Isam zebeba cartilage Embryo



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Functions

1. Support

2. Movement: muscles attach by tendons and use bones as levers to move body

3. Protection

1. Skull – brain

2. Vertebrae – spinal cord

3. Rib cage – thoracic organs

4. Mineral storage

1. Calcium and phosphorus

2. Released as ions into blood as needed

5. Blood cell formation and energy storage

1. Bone marrow: red makes blood, yellow stores fat

Classification of bones by shape


  1. Long bones

  2. Short bones

  3. Flat bones

  4. Irregular bones

  5. Pneumatized bones

  6. Sesamoid bones

Gross anatomy of bones

  1. Compact bone

  2. Spongy (trabecular) bone

  1. Blood vessels

  2. Medullary cavity

  3. Membranes

1. Periosteum

2. Endosteum



Flat bones

  1. Spongy bone is called diploe when its in flat bones

 Have bone marrow but no marrow cavity

Long bones

  1. Tubular diaphysis

or shaft

  1. Epiphyses at the ends: covered with “articular” (=joint) cartilage

  2. Epiphyseal line in adults

 Kids: epiphyseal growth plate (disc of hyaline cartilage that grows to lengthen the bone)

  1. Blood vessels

 Nutrient arteries and veins through nutrient foramen

Periosteum

  1. Connective tissue membrane

  2. Covers entire outer surface of bone except at epiphyses

  3. Two sublayers

 1. Outer fibrous layer of dense irregular connective tissue

 2. Inner (deep) cellular osteogenic layer on the compact bone containing osteoprogenitor cells (stem cells that give rise to osteoblasts)

Osteoblasts: bone depositing cells

 Also osteoclasts: bone destroying cells (from the white blood cell line)



  1. Secured to bone by perforating fibers (Sharpey’s fibers)

Endosteum

  1. Covers the internal bone surfaces

  2. Is also osteogenic



Spongy bone



Spongy bone



  1. Layers of lamellae and osteocytes

  2. Seem to align along stress lines



Compact bone

  1. Osteons: pillars

  2. Lamellae: concentric tubes

  3. Haversian canals

Osteocytes
Factors regulating bone growth

  1. Vitamin D: increases calcium from gut

  2. Parathyroid hormone (PTH): increases blood calcium (some of this comes out of bone)

  3. Calcitonin: decreases blood calcium (opposes PTH)

  4. Growth hormone & thyroid hormone: modulate bone growth

  5. Sex hormones: growth spurt at adolescense and closure of epiphyses

Terms (examples)

  1. chondro refers to cartilage

chondrocyte

 endochondral

 perichondrium


  1. osteo refers to bone

osteogenesis

osteocyte

 periostium


  1. blast refers to precursor cell or one that produces something

 osteoblast

  1. cyte refers to cell

 osteocyte

  1. Intramembranous Ossification

a. Forms flat bones of skull, mandible, clavicle

b. Replacement of mesenchymal membrane with osseous tissue

c. Mesenchymal cells differentiate to osteoprogenitor cells, which then become osteoblasts

d. Osteoblasts create spongy bone, which then remodels into compact bone where necessary

2.Endochondral Ossification

 Most bones formed this way

Mesenchyme creates Cartilage model, which gets replaced by bone

 Replacement begins in middle (diaphysis) & follows in ends (epiphyses)

A)Cartilage model grows in length (interstitial growth) & in width (appositional growth)

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies.

B)Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone.

The perichondrium, which surrounded the cartilage model, now must be referred to as the periosteum.


C) Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center.

D) Bone tissue continues to replace cartilage of the diaphysis, and & continues toward each epiphysis.

The medullary cavity begins to hollow out Blood vessels invade the epiphyses and osteoblasts form secondary centers of ossification.

Cartilage remains only at the ends (articular cartilage) & at metaphysis (epiphyseal plate)


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