7 th lecture December 3, 2015 Cartilage

Cartilage is a tough connective tissue composed of cells embedded in an extracellular matrix that is gel-like and has a rigid consistency. Important for: support the softer tissues formation and growth of long bones Cartilage consists of: The Matrix semi-solid and Cells The firm consistency of the cartilage ECM allows the tissue to bear mechanical stresses without permanent distortion. In the respiratory tract, ears, and nose, cartilage forms the framework supporting soft tissues. Because of its smooth, lubricated surface and resiliency, cartilage provides shock absorbing and sliding regions within joints and facilitates bone movements

PERICHONDRIUM Dense irregularly arranged connective tissue (type I collagen) Ensheaths the cartilage Houses the blood vessels that nourish chondrocytes

CHONDROBLAST Originator of chondrocytes Lines border between perichondrium and matrix Secretes type II collagen and other ECM components

CHONDROCYTE Mature cartilage cell Located in a space called the lacuna Clear areas contain Golgi and lipid droplets

MATRIX Provides the rigidity, elasticity, & flexibility FIBERS – Collagenous and elastic GROUND SUBSTANCE – Glycosaminoglycans (chondroitin sulfates, keratin sulfate, hyaluronic acid) – Proteoglycans: GAGs + core protein – Water

(a) A schematic representation of the most abundant molecules in cartilage matrix shows the interaction between type II collagen fibrils and proteoglycans linked to hyaluronic acid. Link proteins non covalently bind the protein core of proteoglycans to the linear hyaluronic acid molecules. The chondroitin sulfate side chains of the proteoglycan electrostatically bind to (b) A diagram of the transitional area between the perichondrium and the cartilage matrix. Fibroblast-like progenitor cells in the perichondrium give rise to larger chondroblasts, which divide and differentiate as chondrocytes. These functional cells produce matrix components and exist in lacunae embedded in the matrix. Staining differences are apparent between the matrix immediately around each lacuna, called the territorial matrix, and that more distant from lacunae, the interterritorial matrix. Collagen is more abundant in the interterritorial parts of the matrix.

All cartilage derives from the embryonic mesenchyme in the process of chondrogenesis. The first indication of cell differentiation is the rounding up of the mesenchymal cells, which retract their extensions, multiply rapidly, and form cellular condensations. The cells formed by this direct differentiation of mesenchymal cells, now called chondroblasts, have a ribosome-rich basophilic cytoplasm. Synthesis and deposition of the matrix then begin to separate the chondroblasts from one another. During embryonic development, the differentiation of cartilage takes place primarily from the center outward; therefore, the more central cells have the characteristics of chondrocytes, whereas the peripheral cells are typical chondroblasts. The superficial mesenchyme develops into the perichondrium.

CARTILAGE GROWTH Appositional – Increasing in WIDTH; chondroblasts deposit matrix on surface of pre-existing cartilage

CARTILAGE GROWTH Interstitial – Increasing in LENGTH – mesenchyme cell differentiate into chondroblast, then chondroblast secreat ECM to form lacunae, and become chondrocytes

There are three types of adult cartilage distributed in many areas of the skeleton, based on the variations in the composition of matrix components and cells found in each type

HYALINE CARTILAGE FUNCTION – Support tissue and organs – Model for bone development MATRIX – Type II collagen (thin fibrils) – Chondroitin sulfate, keratin sulfate, hyaluronic acid – Water LOCATION – Tracheal rings, nasal septum, larynx, articular surfaces of joints Is the most common cartilage in the body. It is bluish-white and translucent. Important in the formation of long bones of the body in embryo and during growth.

ELASTIC CARTILAGE FUNCTION – Support with flexibility MATRIX – Normal components of hyaline matrix plus ELASTIC fibers LOCATION – External ear, external auditory canal, epiglottis The chondrocytes and overall organization of elastic cartilage are similar to those of hyaline cartilage. Stains For elastin, however, reveal many dark-staining elastic fibers in the matrix (M), in addition to the major components found in hyaline matrix. elastic fibers provide greater flexibility to this form of cartilage. The section in the right includes perichondrium that is also similar to that of hyaline cartilage. (a) X160. Hematoxylin and orcein. (b) X100. Weigert resorcin-fuchsin.

FIBROCARTILAGE FUNCTION – Support with great tensile strength MATRIX – Type I collagen - Oriented parallel to stress plane LOCATION – Intervertebral disks, pubic symphysis An irregular, dense, fibrous tissue with thinly dispersed, encapsulated chondrocytes. No perichondrium, so it blends with adjacent connective tissue.