Download Anterior pituitary hormones

Anterior pituitary hormones
Growth hormone (GH)(Somatotropin)
Factors affecting GH secretion
Gonadotrophic hormones
Follicle stimulating hormone (FSH)
Luteinizing hormone ( LH or ICSH)
Prolactin
Hormones of the middle lobe of the pituitary gland
Actions of MSH
Posterior pituitary hormones
Vasopressin
Oxytocin
Pituitary gland
 The pituitary gland comprises the embryologically
and functionally distinct anterior pituitary
(adenohypophysis) and posterior pituitary
(neurohypophysis). The anterior pituitary hormones and
their corresponding regulatory hormones/factors are
described in detail below.
 Secretion of most of the hormones of the anterior
pituitary is under the control of the hypothalamus.
Secretion also controlled by the rate of secretion of
endocrine gland through negative feedback mechanism.
Growth hormone (GH)(Somatotropin)
 This hormone affects the growth.
 GH is also known as somatotrophic hormone or
somatotropin hormone. It causes the growth of all
tissues of the body that are capable of growing. It
promotes both, i.e., the size of the cell and increase
mitosis with the development of the increased number
of cell.
 The hyposecretion of GH causes the dwarfism.
 The hyposecretion of GH causes the gigantism.
Normal plasma concentration
(adult) 3μg /L.
(Children) 5μg /L.
GH does not affect
directly the cartilage
and bones. However,
GH indirectly
stimulate their growth
with help of several
small proteins ,
collectively known as
somatomedin which
mainly synthesized in
liver.(IGF-1)
• Somatomedin is required for
deposition of chondroitin
sulphates and collagen, both of
which are necessary for the
growth of cartilage and bones.
• GH increases protein synthesis.
• GH increases the formation of
RNA .
• GH is also responsible to
increase fat utilization for
energy purposes .
• GH increases conversion of
glucose to glycogen.
• GH increases blood glucose.
Factors affecting GH secretion
stimulants
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Exercise .
Onset of deep sleep.
Hypoglycemia.
Protein meal.
I.V. infusion of amino acids.
Stress (arterial puncture
,surgery, endotoxin,
vasopressin.
Glucagon
Laevo (-)Dopa
Malnutrition
β-adrenergic blockade.
Inhibitants
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Hyperglycemia.
Obesity.
Hypothyroidism.
Third trimester of pregnancy.
High dose of glucocorticoids.
α-adrenergic blockade.
Thyroid stimulating hormone (TSH)
 TSH is glycoprotein secreted by basophilic staining cells
of the anterior-pituitary. It has molecular weight of
about 28,000.
 TSH stimulates secretion of thyroxine and other
iodothyronines.
 TSH increases oxygen utilization, glucose uptake and
oxidation processes.
 TSH stimulates adenyl cyclase activity and increases the
tissue levels of c-AMP.
Adrenocorticotropic hormone (ACTH)
 ACTH is also known as Corneotropin.
 ACTH is polypeptide consisting of 39 amino acids.
 It is secretes under control of crotitropin releasing
hormone(CRH), of the hypothalamus.
 ACTH stimulates the synthesis of cortisol and
17-ketosteroids by adrenal cortex.
 ACTH is also necessary to maintain adrenocortical size,
structure and vascularity.
 The action of ACTH is mediated by c-AMP.
 ACTH promotes insulin secretion from β-cells of
pancreas.
Gonadotrophic hormones
 Anterior pituitary secretes 3 gonadotrophic hormones:
1) Follicle stimulating hormone (FSH).
2) Luteinizing hormone or interstitial cell stimulating hormone
( LH or ICSH).
3) Prolactin or mammotropin (lactogenic hormone).
 All are water soluble glycoprotein except prolactin (simple
protein). The hypothalamus control the secretion of
gonadotrophic hormones by releasing factors.
 The releasing factors of FSH and LH exert inhibitory effects on
the release of prolactin.
