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The anterior pituitary gland
Adenohypophysis
• The anterior pituitary gland contains five
types of secretory cells which are distinguished
by immunocytochemistry and electron
microscopy
...
Pituitary growth hormones:
• These are two hormones secreted from the
anterior pituitary and their main function is to
regulate the growth of the body
...
It is the most abundant (85%)
...
Both are equally effective
...


2
...
e
...

• They are less effective and appear in
appreciable quantities only during pregnancy
...

• Growth hormones from different animals are
ineffective in man except ‘simian’ growth
hormones which are effective
...

• Growth hormone is secreted in adult humans at
a rate of 0
...
0 mg/day
...

• The average basal plasma level in adults is 2-3
ng/mL, and in children 4 - 6 ng/mL
...

• This bound growth hormone acts as a hormone
reservoir to dampen the fluctuations in the
level of the free hormone in the plasma
...

• Its biologic half-life in the plasma is about 20
minutes
...
Chondrogenesis (cartilage formation) of
the epiphyseal plates of long bones
...


• 2
...

• The increase in cell size stimulates cell
division
...

• There is positive nitrogen, phosphorus, Ca2,
Na, and K balance because these elements are
directed to the growing tissues
...


• The above actions are not direct actions of GH
...


3
...


• The FFA provide a ready source of energy for
the tissues which spares glucose and amino
acids
...

• 4
...
g
...

• This is a “central pro—insulin action”

• On the other hand, growth hormone provides
large amounts of FFA and stimulates their use
by tissues for their energy needs
...

This is a “peripheral anti-insulin action”
...


• If a high level of GH is maintained for
sometime — maintained hyperglycemia
(pituitaly diabetes)
...

• If the high level of GH is maintained for a long
period, the β cells are over stimulated by both
GH and hyperglycemia to the point of
exhaustion
→ insulin level drops → more pronounced
hyperglycemia
(diabetes
mellitus)
...
Na+ and K+ retention:
• Growth hormone stimulates Na+ and K+
reabsorption from the renal tubules
...


Somatomedins (insuhn-like growth factors)
• Somatomedins are polypeptide growth factors
produced by the liver and other tissues in
response to stimulation by GH
...

• It was found that the structure of somatomedins is
similar to that of insulin and they have a weak
insulin-like activity, so the old name of
somatomedins is now replaced by the new term
“Insulin-like growth factors” (IGFs)
...


• It has a strong chondrogenic and protein anabolic
actions which promote growth of all tissues
except the nervous tissue
...
IGF-I has a
weak insulin like and antilipolytic actions:
• The half-life of IGF-I is about 20 hr, which
prolongs the duration of action of growth
hormone
...

• It is produced by different tissues, but the
stimulus that regulates its production is unknown
...


•
•

•
•

Importance of growth hormone in children
and in adults
Growth hormone secretion continues in man
throughout life - with a declining rate though
...
But what
is its function in adults after growth is
accomplished ?
In fully grown adults, growth hormone has a
protein sparing effect
...


• During this period, growth hormone helps
tissues to take their requirements of energy
from fat stores
...


Control of growth hormone secretion
• The basal secretion of growth hormone from
the pituitary gland is controlled by two factors
...
The hypothalamic GRH and GIH
(somatostatin):
• The
rate
of
GH
secretion from the pituitary fluctuates
markedly up and down mostly due to
fluctuations in the rate of the hypothalamic
GRH secretion
...
A negative feedback mechanism:
• Growth hormone stimulates the release of IGFI from tissues, and IGF-I stimulates the release
of GIH from the hypothalamus and directly
inhibits the release of GH from the anterior
pituitary
...

• The FFAs inhibit the release of GH
...
Decrease of energy supply below energy
needs, e
...
hypoglycemia, muscular exercise,
and fasting
...
Certain amino acids, e
...
arginine and
after a high protein meal
• 3
...

• 4
...
e
...


• 5
...
e
...


• 6
...
g
...
High levels of glucose or FFAs in the
blood
...
Cortisol
...
REM sleep
...
IGF-I
...

• Increase in weight alone is not a sure sign of
growth as it could ‘be due to accumulation of
fat or due to salt and water retention
...
Genetic factors, which determine the rate
and the limits of growth of the individual
...
Diet, which should be balanced ‘and
containing sufficient’ amounts of proteins,
carbohydrates, fats, vitamins, minerals, and
calories
...
Social and emotional deprivation
...

