Skeletogenic Connective Tissues
Cartilages and Bones
Skeletogenic Connective Tissues
Cartilages
Cartilage is a kind of connective tissue
arises from the mesenchyme contains extensive matrix
more than 95% of cartilage volume
Types of cartilages
Hyaline cartilage Elastic cartilage Fibrocartilage
Hyaline cartilage is the most common cartilage in the body
Localization nose, larynx, trachea, and bronchi cartilaginous parts of the ribs articular surfaces of bones epiphyseal plates of the growing bones fetal skeleton
Hyaline cartilage matrix is firm but pliable
Composition: collagen fibrils amorphous ground substance
hyaluronic acidproteoglycansglycoproteins
water
Type II collagen is the major matrix protein
Collagen fibrils are not discernible in histologic sections
because the collagen fibrils are very fine have the same refractive index as the amorphous ground substance
Cartilage matrix organization
Proteoglycan monomers consist of core proteins and chondroitin or keratan sulfates
Monomers are bound to hyaluronic acid by link proteins to form large aggregates
Aggregates are bound to collagen fibrils
Multiadhesive glycoproteins (anchorin, fibronectin)anchor cells to the cartilage matrix
Proteoglycans have an affinity to water molecules
Much of this water is tightly bound to the proteoglycans
cartilage resilience
Some of this water is loosely bound to the proteoglycans
high cartilage matrix permeability
Hyaline cartilage matrix is highly hydrated
Cartilage is avascular tissue
Cartilage lacks blood vessels, lymphatics, and nerves Cartilage matrix is highly permeable Cartilage is supplied by diffusion Diffusion starts from the perichondrium
Substances freely pass cartilage matrix,except high molecular weight proteins
Perichondrium is a connective tissue cartilage envelope
Outer fibrous layerdense connective tissue
Inner cellular layer loose connective tissueblood vesselscondrogenic cells chondroblasts
Perichondrium functions
cartilage protection cartilage supply new cartilage cell formation cartilage growth
Articular cartilage lacks the perichondrium
it is supplied by diffusion from synovial fluid
Cartilage cells
Chondrogenic cells reside in the perichondrium give rise to chondroblasts
Chondroblasts reside in the perichondrium are capable of mitotic divisions secrete extracellular matrix give rise to chondrocytes
Chondrocytes are surrounded by matrix are housed in lacunae
are capable of mitotic divisions secrete extracellular matrix mature cells form isogenous groups
Isogenous groups
are located in the mature cartilage zone contain from 4 to 8 mature chondrocytes result from successive mitotic divisions are surrounded by cartilage matrix
Chondroblasts and chondrocytes secrete cartilage matrix and are similar in morphology
Chondrocyte ultrastructure
abundant rER extensive Golgi apparatus a few mitochondria (anaerobic cells)
many vacuoles with collagen precursors and glycoproteins large amounts of lipid and glycogen inclusions
Cartilage growth mechanisms
Appositional growthchondroblast mitotic divisionchondroblast matrix secretion
Interstitional growthchondrocyte mitotic divisionchondrocyte matrix secretion
Hormonal regulation of matrix secretion and cartilage growth
Stimulation - STH, thyroxine, testosterone Inhibition – glucocorticoids, estrogens
Age-related hyaline cartilage changes
matrix composition changes matrix permeability becomes worse chondrocytes swell and die matrix undergoes mineralization mineralized cartilage is replaced by bone
mineralized cartilage is basophilic
Elastic cartilage
is found in the ear, auditory tube, epiglottis, and the larynx contains matrix rich in elastic fibers possesses the perichondrium shows isogenous groups is never calcified with age
elastic fibrils are revealed by orcein
Fibrocartilage
exists in the annulus fibrosus of intervertebral disks the pubic symphysis menisci of the knee jointsin the large tendon insertions
its matrix contains fewer amorphous ground substance more collagen fibers
lacks the perichondrium is capable of calcification
Fibrocartilage matrix contains type I and type II collagen
collagen fibers are arranged in parallel bundles
chondrocytes lie longitudinally
between collagen bundles
Cartilage has limited ability for repair
owing to cartilage avascularity chondrocyte immobility limited mature chondrocyte proliferation
Some repair can occur if defect involves the perichondrium
Skeletogenic Connective Tissues
Bones
Bone as an organ
Consists of bone tissue periosteum endosteum blood vessels articular cartilages bone marrow (red and yellow)
Bone functions
serves as a support for the body provides for attachment of muscles protects the CNS and vital organs contains the red and yellow bone marrow is an important calcium reserve
Bone tissue matrix
Organic portiontype 1 collagen fibers amorphous ground substance (chondroitin sulphate, keratan sulphate, and osteomucoid)
Inorganic portion calcium, phosphorus, citrate, bicarbonate, magnesium,potassium, sodium, and hydroxyapatite crystals [Ca10(PO4)6(OH)2]
Mineralized bone matrix prevents free diffusion
