Cartilage

1. Cartilage Dr. Ahmad Al-Taib Written by: Albara Marwa,, Abo Malik Group A leader

2. What is cartilage? • It is a special type of connective tissue with a firm extracellular matrix.

3. Location • Cartilage is found in: • Respiratory tract • External ear • Intervertebral disc • Articular surface of bones (in joints) • Skeleton of fetus

4. Components • Cartilage consists of three components: • Cells • Matrix (between the cells) • Perichondrium (outer layer)

5. Cartilage cells • Cartilage contains three types of cells: • Chondrogenic cells • Chondroblast • chondrocyte

6. 1. Chondrogenic cells • Originate from mesenchymal cells • Spindle shaped cells with oval nuclei • Found in the perichondrium • Differentiate into chondroblasts (Differentiation of cells does not include cell division but only a change in structure)

7. 2.Chondroblasts • Basophilic flat cells with flat nuclei • Protein-secreting cells • Secrete cartilage matrix • Found in the perichondrium • Originate from chondrogenic cells

8. 3. Chondrocyte • Each chondroblast secretes the matrix & becomes a chondrocyte with a large rounded nucleus. • The chondrocyte is the mature cartilage cell which also secretes matrix. • Each chondrocyte is situated in a small space called a lacuna surrounded by the matrix. • The chondrocyte can divide in the lacuna • There is no connection between the lacunae.

9. Cartilage Matrix • The matrix is an avascular extracellular material secreted by chondroblast & chondrocyte. • Cartilage matrix consists of: • Fibers: collagen type I or type II or elastic fibers. • Ground substance: glycoproteins & chondroitin sulphate.

10. Perichondrium • A dense vascular connective tissue on the surface of cartilage. • It consists of: • Outer fibrous layer of dens CT (Type I collagen). • Inner cellular layer of chondrogenic cells & chondroblast. • Its function is growth of cartilage

11. Types of cartilage • There are three types according to the fibers in the matrix: • Hyaline cartilage • Elastic cartilage • Fibrocartilage

12. Similarities between types of cartilage • All types have chondrocyte in lacunae. • All types have avascular matrix. • All types have perichondrium EXCEPT: • Fibrocartilage • Articular cartilage

13. Hyaline cartilage • Found in: • Respiratory tract • Articular cartilage • Chondrocytes divide and form small groups called isogenous group. • Collagen type II in a basophilic matrix, but the collagen is not visible with the L.M. • The matrix is more basophilic near the chondrocyte. • Articular cartilage lacks perichondrium and it receives nutrient from the synovial fluid

14. Elastic cartilage • More chondrocytes and less matrix than hyaline cartilage. • Many elastic fibers in the matrix and in the perichondrium. • Collagen type II is also present • Examples: External ear & epiglottis. • Elastin stain stains elastin black

15. Fibrocartilage • Parallel bundles of acidophilic type I collagen fibers in the matrix. • (Note: Collagen type I is stronger than type II). • Chondrocytes form parallel rows. • Chondrocytes arise from fibroblasts. • More fibers and less chondrocytes than that in hyaline and elastic cartilage. • No perichondrium • Example: Intervertebral disc

16. Cartilage growth • Cartilage arises from mesenchyme during chondrogenesis • Cartilage grows by two methods: • Appositional growth : on surface from perichondrium. • Interstitial growth: deep in matrix.

17. Repair of cartilage • Cartilage has a limited ability for repair. • Injured cartilage is replaced by Connective tissue.