HISTOLOGY The cartilage

The Objective To give information about:- ****TYPES OF CARTILAGE ****Perichondrium ****Cartilage cells ****Growth of Cartilage

The cartilage * Cartilage is a specialized type of connective tissue. * Consists, like other connective tissues , of cells and extracellular components. The matrix or ground substance of cartilage consists mainly of glyco-protein material, and chondroitin.

* Does , unlike other connective tissues , not contain vessels or nerves. * Cartilage surrounded by a layer of dense connective tissue , (the perichondrium).

The process by which bone tissue follows the cartilage model and slowly replaces it is known as ossification. Permanent cartilage (cartilage which does not become ossified) is found in the tip of the nose, in the external ear and in the walls of the trachea and the larynx .

**Perichondrium The perichondrium is a sheath of dense connective tissue that surrounds cartilage in most places, forming an interface between the cartilage and the tissue supported by the cartilage. Perichondrium contains (B.V, nerves and lymphatic vessels).

It is composed of 2 layers , the outer one which is fibrous containing collagen fibers and inner layer which is cellular containing flat cells called chondrogenic cells which are differentiated from mesenchymal cells , this layer called chondrogenic layer, the inner portion of this layer is rich with chondroblast which differentiated into chondrocytes.

Function of the perichondrium 1-Essential for growth and development of bone. 2-Nutrition (because the cartilage is devoid of blood vessels so the Perichondrium pass the blood from c.t. through the matrix to the chondrocytes). 3-Supports soft tissues.

Cartilage cells A-Chondrogenic cells: Are spindle -shaped, narrow cells that derived from mesenchymal cells. These cells can differentiate into chondroblasts as well as into osteoprogeniter cells.

B-Chondroblasts : Are derived from two sources; 1- Mesenchymal cells 2-Chondrogenic cells of the inner cellular layer of the perichondrium C-Chondrocytes: Are chondroblasts that are surrounded by matrix

**TYPES OF CARTILAGE 1- Hyaline Cartilage Hyaline cartilage, a bluish-gray, semi translucent, is the most common cartilage of the body.

It is located in the nose and larynx, on the ventral ends of the ribs where they articulate with the sternum, and in the tracheal rings and bronchi. Hyaline cartilage is also located on the articulating surfaces of the moveable joints of the body.

                                                                                                                                          

. Photomicrograph of hyaline cartilage

Photomicrograph of hyaline cartilage

Photomicrograph of hyaline cartilage

Matrix of hyaline cartilage The matrix is subdivided into two region; the territorial, or capsular matrix around lacuna and the interterritorial matrix between the cells. Fresh cartilage contains about 75% water which forms a gel with the components of the ground substance. Cartilage is nourished by diffusion of gases and nutrients through this gel.

2-Elastic Cartilage Elastic cartilage is located in the pinna of the ear, the external and internal auditory tubes, the epiglottis, Because of the presence of elastic fibers, elastic cartilage is somewhat yellow and is more opaque than hyaline cartilage in the fresh state.

The perichondrium is rich in elastic fibers The perichondrium is rich in elastic fibers. The matrix consist of branching elastic fibers interposed with type II collagen fiber bundles, giving it much more flexibility than H.C.

                                                                                                                                           Elastic Cartilage

Elastic Cartilage

Elastic Cartilage

3-Fibro cartilage is a form of connective tissue transitional between dense connective tissue and hyaline cartilage. Chondrocytes may lie singly, but most often they form short rows between dense bundles of collagen fibres.

In contrast to other cartilage types, collagen type I is dominant in fibro cartilage. is typically found in relation to joints (forming intra-articular lips) and is the main component of the intervertebral disks.

-Fibro cartilage

Photomicrograph of fibrocartilage Photomicrograph of fibrocartilage. Note the rows of chondrocytes separated by collagen fibers.

1-Interstitial growth (endogenous growth), Growth of Cartilage Growth occurs by two mechanisms Interstitial growth – 1-Interstitial growth (endogenous growth), it occurs only in young cartilage (mainly in immature cartilage) in which the Chondrocytes lies in the central part of the cartilage divide and increase in number and secrete intercellular substance and causing increase of width from inside to outside.

Appositional growth (exogenous growth) it occurs also in mature cartilage , the chondroblasts within the inner layer of perichonderium multiply and some of them form intercellular substance and become chondrocytes where as the other remain chondroblasts , this way causing increase of width from outside to inside.

Peripheral mitosis and differentiation of fibroblas Appositional growth : Peripheral mitosis and differentiation of fibroblas Interstitial growth : Mitosis of chondrocytes & deposition of new matrix