Histology of Cartilage
Dr. Muhammad Rafique Assistant Professor 1/1/2008
Definition of Cartilage Discuss general features of cartilage Describe the Hyaline Cartilage Discuss the Fibrocatilage Describe the Elastic Cartilage
Cartilage is a solid connective tissue that is to a certain extent pliable, making it resilient. These characteristics of cartilage are due to the nature of its matrix. The ground substance of cartilage is rich in proteoglycans consisting of chondroitin sulphate and containing chodrocytes and collagen fibers. Cartilage is a type of connective tissue so that it consists of cells (chondroblast and chondrocytes), fibres (collage) and ground substance proteogylcans which is mainly chondroitin sulfate. The cartilage is completely devoid of blood vessels. It receives nourishment form the adjacent connective tissue or from the synovial fluid. The cartilage also does not has nerve fibers and lymphatic vessels.
The sheath of connective tissue which surround the most of the thpyes of cartilages except articular cartilage. It contains blood vessels which sullying the nutrients to the underlying avascular cartilage. The perichondrium consists of two layers
Outer fibrous layer: which contains collagenous and elastic fibers and blood vessels Inner cellular layer: which composed of chondroblast, few collagen fibers and blood vessels.
Classification Of Cartilage
The cartilage classified on the basis of types and visibility in cartilage; They are three types of cartilage Hyaline Cartilage Fibrocartilage Elastic cartilage
Hyaline cartilage is the most abundant variety. Hyaline cartilage is characterized by a glassy matrix. The word hyaline is derived from the Greek word "hyalos" which means glass. . The hyaline cartilage consists of cells which are suspended into homogenous ground substance. Like other connective tissue the cartilage consists of three components 1. Cell 2. Fibers 3. Ground Substance
Cells of Hyaline Cartilage
The hyaline cartilage is surrounded by perichondrium and cosists of two types of cells: Chnodrocyte Chondroblast The chondrocytes are mature cells are usually present throughout the cartilage. The cells occupied the smaller clear spaces in the matrix which are called as the lacunae
Arrangement of Chondrocytes
In the central region of cartilage the chondrocytes are usually arranged in groups. These group are called as the Isogenous groups. That means a single chondrocytes first occupies the lacuna than it divides into two, these two cells than divided in the group of four so that a single isogeonus group consists either two or four cells
The matrix near the isogenous groups of chondrocytes contains larger amounts and different types of glycosaminoglycans than the matrix further away from the isogenous groups. This part of the matrix is also termed territorial matrix or capsule. In H&E stained sections the territorial matrix is more basophilic, i.e. it stains darker.
The remainder of the matrix is called the interterritorial matrix. Fresh cartilage contains about 75% water which forms a gel with the components of the ground substance. Cartilage is nourished by diffusion of gases and nutrients through this gel.
Arrangement of Chondrocytes
Near the periphery the chondrocytes gradually lose their definite grouping and they are arrange in a row. The chondrobalsts are active dividing cells and they are present at the periphery and cellular layer of perichondrium. When they divide and mature they produce chondrocytes. The fibroblasts are also present in perichondrium and they provide the chondroblast.
Matrix appears homogenous under the light microscope and composed of type collagen fibers type II. The collagen fibers very thin and they same refractive index as ground substance that’s why on microscopical examination the ground substance appears homogenous. It consists of proteoglycan rich in chondrotin sulfate and small quantities of hyaluronic acid and keratan sulfate
Near the periphery and below the perichondrium the definite grouping of chondrocytes lost and they are arranged in rows of narrow elongated cells Distributions: Articular Cartilage Costal Cartilage Nasal Cartilage Cricoid, Thyroid & Aryteniod Cartilages of Larynx Cartilages of Trachea & Bronchi
Fibrocartilage consists of numerous collagen fibers which type II. These fibers are arranged in the groups which are parallel to each other. The chondrocytes are arrange in the rows along parallel to long axis of collagen fibers and they are not form Isogenous groups. The chondrocytes are present in lacunae.
The cartilage deficient in Perichondrium. Distributions: Intervertebral discs Pubic Symphysis Intra-articular Discs
Has outer covering of Perichondrium. This cartilage appears yellowish and translucent but more opaque than the hyaline cartilage. The chondrocytes are lying with the lacunae in the isogenous group like hyaline cartilage.
But the matrix of elastic cartilage contains a large number of elastic fibers which branched and interlace with each other to form a closely woven network. Distributions: Auricle of the external ear Cartilaginous part of external auditory tube Epiglottis Small cartilages of Larynx (Cuneiform and corniculate )