29 min of phys 2 feb 26

Overview of Growth Hormone and Its Functions

  • Different organs possess adipose cells with receptors that bind growth hormone (GH).
    • Function: Signals adipose cells to mobilize and release fatty acids.
    • This process is called lipolysis.
    • Inverse of lipogenesis.

Lipolysis and Lipogenesis

  • To regulate stored lipid release, one would want to stimulate lipolysis.
  • Simultaneous inhibition of lipogenesis leads to a combined effect of mobilizing energy.
    • Growth hormone inhibits lipogenesis while promoting lipolysis, leading to increased fatty acid release.

Actions of Growth Hormone

  • Mobilization of energy from triglycerides:
    • Releases free fatty acids and glycerol into the blood for energy uptake by other cells.
  • **Impact on different cell types: **
    • Acts on bone cells to stimulate growth.
    • Stimulates muscle cells to produce more actin and myosin (contractile fibers).
    • Affects nervous and immune cells.

Connection to Insulin

  • Insulin counteracts growth hormone's effects:
    • Stimulates lipogenesis.
    • Inhibits lipolysis.

Diabetogenic Effect of Growth Hormone

  • Increased glucose levels in diabetes can be compared to high fatty acids from adipose cells.
    • Both lead to the release of energy sources for cellular uptake.
  • Insulin-like growth factor 1:
    • Released from the liver in response to GH.
    • Signals cells to utilize nutrients for growth.

Disorders Related to Growth Hormone

  • Disorders can include dwarfism, gigantism, and acromegaly.
    • Dwarfism: Result of insufficient growth hormone pre-puberty.
    • Gigantism: Caused by excess growth hormone pre-puberty when growth plates are open.
    • Acromegaly: Result of excess growth hormone post-puberty, leading to thickening of bones after epiphyseal plates have closed.
    • Symptoms include coarsened features (e.g., protruding jaw, large hands).

Examples and Cases

  • Yao Ming: A reference to a known case of gigantism.
  • Discussed Andre the Giant as a case of acromegaly and his massive size.
    • Faced challenges associated with his size, including health issues.

Genetic Factors in Growth Disorders

  • Disorders have genetic underpinnings.
    • Myostatin: A gene that regulates muscle growth; mutations may lead to muscle hypertrophy (example: double-muscled cattle).
    • Genetic defects can produce observable phenotypes, demonstrating the connection between genetics and physiology.

Myostatin and Muscle Growth

  • Defective myostatin leads to elevated muscle growth.
    • Myostatin prevents muscle overgrowth.
  • Phenotype interpretation: A mutation can lead to significant changes in physical traits.

Thyroid Function and Disorders

  • Thyroid Gland Structure: Contains follicles filled with colloid, where thyroid hormone precursors are produced.
    • Iodine is crucial for thyroid hormone production (T3 and T4).

Types of Thyroid Disorders

  • Hyperthyroidism: (Example: Graves' Disease)
    • Autoimmune disease where antibodies mimic TSH, stimulating thyroid hormone release.
    • Symptoms include weight loss, increased metabolism, and bulging eyes (exophthalmos).
  • Hypothyroidism: (Example: Hashimoto's Disease)
    • Autoimmune disorder that leads to inadequate hormone production.
    • Symptoms include weight gain, fatigue, and cold intolerance.

Thyroid Hormone Production Process

  • Iodine Uptake: Thyroid cells actively trap iodine from the blood.
  • Thyroglobulin Production: Synthesized in the rough endoplasmic reticulum and secreted into the lumen for hormone formation.
  • Hormone Assembly:
    • Thyroid hormones are produced by iodinating tyrosine residues in thyroglobulin.
    • Formation of T3 (triiodothyronine) and T4 (thyroxine) from iodinated compounds.

Conclusion

  • Importance of both growth hormone and thyroid hormones in regulating metabolic processes and growth.
  • Understanding genetic influences on physiological traits can provide insights into growth-related disorders.