Fibrocartilage.

Fibrocartilage shows rows of chondrocytes aligned parallel to the direction of greatest stress and separated by parallel or irregular bundles of type I collagen fibers. No separate perichondrium is present on fibrocartilage. (a): Micrograph of pubic symphysis shows staining variations in the matrix caused by varying concentrations of collagen (C). Lacunae (arrows) of chondrocytes are also seen. A section of intervertebral disk. X100. Masson trichrome. (b): The axial aggregates of chondrocytes are separated by collagen. Fibrocartilage is also frequently found in the insertion of tendons on the epiphyseal hyaline cartilage. X400. Picrosirius-hematoxylin.

In fibrocartilage dense collagen fibers can form either irregular or parallel bundles between the axial aggregates of chondrocytes. The general orientation of the collagen depends on the stresses on fibrocartilage, since the collagen bundles take up a direction parallel to those stresses. There is no distinct perichondrium in fibrocartilage.

Intervertebral disks are composed of fibrocartilage primarily. They are situated between the vertebrae and are held to them by ligaments. Each disk has two major histological components: the peripheral annulus fibrosus rich in bundles of type I collagen and the central nucleus pulposus with a gel-like matrix rich in hyaluronic acid. Intervertebral disks act as lubricated cushions and shock absorbers preventing adjacent vertebrae from being damaged by abrasive forces or impact during movement of the spinal column.

STRUCTURE OF BONE:

- CELLS

- INTERCELLULAR SUBSTANCE (MATRIX)

CELLS:
Osteocytes	They are mature bone cells imprisoned within bone matrix.
Osteoblasts	These are bone producing cells.
Osteoclasts	These are bone removing cells.
Osteoprogenotor cells	These cells give rise to osteoblasts and osteocytes.
INTERCELLULAR SUBSTANCE:
Ground substance	It is mimeralized cementing substance.
Collagen fibres	They are made up of Type II collagen fibres.

COMPACT BONE:

COMPACT BONE
1. external circumferential lamellae	They form the external wall of the compact bone (beneath the connective tissue periosteum).
2. osteogenic layer
a. osteon	It consists of Haversian canal surrounded by the lamellae arranged in the form of concentric rings.
b. interstitial lamellae	These lamellae are remnants of osteons the greater parts of which have been destroyed.
3. internal circumferential lamellae	They form the internal wall of the compact bone (along the marrow cavity).

Дата добавления: 2015-10-30