“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