Growth hormone is synthesised by somatotrophs of anterior pituitary.

 #STRUCTURE OF GROWTH HORMONE :

* Growth hormone is polypeptide containing 191 amino acids .

# REGULATION OF GROWTH HORMONE SYNTHESIS :

1) HYPOTHALAMUS :

* Ventromedial nucleus of hypothalamus releases growth hormone releasing hormone ( GHRH ).

* GHRH reaches anterior pituitary through portal system and it has stimulatory effect on somatotrophs .

2) Negative feedback of growth hormone :

* When growth hormone increases , it inhibits release of GHRH from hypothalamus which eventually decreases synthesis of growth hormone from anterior pituitary .

3) SOMATOMEDINS :

* These are also called insulin-like growth factors -I .

* They have negative feedback on somatotrophs.

4 ) Other metabolites : 

* Increase in in glucose and free fatty acid level in the blood decreases growth hormone release.

5) Physiological conditions affecting growth hormone :

* Exercise increases growth hormone release

* Stress increases growth hormone release

# MECHANISM OF ACTION OF GROWTH HORMONE :

1) Action of growth hormone directly on tissue :

* Growth hormone binds to receptor present on the cell surface .

* The mechanism of action it is through jak-stat pathway.

* Jak stat pathway leads to  increased translation of certain proteins and alters metabolism.

2) Action of growth hormone via somatomedins :

* In the liver somatomedins are synthesized in the presence of growth hormone .

* Somatomedins have more half life then growth hormone .

* Somatomedins have similar effects on body like growth hormone.

* Growth hormone have both anabolic and catabolic effects.

* It leads to to catabolism of lipids (lipolysis ) and anabolic actions on protein metabolism.

#EFFECTS OF GROWTH HOMRMONE ON PROTEIN METABOLISM:

*Growth hormone increases uptake of amino acids by the cells and decreases catabolism of protein

* Growth Hormone increases synthesis of proteins by acting on nucleus.

* This leads to to increase in lean body mass.

# EFFECTS OF GROWTH HORMONE ON FAT METABOLISM :

* Growth hormone acts on adipocytes and increases lipolysis.

* Therefore free fatty acids in the blood increases as fat is mobilized from adipocytes.

* These free fatty acids are used for energy production.

# EFFECT OF GROWTH HORMONE ON CARBOHYDRATE METABOLISM:

* Growth hormone leads to development of resistance to insulin.

* Which leads to to decreased uptake and utilisation of glucose.

*In the presence of growth hormone blood glucose level increases.

#EFFECT OF GROWTH HORMONE ON GWOWTH (BONES ) :

* Growth hormone activates chondrocytes and increases bone mass

* In the deficiency of growth hormone dwarfism occurs.

#APPLIED PHYSIOLOGY OF GROWTH HORMONE :

1) Effects due to increasing growth hormone:

#GIGANTISM :

Excessive growth hormone before fusion of epiphyseal plates,then it leads to excessive growth resulting into gigantism.

#CAUSES OF GIGANTISM :

* Tumour in pituitary gland or in the hypothalamus which increases growth hormone.

#FEATURES OF GIGANTISM :

1)Presense of excessive long bones.

2 ) Enlarged body.

#ACROMEGALY :

If there is increase in growth hormone after fusion of epiphyseal plates , then it leads to acromegaly.

₹CAUSES OF ACROMEGALY :

*Increasing growth hormone may be due to tumor of somatotrophs or hypothalamus 

# FEATURES OF ACROMEGALY :

1) Enlargement of acral parts of the body like hands and feet .

2)Membranous bones increase in thickness .

3) Prognathism which is  protrusion of lower jaw .

4) Supraorbital ridges become prominent .

5) The even develop diabetes.

Effects due to decrease in growth hormone

DWARFISM :

* It is of two types

1)PITUITARY DWARFISM :

* Where there is some defect in in anterior pituitary and growth hormone decreases.

2) LORAIN DWARFISM :

* In this condition growth hormone secretion is normal but somatomedins are very low.

* Which results into dwarfism.