Growth hormone

Hormone : secretory product of ductless gland released directly into circulation in small amount in response to a specific to produce response in the target cell/organ.

Growth Hormone – secreted by Acidophil Somatotroph of the Anterior lobe / Anterior pituitary / Adenohypophysis.

Control of GH secretion : Release of GH is primarily undercontrol of

a) GHRH: GH-Releasing Hormone 

b) GHIH: GH-Inhibiting hormone

ACTIONS OF GROWTH HORMONE:

a) Protein Metabolism : Protein anabolic action attained by

  1. affecting translation
  2. increase transport of neutral and basic Amino Acids into cells from E. C. F and thus decrase plasma amino acid level
  3. stimulate erythropoiesis
  4. increase amino acid excretion from collagen catabolism

b) Mineral Metabolism :

  1. increase Calcium absorption from GIT
  2. decrease Na, K, Ca, P excretion from Kidneys and divert them to growing tissues.

c) Carbohydrate Metabolism : GH is Diabetogenic because it produces Hyperglycemia by

  1. increasing hepatic glucose output
  2. directly antagonizing insuline effect on Adipose and Skeletal Muscle to decrease Glucose uptake

d) Fat Metabolism :

  1. Catabolic effect i.e. increase mobilization of fats from Adipose Tissue and thus increase free fatty acid in plasma and stimukating gluconeogenesis and store it as energy in case of fasting.
  2. Ketogenic effect : increase hepatic oxidation of fatty acid to ketone body, acetoacetic acid beta-hydroxybutyric acid

GH increases growth of Thymus

Increased

On removal of anterior pituitary –

a)Kidney size decrease

b)Renal Blood Flow decrease

c) GFR decrease

d)Tubular PAH secretion decrease

(the effects of GH on skeletal growth are mediated by Somatomedins)

GH increases number of cells whereas Insulin causes cytoplasmic growth.

Before Epiphyseal Closure : GH stimulates proliferation of Chondrocytes, appearance of Osteoblast, Incorporation of Sulphates into Cartilage and thus increase thickness of epiphyseal endpkate accounting for increase in linear skeletal growth

After Epiphyseal Closure : bone THICKENING occurs and no change in bone length occurs.

Applied Aspect:

1)Hypersecretion of GH

GH secretion high during Adolescence i.e. before Epiphyseal Closure thus there is excessive growth of long bones.

a) Tall Stature

b) Bilateral Gynaecomastia

c) Large hands and feet

d) Loss of libido/impotence

d/t acidophilic cell tumour of anterior pituitary thus increase in GH secretion during adulthood i.e. after epiphyseal closure

a) Thyroid Gland Hypertrophy

b) Hepatomegaly

c) Nephromegaly

d) Enlarged Hands

 

e) Gynaecomastia

f) Osteoarthritis

g) Prognathism

h) Kyphosis

2)Hyposecretion of GH (Dwarfism)

a) Plumpness

b) Small Genitalia

c) Delayed skeletal and muscle development

d) Delicate Extremities

e) Growth Retardation

-Dharmin Doshi, MIMER Medical College

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