Bone Growth

1. Bone Growth Justin, Mara, Anna, Tania, Jacqueline, Gigi, Lindsay

2. Zone of Resting Cartilage • Cartilage is a flexible connective tissuefound in many areas in the bodies of humans and other animals. • immediately adjacent to epiphysis are irregularly scattered cartilage cells, called the resting cell zone • this is germinal layer that supplies the developing cartilage cells • anchors growth plate to bone

3. Zone of Calcification • In this zone, chondrocytes, which are the only cells found in healthy cartilage, are either dying or dead, leaving cavities that will later become invaded by bone-forming cells. • Chondrocytes die when they can no longer receive nutrients or eliminate waste by diffusion. • This is because the calcified matrix is much less hydrated than hyaline cartilage.

4. Zone of Maturation and Hypertrophy • there is no active growth in this layer (no cellular division) and the chondrocytes (cells found in healthy cartilage) begin to terminally differentiate • layer in which chondrocytes become enlarge and swollen in the process of maturation leading to cell death • they hypertrophy at expense of extracellular matrix & these enlarged cartilage cells • synthesis of extracellular matrix permits newly divided cells to separate from each other; • columns of cartilage cells extend toward metaphysic (wider portion of a long bone adjacent to the growth plate, being constantly lengthened by cell division occurring at the base

5. Zone of Maturation and Hypertrophy Continued • cells nearer the metaphysis begin to undergo changes that ultimately lead to their destruction • increase in enzyme activity increases the concentration of phosphate ions, which are required in the calcification process • an absence of alkaline phosphatase and there is deficient mineralization of the matrix and widening of the growth plate • this is weakest portion of the growth plate

6. 1. Zone of Resting Cartilage 3. Zone of Maturation/ Hypertrophy 4. Zone of Calcified Cartilage 2. Zone of Proliferation

7. Hormones involved in Bone Growth • Hormones that affect bone growth and development are secreted by pituitary, thyroid gland, parathyroid glands, and the ovaries and testes

8. Pituitary Gland • Secretes growth hormone (somatotropin) which stimulates activity in the epiphyseal plates • Main Regulator of Height • Stimulates bone and Muscles growth • Maintains the normal Rates of Protein Synthesis • Speeds the release of fats as an energy source for growth

9. Parathyroid Glands • When a low blood calcium condition exists the gland responds by releasing the parathyroid hormone • Stiumlatesosteoclasts to break down bone tissue • As a result, calcium salts are released into the blood • If blood calcium level is excessively high, the thyroid gland responds by releasing calcitonin which inhibits the osteoclast activity allowing the osteoblasts to form bone tissue

11. Calcitonin • A peptide hormone produced by cells within the thyroid gland • Secretion is stimulated by high blood calcium concentrations, and it acts as a physiologic antagonist to PTH • Osteoclasts have receptors for calcitonin, but the effects are transient. Calcitonin also: • inhibits osteoclastresorption • delays calcium absorption from the intestine • increases calcium urinary excretion

12. Vitamin D • 1,25 dihydroxyvitamin D is an active hormone which is produced by the kidney • It is not really a vitamin, but the name was given many years ago, before anybody knew the function of this molecule. Vitamin D receptors are present in bone, kidney, intestines, and other cells. The chemical name is 1,25-dihydroxy-cholecalciferol, and it • promotes gastrointestinal absorption of calcium and phosphorus. • is necessary for bone mineralization. • stimulates bone resorption when given in high doses

13. Thyroid Hormone • Produced by the thyroid gland. Bone cells have receptors for thyroid. This hormone also: • is necessary for growth and maturation of the skeleton. • causes increased osteoclastic bone resorption and osteoporosis when levels are too high.

14. Summary of the effects of hormones on skeletal metabolism Increase Bone resorption • Parathyroid hormone GlucocorticoidsThyroid Hormone Vitamin D metabolites in high doses Decrease Bone Resorption • CalcitoninGonadal steroids Increase Bone Formation • Growth hormone Vitamin D metabolites Gonadal steroids Decrease Bone Formation • Glucocorticoids

15. Osteoporosis • A disease that effects your bones and makes them thin & brittle with several holes in them like a sponge. • Leads to broken or fractured bones which can be disabling • Caused by lack of estrogen or testosterone: hormones that protect against bone loss • Common in women after menopause & men older than 65 • More common in women than men • Vitamin D and calcium deficiencies contribute to bone thinning and increase risk of Osteoporosis

16. Osteoporosis Stages

17. Aseptic necrosis • a disease where there is cellular death (necrosis) of bone components due to interruption of the blood supply. • Blood is responsible for providing oxygen and nutrients to the bone tissue. • Without blood reaching bone tissue, the bone tissue dies and the bone collapses. • Common Causes: • Chemotherapy • Alcoholism • Excessive steroid use • Fractured bones • Dislocated joints

19. Osteomalacia • softening of the bones due to a lack of vitamin D or a problem with the body's ability to break down and use this vitamin. • The softer bones in osteomalacia have a normal amount of collagen, which gives the bones its structure. However, they lack the proper amount of calcium which makes them so soft. • Syptoms include: • Bone fractures that happen without a real injury • Muscle weakness • Widespread bone pain, especially in the hips • Commonn Causes • Lack of vitamin D • Not enough exposure to sunlight • Inability for intestines to fully absorb vitamin D

20. Rickets • Rickets is a disorder caused by a lack of vitamin D, calcium, or phosphate. It leads to softening and weakening of the bones. • Also caused by lack of Vitamin D. Vitamin D helps the body control calcium and phosphate levels. If the blood levels of these minerals become too low, the body may produce hormones that cause calcium and phosphate to be released from the bones. This leads to weak and soft bones. • Symptoms: • Bone pain/tenderness • Dental deformities • Impaired growth • Short stature (adults less that 5 ft. tall) • Skeletal deformities

21. Rickets