Growth Hormone

Growth Hormone


GROWTH HORMONE (GH)/SOMATOTROPIN

  • Polypeptide.
  • Synthesized & secreted by somatotropes.
  • Subtype of acidophilic cells in adenohypophysis.

PHYSIOLOGICAL EFFECTS:

  • Two major action –
  • Stimulation of skeletal growth.
  • Regulation of metabolism.

1. STIMULATION OF SKELETAL GROWTH:

  • Mediated by “Somatomedins”/“Insulin-like Growth Factors” (IGF).
  • Synthesized in liver.
  • Somatomedin (IGF-1) stimulates proliferation of chondrocytes & osteocytes.
  • Increases chondroitin sulfate deposition in cartilage.
  • Increases ossification of newly formed cartilage.

CONDITIONS ASSOCIATED:

1. GH deficiency in early life –

  • Causes dwarfism (reduced height).
  • Yet, associated with Normal body proportion.

2. GH excess in early life –

  • Leads to gigantism.

3. GH excess in adulthood –

  • Results in Acromegaly.

2. REGULATION OF METABOLISM:

2a. On Protein metabolism:

  • Predominantly anabolic effects on skeletal & cardiac muscle.
  • By promoting amino acid transport into cells & Increasing protein synthesis.

2b. On Carbohydrate & Fat metabolism:

  • Effects complicated by,
  • Anti-insulin effect of GH.
  • Insulin-like effects of somatomedins.

2c. Anti-insulin effects of GH – 

  • Decreased peripheral glucose utilization.
  • Increased gluconeogenesis.
  • Hyperglycemia.
  • Lipolysis.

Conditions associated:

  • “Insulin-Resistant Diabetes mellitus” –
  • Caused by GH excess, (mainly by anti-insulin effects of GH).

2d. Insulin-like effects of somatomedins/IGF – 

  • Anti-lipolytic activity.

3. GH on kidneys:

  • Promotes renal reabsorption of Ca2+, Na2+, K+& Cl

REGULATION:

  • Regulated by hypothalamic GHRH.
  • GH secreted in pulsatile fashion throughout life.
  • Elevated secretion rate immediately after birth & at puberty.
  • Large bursts of secretion at night during deep sleep onset.

FACTORS INFLUENCING GH SECRETION –

1. Stimuli increasing GH secretion –

  • Hypoglycemia.
  • Exercise.
  • Fasting.
  • Protein meals.
  • Aminoacids (like arginine).
  • Stress.
  • Glucagon.
  • Pyrogen.
  • Lysin vasopressin.
  • L-dopa & α-adrenergics.
  • Estrogen & androgens.
  • 2-deoxyglucose.

2. Stimuli decreasing GH secretion:

  • REM sleep.
  • Glucose.
  • Somatostatin.
  • Cortisol.
  • FFA.
  • GH itself decreases
  • IGF- 1.
  • Medroxyprogesterone.

Exam Question

GROWTH HORMONE

  • Effect on skeletal growth mediated by “Somatomedins”/”Insulin-like Growth Factors” (IGF)
  • GH, through somatomedin (IGF-1), stimulates proliferation of chondrocytes & osteocytes, resulting in increased chondroitin sulfate deposition in cartilage.
  • Growth hormone excess in adulthood results in acromegaly.
  • Anti-insulin effects due to the direct effect of GH include decreased peripheral utilization of glucose, increased gluconeogenesis & hyperglycemia. 
  • Insulin-like effects due to somatomedins(IGF) include “Anti-lipolytic” activity.
  • GH is secreted in a pulsatile fashion.
  • Large bursts of secretions occur at night during the onset of deep sleep.
  • Stimuli increasing GH secretion – Exercise, hypoglycemia, fasting & stress.
  • Stimuli decreasing GH secretion – REM sleep, Somatostatin & Cortisol.
  • GH deficiency leads to “delayed fusion of epiphysis” – Ie., Proportionate dwarfism.
  • Short stature, secondary to growth hormone deficiency is associated with “Normal body proportion”.
Don’t Forget to Solve all the previous Year Question asked on Growth Hormone

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