h e s e c o n d a r y s e x c h a r a c t e r i s t i c s , a n d
promotes changes in the mucous lining of the uterus
( e n d o m e t r i u m ) d u r i n g t h e m e n s t r u a l c y c l e .
Progesterone prepares the uterus for the reception
and development of the fertilized ovum and
maintains the lining during pregnancy.
Today, progesterone and estrogen hormones
(naturally derived) are incorporated into oral
contraceptives or birth control pills. The combination
of hormones released through this monthly series of
pills fools the body into not preparing (building-up of
uterine lining) for implantation of an embryo. Because
the uterus has not prepared for implantation,
pregnancy cannot occur.
Female accessory sex organs are also divided into
internal and external accessory sex organs. See section
titled Female Reproductive System for more
information on the female accessory sex organs.
Female Secondary Sex Characteristics
Female secondary sex characteristics influenced
by the hormone estrogen are listed below.
Development of the breasts and the ductile
system of the mammary glands within the
Increased quantities of fatty (or adipose) tissue
in the subcutaneous layer, especially in the
breasts, thighs, and buttocks.
Increased vascularization of the skin.