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“Cartilage and Bone”
Remember the four basic types of tissue…
EpitheliumConnective tissue
Connective tissue proper Cartilage Bone Blood
Muscle tissueNervous tissue
Bone Blood
cartilage
CT Cartilage
Cartilage is connective tissue Cells = chondroblasts & chondrocytes Abundant extracellular matrix:
Fibers: collagen & elastin ground substance: complex sugar molecules 60-80% water (responsible for the resilience) No nerves or vessels Covered by perichondrium
Nutrition: diffusion from blood capillaries in perichondrium and/or adjacent tissues.
Function: support of soft tissues a model for formation and growth of long bones durability of articular joints
Distribution of Cartilage
More prevalent than in adult
Skeleton initially mostly cartilage
Bone replaces cartilage in late fetal and childhood periods
Cartilage in Embryo
cartilage in adults Nose Joint surfaces Costal Larynx - voice box rings of trachea & bronchi
External ear Epiglottis Eustachian tube
• IVDs• Pubic symphysis• meniscus in knee joint
Cells of the cartilage
Chondroblasts:LM: oval basophilic cells, found at the periphery of the cartilage. E.M: chondroblasts show all the features of protein synthesizing cells, as they contain:Abundant RER.Prominent Golgi apparatus.Many mitochondria.Vesicular nucleus (containing euchromatin).Function:They are the matrix forming cells, they synthesize the protein & fibers (collagen type 2) of the matrix. Each chondroblast becomes surrounded by the fibers & matrix that it produces & becomes imprisoned inside a space called lacuna & then it is called chondrocyte.
Chondrocytes: - the mature cartilage cells. - LM: large cells, flattened with their long axis parallel to the surface. -Towards the interior, they become rounded. -vacuolated basophilic cytoplasm, rich in phosphatase E. - EM: similar to fibroblasts in having:The basophilia decreases as we go towards the center of the cartilage mass while the glycogen content increases.Young chondrocytes can divide inside lacunae once or twice to form Cell nests. Mature chondrocytes do not divide.Function:responsible for synthesis and formation of matrix.
Matrix of cartilageFibers:- Collagen fibers of the type 2, but they are finer than those of fibrous or dense connective tissue. - Elastic fibers are also seen in the matrix of a certain type of cartilage.
Ground substance:- It is formed of proteoglycans, which are molecules formed of:-Glycosaminoglycans (polysaccharide: chondrointin sulfate and keratan sulfate.- Protein core, to which the glycosaminoglycans is joined - Hyaluronic acid is attached to this complex. The chondroitin sulphate is responsible for the basophilia of the matrix
Types of Cart i lage
Hyaline carti lage
Elastic cart i lage Fibrocart i lageflexible and resilientCollagen type IIChondrocytes: sphericalLacuna (cavity in matrix holding chondrocyte)
highly bendableelastic + collagen type I I
compression and tensionRows of collagen type I
+rows of chondrocytes
The perichondrium is formed of 2 layers:1.An outer fibrous vascular layer.2.An inner cellular layer containing chondroblasts.
The perichondrium merges gradually into the cartilage on one side & into the surrounding connective tissue on the other. It contains the blood vessels & nerves needed to supply the cartilage.
Chondrocytes
Elastic Cartilage
Fibrocarti lageType I and II col lagen. No identif iable perichondrium
Vertebra
Vertebra
Michigan Medical School Histology Slide Collection
Netter
Growth of cartilage Appositional
“Growth from outside” Chrondroblasts in perichondrium (external covering of
cartilage) secrete matrix
Interstitial “Growth from within” Chondrocytes within divide and secrete new matrix
Cartilage stops growing in late teens (chrondrocytes stop dividing)
Regenerates poorly in adults
Beginning of cart i lage Formation
Source Undetermined
Differentiation of chondrogenic cells
Isogenous group
Perichondrium
Isogenous group
Lacuna
Michigan Medical School Histology Slide Collection Kierszenbaum, p. 115
Carti lage Changes with AgingNot much changes with collagen.
The proteoglycans produced in older individuals are smaller with shorter chondroitin sulfate chains than in younger individuals.
Chondrocytes seem less efficient in renewing the matrix thus reducing proteoglycan contents.
These changes might reduce water contents in the matrix and make the cartilage less able to resist compressive forces.
These changes, in turn, would make matrix more vulnerable to injuries in weight-bearing, and the inflammatory response to injury would cause painful symptoms of arthritis.
Carti lage Damage
Source Undetermined