Cartilage Histology

Skeletal system The skeletal system is composed of highly specialized forms of supporting/connective tissue, based on collagen and acellular matrix, and the synthetic cells which produce them. Cartilage and bone are two specialized types of connective tissue. Both tissues are of mesenchymal origin. Both are composed of cells that secrete an extracellular matrix (ECM).

Cartilage Cartilage is avascular and possesses no lymph vessels or nerves and the exchange of metabolites between chondrocytes and surrounding tissues depends on diffusion. Cartilage form with the differentiation of primitive mesenchymal cells to form cartilage precursor cells called chondroblasts. Each chondroblast then form mature cartilage cells, known as chondrocytes reside in lacunae. Each lacuna is surrounded by a basophilic region known as territorial region or matrix. The area of lighter basophilia is the inter-territorial zone..

Chondrocytes

Cartilage Most mature cartilage have a surrounding layer called the perichondrium, divided into an inner cellular and an outer fibrous layer. Perichondrium have the capacity to transform into chondroblasts and form new cartilage by appositional growth. There is very limited capacity in mature cartilages masses for interstitial growth by further division of chondrocytes. The hyaline cartilage of the articular surfaces of joints does not have perichondrium on the surface, and has no capacity to regenerate new cartilage after damage.

Growth of cartilage Appositional growth - the process that forms new cartilage at the surface of an existing cartilage, by the development of new cells from the chondrogenic layer of the perichondrium. This type of growth results in the formation of new chondrocytes. Interstitial growth, the process that forms new cartilage within an existing cartilage mass by the mitotic division of chondrocytes within their lacunae cells. This type of growth occurs only during the early stages of cartilage formation and the epiphyseal plates of long bones.

3 Types of cartilage Hyaline cartilage - the most common form and the matrix contains type II as the principal collagen type. Elastic cartilage is more pliable and distensible, in addition to collagen type II, an abundance of elastic fibres within its matrix. Fibrocartilage, present in regions of the body subject to great stress or the demands of weight bearing, is characterized by a dense network of coarse type I collagen fibres.

Hyaline cartilage The most common cartilage, is noted for the smooth homogeneous appearance of its ECM ("hyaline" = resembling glass). Hyaline cartilage makes up the fetal skeleton until it is replaced with bone, the anterior portion of the ribs (costal cartilage), and respiratory structures (trachea and bronchi). It also forms the epiphyseal growth plate in long bone and the articular cartilage of synovial joints.

Hyaline cartilage matrix A. Chondrocytes B. Three major class of molecules: 1. Collagen molecules-major matrix protein (type II) and other types VI, IX, X and XI. 2. Proteoglycan – 3 types of GAGA (hyaluronan, chondroitin and keratin sulfate) The chondroitin and keratin sulfate are joined to a core protein to form a proteoglycan monomer. Aggrecan molecules have a large negative charge with an affinity for water. 3.Glycoproteins: Noncollagenous and nonproteoglycan-linked glycoproteins. Anchorin, tenascin, and fibronectin,chondronectin.

Molecular structure of Hyaline cartilage matrix

Hyaline cartilage Perichondrium is a layer of dense connective tissue that surrounds hyaline cartilage except at articular surfaces. These have the capacity to transform into chondroblasts and form new cartilage by appositional growth. The matrix that is adjacent to chondrocytes is called the territorial matrix. The basophilia is due to the high concentration of negative ions (chondroitin and keratin sulfate), poor in collagen. As the ions diffuse further away from the cell, the basophilia is less intense, reflecting the decrease in negative ion concentration. Mature chondrocytes are characterized by small nuclei with dispersed chromatin and basophilic, granular cytoplasm, reflecting a well developed rough endoplasmic reticulum. Cytoplasm is rich in glycogen and lipid droplets

Hyaline cartilage

Degeneration of hyaline cartilage 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. This type of bone formation allows the lengthening of long bones like the femur, and starts in the epiphysis of the long bone.

Elastic cartilage Elastic cartilage occurs in the external ear and external auditory canal, the epiglottis, eustachian tubes and the larynx. The histological structure of elastic cartilage is similar to that of hyaline cartilage, but elasticity is due to bundles of elastic fibres in the cartilage matrix. Collagen (stained red) is a major constituent of the cartilage matrix and makes up the bulk of the perichondrium (P) intermingled with a few elastic fibres.