• 4
...

• In normal children, after a period of illness, a
period of “catch-up growth” follows in which
the rate of growth increases by up to 400%
until the period of inhibited growth is
compensated for
...
Hormones:
• Besides growth hormone, several other
hormones are essential for growth
...

• The spurt of growth at puberty is caused by
sex hormones
...
It is dependent on fetal IGF-ll
formed by different tissues, and fetal insulin
...

• They
are
“the
growth
promoters” in the early few months after birth
...
i
...

they
do
not
promote
growth by themselves, but their - presence in
adequate amounts is essential for the growth
process
...

• Thyroid hormones are responsible for
completing the anatomical and functional
development of the brain
...


• b) Insulin and sufficient amounts of
carbohydrates
are
essential
for
the
growth process
...

• c) Sex hormones: The spurt of growth which
occurs at puberty is due to the surge of sex
hormones (androgens or estrogens) which
occurs at this time
...
In
addition, androgens have a direct protein
anabolic action
...

• This explains why patients with precocious
puberty’ are dwarfs
...

• It also explains why men castrated before puberty
(eunuchs) tend to be tall
...


The rate of growth
• The growth period in boys extend from birth till
the age of about 20 years (18 years in girls)
...

• This rate drops sharply in the first two years down
to about 8 mm/month then the drop continues at a
slower rate
...


• Brain growth takes different course
...

• Growth in infants is not a continuous steady
process,
but
for
unknown reasons it is rather episodic
...
5 -2
...


Effects of hypersecreton of growth
hormone
• Hypersecretion of growth hormone comes
from functioning tumors of somatotrope cells
of the anterior pituitary
...


Gigantism
• Gigantism is a syndrome caused by
hypersecretion of growth hormone before union
of epiphyses (i
...
before the onset of puberty)
...

• The stature increases markedly and the patient
appears as a giant
...

• Diabetes mellitus is frequent (the diabetogenic
effect of growth hormone)
...


Growth Hormone Excess
• in childhood leads to gigantism

Acromegaly
• Acromegaly is a syndrome caused by
hypersecretion of growth hormone after union
of epiphyses (i
...
after the onset of puberty)
• There is no linear growth of the body, but
marked growth of the acral parts
...

• Growth of the ears, nose, supraorbital ridges,
and mandible gives the characteristic
acromegalic facies
...

This condition is
known as
acromegaly
...
The span
becomes longer than the height of the body
...

• Growth hormone synergizes with ACTH to
increase the size and secretion of the adrenals,
and with androgens to produce hirsutism (i
...

growth of hair on the trunk and limbs) and to
increase the size of the male accessory sex
organs
...

• The increase in the size of the
heart without parallel increase in its blood
supply leads to high tendency of myocardial
ischemia and a special type of cardiomyopathy
“acromegalic cardiomyopathy”
...

• Pressure on the optic chiasma by the pituitary
tumor could lead to bitemporal hemianopia
...
g
...

• Local irradiation to destroy the tumor or
surgical removal of the tumor could be done


...

• If the deficiency occurs during the growth
period in young age, it leads also to dwarfism
...

• According to the mechanism which causes the
lack of GH activity, there are four types of
dwarfism:
• a
...
Can be treated by synthetic GRH or
GH
...
Laron dwarfism: Caused by lack of
response of the tissues to the secreted GH due to
absence of GH receptors on the cells can be
treated by IGF-I

• C
...
The
receptors for GH on the cells are normal
...
Dwarfism of precocious puberty:
• Precocious puberty is caused by secretion of sex
hormones in a very young age leading to very
early onset of pubertal changes
...
Once
epiphyses are fused, dwarfism can not be treated
...
e
...

• Except for their small size, and some acceleration
of the aging process, dwarfs have normal
functioning of different organs
...

• There is normal maturation of the sexual organs
and functions
...
The metabolic rate is
normal
...

• Lack of GH accelerates the aging process
because of the absence of its protein sparing,
and lipolytic effects
...
This
leads to wrinkling of the skin, reduced
performance of different organs, and reduced
muscle mass and performance
...


• The decline in the GH level in old age is partly
responsible for the aging effects
...
increased protein deposition, especially in
muscles
...
decreased fat deposits
...
a feeling of increased energy and increased
physical activity
...


