518
UNIT THREE
1. Structure of the glands
a. Each gland is small and yellow-brown, within a
thin connective tissue capsule.
b. Each gland consists of secretory cells well supplied
with capillaries.
2. Parathyroid hormone (PTH)
a. PTH increases blood calcium ion concentration
and decreases blood phosphate ion concentration.
b. PTH stimulates resorption of bone tissue,
causes the kidneys to conserve calcium ions and
excrete phosphate ions, and indirectly stimulates
absorption of calcium ions from the intestine.
c. A negative feedback mechanism operating
between the parathyroid glands and the blood
regulates these glands.
13.8
ADRENAL GLANDS (PAGE 504)
The adrenal glands are located atop the kidneys.
1. Structure of the glands
a. Each adrenal gland consists of a medulla and a
cortex.
b. The adrenal medulla and adrenal cortex are
distinct glands that secrete different hormones.
2. Hormones of the adrenal medulla
a. The adrenal medulla secretes epinephrine and
norepinephrine.
b. These hormones are synthesized from tyrosine and
are chemically similar.
c. These hormones produce effects similar to those of
the sympathetic nervous system.
d. Sympathetic impulses originating from the
hypothalamus stimulate secretion of these hormones.
3. Hormones of the adrenal cortex
a. The cortex produces several types of steroids that
include hormones.
b. Aldosterone
(1) It causes the kidneys to conserve sodium ions
and water and to excrete potassium ions.
(2) It is secreted in response to increased potassium
ion concentration or presence of angiotensin II.
(3) By conserving sodium ions and water, it helps
maintain blood volume and pressure.
c. Cortisol
(1) It inhibits protein synthesis, releases fatty
acids, and stimulates glucose formation from
noncarbohydrates.
(2) A negative feedback mechanism involving
secretion of CRH from the hypothalamus
and ACTH from the anterior pituitary gland
controls its level.
d. Adrenal sex hormones
(1) These hormones are of the male type although
some can be converted into female hormones.
(2) They supplement the sex hormones produced
by the gonads.
13.9
PANCREAS (PAGE 509)
The pancreas secretes digestive juices as well as hormones.
1. Structure of the gland
a. The pancreas is posterior to the stomach and is
attached to the small intestine.
(3) Prolactin release-inhibiting hormone from the
hypothalamus restrains secretion of prolactin,
whereas the yet to be identiF
ed prolactin-
releasing factor is thought to promote its
secretion.
d. Thyroid-stimulating hormone (TSH)
(1) TSH controls secretion of hormones from the
thyroid gland.
(2) The hypothalamus, by secreting thyrotropin-
releasing hormone, regulates TSH secretion.
e. Adrenocorticotropic hormone (ACTH)
(1) ACTH controls the secretion of certain
hormones from the adrenal cortex.
(2) The hypothalamus, by secreting corticotropin-
releasing hormone, regulates ACTH secretion.
f. ±ollicle-stimulating hormone (±SH) and luteinizing
hormone (LH) are gonadotropins that affect the
reproductive organs.
2. Posterior pituitary hormones
a. The posterior lobe of the pituitary gland largely
consists of neuroglia and nerve F
bers that originate
in the hypothalamus.
b. The two hormones of the posterior pituitary are
produced in the hypothalamus.
c. Antidiuretic hormone (ADH)
(1) ADH causes the kidneys to excrete less water.
(2) In high concentration, ADH constricts blood
vessel walls, raising blood pressure.
(3) The hypothalamus regulates ADH secretion.
d. Oxytocin (OT)
(1) OT has an antidiuretic effect and can contract
muscles in the uterine wall.
(2) OT also contracts certain cells associated with
production and ejection of milk from the milk
glands of the breasts.
13.6
THYROID GLAND (PAGE 499)
The thyroid gland is located in the neck and consists of
two lateral lobes.
1. Structure of the gland
a. The thyroid gland consists of many hollow
secretory parts called follicles.
b. The follicles are fl
uid F
lled and store the hormones
the follicle cells secrete.
c. Extrafollicular cells secrete calcitonin.
2. Thyroid hormones
a. Thyroxine and triiodothyronine
(1) These hormones increase the rate of
metabolism, enhance protein synthesis, and
stimulate lipid breakdown.
(2) These hormones are needed for normal growth
and development and for maturation of the
nervous system.
b. Calcitonin
(1) Calcitonin lowers blood calcium and
phosphate ion concentrations.
(2) This hormone prevents prolonged elevation of
calcium after a meal.
13.7
PARATHYROID GLANDS (PAGE 502)
The parathyroid glands are on the posterior surface of the
thyroid.
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