Bone Growth
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Transcript of Bone Growth
BONE GROWTHJustin, Mara, Anna, Tania, Jacqueline, Gigi, Lindsay
Zone of Resting Cartilage Cartilage is a flexible
connective tissue found 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
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.
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
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
1. Zone of Resting Cartilage
2. Zone of Proliferation
3. Zone of Maturation/ Hypertrophy
4. Zone of Calcified Cartilage
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
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
Parathyroid Glands When a low blood calcium condition
exists the gland responds by releasing the parathyroid hormone
Stiumlates osteoclasts 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
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 osteoclast resorption delays calcium absorption from the intestine increases calcium urinary excretion
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
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.
Summary of the effects of hormones on skeletal metabolism
Increase Bone resorption Parathyroid hormone
Glucocorticoids Thyroid Hormone Vitamin D metabolites in high doses
Decrease Bone Resorption Calcitonin
Gonadal steroids Increase Bone Formation Growth hormone
Vitamin D metabolites Gonadal steroids
Decrease Bone Formation Glucocorticoids
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
Osteoporosis Stages
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
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
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
Rickets