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