Cartilage

2. Fibroblasts

Of the dense collagenous connective tissue differentiate into chondrocytes in regions of stress and transform the tissue into fibrocartilage

Territorial matrix (matrix adjacent to the chondrocyte)

) is poor in collagen but rich in glycosaminoglycans Stains deeply basophilic. It is also metachromatic and stains more intensely with periodic acid and Schiff reagent (PAS) than other areas of the matrix Interterritorial matrix contains more fibers.

Cartilage and Bone

*Are specialized types of connective tissue, each of which has a unique matrix, fiber population, and characteristic cells *Matrix of cartilage is firm but pliable *(Matrix of bone is calcified and forms the skeleton in higher vertebrates *Both bone and cartilage function in support, but bone also serves as a reservoir for calcium and phosphate, protects vital organs, and contains bone marrow, which functions in hemopoesis

Fibrocartilage

*Does not occur alone, but is found in conjunction with hyaline cartilage and other fibrous tissues *Associated with dense connective tissues. Borders not clear cut, hence shows gradual transition *Located where support and tensile strength is of utmost importance, such as in the intervertebral discs, articular discs, pubic symphysis and at the intersections of some tendons and ligaments

Fibrocartilage matrix

*Is composed of Type I collagen, chondroitin sulfate and dermatan sulfate *Collagen fiber bundles are arranged parallel to the stress placed on the cartilage and chondrocytes lie in longitudinally columns between them

Hyaline cartilage matrix

*Is composed of amorphous ground substances and Type II collagen fibrils *Collagen constitutes about 40% of the total matrix, is not discernible in histologic sections because the fibrils are very fine and have the same refractive index as the matrix

Hyaline cartilage (fibers)

Acidophilic collagenous, rarely in definite bundles forming a fine feltwork of type II collagen, absent around territorial areas. Masked by dense matrix (same refractive index) and can be visualized with polarized microscope

4.Chondrocyte

At the periphery young chondrocytes have an elliptical shape. Matured chondroblasts located in the lacunae of cartilage and are surrounded by matrix Located superficially, chondrocytes are ovoid and positioned so that their longitudinal axes lie parallel to the cartilage surface

Clinical

Cartilage cells can give rise to; Benign tumor - Chondroma Malignant tumor - Chondrosarcoma

Cartilage (classification of Cells) Hyaline

Chondroblasts are elliptical and flattened, with rounded nuclei containing one or two small nucleoli. Cytoplasm contains lipid droplets. Forms sulfated protein polysaccharides of matrix. Chrondrocytes are ovoid or spherical and occupy small cavities, or lacunae. Large central nucleus, one or two nucleoli, and cytoplasm basophil, vacuolated with glycogen and pigment granules and cytoplasmic processes. Group of cells in a lacunae called isogeneous group, or cell nest

Histophysiology

Chondrocytes manufacture the matrix through which nutrients and waste materials pass to and from the cells via diffusion Hormones influence the growth of cartilage: thyroxine, testosterone and growth hormone increase the growth rate; cortisone hydrocortisone and estradiol decrease it

Cartilage growth and repair

Damaged cartilage undergoes slow and often incomplete regeneration, except in young children, by activity of cells in the perichondrium. In extensively damaged areas perichondrium produces scar of dense connective tissues instead of forming new cartilages. The poor regenerative capacity is partly due to its avascularity.

CARTILAGE GROWTH AND REPAIR

During embryonic development , differentiation of cartilage takes place from center outwards. Hence, the more central cells have the characteristics of chondrocytes, while the peripheral cells are typical chondroblast. Superficial mesenchyme develops into the perichondrium Further growth of cartilage A. Interstitial growth - mitotic division of existing chondrocytes B. Appositional growth - Differentiation of perichondrial cells Both contribute to growth of matrix. Interstitial growth is less important postnatally. Occurs in early cartilage formation. Leads to increase tissue mass by expanding matrix from within. Also occurs in epiphyseal plate of long bones and within articular cartilage. Important in increasing the length of long bone Appositional - increase in girth

Elastic cartilage (fibers)

Elastic, elements vary in thickness and amount; predominate. In general, larger and more intensely packed in the interior. Stain black with Verhoeff's elastic tissue stain.

9.Location

Hyaline cartilage is the most common cartilage in the body. It is found at the articular ends of long bones; in the nose, larynx, trachea and the bronchi; and it serves as the skeleton of the fetus, epiphyseal plate and attaches rib to the sternum.