Prolactin
• Prolactin is a polypeptide hormone secreted by
the mammotrope cells of the anterior pituitary
...

• Its physiological actions appear when its level
rises in a pregnant or a lactating woman
...
Synergism with estrogen to stimulate the
development of the duct system of the
mammary glands, although estrogen alone can
do this function
...
Lactogenesis:
• Prolactin initiates milk secretion in mammary
glands primed by estrogen and progesterone
...


• Prolactin is essential for initiating milk
secretion after delivery
...

• With breast- feeding, suckling reflexly
stimulates prolactin secretion, which in turn
stimulates milk secretion
...


• Then, the reflex declines gradually until it
disappears, and the level of prolactin goes back
to its pre-pregnancy level
...

• High levels of estrogen block prolactin
receptors in the breast and prevent its
lactogenic action
...
Prevention of ovulation:
• Prolactin inhibits the release, and blocks the
actions of the hypothalamic gonadotropinreleasing
hormone
and
pituitary
gonadotropins
...
This action needs high prolactin
concentration
...

• However, this is not a reliable method because
the level of prolactin declines after the second
or third month of lactation
...

• This activity is tonically inhibited by continuous
release of the prolactin inhibiting hormone (PIH)
of the hypothalamus
...

• Prolactin secretion is stimulated by inhibiting the
release of dopamine and inhibited by stimulating
the release of dopamine from the hypothalamus
...

• Prolactin stimulates the release of dopamine
from the hypothalamus, and this inhibits the
release of prolactin from the anterior pituitary
...


Prolactin secretion is stimulated by:
• 1
...
Suckling
...

• 3
...
Exercise
• 5
...

This
hormone
is
possibly
the
PRH
...
Stress, surgical or psychological
• 7
...
Dopaminergic
blockers,
e
...

phenothiazines
...
L-Dopa
• 2
...
g
...


Effects of hyper secretion of prolactin
• Hyper
prolactinemia
results
from
“prolactinomas”
prolactin-secreting
tumors of the mammotropes of the anterior
pituitary
...

• It is found in over 10 % of the
population, but clinical manifestations appear
in a small minority
...
Hypogonadism:
Due to inhibition of release and actions of the
Pituitary gonadotropins
...
In
women:
Oligomenorrhea
or
amenorrhea,
infertility,
loss
of
libido, and dyspareunia from hypoestrogenism
...
In men: Reduced volume of ejaculate,
oligospermia
or
azoospermia, loss of libido, and impotence

• 2
...
e
...

• 3
...


Treatment
• Dopamine or dopamine agonists, e
...

bromocriptine
are
successful
in
suppressing prolactin secretion and reducing
the size of the tumor
...


The pituitary gonadotropins
• Gonadotropins are hormones which act on the
gonads (testes or ovaries)
...
e
...

• Both hormones are secreted in response to
stimulation by the hypothalamic gonadotropinreleasing hormone (GnRH)

Follicle-stimulating hormone (FSH)
• Actions
• In the male: It is essential for spermiogenesis
– the final stage of spermatogenesis
• In the female: It stimulates the growth and
maturation of the graafian follicle
...

• In the female: It reduces ovulation by rupture
of the graafian follicle, formation of the
corpus, formation of the corpus luteum, and
secretion of estrogen and progesterone by the
corpus luteum
...

• Infarction of the gland follows some cases of
postpartum hemorrhage if it reaches the stage
of
shock
(Sheehan
syndrome)
...

• The patient can not tolerate stressful
conditions
...


• Zona glornerulosa, and its aldosterone
secretion are maintained
...

• Salt depletion does not occur, except in longstanding cases
...

• iii) Hypogonadism: There is atrophy of the
gonads
...
Menstrual cycles
stop
...
In adults, the aging process is
accelerated
...

• ii) Lack of growth hormone
...

Hypophysectomy improves diabetes mellitus
and potentiates the hypoglycemic effect of
insulin
...

• Rapid recovery occurs due to several reasons:
1
...

• ADH is released from these new ends
...
The osmotic load to the renal tubules
decreases
...
A lso lack of
glucocorticoids decreases the ability of the
kidney to excrete a high water load
...

• F) Bodyweight:
• There is no loss of weight
...

• The cachexia and emaciation which was reported
before in cases of hypopituitarism was due to
“anorexia nervosa” which may be present in some
cases

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