GROWTH HORMONE

1. GROWTH HORMONE ENDO BLOCK 412 Dr. Shaikh Mujeeb Ahmed Assistant Professor AlMaarefa College

2. Objectives The student should be able to: • Identify the factors that affect growth beside the growth hormone. • Identify the hormones that affect growth beside the growth hormone. • Describe the metabolic effect of growth hormone. • Identify the relationship between growth hormone and insulin-like growth factors. • Explain the functions of the growth hormone. • Define the factors that influence the growth hormone secretion. • Describe the growth hormone abnormalities. • Describe the functions of melatonin hormone. • Explain the biological effect of melatonin hormone.

3. Endocrine Control of Growth • Growth depends on growth hormone but is influenced by other factors as well • Genetic determination of an individual’s maximum growth capacity • An adequate diet • Freedom from chronic disease and stressful environmental conditions • Normal levels of growth-influencing hormones

4. Hormones regulating growth • Thyroid Hormone • Insulin: Stimulates IGF-1 • Prolactin: Stimulates IGF-1 • Testosterone • Estrogen

5. Growth • Other hormones besides growth hormone are essential for normal growth • Thyroid hormone • Growth severely stunted in hypothyroid children • Hypersecretion does not cause excessive growth • Insulin • Deficiency often blocks growth • Hyperinsulinism often spurs excessive growth • Androgens • Play role in pubertal growth spurt, stimulate protein synthesis in many organs • Effects depend on presence of GH • Estrogens • Effects of estrogen on growth prior to bone maturation are not well understood poorly

6. Growth Stages - Regulation • Prenatal – Maternal factors, Fetal Insulin, & IGF • Growth in infancy – Genetic factors, GH production, Thyroid hormone, IGF • Adolescence- GH, Insulin, IGF & Sex hormone surge

7. Growth hormone (GH) • A peptide hormone (~200 amino acids) • Also known as somatotropin: • tropic hormone that affects somatic cells

8. Growth Hormone

9. GH Function: Direct Effect • GH binds directly to its target cells: • bones & muscles • Stimulates growth • Hypertrophy: increase in size/volume of cells • Example: increase in bone thickness • Stimulates cell reproduction • Increased rate of mitosis • Hyperplasia: increase in the number of cells, proliferation rate • Example: increase in bone length • Stimulates cell metabolism • Increase protein synthesis • Increase fat breakdown for energy • Increase glycogen breakdown so that there is an increase in blood glucose levels to fuel cell growth

10. Bone growth at the epiphyseal plate

11. GH function on metabolism • Stimulates cell metabolism • Increase protein synthesis • amino acid transport through cell membrane •  catabolism of protein • Increase fat breakdown for energy • Carbohydrate metabolism •  use of glucose for energy •  glycogen deposition in the cell •  blood glucose levels •  insulin secretion

12. GH Function: Indirect Effect • Most growth occurs through the indirect method • GH acts as a tropic hormone • Signals the liver to produce Insulin-like Growth Factors (IGF)

13. Growth Regulation: Neuroendocrine pathway

14. IGF-1: Insulin-like Growth Factor 1 • targets almost every cell in the body including the muscle, cartilage, bone, and skin cells • Stimulates hypertrophy and hyperplasia of the cells

15. hypothalamus growth hormone releasing hormone (GHRH) growth hormone inhibiting hormone Somatostatin (GHIH) anterior pituitary growth hormone (GH) liver Insulin-like growth factor 1 (IGF-1) Growth Hormone Regulation GH half-life is 20 – 30 min

16. Negative Feedback • High levels of IGF-1 • Stimulates GHIH/SS • decreased secretion of GH • High levels of GH • inhibits GHRH

17. GH Secretion • Secreted in bursts (not continuous) • GH his released most during sleep • optimal at night time • Changing sleeping pattern affects GH release • GH production declines with age

18. Increasing GH Production • Exercise regularly • 8 hours of sleep • Protein-rich diet • Avoid Stress

19. GH Associated Disorders • Dwarfism • Gigantism • Acromegaly

20. Dwarfism • Deficiency in GH • Short stature • Adult 4'10" or shorter • Proportional body • Affects 1/10 000 • Occurs in children • GH absent during child’s development

21. In one type of dwarfism (the African pygmy and the Lévi-Lorain dwarf), the rate of growth hormone secretion is normal or high, but there is a hereditary inability to form somatomedin C, which is a key step for the promotion of growth by growth hormone.

22. Gigantism – Vertical Growth • Excessive growth and height • Continuous secretion of GH • Hyperglycemia or full blown diabetes mellitus • Open epiphyseal plate • Affects bone growth length • Occurs during childhood

23. World’s Tallest Man: Robert Wadlow (1918-1940) 8 feet 11 inches and 439 pounds when he died

24. Tallest person alive • Sultan Kosen • born in Turkey • 8 feet 1 inch http://www.youtube.com/watch?v=ODFHC2XCtjU http://www.youtube.com/watch?v=Rf-lcBzZwC4

25. Gigantism Cause • Pituitary Adenoma • Tumour formed by pituitary gland • Secretes excessive GH / IGF-1 • Non cancerous • Average brain size • Skull grows but brain size stays the same, thus the brain function is unchanged

26. Gigantism Problems • Poor blood flow due to large body • Increased muscle mass but weaker muscle • Excess GH produces salt in muscle tissues • Muscles swell with water • Results in disproportional muscle growth  weaker muscles

27. Comparing Growths

28. Acromegaly – Lateral Growth • Increased GH secretion in adults • Closed epiphyseal plate • Bone lengthening stopped • Bone width increases • Slow progression

29. Acromegaly: Physical Effects • Bone thickens • Forehead expands • Eyebrow ridges bulge outwards • Cheekbones more prominent • Mandible enlarges and pushes lower teeth outwards and become widely space

30. Acromegaly: Physical Effects • Soft tissue harden • Deeper voice because larynx enlarges • Bigger tongue and lips that affects breathing • Cartilage in nose enlarges making nose broader

31. Acromegaly: Effect on Muscles • Impaired Movements • Enlargement of bones crushes peroneal nerve in knee • Nerve carries messages to move foot and lower leg • Nerve cannot send messages to leg to trigger walking motion • Also cause muscle numbness • Leads to early death

32. Acromegaly: Heart Defects • Heart tissue stiffen • heart cannot contract and relax • Ventricle harder to fill up • Heart grows bigger in order to pump out sufficient blood

33. Acromegaly: Lung Defect • As bones grow, rib cage expands • Diaphragm is stretched thin and loses elasticity • Breathing is reduced

34. The Pineal Gland • The pineal gland is a small, cone – shaped structure located in the center of the brain, diencephalon. • The pineal gland is composed of pinealocytes & glial cells. • Connects endocrine with nervous system

35. Functions • Secretion of the Hormone Melatonin • Regulation of Endocrine Functions • Conversion of Nervous System Signals to Endocrine Signals • Causes Feeling of Sleepiness • Influences Sexual Development

36. Precursor of melatonin is serotonin. • Synthesis and secretion of melatonin is affected by light exposure to the eyes.

37. Biological Effects of Melatonin • Helps keep body’s circadian rhythms in synchrony with light-dark cycle • Effects on Reproductive Function • Anti-gonadotropic • Effects on Sleep and Activity • Acts as antioxidant to remove free radicals • Alterations in melanin pigment distribution

38. References • Human physiology, Lauralee Sherwood, seventh edition. • Text book physiology by Guyton &Hall,11th edition. • Physiology by Berne and Levy, sixth edition.