Special CT: Cartilage and Bone

• Cartilage are characterized by an extracellular matrix enriched with glycosaminoglycans and proteoglycans that interact with collagen and elastic fibers
• cartilage


  resilient but cannot be distorted
• • shock absorbent
  • sliding area for joints
  • development of bone 


  functions of cartilage
• collagen II 


  hyaline
• collagen II + elastic fibers

  elastic
• collagen I

  fibrocartilage
• cartilage are mainly avascular and nourished only by diffusion
• Chondroblasts produce matrix, surround themselves, and become Chondrocytes
• cartilage has no blood vessels; so diffusion must bring in nutrients & remove wastes; healing
• hyaline cartilage located in the articular surfaces of movable joint, walls of larger excretory passages, ventral ends of the ribs
• hyaline cartilage 40% of dry weight is attributed to collagen II
• chondronectin


  adhesion molecules
• perichondrium covers the cartilage and is composed of collagen I
• chondrocytes shrink during processing
• hyaline cartilage respire under low O2 tension
• SOMATOSTATIN -> SOMATOMEDIN C -> Cartilage growth
• regeneration is slow
• types of growth: interstitial and appositional
• interstitial: resulting from mitotic division from pre-existing chondrocytes; common only in the first weeks of life
• appositional: due to differentiation of perichondrial cells; more common
• elastic cartilage - found in the auricle of the ear, walls, of the external auditory canal (eustachian tube), epiglottis, and cuneiform cartilage of the larynx
• elastic cartilage stained by elastic stains (orcein)
• elastic cartilage - less susceptible to degeneration than hyaline cartilage
• fibrocartilage - intermediate between dense connective tissue and cartilage
• fibrocartilage found in intervertebral disks and pubic symphysis
• fibrocartilage associated with dense connective tissue
• fibrocartilage chondrocytes occur singly or in isogenou groups and arranged in long rows
• bone - the hardest tissue in the body
• bone - second only to cartilage in withstanding stress
• bone is a specialized CT composed of intracellular calcified material (OSTEOID) and three different types of cells : OSTEOBLAST, OSTEOCLAST and the OSTEOCYTE
• • supports fleshy structures
  • protects vital organs
  • hematopoietic
  • reservoir of calcium, phosphate, and other ions
  • provide a system of levers

  functions of bone
• all bones are lined on both internal and external surfaces by layers of tissues containing osteogenic cells
• endosteum - inner surface
• periosteum - outer surface
• bone is difficult to study because of its hardness
• grinding of bone slices - do not preserve cells but provide detailed studies of the matrix, the lacunae, and its canaliculi
• decalcification - commonly done with 5% NITRIC ACID or with a chelating agent (EDTA)
• osteoblasts - Bone forming cells found in all bone surface
• osteoblasts - Small cells synthesize and secrete osteoid, and important part of the ground substance
• osteoblasts - Collagen fibrils line up in osteoid and serve as a framework for the deposition of calcium and phosphate