Anterior and Posterior Pituitary Hormones

Anterior Pituitary Hormones

• Growth Hormone (GH): Promotes overall body growth by influencing protein creation, cell division, and differentiation.
• Adrenocorticotropin (ACTH): Regulates the release of specific adrenal cortex hormones that control glucose, protein, and fat metabolism.
• Thyroid-Stimulating Hormone (TSH): Controls the thyroid glands secretion of thyroxine and triiodothyronine, which regulate most cellular chemical reactions.
• Prolactin: Stimulates mammary gland development and milk production.
• Gonadotropic Hormones (GnRH): Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) regulate growth and functions of ovaries and testes, including reproductive activities.

Posterior Pituitary Hormones

• Antidiuretic Hormone (ADH) (Vasopressin): Controls water excretion in urine, regulating fluid concentration.
• Oxytocin (OT): Facilitates milk ejection during breastfeeding and promotes childbirth.

Anterior Pituitary Structure

• Highly vascular gland with extensive capillary sinuses.
• Blood flow: Hypothalamus → Hypothalamic-Hypophysial Portal Vessels → Anterior Pituitary Sinuses.

Posterior Pituitary Structure

• Extension of neurons from the hypothalamus' paraventricular and supraoptic nuclei.
• Neuron cell bodies located in the hypothalamus, axons extend through the infundibulum to the posterior pituitary.
• Posterior pituitary stores and releases hormones produced by the hypothalamus.

Neurohypophysis Hormones

• Oxytocin:
  • Polypeptide hormone formed in the paraventricular nuclei.
  • Stimulates uterine contractions and cervical dilation.
  • Receptors increase in the uterus during pregnancy, enhancing sensitivity to oxytocin's effects.
  • Released throughout childbirth via positive feedback.
  • Essential for milk ejection reflex (let-down) during breastfeeding.
• Antidiuretic Hormone (ADH):
  • Polypeptide hormone formed in the supraoptic nuclei.
  • Osmoreceptors in the hypothalamus monitor blood osmolarity (solute concentration).
  • ADH increases water permeability in collecting ducts and tubules, conserving water and producing concentrated urine.
  • Absence of ADH makes collecting ducts impermeable to water.
  • Aquaporins (water-permeable pores) in cell membranes facilitate water reabsorption.

Growth Hormone Effects

• Stimulates osteoblasts (bone-forming cells), increasing bone thickness throughout life, particularly in membranous bones (e.g., jaw, skull).
• Promotes the production of somatomedins (insulin-like growth factors) by the liver and other tissues.
• Somatomedins enhance bone growth, similar to insulin's effects on growth.

Growth Hormone Regulation

• Primarily regulated by nutritional state, especially protein nutrition.
• Deficiency or increased tissue protein need (e.g., after exercise) stimulates growth hormone secretion.
• Growth hormone promotes new protein synthesis and conserves existing proteins.

Abnormalities of Growth Hormone Secretion

• Panhypopituitarism:
  • Deficient secretion of all anterior pituitary hormones.
  • Can be congenital or develop at any age, often caused by pituitary tumors or blood vessel thrombosis.
  • Symptoms include hypothyroidism, decreased glucocorticoid production, and suppressed gonadotropic hormones.
• Dwarfism:
  • Anterior pituitary deficiency during childhood.
  • Proportional growth but at a significantly slower rate.
  • May involve only growth hormone deficiency, allowing sexual maturity.
  • Some dwarfism result from a hereditary inability to produce somatomedin C.
• Acromegaly:
  • Excess growth hormone after adolescence, causing bone thickening and soft tissue growth.
  • Caused by pituitary adenomas (acidophilic tumors).
  • Symptoms include enlarged hands and feet, altered face shape, headaches, joint pain, vision changes, and increased skin tags.

Role of Decreased Growth Hormone in Aging

• Reduced growth hormone accelerates aging features, including skin wrinkling, organ function decline, and muscle mass loss.
• Contributing factors include decreased protein deposition and increased fat deposition.

Growth Hormone Therapy

• Recombinant growth hormone treatment is available.
• Effective for treating pure growth hormone deficiency in dwarfs.
• In older individuals, beneficial effects include increased protein deposition, reduced fat deposits, and increased energy.
• Undesirable side effects include insulin resistance, edema, carpal tunnel syndrome, and joint pain.
• Growth hormone therapy is generally not recommended for healthy elderly individuals with normal endocrine function.

This quiz covers the major hormones produced by the anterior and posterior pituitary glands, including their roles in regulating growth, metabolism, and reproductive functions. Test your knowledge on Growth Hormone, ACTH, TSH, and more. Understand the significance of these hormones in human physiology.