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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.