Cartilage
I. General Characteristics
§ Well defined structural organization
§ Consists of abundant intercullar material, matrix, produced by cells entrapped there
§ Surrounded by fibrous connective tissue called perichondrium
§ Support, growth of bones, articulation of bones
II. Basic structure
§ Chondroblasts- immature cartilage cell located on periphery (perichondrium) of cartilage
§ Chondrocyte- mature cartilage cell
§ Lacuna- space in cartilage occupied by chondrocyte
§ Capsule-basophilic cartilage matrix surrounding lacuna
§ Isogenic cell nest- cluster of chondrocytes from division of mature chondrocyte into daughter cells
§ Chondrocytes lay down and maintain surrounding matrix
§ Nutrition to all chondrocytes is via diffusion through matrix, limits size of cartilage
§ Cartilage is surrounded by dense irregular connective tissue- perichondrium
§ Perichondrium
Protection- outer fibrous layer; abundant type I cartilage and fibroblasts
New cartilage- inner chondrogenic layer, type I cartilage and some fibroblasts, osteoprogenitor cells (stem cells)
§ Osteoprogenitor cell- one step beyond mesenchymal cell, depending on stimulus:
Cartilage- chondroblast to chondrocyte
Bone- osteoblast then osteocyte
III. Chemical composition
§ Water 70%
§ Type II collagen (40% dry weight)
§ GAGs- abundant chondroitin 4-sulfate, chonroitin 6-sulfate, and keratin sulfate. Concentrated in capsular areas, thus strong baso philia
§ Various proteins and glycoproteins
IV. Types of cartilage
A. Hyaline cartilage
§ Most prevalent in body
§ Bluish white when fresh, appears glassy and homogeneous due to fine type II collagen fibrils not resolvable
§ Perichondrium may or may not be present
§ Locations: ala of nose, costal cartilage, respiratory tract, fetal skeleton, artic surf of synovial joints
B. Elastic cartilage
§ Presence of elastic fibers in matrix with type II collagen
§ Thickness of fibers permits them to be resolved by Lm
§ Fibrous appearance
§ More flexibility
§ Always associated with perichondrium
C. Fibrous cartilage
§ Presence of type I collagen in matrix with type II collagen
§ Type I fibers resolvable with LM, seen swirling through matrix, may form bundles
§ Found in high stress areas such as bone and muscle
§ Perichondrium is never associated with fibrocartilage
§ Locations: intervertebral disks, public symphysis, intersections of tendons, temporomandibular joint articular surface
V. Growth of cartilage
A. Appositional growth
§ Due to division and differentiation of chondroblasts on outer surface of collagen, Cartilage is added to periphery
§ Osteoprogentifor cell à chondroblast à chondrocyte à outer matrix
B. Interstitial growth
§ Growth due to division of pre-existing,medially cocated chondrocytes, and their elaboration of additional matrix adds to inner mass of cartilage. Chondroblasts are never necessary for this.
Tags: Appositional growth, Cartilage, Chondroblasts, chondroitin, fibrocartilage, Hyaline cartilage, keratin sulfate, Lacuna, Osteoprogentifor cell, Perichondrium
