Histology of Cartilage PDF

## Histology of Cartilage ### Definition Cartilage is a specialized type of dense connective tissue designed to give support, bear weight and withstand tension, torsion and bending. ### General Features - Cartilage support regions of the body that require flexibility. - Avascular-nourished by? - N...

## Histology of Cartilage ### Definition Cartilage is a specialized type of dense connective tissue designed to give support, bear weight and withstand tension, torsion and bending. ### General Features - Cartilage support regions of the body that require flexibility. - Avascular-nourished by? - Non-nervous structure. - Poor regeneration capacity. - Growth takes place by 2 methods-appositional growth and interstitial growth. - Usually surrounded by perichondrium (except articular cartilage and fibro cartilage). ### Perichondrium - Cartilage is covered externally by a dense connective tissue sheath known as perichondrium except articular cartilage and fibro cartilage. - Has two layers-outer fibrous layer (vascular) and inner chondrogenic layer (cellular). - Has cells which can regrow cartilage to some extent if the cartilage is damaged. ### Components - **Cells**: mesenchymal cells, chondroblasts and chondrocytes - **Fibres**: collagen and elastic - **Ground Substance**: mucopolysaccharides (chondroitin sulphate) ### Cells of the Cartilage - They are derived from undifferentiated mesenchymal cells. - Young cells are small with branched cytoplasmic processes known as chondroblasts, they multiply to chondrocytes. - Older and mature cells are known as chondrocytes. - Chondrocytes are bigger in size and are found in spaces called as lacunae. - They are found groups of 2-4 cells together known as cell nest. - They are responsible for production of fibres and ground substance of the cartilage. - Old mature cells are incapable of multiplication. ### Classification/Types - Hyaline Cartilage - Elastic Cartilage - Fibro Cartilage ### Areas Found | Cartilage | Occurence | |---|---| | Hyaline Cartilage | Epiphyseal growth plate, ribs, respiratory tract, articular cartilage | | Elastic Cartilage | Pinna, epiglottis, external auditory meatus, arytenoid corniculate, cuneiform cartilage. | | Fibro Cartilage | Intervertebral discs. | ### Histological Features or Microscopic Features or Microscopic Anatomy #### Hyaline Cartilage - Characterized by the presence of highly basophilic homogeneous matrix. - Appear homogeneous as the collagen fibres present in them have the same refractive index as ground substance. - Perichondrium present. - Cells encapsulated in groups of 2-4 cells. - Matrix around the cells is brighter and deep in colour than other areas, this matrix is known territorial matrix. - Two groups of cells are separated by a lightly coloured matrix known inter-territorial matrix. - In embryo, hyaline cartilage forms temporary skeleton that is replaced by bone. - Osteo-arthritis occurs during ageing which involves gradual loss or changed physical properties of hyaline cartilage that lines articular ends of bones on joints. - Joints that are weight bearing, heavily used are more prone to cartilage degeneration. - Fragments released by wear and tear to articular cartilage trigger secretion of matrix metallo -proteases from macrophages which cause damage, pain and inflammation with the joint. - **Matrix of hyaline cartilage:** - Dry weight of hyaline cartilage is 40% which is embedded in hydrated gel of proteoglycans and structural glycoproteins. - Proteoglycans cause matrix to be basophilic. - Most of the collagen in hyaline cartilage is type II collagen. - Most abundant proteoglycan of hyaline cartilage is aggrecan (core protein) which consists of 150 GAG's side chains of chondroitin sulphate, keratin sulphate. - Proteoglycans non-covalently bound by link proteins to long polymers of hyaluronic acid. - Proteoglycan complexes bind to type II collagen. - Water bound to GAG's in proteoglycans constitute 60-80% of fresh weight of fresh hyaline cartilage. - Another important component of matrix is chondronectin which is a multi adhesive protein that binds specifically to GAG's, collagen II and integrins. - **Two types of matrix:** - **Territorial matrix**: immediately around lacunae housing chondrocytes, matrix stains deeper giving capsule like appearance. - **Interterritorial matrix**: pale staining matrix separating cell nests. - **Chondrocytes of hyaline cartilage:** - Occupy little in hyaline cartilage mass. - Two types of chondrocytes are present. - Young chondrocytes or chondroblast which have elliptical shape present at periphery of cartilage. - Chondrocytes which are round present deeper in cartilage appear in groups up to 8 cells that originate from mitotic divisions of single chondrocyte called as isogenous aggregates or cell nests. - Due to devoid of capillaries, chondrocytes respire under low oxygen tension. - So hyaline cartilage metabolize glucose mainly by anaerobic glycolysis to produce lactic acid as end product. - Chondrocyte synthesis of sulphated GAG's and secretion of proteoglycans is accelerated by hormones and growth factors. - Major regulator of hyaline cartilage growth is pituitary derived growth hormone. - **Perichondrium of hyaline cartilage:** - Except in articular cartilage of joints, hyaline cartilage is covered by a layer of dense connective tissue called as perichondrium. - Perichondrium is essential for growth and maintenance of cartilage. - Perichondrium consists type I collagen and fibroblast. - Among these fibroblasts, inner layer of perichondrium are progenitor cells for chondroblasts. - There are two types of hyaline cartilages: - **Costal cartilage:** These are bars of hyaline cartilage that connect the ventral ends of ribs to sternum. Cellularity of costal cartilages decrease by age. - **Articular cartilages:** The articular surfaces of most synovial joints are lined by hyaline cartilage. These are not covered by perichondrium. Acts as shock absorbers. #### Elastic Cartilage - Perichondrium present. - Characterized by the presence of elastic fibres in abundance which branch and anastomose. - Chondrocytes are larger than those of hyaline cartilage and present in singly. #### Fibro Cartilage - Perichondrium is characteristically absent. - Has thick bundles of collagen fibres. - Chondrocytes are seen between these fibres in singly in narrow rows. ### Features of Identification | Hyaline Cartilage | Elastic Cartilage | Fibro Cartilage | |---|---|---| | 1. Perichondrium present. | 1. Perichondrium present. | 1. Perichondrium absent. | | 2. Ground substance highly basophilic and homogeneous | 2. Numerous elastic fibres | 2. Bundles of collagen fibres | | 3. Chondrocytes in lacunae and in groups | 3. Single chondrocytes in lacuna | Few chondrocytes seen | ### Chondrogenesis - Cartilage forms from embryonic mesenchyme by the process called as chondrogenesis. - First indication of this process is rounding up of mesenchymal cells which have extensions and divide rapidly called as chondroblast and chondrocytes. - When proliferation is ceased, these cells have basophilic cytoplasm, rich in RER for collagen synthesis. - Production of ECM encloses these cells in cavities called lacunae. ### Applied Histology - Osteoarthritis - Slip disc - Hyaline cartilage have a tendency to ossify with age. A diagram of a synovial joint was provided to illustrate the above. ### Questions - What are the types of cartilage? Give examples. - What is perichondrium? - What are cell nest? How are they formed? - What are the components of cartilage - Give the identifying features of each variety of cartilage - What is calcification of cartilage? ### Thank You **Note:** This is a transcription and summarization of the document. The images were not included in the markdown output.