Pituitary Gland Disorders
• Diabetes Insipidus (DI) is very different from
the disease called sugar diabetes (diabetes
mellitus)
– DI is caused by the insufficient release of ADH
from the neurohypophysis. Without ADH acting
on the collecting ducts in the kidneys, the
normal urine output of 1–1.5 liters per day
increases to over 2.5 liters per day and
dehydration and hypernatremia results
The Thyroid Gland
• The butterfly-shaped thyroid gland is located
inferior to the larynx and anterior to the
trachea. It has two laterally placed lobes
separated by a bridge-like isthmus
The Thyroid Gland
• Most of the thyroid gland is composed of
spherical groups of follicular cells called
thyroid follicles
– The follicles store
a 100-day supply
of its two hormones
in an inactive
gel-like substance
called TGB (for
thyroglobulin)
Thyroid Hormones
• TGB is a large glycoprotein made
from the oxidation and
iodination of molecules of the
amino acid. tyrosine
• The two hormones released
from TGB are:
–thyroxine or T4
(tetraiodothyronine)
–and T3
(triiodothyronine)
Thyroid Hormones

In the blood, T3 and T4 are bound to pre-albumins, albumin,
and a specific carrier protein called thyroid-binding globulin
(TBG)
– Most T4 released from the thyroid is converted
“peripherally” (by enzymes in the blood) into T3 ,
which is a more active hormone
• Together with hGH and insulin, thyroid
hormones accelerate body growth,
particularly the growth of the nervous and
skeletal systems
Thyroid Hormones
• Thyroid-stimulating hormone (TSH) is released
by the anterior pituitary gland in response to
TRH secreted into the portal system
– The hypothalamus
responds to higher
circulating levels of
T3 and T4 via negative
feedback to inhibit
TRH secretion
1 Low blood levels of T3
Thyroid Hormone
Regulation
and T3 or low metabolic
rate stimulate release of
Hypothalamus
TRH
2 TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
5 Elevated
T3inhibits
release of
TRH and
TSH
(negative
feedback)
TSH
3 TSH released into
blood stimulates
thyroid follicular cells
Anterior
pituitary
4 T3 and T4
Thyroid
follicle
released into
blood by
follicular cells
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones
Thyroid Hormones
• A goiter is an enlargement of the thyroid
gland and may be associated with
hyperthyroidism, hypothyroidism, or
euthyroidism
– In many third-word countries
dietary iodine intake is inadequate;
the resultant low level of thyroid
hormone in the blood stimulates
secretion of TSH, which causes
thyroid gland enlargement
The Parathyroid Glands
• The parathyroid glands are small, round
masses of tissue attached to the posterior
surface of the lateral lobes of the thyroid
gland
– There are usually two
parathyroid glands
attached to each
lobe of the thyroid,
one superior and one inferior
Parathyroid Hormones
• Calcitonin (Thyrocalcitonin) is made by the
parafollicular (C-cells) of the thyroid gland
and
when secreted lowers the blood calcium level
• An increase in blood calcium will stimulate
the C-cells of the thyroid to secrete calcitonin
– Increased calcitonin will cause a negative
feedback inhibition of parathyroid hormone
(PTH) which
causes a decrease in blood calcium and an increase in
blood phosphate levels
PARATHYROID HORMONES
(Interactions Animation)
• Calcitonin
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Parathyroid Hormones
• Parathyroid hormone (PTH) is made by the
more numerous chief (principal) cells of the
gland
– PTH increases absorption
of Ca2+ from the GI tract
and stimulates osteoclastic
activity so that Ca2+ is
released from bone into
the blood
PARATHYROID HORMONES
(Interactions Animation)
• Parathyroid Hormone
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Calcium Regulation
1 High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
3 Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
6 CALCITRIOL stimulates
increased absorption of
Ca2+ from foods, which
increases blood Ca2+ level.
5 PTH also stimulates
the kidneys to release
CALCITRIOL.
4 PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level.
2 CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
The Adrenal Glands
• There are two adrenal glands, one superior to
each kidney (also called the suprarenal
glands). During embryonic development, the
adrenal glands differentiate into two
hormones
structurally and functionallySteroid
distinct
regions
like cortisol
• the adrenal cortex
• the adrenal medulla
Catecholamines like
norepinephrine
The Adrenal Glands
The Adrenal Cortex
• The adrenal cortex is peripherally located and
makes up 80-90% of the total weight of the
gland
– The cortex is subdivided into three zones, each of
which secretes a different group of steroid
hormones, all formed
from the cholesterol
molecule
Adrenocortical Hormones
• Just deep to the CT capsule, the cells of the
zona glomerulosa synthesize
mineralocorticoid hormones
• The middle zone, or zona fasciculata, secrete
mainly glucocorticoid hormones,
primarily cortisol
• The inner zona reticularis
is the site of synthesis
of weak androgens
(masculinizing hormones)
Adrenocortical Hormones
• Mineralocorticoids regulate the concentrations of Na+
and K+ in the blood (affects blood volume/pressure)
– Aldosterone is the major hormone in this group
• Glucocorticoids influence glucose metabolism and the
ability to resists the effects of stress
– Cortisol is the major hormone in this group
• Weak androgens (masculinizing sex hormones) have
little effect in men, but play an important role in
promoting libido in women
RAAS
• The most important effects of aldosterone is
seen in the renin-angiotensin-aldosterone
system (RAAS)
– The RAAS is stimulated by a decrease in blood
volume and/or blood pressure – as in cases of
dehydration or hemorrhage. Low BP stimulates
juxtaglomerular cells
in the kidney to
secrete the
enzyme renin
RAAS
 Renin converts the plasma protein angiotensinogen
(produced in the liver) into angiotensin I. As
angiotensin I circulates to the lungs, an enzyme called
angiotensin converting enzyme (ACE) converts
angiotensin I to angiotensin II
– Angiotensin II stimulates the adrenal cortex to secrete
aldosterone (salt and H20 resorption indirectly increases
BP), and it is a
potent vasoconstrictor (which
directly increases BP)
RAAS
Glucocorticoids
• Glucocorticoids (mainly cortisol) regulate
metabolism by promoting the breakdown of
proteins and fats to form glucose
(gluconeogenesis). Increased blood sugar levels
assist the body to cope with stress
– Their inflammatory effects result from inhibiting
white blood cells. Unfortunately they also retard
tissue repair and slow wound healing
• glucocorticoids are very useful in the treatment of chronic
inflammatory disorders such as Lupus, though long term
side-effects are severe