504
UNIT THREE
cortex
(f g. 13.28)
. These regions are not sharply divided,
but they are distinct glands that secrete different hormones.
The
adrenal medulla
(ah-dre
nal me-dul
ah) consists of
irregularly shaped cells grouped around blood vessels. These
cells are intimately connected with the sympathetic division
of the autonomic nervous system. The adrenal medullary
cells are modiF
ed postganglionic neurons, and preganglionic
autonomic nerve F
bers lead to them directly from the central
nervous system (see chapter 11, p. 424).
The
adrenal cortex
(ah-dre
nal kor
teks) makes up the
bulk of the adrenal gland. It is composed of closely packed
masses of epithelial layers that form an outer, a middle, and
an inner zone of the cortex—the zona glomerulosa, the zona
fasciculata, and the zona reticularis, respectively
(f gs. 13.28
and
13.29)
.
Hormones of the Adrenal Medulla
The cells of the adrenal medulla (chromafF n cells) produce,
store, and secrete two closely related hormones,
epinephrine
PRACTICE
28
Where are the parathyroid glands located?
29
How does parathyroid hormone help regulate the concentrations
of blood calcium and phosphate ions?
30
How does the negative feedback system of the parathyroid
glands diF
er from that of the thyroid gland?
13.8
ADRENAL GLANDS
The
adrenal glands
(suprarenal glands) are closely asso-
ciated with the kidneys. A gland sits atop each kidney like
a cap and is embedded in the mass of adipose tissue that
encloses the kidney.
Structure of the Glands
The adrenal glands are shaped like pyramids. Each adrenal
gland is vascular and consists of two parts. The central por-
tion is the adrenal medulla, and the outer part is the adrenal
PTH
Ca
+2
+
Bone
releases Ca
+2
PTH
PTH
Ca
+2
+
Ca
+2
Bloodstream
Parathyroid glands (on
posterior of thyroid gland)
Decreased blood calcium
stimulates parathyroid
hormone secretion
Increased blood
calcium inhibits
PTH secretion
Kidneys
conserve Ca
+2
and
activate Vitamin D
Intestine
absorbs Ca
+2
Release into
bloodstream
Stimulation
Inhibition
Active
Vitamin D
FIGURE 13.27
Parathyroid hormone (PTH) stimulates bone to release calcium (Ca
+2
) and the kidneys to conserve calcium. It indirectly stimulates
the intestine to absorb calcium. The resulting increase in blood calcium concentration inhibits secretion of PTH by negative feedback.
(
+
= stimulation;
= inhibition)
TABLE
13.9
|
Disorders of the Parathyroid Glands
Condition
Symptoms/Mechanism
Cause
Treatment
Hyperparathyroidism
±atigue, muscular weakness, painful joints, altered mental functions,
depression, weight loss, bone weakening. Increased PTH secretion
overstimulates osteoclasts.
Tumor
Remove tumor, correct bone
deformities
Hypoparathyroidism
Muscle cramps and seizures. Decreased PTH secretion reduces osteoclast
activity, diminishing blood calcium ion concentration.
Inadvertent surgical
removal; injury
Calcium salt injections, massive
doses of vitamin D
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