8.Regeneration

Hyaline cartilage regenerates very poorly and often the perichondrium forms scar tissue

7. Regressive change

Hyaline cartilage undergoes regressive changes. The cells hypertrophy and die and the matrix becomes calcified (Hyaline cartilage is avascular) Some of these changes also occur in the process by which cartilage participates in endochondral bone formation

histogenesis

In the embryo, mesenchymal cells differentiate into chondroblasts. These basophilic cells secrete matrix and become incarcerated by it, thus becoming chondrocytes Chondroblasts Mesenchymal cells

3.Chondrogenic cells ( chondroblasts

In the inner layer of the perichondrium differentiate into chondroblasts, the cells that produce cartilage

lacunr rim

Inner layer of the territorial matrix. Consists of loose collagen fibrils

Histogenesis

Intestitial (growth from within) occurs only in young cartilage from cell divisions within the cartilage Appositional growth occurs from chondrogenic cells in the perichondrium differentiating into chondroblasts, forming a new layer of cartilage around the periphery of the existing cartilage

2.Perichondrium

Is a dense connective tissue region surrounding cartilage, except at articular surfaces Composed of an outer fibrous layer containing Type I collagen, fibroblasts, blood vessels, nerves and lymphatics.

Fibrocartilage

Is associated with the capsules and ligaments of joints Serves as a transition between connective tissue and cartilage, as in the annulus fibrosus of the intervertebral discs

Elastic cartilage

Is often found with hyaline cartilage. It possess a perichondrium grows by apposition and does not degenerate as readily as hyaline cartilage Has fibers in addition Yellowish in color due to elastin (fresh)

Fibrocartilage

Lacks a pericondrium No appositional growth

Chondrocytes

Located deeper, they are more spherical Isogenous groups (groups of four to eight cells) found in young cartilage are suggestive of internal growth Electron micrographs display irregular chondrocyte surfaces with some small processes. They also display an extensive Golgi apparatus, have an abundant rough endoplasmic reticulum and contain lipid droplets and glycogen deposits

Elastic cartilage

Located where support with flexibility is required as in the auricle of the ear, walls of external auditory canal, auditory tube and epiglottis Matrix is identical to that of hyaline cartilage, except it also contains a network of elastic fibers that impart to it a yellowish color

Clinical

Osteoarthritis Osteoarthritis is the disease process by which joints wear out. As the joint surface wears away it sheds wear particles which stimulate the joint lining to produce fluid, causing the knee to swell. When the articular cartilage wears through, the underlying bone becomes exposed. The exposed bone rubs against exposed bone when walking and this causes pain.

Clinical

Osteogenesis imperfecta Genetic defect involving type l collagen, resulting in spontaneous fractures of bone and blue sclera of the eye.

clinical

Osteopetrosis Increased osteoblastic activity than osteoclastic activity.

Elastic cartilage (Cells)

Oval, few and scattered. Same cell types as in hyaline but less accumulation of fat and glycogen

Clinical (osteoporosis)

Primary Osteoporosis ( Senile or post menopausal): It is a critical loss of bone mass associated with a deficiency of either GH (Growth hormone) (senile) or estrogen ( Post menopausal). Decreased estrogen levels result in increased secretion of IL-1(a potent stimulator of osteoclasts) from monocytes. Vertebral compression fractures, femoral head fracture, or slow healing of fractured bones-are common clinical findings.

Clinical

Rickets- Lack of minerals within osteoid, which occurs as a result of Vitamin D deficiency in children. Adults - Osteomalacia. Vitamin D metabolism: Sources include dietary intake and production by skin keratinocytes, stimulated by sunlight. Vit D is hydroxylated in liver- 25(OH) VitaminD and to 1,25 dihydroxy vitamin D in the kidney, the active metabolite. This stimulates absorption of calcium and phosphates from the intestinal lumen and elevates blood levels and thereby mineralization of bone matrix.

Elastic cartilage (matrix)

Semisolid. Quantity large and resilient owing to elastic fibers masking collagenous fibers. Grows appositionally and interstitially. Yellow color in the fresh state. More opaque than hyaline and less likely to undergo retrogressive changes.

Matrix of hyaline cartilage

Semisolid. Quantity great. Homogeneous and glassy in fresh preparations. Consists of sulfated glycosaminoglycans, keratin sulfate, and some hyaluronic acid. Territorial areas (cartilage capsules) basophil, and metachromatic with toluidine blue and show a strongly positive PAS reaction. Grows appositionally (exogenously) and interstitially (endogenously) except at articular surfaces. Avascular, with nutrients and oxygen reaching cells via long-range diffusion. With age, basophilia lessens and retrogressive calcification changes occur.

Hyaline Cartilage Matrix

composed of amorphous ground substances ( hyaluronic acid,proteoglycans , some glycoproteins) and Type II collagen fibrils and small amount of Types VI and IX *Collagen constitutes about 40% of the total matrix, is not discernible in histologic sections because the fibrils are very fine and have the same refractive index as the matrix. Hence, is glassy in appearance *Capsular matrix (matrix adjacent to the chondrocyte) is poor in collagen but rich in glycosaminoglycans *Stains deeply basophilic. It is also metachromatic and stains more intensely with periodic acid and Schiff reagent (PAS) than other areas of the matrix

Territorial matrix

made of randomly arranged tyoe II collagen fibrils surrounded by proteoglycans