5- cartilage

Cartilage

- Cartilage is a special type of CT possesses a

firm pliable matrix that can resist

mechanical stress, act as a shock absorber.

- Cartilage together with long bone form the

skeleton and support the body .

- Cartilage form the fetal skeleton.

- Cartilage is non-vascular structure and not

supplied with nervous or lymphatic tissues.

- Cartilage is formed of:-

- Cells ------ Chondroblasts

Chndrocytes

Chondrogenic cells

- Fibers ---- Collagen fibers

Elastic fibers

- Matrix ----- Proteoglycans

Glycosaminoglycans

Cartilage cells

1- Chondrogenic cells :- ?????????

- Derived from mesenchymal cells

- Spindle shaped cells with ovoid nucleus ,

small Golgi, few mitochondria, and rER.

- These cells can differentiate into both

chondroblast and chondrocytes.

- Derived from mesenchymal cells within

the center of chondrofication, or from

chondrogenic cells.

- They are ovoid, basophilic cells, rich with

rER, well developed Golgi, numerous

mitochondria, and more secretory vesicles.

- Form the collagen fibers and the matrix

2- Chondroblasts :-

- They are chodroblasts that are surrounded

by matrix (within lacuna).

- They are ovoid near the periphery, and more

rounded deeper in the cartilage.

- The cell has large nucleus, and prominent

nucleolus, and the usual organelles.

3- Chondrocytes:-

E/M showing 3 chondrocytes in their lacunae. Cells

have abundant rough endoplasmic reticulum. Fine

collagen fibers are prominent around the

chondrocytes.

Types of Cartilage

There are three types of cartilage according to the

type of fibers present in the matrix:-

- Hyaline Cartilage: type II collagen fibers.

- Elastic cartilage: type II collagen fibers

and abundant elastic fibers.

- Fibrocartilage: dense, coarse type I collagen

fibers.

Hyaline Cartilage

- It is a bluish gray, semi-translucent, pliable

substance.

- It is the commonest type, present in the nose,

larynx, trachea, bronchi, articulated surfaces

of joints, on the ventral ends of ribs ( costal

cartilage).

- It is covered with dense fibrous CT called

perichondrium.

- Matrix, formed by the chondrocytes, is rich in

proteoglycans and glycosaminoglycans, and

contain type II collagen fibers.

- The matrix is subdivided into two types:-

Territorial; a pericellular capsule (around

lacunae), and Interterritorial;

- Chondrocytes and chondroblasts.

hyaline cartilage showing the

chondrocytes in the matrix

lacunae (?? cell nest ??).

The upper and lower parts of

the show the perichondrium

stained pink.

Note the gradual

differentiation of cells from

the perichondrium into

chondrocytes.

Elastic Cartilage

- It is located in the ear pinne, external and

internal auditory tube, and epiglottis.

- It is similar to hyaline cartilage, as it is formed

of perichondrium, matrix, chonrocytes, and

chondroblasts. But, the matrix contain more

elastic fibers as well as collagen type II fibers.

Elastic cartilage,

stained for elastic

fibers. Cells are not

stained. This flexible

cartilage is present,

for example, in the

ear pinna and in the

epiglottis.

Fibrocartilage

- Unlike elastic or hyaline cartilage, it does not

possess perichondrium, and the matrix is rich

in bundles of collagen type I.

- It is located in the inter-vertebral disks,

tendons at insertion to bone, symphysis pubic.

- The chondrocytes are differentiated from

fibrocytes, and arranged in rows surrounded

by bundles of collage fibers.

Fibrocartilage showing

rows of chondrocytes

separated by collagen

fibers.

Fibrocartilage is

frequently found in the

insertion of tendons on

the epiphyseal hyaline

cartilage.

Histogenesis of hyaline cartilage. A: The mesenchyme is the

precursor tissue of all types of cartilage. B: Mitotic proliferation

of mesenchymal cells gives rise to a highly cellular tissue. C:

Chondroblasts are separated from one another by the formation

of a great amount of matrix. D: Multiplication of cartilage cells

gives rise to isogenous groups, each surrounded by a condensation

of territorial (capsular) matrix.