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ENDOCRINE CONTROL OF GROWTH

ENDOCRINE CONTROL OF GROWTH. George Liapakis , PhD. What makes children grow ? . The continuous net protein synthesis. Growth of soft tissues . Lengthening of long bones. This occurs under the influence of growth hormone (GH ).

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ENDOCRINE CONTROL OF GROWTH

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  1. ENDOCRINE CONTROL OF GROWTH George Liapakis, PhD

  2. What makes children grow? The continuous net protein synthesis Growth of soft tissues Lengthening of long bones This occurs under the influence of growth hormone (GH)

  3. Growth hormone (GH) is secreted by the anterior pituitary.

  4. Composition of long bones • A long bone consists of cells and osteoid • Osteoid is an extracellular organic matrix produced by specific cells (osteoblasts) • Osteoid is composed of collagen fibers in a semisolid gel and it is flexible. • Bone is made hard by the precipitation of calcium phosphate crystals, within osteoid (calcified osteoid). • An osteoblast, trapped within a calcified osteoid, is called osteocyte and cannot form anymore bone.

  5. Anatomy of long bones Epiphyses: Tworounded ends of the bone at its joints with adjacent bones Diaphysis: Cylindrical shaft Marrow cavity : A central cavity, which is filled with bone marrow, the site of blood cell production

  6. Epiphysealplate: A layer of cartilage, separating the diaphysis from the epiphysis. Cartilage is similar to bone, except that it is not calcified. Theactivity of cartilage cells plays an important role in thegrowth in lengthof long bones.

  7. Growth in length of a long bone The cartilage cells on the outer edge of the plate next to the epiphysis divide and multiply, widening the epiphyseal plate. The older cartilage cells toward the diaphyseal border die and are replaced by osteoblasts.

  8. Growth in length of a long bone Osteoblasts lay down bone in the disintegrating cartilage until bone entirely replaces cartilage on the diaphyseal side of the plate (ossification) When ossification is complete, the bone on the diaphyseal sidehas lengthened and the epiphyseal plate has returned to itsoriginal thickness.

  9. GH stimulates proliferation of epiphyseal cartilage and the activity of osteoblasts. • GH promotes lengthening of long bones only as long as the epiphyseal plate remains cartilaginous (or it is “open.”) • The epiphyseal plates ossify, (or “close”) and the bones cannot lengthen any further at the end of adolescence under the influence of sex hormones, despite the presence of GH.

  10. Growth Hormone promotes bone growth by increasing its thickness

  11. Growth in thickness of a long bone Osteoblastsadd new bone on top of the outer surface of existing bone. Osteoclastsplay the role of thebone breaker by dissolving the inner bone which is located next to the marrow cavity. The marrow cavity enlargesalong with an increase in the bone’s perimeter.

  12. Growth Hormone (GH) promotes growth of soft tissues GH increases the number of cells Hyperplasia It stimulates cell division It prevents cell death GH increases the size of cells Hypertrophy It stimulates protein synthesis It inhibits protein degradation It promotes cellular uptake of amino acids

  13. GH exerts its growth-promoting effects indirectly by stimulating insulin-like growth factor (IGF) IGF is produced in many tissues and mostly in the liver and acts on the target cells

  14. Despite the fact that GH is necessary for promoting growth, it is still secreted in adults in whom growth has already ceased. GH has additional important effects not related to growth

  15. GH exerts direct metabolic effects not related to growth

  16. Muscles use the mobilized fatty acids instead of glucose as a metabolic fuel Brain uses only glucose as metabolic fuel.

  17. The overall metabolic effect of GH is to mobilize fat stores as a major energy source while conserving glucose for the brain. GH secretion increases in situations (exercise or stress) in which the energy needs of our body exceed available glucose stores.

  18. FACTORS THAT INFLUENCE GROWTH HORMONE SECRETION

  19. Abnormal secretion of GH Gigantism Acromegaly Dwarfism

  20. Dwarfism • It starts inchildhood • Short stature, which is caused by retarded skeletal growth • Inabilityof pituitary to secrete GH, or hypothalamus to secrete GHRH. • After growth is complete, the GH deficiency produces relatively few symptoms (reduced skeletal muscle mass and strength and decreased bone density)

  21. Gigantism • It starts inchildhood • Hypersecretionof GH, (tumor in the anterior pituitary) • Rapid growth in height.

  22. Acromegaly • It starts after adolescence when the epiphyseal plates have already closed. • Hypersecretionof GH, (tumor in the anterior pituitary) • Growth of bones in thickness and proliferation of soft tissues. Bone thickening is most obvious in hands, feet and face.

  23. SUMMARY Growth hormone (GH) is secreted by the anterior pituitary. GH: Growth in length of a bone GH: Growth in thickness of a bone Growth-promoting effects of GH: Insulin-like growth factor (IGF) GH promotes growth of soft tissues (hyperplasia, hypertrophy) Metabolic effects of GH not related to growth (blood glucose, fatty acids) The overall metabolic effect of GH is to mobilize fat stores as a major energy source while conserving glucose for the brain. Factors that influence GH secretion Abnormal secretion of GH: Dwarfism, gigantism, acromegaly

  24. NEXT LECTURE THYROID GLAND

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