Histology LEC Skeletal Tissues: Tendons and Bone Development and Growth

SKELETAL TISSUE

Mesodermal in origin

Rigid form of connective tissue due to calcification of ground substance

Internal support

Attachment of muscles and tendons

Contains bone marrow

Protect vital organs

Calcium storage

Skeletal Tissue Functions

Mg2+, Ca2+, Na+

Inorganic elements of Skeletal Tissue

calcified matrix

Organic elements of Skeletal tissue

Sulphate GAGs

predominant such as Chondrotin and Keratin sulfate

Proteoglycans

Ground substance of Cartilage is made up of?

Chondrocytes

Maintain the integrity of the cartilage matrix

Arranged in clusters of 2-4 enclosed by amorphous cartilage matrix

TENDONS

Tough flexible straps that connect muscles to bone

Poorly vascularised and heals slowly

Compact linear collagen fibers with nuclei of inactive

Tendons are composed of?

Myotendinous junctions

Tendons anchor to muscle through?

Periosteum or Sharpey's Fibers

Tendons anchor to bone through?

BONE DEVELOPMENT AND GROWTH

BONE MATRIX AND MINERALIZATION

70%

Inorganic salts

30%

Organic

Inorganic Salts of Bone

Mainly calcium and phosphate in the form of hydroxypatite crystals

Magnesium carbonate

Sodium

Potassium

Organic Compounds of Bone

Tupe I collagen creates hole zones, the initial site for mineralization

Ground substance proteoglycans consist of hyaluronic acid and chondroitin sulphate

Osteocalcin: involved in binding calcium during mineralization

Osteonectin: bridging function between collagen and mineral component Sialoprotein

Tupe I collagen

creates hole zones, the initial site for mineralization

Ground substance proteoglycans

consist of hyaluronic acid and chondroitin sulphate

Osteocalcin

involved in binding calcium during mineralization

Osteonectin

bridging function between collagen and mineral component

Sialoprotein

promotes calcification

Process of bone formation

1. Collagen and other organic components synthesized from RER of

2. osteoblasts -> Golgi Apparatus -> secreted as osteoids

3. After maturation phase, calcium phosphate salts precipitate in the hole zones

4. Pyrophosphate: inhibitor that controls bone mineralization

5. Alkaline Phosphatase: neutralize effect of pyrophosphate

INTRAMEMBRANOUS OSSIFICATION

Skull vault, maxilla, mandible

Occurs within membranes of condensed, primitive mesenchymal tissue

INTRAMEMBRANOUS OSSIFICATION PROCESS

1. Mesenchymal cells differentiate into osteoblasts that begin synthesis of osteoid at "centers of ossification"

2. Mineralization of osteoid

3. Osteoblasts trapped in lacunae evolve into osteocytes and cytoplasmic extensions shrink and form canaliculi

4. Osteoprogenitor cells continue to form osteoblasts

5. Fusion of adjacent ossification centers occurs

6. Woven bone is remodelled by osteoclastic activity and subsequent osteoblastic deposition of mature compact bone

ENDOCHONDRAL OSSIFICATION

Long bones, vertebrae, pelvis, skull base

Permits functional stress to be sustained during skeletal growth

Zone of Reserve Cartilage

Zone of Proliferation

Zone of Maturation

Zone of Hypertrophy and Calcification

Zone of Cartilage Degeneration

Osteogenic Zone

ENDOCHONDRAL OSSIFICATION: Process of Primary Ossification

Zone of Reserve Cartilage

Cartilage model is first formed in hyaline cartilage

Zone of Proliferation

Appositional growth occurs to form the different parts of bone

Zone of Maturation

Chondrocytes within the model enlarge and resorb the cartilage so as to leave perforated trabeculae of cartilage matrix

Zone of Hypertrophy and Calcification

Cartilage matrix is ossified

Zone of Cartilage Degeneration

Chondrocytes degenerate, primitive mesenchymal cells and blood vessels invade the spaces occupied by chondrocytes and differentiate into osteoblasts and hematopoietic cells

Osteogenic Zone

Osteoblasts begin to form woven bone

Process of Primary Ossification

1. Perichondrium develops osteogenic potential and assumes the role of periosteum

2. Periosteum lays down a thin layer of bone on the surface

3. Results in bony diaphysial shaft with cartilaginous epiphyses at each end

Process of Secondary Ossification

Conversion of central epiphyseal cartilage into bone

As the shower thoughts says

If humans can get lung cancer because of their lungs, do fishes get gill cancer because of their gills?