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Growth Hormone (hGH)
. Somatotropin
Small protein expressed from anterior lobe of pituitary
produced by Somatotroph cells of the anterior pituitary
Growth hormone (hGH) is a peptide hormone
Essential for normal development
Promotes growth, especially in children and at puberty
INDIRECT ACTIONS OF hGH
 The effect of hGH on the liver is to produce a number
of Somatomedins or growth factors now usually
called Insulin-like Growth Factors – IGFs.
 The actions of hGH are mediated mainly through
IGF-1, the effects of which are to stimulate growth in
bone, protein synthesis in muscle and lipolysis of fat.
Somatic growth
 hGH stimulates linear bone growth primarily by
increasing amino acid uptake and protein synthesis in
(bone cells).
 It acts indirectly through stimulating the synthesis of
somatomedins ( insulin-like growth factors (IGF) by the
liver
 cause secretion of collagen and minerals necessary for
cartilage and bone growth.
 hGH causes an increase in organ size and function. It
promotes both increased sizes of cells and increased
mitosis, with development of increased numbers of
cells.
Non-Growth Actions of hGH
 hGH also has direct actions on fat cells, liver and
muscles which are not growth promoting but are
metabolic in function.
 It causes the breakdown of fat
 - Increased rate of protein synthesis in all cells
of the body t
 stimulates glucose produced by gluconeogenesis
bringing about a rise in plasma glucose.
-
Effect Metabolism
Effect on CHO and fat metabolism
(Diabetogenic)
 The effect of hGH on metabolism is to increase the energy
substrates, glucose and free fatty acids,
The effect of hGH on increasing serum glucose levels is two-fold
 glucose uptake by muscle and adipocytes is decreased.
 glucose synthesis (gluconeogenesis) by the liver is stimulated.
Effect Metabolism (cont..)
Effect on Fat Metabolism
Causes Insulin Resistance
 hGH decreases body fat by increasing lipolysis in adipose tissue
leading to decreased fat storage and increased FFA concentration
in circulation i.e. it causes mobilization of fats.
 The result is decreased fat storage
 - High blood glucose& fatty acids causes Insulin Resistance
Effect on protein and electrolyte metabolism
(Protein Sparing)
 Growth hormone is a protein anabolic hormone
 Increase in lean body mass and a decrease in body fat along
with an increase in metabolic rate and in serum cholesterol
Effect on Tissues

 The mediators of hGH action are called insulin-like
growth factors (IGF) or Somatomedins which are
produced by the liver
 In addition, hGH increases lean body mass through the
increase of muscle protein synthesis.
 -Size of internal organs also increased
 Following puberty, hGH levels decline during adulthood
and decrease further with aging.
Hypothalamus –Ant: Pituitary
 The synthesis and release of GH is under the control
of the hypothalamic hormones.
 The hypothalamus produces a pair of hormones,
growth hormone releasing hormone (GHRH) and
 Growth hormone inhibitory hormone (GHIH or
Somatostatin).
 Both act on the anterior pituitary to stimulate or
inhibit the production of growth hormone.
= Somatostatin
(GHIH)
= Somatomedin-C
Regulation of release of growth
hormone
 The regulation of the ‘HYPOTHALAMIC –PITUITARY axis’ is by IGF-1, which acts on
the hypothalamus to inhibit GHRH and stimulate Somatostatin or (GHIH).
 Circulates in the blood tightly bound to a large plasma protein.
 Has a long half-life.
 The levels of hGH rise during sleep, in adults as well as children.
Excess and deficiency of HGH
Excess HGH
 The most common cause of excess is a pituitary tumor.
 In children who are still growing, excess hGH causes
Gigantism.
 In adults whose long bones can no longer be extended, the
condition is known as Acromegaly.
Giagantism
Due to tumour in the cells secreting growth
hormone in the anterior pituitary.
-Increased secretion of growth hormone
before adolescence (before union of the ends
of the bones with the shafts (bone
maturation).
-The giant becomes longer than usual) more
than 2 meters length
-Muscles may be well developed but later
undergo some atrophy and weakening.
-The life span is shorter than normal
Acromegaly
 An excessive production of growth hormone in an adult results in
enlargement of skeletal extremities.
 For instance, the flat bones and soft tissues of the hands, feet,
face,nose (acromegalic facies) and lower jaw (prognathism) and
forehead become enlarged and the skin becomes coarse.
 Growth hormone can also stimulate the growth of connective tissue
such as ligaments, capsules and synovial membranes.
 Another condition commonly associated with Acromegaly is diabetes
mellitus. As growth hormone causes tissue resistance to insulin and
is therefore Diabetogenic.
 -liver, kidney, spleen becomes larger than normal
Growth hormone deficiency (Dwarfism)
 the child becomes shorter than normal
 -Occurs when growth hormone decreases
 or become absent in childhood and
 before adolescence
 In adults a growth hormone deficiency is not a major problem
and is very treatable