Elastic cartilage Elastic cartilage has elastic fibers in its ECM. Elastic fibers provide an increased amount of flexibility designed to withstand repeated flexions and extensions.

Elastic cartilage Elastic cartilage possesses a perichondrium and is nearly identical to hyaline cartilage except for a network of elastic fibers. Elastic cartilage contains type II collagen, and is less prone to degeneration than hyaline cartilage and is located in areas where flexible support is required.

Elastic cartilage – elastin fibers in the matrix Perichondrium Chondroblasts Chondrocytes

Fibrocartilage Fibrocartilage is found in the intervertebral discs, pubic symphysis, meniscus of knee and insertion of tendons to bone. Fibrocartilage lacks an identifiable perichondrium. It has a matrix with large bundles of type I collagen in addition to type II collagen imparts resistance to compression. Fibrocartilage is a combination of dense connective tissue and cartilage (alternating layers of cartilage matrix and thick layers of dense collagen fibres).

Fibrocartilage

Fibrocartilage between two pieces of bone

Clinical Correlation Achondroplasia Most common form of inherited dwarfism. Hereditary defect Autosomal dominant Mutation in fibroblast growth factor receptor 3 (FGFR3) Mutations cause a gain of function of the FGFR3 gene, resulting in decreased endochondral ossification, inhibited proliferation of chondroblasts in growth plate cartilage, decreased cellular hypertrophy, and decreased cartilage matrix production.

Achondroplasia Long bones are short and thick. Short extremities- dwarfism. Cranial and vertebral bones spared, relatively large head and trunk. Normal intelligence, life span and reproductive ability.

Osteoarthritis Osteoarthritis is a degenerative joint disease due to excessive wear and tear leading to degenerative change in the articular cartilages of both opposing bone ends which participate in the joint.

Osteoarthritis Articular cartilage has no perichondrium Renewal process of mature cartilage is very slow due to stable type II collagen and low activity of metalloproteinase

Disc degeneration and prolapse The intervertebral discs act as shock absorbers, supporting and springing the vertebral column and are particularly vulnerable to damage because of the weight they have to support. These can lead to weakening of the annulus fibrosus which may give way, allowing the soft central nucleus pulposus to extrude (disc prolapse) through into the spaces beneath the ligaments and elsewhere. This leads to soft tissue swelling around the protrusion, and may involve the spinal nerves emerging from the spinal column.

Disc degeneration and prolapse

What type of basic tissue type is cartilage. a. Muscle b. Nervous c What type of basic tissue type is cartilage? a. Muscle b. Nervous c. Cartilage d. Epithelium e. Connective tissue How many types of cartilage are there? a. 1 b. 2 c. 3 d. 4 e. 5

What do you call the space where a chondrocyte sits in. a What do you call the space where a chondrocyte sits in? a. Space of Disse b. Space of Mall c. Vacuole d. Lacuna e. Howship's Lacuna What stain would be best to demonstrate the elastic fibers in elastic cartilage? a. Wright's stain b. Hematoxylin and eosin stain c. Sudan stain d. Silver impregnation e. Resorcin fuchsin and orcein D, E

Which type of cartilage is found in the walls of the eustachian tube? a. Hyaline cartilage b. Elastic cartilage c. Fibrocartilage d. All of the above e. None of the above Which type of cartilage forms the skeleton of the fetus? a. Hyaline cartilage b. Elastic cartilage c. Fibrocartilage d. All of the above e. None of the above b

Which type of cartilage forms the intervertebral disc. a Which type of cartilage forms the intervertebral disc? a. Hyaline cartilage b. Elastic cartilage c. Fibrocartilage d. All of the above e. None of the above What type of tissue makes up the "Adam's apple"? a. Hyaline cartilage b. Fibrocartilage c. Elastic cartilage d. Both a and b e. Both a and c

Which type of cartilage is characterized by the presence of elastic fibers? a. Hyaline cartilage b. Elastic cartilage c. Fibrocartilage d. All of the above e. None of the above Which type of cartilage is highly vascular? a. Hyaline cartilage b. Elastic cartilage c. Fibrocartilage d. All of the above e. None of the above