U01.08.06 Growth hormone

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  • Also called Somatotropin
  • Secreted by the anterior pituitary (acidophilic somatotrophs)
  • Plays a key role in growth, metabolism, and tissue repair

Regulation of Secretion

Stimulators (↑ GH secretion) Inhibitors (↓ GH secretion)
GHRH (from hypothalamus) Somatostatin (GHIH)
Deep sleep Aging
Hypoglycemia Obesity
Exercise Hyperglycemia
Stress Somatomedin (IGF-1, negative feedback)
Puberty

Mechanism of Action

  1. GHRH from the hypothalamus stimulates GH release from the anterior pituitary.
  2. GH acts on the liver and other tissues to produce IGF-1 (somatomedin C).
  3. IGF-1 mediates growth-promoting effects on bone, cartilage, and muscle.
  4. GH also has direct metabolic effects that oppose insulin (diabetogenic).

Physiologic Effects of GH and IGF-1

Target / Effect GH Direct Action IGF-1 Mediated Action
Protein metabolism ↑ Amino acid uptake, ↑ Protein synthesis ↑ DNA/RNA synthesis
Carbohydrate metabolism ↓ Glucose uptake (anti-insulin effect) → ↑ blood glucose —
Lipid metabolism ↑ Lipolysis (fat breakdown) —
Bone & connective tissue — ↑ Chondroitin sulfate, collagen, cell size and number → linear growth
Liver ↑ IGF-1 synthesis —

Summary Pathway

Hypothalamus → (GHRH ↑, Somatostatin ↓) → Anterior Pituitary (GH) → Liver (IGF-1) → Growth & Metabolism

Clinical Correlations

Condition Pathophysiology Clinical Features Treatment
Gigantism GH excess before epiphyseal closure Tall stature, enlarged hands/feet Surgery or Somatostatin analogs (Octreotide)
Acromegaly GH excess after epiphyseal closure Large jaw (prognathism), enlarged organs, glucose intolerance Octreotide or transsphenoidal surgery
GH Deficiency Pituitary or hypothalamic lesion Short stature, delayed growth GH replacement therapy

Learning Objectives

By the end of this topic, you should be able to:

  1. Describe the source, control, and actions of GH and ADH.
  2. Explain how GH stimulates growth via IGF-1.
  3. Recognize clinical disorders associated with GH.

Activity:

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