2425_Control_of_Growth_GH__IGF__Thyroid

Role of Growth Hormones

Introduction

  • Dr. Brendan Higgins presents on the influence of growth hormones in human physiology.

  • Focus on hGH (human Growth Hormone), IGFs (Insulin-like Growth Factors), thyroid hormones, and sex steroids.

Growth Hormones Overview

Major Hormones Involved

  • Human Growth Hormone (hGH): Responsible for growth and metabolism.

  • Insulin-like Growth Factors (IGFs): Mediators of growth effects derived from hGH.

  • Thyroid Hormones: Crucial for growth regulation, development, and metabolic functions.

  • Sex Steroids: Influence growth during puberty and regulate hormonal interactions.

Hypothalamic-Pituitary Axis

Hormonal Signals

  • Hypothalamic Hormones: GHRH (Growth Hormone-Releasing Hormone), GHIH (Growth Hormone-Inhibiting Hormone), TRH (Thyrotropin-Releasing Hormone), and others.

  • Pituitary Glands: Anterior pituitary secretes GH, PRL, FSH, and LH which target various tissues.

Feedback Mechanisms

  • Hormonal feedback loop involving hGH, IGF-1, and thyroid hormones to regulate growth and metabolism.

Human Growth Hormone (hGH)

Structure and Function

  • Polypeptide hormone secreted by the anterior pituitary.

  • Regulates metabolism, protein synthesis, and promotes bone growth.

Secretion Patterns

  • Characterized by pulsatile release—largest surge occurs shortly after sleep onset.

  • Influenced by exercise, sleep, and nutritional status.

Disorders Related to hGH

  • Dwarfism: Caused by insufficient hGH levels during childhood.

  • Gigantism/Acrromegaly: Result from hGH overproduction, often due to pituitary tumors.

Insulin-like Growth Factors (IGFs)

Production and Function

  • IGF-1 primarily produced in the liver, modulated by hGH.

  • Responsible for growth promotion and cellular proliferation.

  • Involves various binding proteins (IGFBPs) that regulate IGF availability and action.

IGFBPs Role

  • Six different IGFBPs control the actions of IGFs, affecting their bioavailability and signaling pathways.

Effects of hGH

Mechanisms of Action

  1. Stimulates growth via GHRH: Increases production of IGF-1.

  2. Inhibitory action via GHIH: Decreases GH release.

  3. Metabolic effects: Increases lipolysis and reduces glucose uptake by adipose tissue.

Target Tissues

  • Affects liver, muscle cells, adipose cells, and promotes growth effects.

Thyroid Hormones

Overview and Function

  • Thyroid hormones (T3, T4) play critical roles in metabolism, growth regulation, and thermogenesis.

Regulation

  • Regulated by the hypothalamic-pituitary-thyroid axis with negative feedback mechanisms.

Interaction with Growth Hormones

  • Thyroid and sex steroids cooperate with hGH for optimal growth outcomes.

Sex Steroids and Growth

Mechanisms of Action

  • Modulate both hGH secretion and responsiveness to IGF-1.

  • Testosterone and estrogens influence growth spurts and epiphyseal closure during puberty.

Effects of Estrogens

  • Critical for linear growth acceleration and bone maturation during puberty; also involved in osteoporosis risk post-menopause.

Conclusion

Summary of Growth Regulation

  • Growth and maturation require a complex interplay of hormones (hGH, IGF-1, thyroid hormones, sex steroids) influenced by nutrition.

  • Proper hormonal balance is essential for maintaining healthy growth and development throughout life.