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 fibrilarticular surface, rib cartilage, trachea and bronchi

b. Fibrous cartilage:large amount of collagenous fiber bundles cells are small and lessintervertebral 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 nucleusbasophilic cytoplasmlocated 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 cytoplasmadjacent cells connect in bone

canaliculus by gap junctions---function:

Maintain bone matrix

d. osteoclast

---structure: LM: multinuclear large cell, 30-100um 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

②Bone matrix

---organic matter:

bone collagen fiber -collagenous fiber (type I collagen)

ground substance:

glycosaminoglycan

---inorganic matter: bone salts

Hydroxyapatite crystal: Ca10(PO4)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 b

one 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: DCTouter layer:more fiber bundles

form perforating fiberinner layer:

rich in BV, N and osteoprogenitor cells---endosteum: thin, a layer of osteoprogenitor cell

and CT---function: provide nutrition and osteoblast for bo

ne growth and repairing

3)     osteogenesis

Self study!