Follicle stimulating hormone (FSH)
 FSH is found in plasma of both males and females.
 FSH stimulates the maturation and growth of ovarian
follicles. The cyclic AMP formation is increased in these
target tissue.
 In males, FSH causes the growth of testes and induces
spermatogenesis.
 Girls have significantly higher FSH in comparison to the
boys at age 5, 10 and 12 years.
Luteinizing hormone ( LH or ICSH)
 LH is glycoprotein, is necessary for proper maturation
and function of gonads in both men and women.
 Both LH and FSH are required for spermatogenesis.
 All the effect of LH are mediated by way of testosterone.
 Testosterone and FSH are hormones which are directly
on the seminiferous tubular epithelium.
 FSH and LH are present in the plasma of both males and
females at all ages.
 FSH and LH, in ovulating females, rise sharply from the
basal level just prior to ovulation and then rapidly fall.
Prolactin
 In females, prolactin hormone stimulates milk production and
is required for establishing a functional corpus luteum in some
species.
 Hyperprolactinemia. There are many causes of
Hyperprolactinemia including pregnancy, lactation, pituitary
tumors, renal failure and the use of drugs that have
dopamine agonist effects.
 Prolactin synergizes with LH and testosterone to increase the
reproductive functions in males.
 In case of pituitary tumor, all men with small amount of
prolactin are impotent regardless of their plasma testosterone
levels.
Hormones of the middle lobe of the
pituitary gland
 The middle lobe of pituitary gland secretes MSH
(melanocytes stimulating hormone). Also known as
intermedin.
 2 forms of MSH are found α–MSH and β–MSH.
 α–MSH is a single chain (13 amino acids).
 β–MSH is polypeptide (22 amino acids).
 MSH secretion is inhibited by corticosteroids and its
activity is inhibited by catecholamines .
Actions of MSH
 Both α–MSH and β–MSH increase melanin biosynthesis
by stimulating melanocytes present in dermis and
epidermis of the skin.
 MSH promotes the dispersion of the melanin pigment in
entire cells making them dark in appearance.
 30-60 mg cortisone is given orally to prevent excess
deposition of melanin in skin.
 Increase in pigmentation is seen in Addison's disease,
some cases of thyrotoxicosis and pregnancy .
Posterior pituitary hormones
 Posterior lobe of pituitary gland secretes 2 important
hormones:
1) Vasopressin (Pitressin , Antidiuretic hormone, ADH).
2) Oxytocin (Pitocin)
Vasopressin
It is a cyclic octapeptide
Factors that stimulate vasopressin
secretion:
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Pain.
Emotional state.
Haemorrhage.
Dehydration.
Salt intake.
Acetylcholine.
Anaesthetic drugs.
Morphine, nicotine and
barbiturates.
Factors that inhibit vasopressin
secretion:
1) Epinephrine.
2) Caffeine.
Vasopressin(ADH) functions
1) Regulation of water balance by promoting reabsorption
of water in the cells of distal tubules.
2) Its powerful action is raising blood pressure.
Failure of hypothalamus to produce enough ADH or
preventing of release by damage of the nerve tracts causes
an important disorder known as diabetes insipidus, in
which volume of urine increases to as much as 20 liters per
day. Therefore, the specific gravity of urine decreases to
very low (1.001). Normal secretion and release of ADH are
regulated by osmoreceptors in the diencephalon of brain.
Oxytocin (pitocin)
 Greek word, oxytocin= rapid birth.
 Oxytocin is also octapeptide.
 Oxytocin is powerful stimulant of uterine contraction.
The pregnant uterus is more susceptible.
 Oxytocin appears to be natural initiator of labour.
 It also facilitates upward movement of spermatozoa in
vagina and the fallopian tubes.
 It also stimulates the contraction of myoepithelial tissue
around the ducts of the lactating mammary, thereby,
stimulate the ejection of milk (milk letdown action)