Histology of Cartilage PDF

Histology of Cartilage By: Dr. Moustafa Al Sawy Dr. Shaimaa Mohamed Amer MBBCH, M.SC. M.D HISTOLOGY MBBCH, M.SC. M.D HISTOLOGY Associate Professor of Histology & Cell Biology...

Histology of Cartilage By: Dr. Moustafa Al Sawy Dr. Shaimaa Mohamed Amer MBBCH, M.SC. M.D HISTOLOGY MBBCH, M.SC. M.D HISTOLOGY Associate Professor of Histology & Cell Biology Associate Professor of Histology & Cell Biology Certified Medical Educator Learning objectives KnowledgeLearning & Cognitive: Objectives At the end of the lecture , each student will be able to: 1.Classify histologically the cartilage. 2. Describe the histogenesis and growth of cartilage. 3.Describe the light and electron microscopic features of hyaline, elastic and white fibrocartilage. 4. Differentiate between different types of cartilage under the microscope.  Cartilage General Characteristics 1.It is a special type of connective tissue which has a rubbery rigid flexible matrix , fiber population and characteristic cells. 2.It develops form the mesenchyme. 3.Unlike other C.Ts, it is not traversed by blood vessels, nerves or lymphatics and nourished by diffusion. (It is liable all the time to pressure). 4.Cartilage functions primarily to support soft tissues and assist in the development and growth of long bones.  Classification of Cartilage It is classified into 3 groups according to differences in the abundance and type of fibers in the ground substance: 1. Hyaline cartilage 2. Yellow elastic cartilage 1. White fibrocartilage  1.Hyaline Cartilage It is the most common type of cartilage. Structure: A. Perichondrium B. Cells C. Matrix Sites of hyaline cartilage: *Costal cartilage *Long bones of fetal skeleton *Articular cartilage *Trachea & bronchi  A.Perichondrium A- Perichondrium *It is a connective tissue membrane present on the surface of the cartilage except inside joint cavities. *It is made of 2 layers: 1. An outer fibrous layer : dense CT rich in type I collagen, fibroblasts and few blood vessels. 2. An inner vascular & cellular layer (chondrogenic layer): contains chondroblast (forming new cartilage). *It contains blood vessels to supply the cartilage with nutrition ( by diffusion) as the cartilage is non vascular.  A.Perichondrium *The hyaline cartilage of articular surface of joints does not have perichondrium on the surface & has no capacity to regenerate cartilage after damage. Functions of perichondrium: *Nutritive function (through its blood vessels). *Chondrogenic function (formation of new cartilage ) during growth & regeneration. *Gives attachment to muscles & tendons.  B. Cells 1- Chondroblasts (immature cartilage cell):- Origin: Undifferentiated mesenchymal cells Site: Found in inner chondrogenic layer at periphery of the cartilage , present singly & parallel to the surface. LM: Shape –Oval, Cytoplasm –basophilic, Nucleus- pale oval. EM: The cell shows all feature of protein synthesing cells extended chromatin Golgi apparatus & RER. Glycogen granules & lipid droplets are scattered in the cytoplasm. Function: *They elaborate the specialized extracellular matrix of cartilage. *They mature and become imprisoned inside lacunae (chondrocytes).  B. Cells 2. Chondrocytes (mature cartilage cell):- Site & LM: They are basophilic cells present in lacunae. Each lacuna is surrounded by a condensed matrix (capsule or territorial matrix). The superficial cells are small, flat & arranged parallel to the surface. They are present singly in their lacunae (young chondrocytes). Young chondrocytes can divide inside lacunae once or twice forming cell nest. Mature chondrocytes do not divide. The deeper chondrocytes (mature or old type) are large rounded oval or triangular and arranged perpendicular to the surface. They are found in their lacunae either single or in groups (cell nests 2,4,6 & 8).  B. Cells EM: The cell shows all feature of protein synthesing cells extended chromatin Golgi apparatus & RER. Glycogen granules & lipid droplets are scattered in the cytoplasm. Function : *Chondrocytes form & secrete extracellular matrix. *Old chondrocytes secretes alkaline phosphatase enzyme.  C. Matrix *It appear homogenous & basophilic. *It is a complex mixture of glycosaminoglycans ( hyaluronic acid & chondroitin sulfate) and structural glycoprotein (chondronectin ). Its basophilia is due to the presence of glycosaminoglycans. The matrix contains collagen fibers type II & elastic fibers but they do not appear because : They are very thin to be seen by the LM. They have the same refractive index of the matrix. Cartilage Matrix  2.Yellow Elastic Cartilage It is similar to hyaline cartilage always having perichondrium but the matrix contains abundant yellow elastic fibers. Sites: Ear pinna External auditory meatus Eustachian tube Epiglottis  3.White fibrocartilage It has no perichondrium (intra articular). The matrix contains abundant parallel collagen fibers type I separated by rows of chondrocytes. It has a great strength & flexibility. Sites: Symphysis pubis Intervertebral discs Interarticular cartilages  Cartilage Histogenesis Histogenesis (growth) of cartilage (especially the hyaline cartilage) is affected by certain hormones and vitamins. It occurs by the following two processes: a. Interstitial growth results from cell division of preexisting chondrocytes. This type of growth occurs only during the early stages of cartilage formation and in articular cartilage and the epiphyseal plates of long bones. b. Appositional growth results from differentiation of chondrogenic cells in the perichondrium. This type of growth results in the formation of chondroblasts and new chondrocytes, which elaborate a new layer of cartilage matrix at the periphery. Degeneration of hyaline cartilage occurs when chondrocytes undergo hypertrophy and die and the matrix becomes calcified, a process that becomes more frequent with age. Degeneration of hyaline cartilage is a normal part of endochondral bone formation.  Healing of cartilage Cartilage has limited ability for repair after injury. This is due to: 1. The avascularity of cartilage 2. The immobility of the chondrocytes, and the limited ability of mature chondrocytes to proliferate. *If extensively damaged, the cartilage tear will be repaired with fibrous tissue.  Medical Application Osteoarthritis, a degenerative joint disease, is one of the most common types of joint diseases. The disease is characterized by chronic joint pain with various degrees of joint deformity and destruction of the articular cartilage. There is a decrease in proteoglycan content, which results in reduction in intercellular water content in the cartilage matrix. Chondrocytes also play an important role in the pathogenesis of osteoarthritis. By producing interleukin-1 (IL -1) and tumor necrosis factor ᾳ (TNF -ᾳ), these leading to stimulate the production of metalloproteinases, whereas synthesis of type II collagen and proteoglycans by the chondrocyte is inhibited.  Case Scenario An investigator is studying traumatic knee joint injuries in college athletes. Images and tissue samples are collected from 4 athletes with cartilaginous injury and 4 athletes with bone fractures. After 8 weeks, the athletes with bone fractures show almost complete resolution, while the athletes with cartilaginous injuries show only minimal signs of healing. The investigator hypothesizes that this is due to the absence of progenitor cells for matrix regeneration. Transplant of which of the following tissues would most likely promote healing in the group with cartilaginous injury? A. Perichondrium B. Proteoglycans C. Chondronectin D. Osteoblasts E. Mature chondrocytes Any Questions? References: 1.Basic Histology: Text & Atlas. Editor: Luiz Carlos Junqueira, MD, PhD; Jose Carneiro, MD, PhD. 14th Ed. 2. Wheatear’s functional histology: A text & color atlas.15th Ed. 3. AMBOSS platform. Thank You