Bone contains blood vessels enter from the periosteum and endosteum penetrate the matrix via Volkmann’ canals run perpendicularly to the bone surface branch to form the haversian canal vessels
Periosteum covers bones, endosteum lines the marrow cavities
Outer fibrous layerdense connective tissue
Inner cellular layerloose connective tissueblood vesselsosteogenic cells and osteoblasts
Functions: bone growth bone repair
blood supplySharpey’s fibers attach the periosteum to bone
Bone cells
Osteogenic (stem) cells- reside in the periosteum, endosteum, and around bone blood vessels- give rise to osteoblasts
Osteoblastsgive rise to osteocytes
Osteocytes Osteoclasts
arise from blood monocytes
Osteoblasts
reside in the periosteum, endosteum, and around the bone blood vessels
contain well-developed rERGolgi apparatusgranules with matrix precursors
Functions: secrete the bone matrix organic portion take part in matrix mineralization
Osteogenic cell and osteoblasts (electron microphotograph)
Osteocytes
reside in their own lacunae in the bone matrix possess narrow cytoplasmic processes extending through the canaliculi communicate with each other via gap junctions contain heterochromatic nuclei, sparse rER,
and small Golgi apparatus
Function: maintain the bone homeostasis
Osteocyte morphology
Osteocyte in its lacuna (scanning electron micrograph)
Osteoclasts
reside in the periosteum, endosteum, and around the bone blood vessels
are located in the bone surface depressions are multinucleated giant cells display the plasmalemma ruffled border contain numerous lysosomes and phagosomes
Functions: are bone macrophages, responsible for bone resorption and bone remodeling
Osteoclast morphology
Bone matrix resorption
is activated byparathyroid hormone
is inhibited bycalciotonin
Bone tissue types
Coarsely bundled bone tissue (primary, immature)its collagen fibers are arranged in thick bundlesexists mostly in embryogenesisis replaced by secondary bone tissueremains in the tooth sockets, skull sutures, and tendon insertions
Lamellar bone tissue (secondary, mature)its collagen fibers are arranged in lamellaereplaces primary bone tissueexists in postnatal life
Lamellar bone substance types
Spongy bone substance is found at the epiphyses and within the long bone diaphyses, within the flat and short bones lamellae are arranged in irregular trabeculae contains bone marrow spaces
Lamellar bone substance types
Compact bone substance is found at periphery of the long bone diaphyses, the flat and shot bones its lamellae are arranged in osteons
Osteon or haversian system
is cylindrical in shape is composed of 4 to 20 concentric lamellae osteocytes are in lacunae between lamellae
Central haversian canal
Contains blood vessels nerve fibers loose connective tissue osteoblasts and osteoclasts
Compact substance of the long bone diaphysis
Lamella arrangement outer circumferential lamellae osteon layer
osteonsinterstitial lamellae
inner circumferential lamellae
Bone remodeling continues throughout life
it contributes the bone adaptation
Interstitial lamellae are remnants of former osteons
Bone tissues arise from mesenchyme
Intramembranous bone formation direct osteogenesis is typical of flat bone development
Endochondral bone formation indirect osteogenesis occurs in the place of a hyaline cartilage model is typical of long bone development
Intramembranous bone development
mesenchymal cells differentiate intoosteogenic cells
osteogenic cells give rise to osteoblasts osteoblasts elaborate the bone matrix osteoblasts entrapped in matrix become
osteocytes bone matrix, osteoblasts, and osteocytes
constitute a bony trabecula
Intramembranous bone development
bony trabeculae calcify and join together primary bone is replaced by secondary bone
Endochondral bone development
Primary center of ossification occurs at the cartilage model diaphysis midriff vascularization of the perichondrium transformation of chondrogenic cells to osteogenic cells development of osteoblasts perichondrium transformation into the periosteum
Endochondral bone development (continuation)
formation of the perichondral bone (collar or cuff) calcification of cartilage under the perichondral cuff penetration of the cartilage model by the periosteal buds
Endochondral bone development (continuation)
resorption of the mineralized cartilage formation of the endochondral bone
endochondral bone (red) includes mineralized cartilage (blue)
Endochondral bone development (continuation)
appearance of the secondary center of ossification in the epiphyses formation of the epiphyseal plate of growth
Epiphyseal plate of growth
is between the diaphysis and epiphysis includes 5 zones:(1) Zone of resorption(2) Zone of calcified cartilage(3) Zone of hypertrophy(4) Zone of proliferation(5) Zone of reserve cartilage
(1)
(2)
(3)
(4)
(5)
Epiphyseal plates provide bone growth in length
Epiphyseal closure occurs about 20 years of age STH stimulates bone growth (chondrocyte proliferation) Sex hormones stop bone growth (chondrocyte proliferation)
The End
Thank you for attention!
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