Cartilage Flashcards
Cartilage is characterized by an extracellular matrix enriched with
- glycosaminoglycans
- proteoglycans
(Macromolecules that interact with collagen and elastic fibers.)
Cartilage consists of cells called
Chondrocytes
Chondrocytes synthesize and secrete the
extracellular matrix
Chondrocytes are located in matrix cavities called
lacunae
Principal macromolecules present in all
types of cartilage matrix.
- Collagen
- Hyaluronic acid
- Proteoglycans
- small amountsof several glycoproteins
Because collagen and elastin are flexible, the firm gel like consistency of cartilage depends on
electrostatic bonds between collagen fibers and the glycosaminoglycan side chains of matrix proteoglycans.
Three forms of cartilage have evolved
- Hyaline cartilage
- Elastic cartilage
- Fibrocartilage
In all three forms, cartilage is
avascular
(and is nourished by the diffusion of nutrients from capillaries in adjacent connective tissue
(perichondrium) or from synovial fluid in joint cavities)
Chondrocytes exhibit low
metabolic activity
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.
The perichondrium harbors the
vascular supply for the avascular cartilage
and also contains nerves and lymphatic vessels.
Cartilage devoid of perichondrium
Articular cartilage
Articular cartilage is sustained by
the diffusion of oxygen and nutrients from the synovial fluid.
In adult mammals, hyaline cartilage is located in the
- Articular surfaces of the movable joints
- In the walls of larger respiratory passages (nose, larynx, trachea, bronchi)
- In the ventral ends of ribs, where they articulate with the sternum
- In the epiphyseal plate, where it is responsible for the longitudinal growth of bone
Dry weight of hyaline cartilage consists
40% collagen embedded in a firm, hydrated gel of proteoglycans and structural glycoproteins. In
Hyaline cartilage contains primarily
Type II collagen
(although small amounts of
collagen types VI and IX are also present.)
Cartilage proteoglycans contain
chondroitin 4-sulfate, chondroitin 6- sulfate, and keratan sulfate, covalently linked to core proteins.
Proteoglycan aggregates such as……….formed by
** Aggrecan ……**formed by hundreds of proteoglycans are bound noncovalently to long molecules of hyaluronic acid by link proteins
% of the wet weight of hyaline cartilage that is
water.
~ 75%
Link proteins do ?
Link proteins noncovalently bind
the protein core of proteoglycans to the linear hyaluronic acid molecules
An important component of cartilage matrix is the structural multiadhesive glycoprotein called :
Chondronectin.
Chondronectin binds specifically to
- GAGs
- Collagen type II
- Integrins mediating the adherence of chondrocytes to the ECM.
Cartilage matrix is generally basophilic due to
The high concentration of sulfated GAGs
Territorial matrix usually stain differently from the rest of the matrix because
ECM is richer in GAGs and poor in collagen.
Territorial matrix is the area
Immediately surrounding each chondrocyte
Cartilage cells can give rise to benign tumors called
chondroma’s
Cartilage cells can give rise to malignant tumors called
chondrosarcoma’s
Chondrocyte synthesis of sulfated GAGs is stimulated by
Somatotrophin which causes liver to release Insuli like growth factors or somatomedians which stimulate chondrocytes
Allmost all hyaline cartilage is covered by a layer of dense connective tissue called
The perichondrium
A ll hyaline cartilage is covered
by a layer of dense connective tissue
EXCEPT
The articular cartilage of joints
The perichondrium consists largely of
collagen type I fibers and contains numerous fibroblasts.
Elastic cartilage is essentially very similar to hyaline cartilage except that it contains an abundant network of
fine elastic fibers in addition to collagen type II fibrils
Fresh elastic cartilage has a yellowish color owing to the presence of
elastin in the elastic fibers.
Elastic cartilage is found in
- Auricle of the ear
- The walls of the external auditory canals
- The auditory (eustachian) tubes
- The epiglottis
- The cuneiform cartilage in the larynx.
Fibrocartilage is a tissue intermediate between
dense connective tissue and hyaline cartilage
Fibrocartilage is found in
- intervertebral disks
- In attachments of certain ligaments
- In the pubic symphysis
- Fibrocartilage is always associated with dense connective tissue and the border between these two tissues is not clear-cut, showing a gradual transition.
In fibrocartilage the general orientation of the collagen depends on
The stresses on fibrocartilage
Intervertebral disks have has two major histological components:
- Peripheral annulus fibrosus rich in bundles of type I collagen
- Central nucleus pulposus with a gel-like matrix rich in hyaluronic acid
All cartilage derives from the
embryonic mesenchyme
All cartilage derives from the embryonic mesenchyme in the process called
Chondrogenesis
The first indication of cell to cartilage differentiation is
the rounding up of the mesenchymal cells which retract their extensions, multiply rapidly, and form cellular condensations.
The cells formed by this direct differentiation of
mesenchymal cells in cartilage formation are now called
chondroblasts
chondroblasts, have a ribosome
ribosome-rich
basophilic cytoplasm
Further growth of cartilage is attributable to two processes:
- Interstitial growth, resulting from the mitotic division of preexisting chondrocytes
- Appositional growth
Interstitial growth is the less
important of the two processes postnatally. It occurs during the early phases of cartilage formation, when it increases tissue mass by
expanding the cartilage matrix from within
Interstitial growth also occurs in the
epiphyseal plates of long bones and within articular cartilage.
In the epiphyseal plates, interstitial growth is important in
increasing the length of long bones
In articular cartilage, as the cells and matrix near the articulating surface are gradually worn away, the cartilage must be replaced
from within, since there is no perichondrium there to add cells by appositional growth.
