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A hormone is a regulating substance secreted by an endocrine gland.
A target cell is any cell with one or more receptors for a particular hormone.
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All steroid hormones have a cholesterol
molecule at their core. The molecule
consists of three six-sided rings and one
five-sided ring joined together.

The major categories of nonsteroid
hormones are protein hormones,
glycoprotein hormones, peptide hormones,
and amino acid derivative hormones.
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The following is the second messenger mechanism
most completely explained in the text. The hormone
joins a receptor on the cell membrane. This hormonereceptor complex causes a membrane protein called
the G protein to bind to a nucleotide called guanosine
triphosphate. This activates a second membrane
protein called adenyl cyclase. This is an enzyme that
promotes the removal of two phosphate groups from
an ATP molecule in the cytosol. The product of this is
cyclic adenosine monophosphate (cAMP). The cAMP
acts as a second messenger within the cell. The
cAMP activates protein kinases, which are a set of
enzymes that activate other types of enzymes. It is
this final set of specific, activated enzymes that
catalyze the reaction that is characteristic of the cell's
response to the hormone.

Calmodulin is an intercellular molecule
that can bind to calcium ions. The calciumcalmodulin complex that forms can act as
a second messenger, producing the target
cell's response.
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There are nine structural classes of
prostaglandins classified as A through I. The
text discusses the following three classes:
Prostaglandins A result in an immediate fall
in blood pressure accompanied by an increase
in regional blood flow to several areas,
including the coronary and renal systems.
These effects are apparently caused by the
relaxation of smooth muscle fibers in the walls
of certain arteries.

Prostaglandins E have an important
role in various vascular, metabolic, and
gastrointestinal functions. Vascular
effects include regulation of red blood cell
deformability and platelet aggregation.
PGEs also have a role in systemic
inflammations such as fever. PGEs also
regulate hydrochloric acid secretions in
the stomach, helping to prevent gastric
ulcers.

Prostaglandins F play an important role in
the reproductive system. They cause
uterine muscle contraction. PGFs also
affect intestinal motility and are required
for normal peristalsis.

The two subdivisions of the
adenohypophysis are the pars anterior
and the pars intermedia.

There are three types of cells in the
anterior pituitary gland that are identified
by their staining tendency: (1)
chromophobes, which literally means
"afraid of color"; (2) acidophils, which
have an attraction to acid stains; and (3)
basophils, which have an attraction to
basic stains (no percentages are given in
the text).

Growth hormone promotes bodily growth
indirectly by stimulating the liver to produce
certain growth factors that accelerate amino
acid transport into the cell. This allows protein
anabolism at an increased rate, which allows
an increased rate of growth. Growth hormone
promotes growth in bone, muscle, and other
tissue. Growth hormone also stimulates fat
metabolism, accelerates mobilization of lipids
from storage and speeds up catabolism of
those lipids. It also causes blood glucose
levels to rise.

Growth hormone increases blood glucose
levels, promotes fat mobilization and
catabolism and promotes protein
anabolism.

The four tropic hormones secreted by the
basophils of the anterior pituitary gland are
thyroid-stimulating hormone,
adrenocorticotropic hormone, folliclestimulating hormone, and luteinizing
hormone. Follicle-stimulating hormone and
luteinizing hormone are also called
gonadotropins.

Antidiuretic hormone acts to reduce the
volume of urine. It does this by causing
water to be reabsorbed from the tubules of
the kidney and returned to the blood. This
increases the water content of the blood
and reduces the volume of urine.

Oxytocin has two positive feedback
mechanisms associated with it. The first is the
release of milk. The mechanical and
psychological stimulation of the baby's suckling
triggers the release of oxytocin. This provides
more milk, which allows the baby to continue to
suckle, which in turn stimulates the release of
more oxytocin. The other feedback mechanism
is the stimulation of uterine contractions. Once
uterine contractions begin, they push down on
receptors in the pelvis, which triggers the
release of more oxytocin, which causes more
uterine contractions.

Thyroxine and triiodothyronine synthesis
occurs in tiny structural units called follicles.
The colloid produced by the cuboidal cells of
the follicle wall contains the protein-iodine
complexes known as thyro- globulins, the
precursors of thyroid hormones. The thyroid
hormones are stored as thyroglobulins in the
follicles until they are released into the blood.
They are transported in the blood attached to
plasma proteins, principally a globulin called
thyroxine-binding globulin and albumin. They
circulate in the blood as a hormone-globulin
complex.

The parathyroid hormone helps maintain
calcium homeostasis. It acts on bone,
kidney, and intestinal cells to increase the
release of calcium into the blood.

There are three zones in the adrenal
cortex that are involved in hormone
production: (1) The zona glomerulosa
produces aldosterone, which stimulates
the kidney tubules to conserve sodium,
which triggers the release of antidiuretic
hormone, which in turn results in the
conservation of water

(2) The zona fasciculata produces cortisol,
which influences the metabolism of food
molecules and has an antiinflammatory
effect in large amounts. (3) The zona
reticularis produces androgens and
estrogens, which may have a role in
supporting sexual function.

The adrenal medulla secretes two
important hormones, epinephrine and
norepinephrine. Both of these hormones
can bind to the receptors of sympathetic
effectors to prolong and enhance the
effects of the sympathetic nervous system.

Alpha cells in the pancreatic islets produce
glucagon. Beta cells produce insulin. Delta
cells produce somatostatin, and pancreatic
polypeptide cells produce pancreatic
polypeptide.

The pregnancy-promoting hormone is
progesterone.

Human chorionic gonadotropin is
produced by the placenta. It serves as a
signal to the mother's gonads to maintain
the uterine lining rather than allow it to
degenerate and fall away in menstruation.

Atrial natriuretic hormone is secreted by cells in
the atrium in response to increased stretch due
to abnormally high blood volume or blood
pressure. The principal effect of this hormone is
to promote the loss of sodium in the urine. The
increased concentration of sodium in the urine
draws water from the body into the urine, which
acts to decrease blood volume.

The condition resulting from
hypersecretion of growth hormone during
the growth years is giantism. The condition
resulting from hyposecretion of growth
hormone during the growth years is
pituitary dwarfism.

Cushing syndrome causes a fatty "moon
face" with thin, reddened skin.

Exercise along with other lifestyle changes
can control type 2 maturity onset diabetes
mellitus, often without the need for insulin.