Functions of the skeletal system

• Support

• Protection

• Movement

• Storage - Calcium and Phosphorus

• Blood cell production

Components of Skeletal System

Bone

Cartilage: 3 types

• Hyaline - most common, ends of bones; smooth joint mount

• Fibrocartilage - resist mechanical loads

• Elastic - Bend and move to function: recoil

Tendons and ligaments

Bone Histology

Bone Matrix

• Organic - collagen and proteoglycans: Alive: changing

• Inorganic - hydroxyapatite: CaPO₄ Crystals (calcium phosphate)

Collagen

Collagen - Found in most issues: Type I collagen in bone, tendons, skin

Proteoglycans

Glycosaminoglycans (GAGs)

Resist compression: Gel like component

Bone cells

Osteoblasts

• formation of bone via ossification or osteogenesis

• Ossification - formation of bone by osteoblasts

• Osteogenic Cells - become osteoblasts

Osteocytes

• Lacunae - house and protect osteocytes. found in rings of asse matrix. Spaces occupied by osteocyte cell body

• Canaliculi - allows cans to communicate with each other Canals occupied by osteocyte cell processes

Osteoclasts

Destruction of bone: Necessary when bones need repair or nutrients in bone are needed elsewhere in the body: regulated by hormones: resorption is done w/ enzymes and low PM

Intramembranous ossification

Converts woven bone into Lamellar bone

Woven Bone - collagen fibers randomly oriented

• fetal development

• fracture repair

• conversion

Lamellar bone - fibers are oriented in on direction: strong bone: lamellae fibers

Spongy Bone

more space, less bone

Trabeculae - interconnecting rods or plates of bone. spaces filled with marrow.

Cancellous

Bone Marrow

Red Marrow - ends of tons bones and center of other bones: manufactures blood cells

Yellow Marrow - in diaphysis of long bones; compose a of mainly fat; Deep to red

Compact Bone

Osteons (Haversian system) - Blood vessel-filled central canal (Haversian)

• Concentric lamellae of bone surround central canal

Lacunae and Canaliculi contain osteocytes and Fluid

General structure and Gross Anatomy of Long Bones

Diaphysis - elongated cylindrical shaft, Yellow Bone Marrow

Epiphysis - knobby, Enlarged regions at ends: strengthens joints: Attach site for tendons and ligaments rec bone marrow

Metaphysis - region between diaphysis and epiphysis: contains epiphyseal (growth) plate

Articular cartilage - Thin layer of hyaline cartilage covering the epiphysis: reduces friction and absorbs shown in movable joints

Medullary Cavity - Hollow, cylindrical space in diaphysis: contains yellow rea bone marrow in children

Endochondral Ossification

Cartilage formation begins at end of fourth week of development

Some ossification at about week eight:

Steps of Ossification

1. Fetal hyaline cartilage develops

2. Cartilage calcifies and a periosteal bone collar forms

3. Primary ossification center forms in diaphysis

4. Secondary ossification centers form in diaphysis

5. Bone replaces cartilage, except articular cartilage and epiphyseal plates

6. Epiphyseal Plates ossify and form epiphyseal lines

Endochondral Ossification - formation of long bones: Bone growth: bone healing: closure of epiphyseal plate is ossified becoming the epiphyseal line (12-15 yrs old)

Growth of Bone

Interstitial growth - long bones growth in length: occurs in epiphyseal plate

Appositional growth - bones growth in diameter: occurs in periosteum

Factors Affecting Bone Growth

Nutrition

• lack of calcium and other nutrients during development can cause bones to be small

Vitamin D

• necessary for absorption of calcium from intestines

• Rickets - lack of vitamin D during Childhood

Osteomalcia - lack of vitamin ) during Adulthood

Vitamin C

• Necessary for collaged synthesis by osteoblasts

• lack of vitamin C can cause wounds not to heal and teeth to fall out

Hormones

• Thyroid hormone required for growth of all tissues

• sex hormones: Estrogen and testosterone: HGH

Bone Stress

Bone Repair

Ossification

1. Ossification centers form within thickened regions of mesenchyme

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2. Osteoid undergoes Calcification

   

3. Woven bone and surrounding periosteum form

   

4. Lamellar bone replaces woven bone as compact and sponger, bone form

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Cartilage

Consists of specialized cells that produce Matrix

• Chondroblasts - form Matrixes

• Chondrocytes - surrounded by Matrix launce

matrix - collaged and Proteoglycans

Perichondrium - Double-layer CT Sheath. Covers except at articulations

• Inner - more delicate, has fewer fibers, contains chondroblasts

• Outer - Blood vessels and nerves penetrate. No blood vessels in cartilage

Articular cartilage - covers bones at joints; has no perichondrium

Growth

• Appositional - new cells at periphery

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• Interstitial - cells divide and add more matrix between the cells