Regulation and Integration of the Body
Glucagon, released by alpha (
) cells when blood levels of glucose
are low, stimulates the liver to release glucose to the blood.
Insulin is released by beta (β) cells when blood levels of glucose
(and amino acids) are rising. It increases the rate of glucose
uptake and metabolism by most body cells. Hyposecretion or
hypoactivity of insulin results in diabetes mellitus; cardinal signs
are polyuria, polydipsia, and polyphagia.
Endocrine System; Topic: The Actions of Hormones on Target
Cells, pp. 5 and 8.
The Gonads and Placenta
Te ovaries of the female, located in the pelvic cavity, release two
main hormones. Te ovarian follicles begin to secrete estrogens
at puberty under the inﬂuence of FSH. Estrogens stimulate
maturation of the female reproductive system and development
of the secondary sex characteristics. Progesterone is released in
response to high blood levels of LH. It works with estrogens in
establishing the menstrual cycle.
Te testes of the male begin to produce testosterone at puberty
in response to LH. ±estosterone promotes maturation of the
male reproductive organs, development of secondary sex
characteristics, and production of sperm by the testes.
Te placenta produces hormones of pregnancy—estrogens,
progesterone, and others.
Hormone Secretion by Other Organs
Many body organs not normally considered endocrine organs
contain cells that secrete hormones. Examples include the
heart (atrial natriuretic peptide); gastrointestinal tract organs
(gastrin, secretin, and others); the kidneys (erythropoietin); skin
(cholecalciferol); adipose tissue (leptin, resistin, and adiponectin);
bone (osteocalcin); and thymus (thymic hormones).
Te thymus, located in the upper thorax, declines in size and
function with age. Its hormones, thymulin, thymosins, and
thymopoietins, are important to the normal development of the
Developmental Aspects of the Endocrine System
Endocrine glands derive from all three germ layers. Tose
derived from mesoderm produce steroid hormones; the others
produce the amino acid–based hormones.
Te natural decrease in function of the female’s ovaries during
late middle age results in menopause.
All endocrine glands gradually become less eﬃcient as aging
occurs. Tis change leads to a generalized increase in the
incidence of diabetes mellitus and a lower metabolic rate.
The Adrenal (Suprarenal) Glands
Te paired adrenal (suprarenal) glands sit atop the kidneys. Each
adrenal gland has two functional portions, the cortex and the
The Adrenal Cortex
Te cortex produces three groups of steroid hormones from
Mineralocorticoids (primarily aldosterone) regulate sodium
ion reabsorption and potassium ion excretion by the kidneys.
Sodium ion reabsorption leads to water reabsorption, and raises
blood volume and blood pressure. Release of aldosterone is
stimulated by the renin-angiotensin-aldosterone mechanism,
rising potassium ion levels in the blood, and AC±H. Atrial
natriuretic peptide inhibits aldosterone release.
Glucocorticoids (primarily cortisol) are important metabolic
hormones that help the body resist stressors by increasing blood
glucose, fatty acid and amino acid levels, and blood pressure.
High levels of glucocorticoids depress the immune system and
the inﬂammatory response. AC±H is the major stimulus for
Gonadocorticoids (mainly androgens) are produced in small
amounts throughout life.
Hypoactivity of the adrenal cortex results in Addison’s disease.
Hypersecretion can result in aldosteronism, Cushing’s syndrome,
and adrenogenital syndrome.
The Adrenal Medulla
Te adrenal medulla produces catecholamines (epinephrine and
norepinephrine) in response to sympathetic nervous system
stimulation. Catecholamines enhance and prolong the ﬁght-or-
ﬂight response to short-term stressors. Hypersecretion leads to
symptoms typical of sympathetic nervous system overactivity.
Endocrine System; Topic: Response to Stress, pp. 5–8.
The Pineal Gland
Te pineal gland is located in the diencephalon. Its primary
hormone is melatonin, which inﬂuences daily rhythms and may
have an antigonadotropic eﬀect in humans.
Other Endocrine Glands and Tissues
Te pancreas, located in the abdomen close to the stomach, is
both an exocrine and an endocrine gland. Te endocrine portion
(pancreatic islets) releases insulin and glucagon and smaller
amounts of other hormones to the blood.
(Some questions have more than one correct answer. Select the best
answer or answers from the choices given.)
Te major stimulus for release of parathyroid hormone is
Te anterior pituitary secretes all but
A hormone not involved in glucose metabolism is
increases bone formation and lowers
blood calcium levels,
increases calcium excretion from
decreases calcium absorption from the gut,
demineralizes bone and raises blood calcium levels.
Choose from the following key to identify the hormones