Cartilage and Bone

1. Cartilage: organ=Cartilage tissue+perichondrium

1) structure of cartilage tissue ---cell: chondrocyte ---cartilage matrix

① chondrocyte: ---Structure: LM embedded in cartilage lacuna peripheral cells: --small and immature --single and flattened central cell: --large and mature, --round and in group of 2-8 cells --small and round nucleus --basophilic cytoplasm --EM: rich in RER and Golgi complex

*isogenous group: several cells locates in one lacuna, which are derived from a single(same) parent cell

② Cartilage matrix ---ground substance: proteoglycan: --same to loose CT --there are more chondroitin sulfate distributed at the periphery of cartilage lacuna---called as cartilage capsule(basophilic) water ---fiber: type and number of fiber depends on the type of cartilage

2) Classification: according to the fiber a. Hyaline cartilage: less collagenous fibril articular surface, rib cartilage, trachea and bronchi

b. Fibrous cartilage: large amount of collagenous fiber bundles cells are small and less intervertebral disc, symphysis pubis

c. Elastic cartilage: large amount of elastic fiber external ear, epiglottis

3) perichondrium two layers: ---out layer: contain more fiber-protection ---inner layer: more cells-osteoprogenitor cell(fusiform in shape)

4) growth of cartilage ---interstitial growth: inner chondrocyte proliferation→ produce fiber and matrix. immature cartilage ---appositional growth: osteoprogenitor cell→chondroblast → chondrocyte → produce fiber and matrix. growing and mature cartilage

2.Bone ---consists of bone tissue, periosteum and endosteum, bone marrow

1) Bone tissue ① Cells:

a. osteoprogenitor cell: stem cell ---structure: fusiform, small ovoid nucleus slight basophilic cytoplasm exist in periosteum and endosteum ---function: differentiated into osteoblast and chondrocyte

b. osteoblast : ---structure: LM: single layer of cuboidal or low columnar cell round nucleus basophilic cytoplasm located on the surface of bone tissue

EM: fine processes rich in RER, Golgi complex

---function: ⅰ.synthesize bone collagen fiber and ground substance-osteoid ⅱ.release matrix vesicle: 0.1um in diameter membrane-coated function: promote calcification

c.osteocyte ---structure: flattened cell with multiple long thin processes located in bone lacuna and bone canaliculus basophilic cytoplasm adjacent cells connect in bone canaliculus by gap junctions ---function: Maintain bone matrix

d. osteoclast ---structure: LM: multinuclear large cell, um 6-50 nuclei acidophilic cytoplasm located at peripheral part of bone

EM: ruffled border-processes light zone: --under the ruffled border --microfilament primary lysosome, pinosome and secondary lysosome RER, mito. and Golgi ---function: dissolve and absorb bone matrix

② Bone matrix ---organic matter: bone collagen fiber -collagenous fiber (type I collagen) ground substance: glycosaminoglycan

---inorganic matter: bone salts Hydroxyapatite crystal: Ca 10 (PO 4 ) 6 (OH) 2 pin-shaped longitudinal arranged *bone lamella: bone matrix arranged in layers at different direction

2) Architacture of long bone Long bone is an organ, made up of bone tissue(shaft and epiphyses), periosteum and endosteum, bone marrow

① shaft: consists of compact bone a. circumferential lamella: /outer concentrically-arranged /inner around inner surface of bone

b. Haversian system (osteon): /cylindric structure, 3-5mm /central canal: N, BV, CT /Haversian lamella: 4-20 layers

c. interstitial lamella: /irregular lamella /remnant of Haversian or circumferential lamella *perforating canal: /transverse canal /connect with Haversian canal

② epiphyses: composed of spongy bone ---trabeculae: formed by parallelly-arranged lamella form a spongy-liked network ---Bone marrow: hemopoietic tissue

③ periosteum and endosteum: CT membrane ---periosteum: DCT outer layer:more fiber bundles form perforating fiber inner layer: rich in BV, N and osteoprogenitor cells ---endosteum: thin, a layer of osteoprogenitor cell and CT ---function: provide nutrition and osteoblast for bone growth and repairing

3) osteogenesis Self study!