Mucous connective tissue

It is a jellylike tissue containing collagen fibers and a few elastic or reticular fibers. The cells in this tissue are mainly large stellate-shaped fibroblasts. Mucous tissue is the principal component of the umbilical cord, where it is referred to as Wharton’s jelly.

Fig.18. Mucous connective tissue

EMBRYONIC CONNECTIVE TISSUE (MESENCHYME) is composed of star shaped, pale staining mesenchymal cells embedded in a gel-like amorphous matrix containing only a few widely scattered fibers (mostly reticular).

SKELETAL CONNECTIVE TISSUES

CARTILAGE

Cartilage tissue is characterized by an extracellular matrix enriched with glycosaminoglycans and proteoglycans. These macromolecules interact with collagen and elastic fibers.

Variations in the composition of these matrix components produce 3 types of cartilage: hyaline, elastic, and fibrocartilage.

Cartilage is a specialized form of connective tissue in which the extracellular matrix is firm but flexible. This matrix endows cartilage with the resilience that allows the tissue to bear mechanical stresses without permanent distortion.

Functions:

• the main function of cartilage is to support soft tissue;

• being smooth-surfaced and resilient, cartilage is a shock-absorbing and sliding area for joints, thus facilitating bone movements;

• cartilage is also essential for the development and growth of long bones both before and after birth.

Cartilage consists of cells – chondrocytes - and extensive extracellular matrix composed of fibers and ground substance.

Chondrocytes synthesize and secrete the extracellular matrix, and the cells themselves are located in matrix cavities called lacunae.

In all 3 types, cartilage is avascular and is nourished by diffusion of nutrients from capillaries in adjacent connective tissue (perichondrium) or by means of synovial fluid from joint cavities. Cartilage has no lymphatic vessels or nerves.

Fig.19. Hyaline cartilage

HYALINE CARTILAGE.

Hyaline cartilage is the most common form. Fresh hyaline cartilage is bluish-white and translucent. In the embryo, it serves as a temporary skeleton until it is gradually replaced by bone. In adult mammals, hyaline cartilage is located in the articular surfaces of the movable joints; the walls of larger respiratory passages (nose, larynx, trachea, bronchi); and the ventral ends of ribs, where they articulate with the sternum.

Matrix:

• 40% of the dry weight of hyaline cartilage consists of collagen embedded in an amorphous intercellular substance;
• hyaline cartilage contains primarily type II collagen.

In routine histologic preparations, the collagen is indiscernible from the amorphous substance for 2 reasons: the collagen is in the form of fibrils, which have submicroscopic dimensions; and the refractive index of the fibrils is almost the same as that of the ground substance in which they are embedded.

Up to 200 of proteoglycans are noncovalently associated with long molecules of hyaluronic acid, forming proteoglycan aggregates that interact with collagen (Fig.20). The high content of solvation water bound to the negative charges of GAG acts as a shock absorber or biomechanical spring that is of great functional importance, especially in articular cartilages.

Дата добавления: 2015-10-31