Lecture 6: Cartilage (Connective Tissue) PDF

Lecture 6 Cartilage (Connective Tissue) Presented by: Dr. Alyaa Ragaei Professor of Histology  Cartilage Intended learning outcomes (ILOs): By the end of this unit, the student should be able to: 1) Describe the general structure of cartilage....

Lecture 6 Cartilage (Connective Tissue) Presented by: Dr. Alyaa Ragaei Professor of Histology  Cartilage Intended learning outcomes (ILOs): By the end of this unit, the student should be able to: 1) Describe the general structure of cartilage. 2) Explain the nutrition of cartilage. An 3) Describe the structures and correlated functions of the hyaline cartilage, elastic cartilage and the white fibrocartilage. 4) Compare between the hyaline cartilage, the elastic cartilage and the white fibrocartilage  Cartilage Cartilage is a special type of connective tissue. Origin: Mesenchymal cells (UMCs). Cartilage is formed of: 1. Cells (chondrocytes). 2. Extracellular matrix(ECM). The extracellular matrix is  avascular (no blood vessels)  firm,  rubbery. It consists of fibers and ground substance.  Cartilage types There are three types of cartilage according to the type of fibers in the matrix 1) Hyaline cartilage (collagen type II). 2) Elastic cartilage (collagen type II+ elastic fibers). 3) White fibrocartilage (collagen type I). The perichondrium is a dense connective sheath covered all cartilage except articular cartilage and white fibrocartilage.  Hyaline cartilage Hyaline cartilage is the most common type. Sites: Costal cartilage Most of the fetal skeleton Articular cartilage Epiphyseal plate of long bone Wall of large respiratory Passages: (nose, larynx, trachea and bronchi).  Hyaline cartilage structure (perichondrium) 1) Perichondrium: surrounds cartilage A) Outer fibrous layer: Formed of dense irregular connective tissue and blood vessels. Function:  Nutrition of avascular cartilage. B) Inner chondrogenic layer: formed of chondroblasts  Hyaline cartilage structure (Chondroblasts) 2. Chondroblasts: Immature cartilage cell Origin: Mesenchymal cells (UMCs) & pericytes. Site: In the inner layer of the perichondrium. LM appearance: Shape: oval. They are not present inside lacunae. Nucleus: central, oval and vesicular. Cytoplasm: basophilic EM appearance: Show the characters of protein secretory cell (RER, Golgi complex, and mitochondria). Function: Synthesis and secretion of extracellular matrix (ECM) of cartilage Divide and differentiate to chondrocytes. It is responsible for appositional growth (addition new layers on the surface) of cartilage and repair of damage.  Hyaline cartilage structure (Chondrocyte) 2) Chondrocytes: Mature cartilage cell Origin: chondroblasts. Site: Inside the matrix. LM appearance: Cell shape: small and oval cell Nucleus: central dark nucleus. Cells are present inside lacunae. Cells are present in groups (up to 8 cells in one lacuna called cell nests). Cytoplasm: pale basophilic. EM appearance: Show the characters of protein secretory cell (RER, Golgi complex, and mitochondria). It also contains fat droplets and glycogen. Function: Synthesis & secretion of ECM of cartilage. Can divide. Responsible for interstitial growth of cartilage (adding new matrix)  chondrocytes: specialized cells that produce and maintain the extracellular matrix  Extracellular matrix: consist of: 1. Ground substance 2. Fibers  Hyaline cartilage structure (Extracellular matrix) 1) Ground substance: a) Macromolecules: Glycosaminoglycans (GAGs): chondroitin sulphate, keratin sulphate & hyaluronic acid. Proteoglycans: GAGs bind to protein. Glycoprotein: chondronectin for adhesion of cells to matrix components (anchor effect). b) Tissue fluid: 75% of matrix weight. To Allow easy diffusion of O2 and nutrients from blood vessels of perichondrium to avascular cartilage.  Hyaline cartilage structure (Extracellular matrix) 2) Fibers: Fine network of collagen type II The matrix surrounding each chondrocyte: Glycosaminoglycans rich and collagen poor so chondrocyte in lacunae also called territorial or capsular matrix. Matrix stains:  H&E: it appears basophilic and deeply basophilic around chondrocytes. Why ? due to high content of negative charged chondroitin Sulfate.  PAS: it appears PAS Positive. Why ? due to carbohydrate content.  Toluidine blue: it is metachromatically stained. Why ? due to its proteoglycans content.  Fine network of collagen type II can’t be seen, why ? 1) Submicroscopic dimension. 2) Same refractive index of ground substance.  LM: Hyaline cartilage Fibrous layer Chondrogenic layer Perichondrium Chondroblasts Cell nest Matrix Chondrocyte in lacuna  Elastic cartilage LM appearance: Yellow in fresh State. More pliable. Sites: 1. Ear pinna. 2. External auditory canal. 3. Eustachian tube. 4. Epiglottis. 5. Some cartilage of larynx. Structure: Similar to hyaline cartilage except its matrix contains: a) network of elastic fibers b) collagen type II  LM: Elastic cartilage Chondrocytes: Large, scattered Matrix: Elastic fibers and collagen type II Perichondrium present  White fibrocartilage White in fresh state. In regions subjected to pulling force. Sites: 1) Intervertebral disc. 2) Symphysis pubis. 3) Semilunar cartilage of knee. 4) Near tendon insertion. Structure: 1. Rows of chondrocytes. 2. Bundles of collagen type I ( so fibrocartilage matrix is acidophilic). 3. No perichondrium ( blood vessels are present in between collagen fibers).  3. White fibro Cartilage No Perichondrium Chondrocytes: arranged in linear group separated by collagen fibers Matrix: Mainly Collagen I type + collagen II type collagen