Cartilage .pdf

HISTOLOGY OF CARTILAGE DR EMAN SAEED  Learning outcomes Identify the histological structure of: 1. Hyaline cartilage. 2. Yellow elastic fibro cartilage. 3. White fibrocartilage. Differentiate between different types of the cartilage  Carti...

HISTOLOGY OF CARTILAGE DR EMAN SAEED  Learning outcomes Identify the histological structure of: 1. Hyaline cartilage. 2. Yellow elastic fibro cartilage. 3. White fibrocartilage. Differentiate between different types of the cartilage  Cartilage It is a special type of connective tissue with firm consistency of the extracellular matrix. Types of the Cartilage There are 3 types of cartilage: 1. Hyaline cartilage. 2. Yellow elastic fibro- cartilage. 3. White fibro-cartilage.  Hyaline cartilage It is is the most common type of cartilage. Appearance in fresh state it appears translucent pale blue i.e., hyaline = glassy. : Consistency firm or rigid with some degree of flexibility. Structure it is formed of: 1. Perichondrium. 2. Cartilage cells = chondrocytes. 3. Cartilage matrix. Sites 1. It constitutes the majority of the foetal skeleton. 2. Articular surface of bones. 3. Costal cartilage in the thoracic cage. 4. Nose, trachea, bronchi.  Perichondrium It is a vascular connective tissue membrane which surrounds the cartilage except at the articular surfaces of the joints. It is formed of 2 layers: (a) Outer fibrous layer: rich in collagen type I, fibroblasts and blood vessels. (b) Inner chondrogenic layer: It is formed of cartilage forming cells (chondroblast) which can divide and differentiate into chondrocytes which secrete the cartilage matrix. Function of the perichondrium: 1. It acts as source of O2 + nutrients to the cartilage cells. 2. The inner chondrogenic layer is responsible for new cartilage formation  Cartilage cells There are two types of chondrocytes: 1. Young Chondrocytes: They arise from the inner chondrogenic layer. They are flat cells with open-face nuclei and pale basophilic cytoplasm. They are present singly in their lacunae at the periphery of the cartilage and parallel to the perichondrium. 2. Mature “old” Chondrocytes: Site: deep in the cartilage in the form of rows perpendicular to the perichondrium. LM: Shape: They are oval or rounded “when single” and triangular or semicircular (when in groups 2, 4, 8). A group of cells in a single lacuna are called “cell nests”. They have rounded and open face nuclei. They have granular, basophilic cytoplasm rich in glycogen, fat and phosphatase enzyme. EM: They contain rER, ribosomes, well developed Golgi. The surface show short cytoplasm processes.  Cartilage cells are called 1. Osteocytes cells 2. Chondrocytes cells 3. Osteoblast cells 4. Osteogenic cells  Function:  They synthesize and secrete: the components of the cartilage matrix (collagen type II, proteoglycans, glycoprotein and chondronectin).  They can divide So, They are responsible for growth of the cartilage  Hyaline cartilage is present in: 1. Tracheal ring 2. Intervertebral disc 3. Symphysis pubis 4. Ear pinna  Cartilage matrix General characters:  It is rubbery in consistency.  It is non vascular Staining reaction:  The matrix appears homogenous basophilic by Hx, E due to presence of sulphated glycosaminoglycans.  It shows strong PAS positivity. Components: It is composed of: 1. Collagen fibers (Type II): Collagen form 40% of the dry weight of the hyaline cartilage. 2. Proteogycans: chondritin 4 sulphate and 6 sulphate 3. Glycoprotein Called chondronectin 4. Protein: called chondrocalcin. It is essentially identical to hyaline cartilage except that: Appearance Fresh elastic cartilage is yellow in color due to presence of elastic fibers. Consistency elastic and flexible due to presence of elastic fibers  Yellow elastic fibrocartilage. Structure The matrix contains an abundant network of elastic fibers so it can be stained by the standard elastic stains e.g. Verhoeff's stains. Sites Auricle of the ear. External auditory meatus. Eustachian tube. Epiglottis.  It is white in color in fresh state Appearance tense and resists stretch due to Consistency presence of collagen fibers. Structure It differs from hyaline cartilage in: 1. It is not covered by perichondrium but it is surrounded by dense C. T. rich in blood vessels 2. Chondrocytes:  They are arranged in rows or columns.  They are present singly or in groups inside their lacunae. 3. Matrix:  It is acidophilic because it contains bundles of coarse type I collagen fibers in between them rows of chondrocytes.  Sites (1)Interverterbal discs. (2)Semilunar cartilage of knee joints. (3)Symphysis pubis. (4)Lips of glenoid cavity. (5)Terminal parts of tendons.  Perichondrium is not present in : a) Hyaline cartilage b) White fibrocartilage c) Yellow elastic fibrocartilage  Hyaline cartilage Yellow elastic fibrocartilage White fibro cartilage Appearance Translucent pale blue i.e. hyaline Yellow due to presence of elastic White in fresh state. = glassy. fibers. Consistency Rubbery in consistency More flexible due to the presence of Tens and resists stretch due to elastic fibers. presence of collagen fibers. Sites 1-It constitutes the majority of 1-Auricle of the ear. 1. Semilunar cartilage of knee the foetal skeleton. 2-External auditory meatus. joints. 2-Articular surface of bones. 3-Epiglottis 2. Symphysis pubis. 3-Costal cartilage in the thoracic 3. Lips of glenoid cavity. cage. 4-Nose, trachea and bronchi. 4. Terminal parts of tendons. Structure It is formed of: - Perichondrium. The matrix contains an abundant It differs from hyaline cartilage - Cartilage cells = chondrocytes. network of fine elastic fibers -It can in: 1-It is not covered by –cartilage matrix be stained by standard elastic stains perichondrium 2-Chondrocytes: e.g. verhoeff’s stains. arranged in rows or columns. 3- Matrix: The collagen fibers are arranged in bundles between the rows of chondrocytes. Difference between three types of cartilage  References  Junqueira LC, Carneiro J: Junqueira’s Basic Histology. Text and Atlas, fourteenth edition, Copyright © 2016 by McGraw-Hill Education.  Student medical histology book, Mansoura university.