Fibrous, bone, and cartilage

Fibrous, bone, and cartilage

1. skeleton: collagenous (fibrous) tissue, cartilage, and bone

   • endoskeleton
     • :forms within the body, all but dermal bones ex. vertebrae, ribs, limb bones
   • exoskeleton
     • :dermal bone  ex. osteoderm
   • cranial
     • skull
   • post-cranial
     • everything behind the skull

2. mesenchymes: undifferentiated mesoderm cells

   • fibroblast
     • :secrete collagen in connective tissue
     • osteoblasts
       • :forms bone
       • chondroblasts
         • :forms cartilage

3. Connective tissue

   • :distinctive cell type surrounded by an extracellular matrix consisting of protein fibers and ground substance -includes bone, cartilage, and dense connective tissue(=dermis, tendons, ligaments) -some undergo minearalization (=hardening)
   • calcification
     • invertebrates- calcium carbonate vertebrates- calcium phosphate
     • ossification
       • :specialized form of calcification -calcium  phosphate in the form of hydroxyapatite

4. Cartilage

   • cell type: chondrocytes surface: perichondrium EM composition: chondroitin surface + surface -generally avascular so it has no ability to remodel -3 types
   • hyaline cartilage
     • small number of fibers and resists compressive forces ex. endochondral bone precursor, tips of ribs
     • fibrocartilage
       • collagen fibers abundant, resistant tensile forces ex. intervertebral disks
       • elastic cartilage
         • elastic fibers, very flexible ex. internal support for ear

5. Bone

   • -normally vascularized and innervated -can be highly organized ie. Haversian system -storage for calcium and phosphate -70% mineralized -plastic throughout lifetime
   • Based on the position, bone can be classified as _______ (inside) vs. cortical (outside) bone.
     • trabecular
   • osteoblasts
     • secrete new bone tissue and become osteocytes
     • osteoclasts
       • destroy osteocytes, release Ca2+
       • osteocytes
         • mature bone cells; maintain fully formed bone
   • marrow: connective tissue filling spaces in spongy bone
     • found in long and flat bones
   • Bone remodeling
     • -response of bone to mechanical stress depends on force duration
     • atrophy
       • :loss of bone tissue from continued pressure or lack therefore eg. lack of gravity
     • hypertrophy
       • :bone deposition as a result of intermitent stress; increase in bone density eg. throwing arm
     • nonlamellar bone: young
       • evident in LAG
     • lamellar: bone old
       • evident in LAG
     • endochondral
       • (replacement bone)replacement of embryonic cartilage in adult bone features:  -epiphysis (where secondary centers of ossification are) diaphysismetaphysis=epiphyseal plate (where cartilage replacement occurs)
       • Example of an endochondral bone:
         • humerus
       • endochondral ossification= ossification---> chondrogenesis---> cartilage calcification---> ossification
     • intramembranous
       • (membrane bone) bone formed directly when salts are deposited in plates in the dermis and in tendons 1. dermal- forms in dermis 2. heterotopic(sesamoid)- forms in tendons (tendons=in bones that arise after replacing fibrous connective tissue) largest sesamoid=patella Also perichondral/periosteal bone

6. Visually, bone can be classified as spongy (porous) vs. compact (dense) bone.

7. LAGs stand for Lines of Arrested Growth representing periods of interruption of sustained bone deposition.

8. osteon = Haversian system

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