Chapter 6: Osseous Tissue and Bone Structure

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Cells of Bone

Osteoprogenitor -precursor to osteoblast

Osteoblasts -produce bone matrix

Osteocytes -trapped osteoblast

Osteoclasts -dissolve bone matrix

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Compact Verses Spongy Bone

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Long Bone Structure

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Flat Bone Structure

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Ossification

• Endochondrial

• Intramembranous

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Intermembranous

• Typical of flat bones

• Ossification of mesenchymal cells

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Endochondral Ossification

• Long bones

• Hyaline cartilage breaks down

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Postnatal Bone Growth

• Interstitial growth:

• Increase bone length (adolescence)

• Appositional growth:

• Increase thickness and remodeling of all bones

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Epiphysial Plate

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Bone Growth

• Growth hormone stimulates cell division

• Thyroid hormone modulates growth hormone

• Testosterone and estrogens (at puberty)

– Promote adolescent growth spurts

– End growth by inducing epiphyseal plate closure

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Bone Resorption

• Osteoclasts secrete

– Lysosomal enzymes (digest organic matrix)

– Acids (convert calcium salts into soluble forms)

• Dissolved matrix is transcytosed across osteoclast, enters interstitial fluid and then blood

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Control of Remodeling

• What controls continual remodeling of bone?

– Hormonal mechanisms that maintain calcium homeostasis in the blood

– Mechanical and gravitational forces

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Bone Remodeling

• Balance between resorption and formation

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Copyright © 2010 Pearson Education, Inc. Figure 6.11

Bone growth Bone remodeling

Articular cartilage

Epiphyseal plate

Cartilagegrows here.

Cartilageis replacedby bone here.

Cartilagegrows here.

Bone isresorbed here.

Bone isresorbed here.

Bone is addedby appositionalgrowth here. Cartilage

is replacedby bone here.

Hormonal Control of Blood Ca2+

• Calcium is necessary for

– Transmission of nerve impulses

– Muscle contraction

– Blood coagulation

– Secretion by glands and nerve cells

– Cell division

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Hormonal Control of Blood Ca2+

• Primarily controlled by parathyroid hormone (PTH)

• Calcitonin has minor role

• Leptin influences bone remodeling

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Exercise and Bones

• Builds stronger bone

• Inactivity leads to weak bones

– Astronauts shrink as much as 4 inches

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Bone Repair

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Homeostatic Imbalances

• Heterotrophic Bones -abnormal bone formation

– Tendons, joints, kidneys, testes, sclera of the eye

– Fibrodysplasia Ossificans Progressiva

• Dwarfism -pituitary failure

• Acromegaly -bone/cartilage thickening along facial contours

• Gigantism -growth hormone overproduction

• Marfan Syndrome -excessive cartilage at epiphyseal plates

• Rickets -vitamin D deficiency

• Paget's disease

• Osteoporosis

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Osteoporosis

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