Connective Tissue Part 2.2 PDF

CONNECTIVE TISSUE Part 2 | Cartilage and Bone Histology course for Veterinary Medicine students DVM, Lect. Arnoldas Pautienius  Cartilage Cartilage is a form of connective tissue composed of cells called chondrocytes and a highly specialized extracel...

CONNECTIVE TISSUE Part 2 | Cartilage and Bone Histology course for Veterinary Medicine students DVM, Lect. Arnoldas Pautienius  Cartilage Cartilage is a form of connective tissue composed of cells called chondrocytes and a highly specialized extracellular matrix. More than 95% of cartilage volume consists of extracellular matrix, which is a functional element of this tissue. Cartilage is an avascular structure. Therefore, the composition of the extracellular matrix is essential for diffusion of substances between chondrocytes and blood vessels in the surrounding connective tissue.  There are three major types of cartilage 1. Hyaline cartilage is characterized by matrix containing type II collagen fibers, GAGs, proteoglycans, and multiadhesive glycoproteins. 2. Fibrocartilage is characterized by abundant type I collagen fibers as well as the matrix material of hyaline cartilage. 3. Elastic cartilage is characterized by elastic fibers and elastic lamellae in addition to the matrix material of hyaline cartilage.  1. Hyaline Cartilage Throughout the cartilage matrix are spaces called lacunae. Located within these lacunae are the chondrocytes. The homogenous, amorphous extracellular matrix of hyaline cartilage is produced by chondrocytes and appears glassy. Chondrocytes are distributed either singularly or in clusters called isogenous groups!  1. Hyaline Cartilage Hyaline cartilage matrix contains three classes of molecules: collagen molecules, proteoglycan aggregates and multiadhesive glycoproteins. The ground substance of hyaline cartilage contains three types of GAGs: hyaluronan, chondroitin sulfate, and keratan sulfate. A firmly attached connective tissue, the perichondrium, surrounds hyaline cartilage. It is not present on the free, or articular, surfaces of articular cartilage in synovial joints.  Location of hyaline cartilage In a fully grown individual, the remnant of cartilage from the developing skeleton is found on the articular surface of joints (articular cartilage) and in the rib cage (costal cartilages). Hyaline cartilage also exists in the adult as the skeletal unit in the trachea, bronchi, larynx, and nose.  2. Elastic Cartilage In addition to containing the normal components of hyaline cartilage matrix, elastic cartilage matrix also contains a dense network of branching and anastomosing elastic fibers. The elastic material gives the cartilage elastic properties in addition to the resilience and pliability that are characteristic of hyaline cartilage. It is always surrounded by the perichondrium.  Location of elastic cartilage Elastic cartilage is found in the external ear, middle ear, and larynx.  3. Fibrocartilage Fibrocartilage is a combination of dense regular connective tissue and hyaline cartilage. The chondrocytes are dispersed among the collagen fibers singularly, in rows, and in isogenous groups.  3. Fibrocartilage These chondrocytes appear similar to the chondrocytes of hyaline cartilage, but they have considerably less cartilage matrix material. There is also no surrounding perichondrium as in hyaline and elastic cartilage.  Location of fibrocartilage Fibrocartilage is typically present in intervertebral discs, the pubic symphysis, articular discs, menisci of the knee joint and etc. The presence of fibrocartilage in these sites indicates that resistance to both compression and shearing forces is required of the tissue. The cartilage serves much like a shock absorber. The degree to which such forces occur is reflected in the amount of cartilage matrix material present.  Bones Bone is a specialized form of connective tissue that, like other connective tissues, consists of cells and extracellular matrix. The feature that distinguishes bone from other connective tissues is the mineralization of its matrix, which produces an extremely hard tissue capable of providing support and protection.  General structure of bone tissue Within the bone matrix are spaces called lacunae (sing., lacuna), each of which contains a bone cell, or osteocyte. The osteocyte extends numerous processes into small tunnels called canaliculi. Canaliculi course through the mineralized matrix, connecting adjacent lacunae and allowing contact between the cell processes of neighboring osteocytes.  Mature (lamellar) bone is mostly composed of osteons (Haversian systems). These concentric lamellar structures are organized around an osteonal (Haversian) canal that contains the vascular and nerve supply of the osteon. Perforating (Volkmann's) canals are perpendicularly arranged and connect osteonal canals to one another. The lacunae between concentric lamellae contain osteocytes that are interconnected with other osteocytes and the osteonal canal via canaliculi. General structure of bone tissue  Cells of bones In addition to osteocytes, four other cell types are associated with bone: Osteoprogenitor cells are cells derived from mesenchymal stem cells; they give rise to osteoblasts. Osteoblasts are cells that secrete the extracellular matrix of bone; once the cell is surrounded with its secreted matrix, it is referred to as an osteocyte. Bone-lining cells are cells that remain on the bone surface when there is no active growth. They are derived from those osteoblasts that remain after bone deposition ceases. Osteoclasts are bone-resorbing cells present on bone surfaces where bone is being removed or remodeled (reorganized) or where bone has been damaged.