Connective Tissue PDF

Connective Tissue by Boris Kablar, MD, PhD Professor (Slides: Junqueira’s Basic Histology by Mescher) Dalhousie University, Faculty of Medicine Department of Medical Neuroscience/Anatomy  Objectives Describe mo...

Connective Tissue by Boris Kablar, MD, PhD Professor (Slides: Junqueira’s Basic Histology by Mescher) Dalhousie University, Faculty of Medicine Department of Medical Neuroscience/Anatomy  Objectives Describe morphological and functional features of different types of connective tissue, including cartilage and bone. Describe morphological and functional features of the two main processes of ossification, bone resorption/remodeling and repair. Describe morphological and functional features of joints.  Connective Tissue Cells Fibers Ground substance Cells of the Connective Tissue (active) (quiescent) The most common cell type Synthesize the extracellular matrix Healing and scar formation  Cells of the Connective Tissue Macrophages (phagocytes, inflammatory/immune response, derived from bone marrow) Mast cells (histamine, inflammatory/immune response, derived from bone marrow) Plasma cells (antibodies; LM: large basophilic cytoplasm due to RER)  Cells of the Connective Tissue Adipose cells (storage of fats) Leukocytes (migrate from the blood vessels via diapedesis, especially in an inflammatory response)  Fibers of the Connective Tissue Collagen fibers (collagens are a family of mostly structural proteins with more than 25 members)  Fibers of the Connective Tissue Reticular fibers (collagen III) are very thin and only visible with special staining (not in H&E preparations) Elastic fibers (resistant to pulling)  Ground Substance of the Connective Tissue Glycosaminoglycans (GAGs) (polysaccharides, hyaluronic acid) Proteoglycans (protein + GAGs: dermatan-, chondroitin-, keratan-, heparan-sulfate) Glycoproteins (protein + carbohydrates: fibronectin, laminin) Edema Cartilage and bone are forms of connective tissue The three cartilage types consist of the same cell type: chondrocyte. However, the difference between them is in the extracellular matrix.  Hyaline Cartilage PERICHONDRIUM Extracellular matrix: Collagen II ↑ APOSITIONAL GROWTH Proteoglycans Chondronectin ← chondrocyte in lacuna (isogenous group) ↑↓ INTERSTITIAL GROWTH No blood vessels Diffusion Examples: Embryonic skeleton Trachea Articular surfaces of joints (modified) Elastic Cartilage Extracellular matrix: Collagen II Elastic fibers Examples: External ear Eustachian tube Epiglottis Fibrocartilage Extracellular matrix: Collagen I (dense connective tissue), II Examples: Intervertebral discs Symphysis pubis Sternoclavicular joint Temporomandibular joint Menisci Certain tendons  Bone LONG BONES (tibia): Epiphysis (ends) Metaphysis (in between) Diaphysis (shaft) ← Marrow SHORT (carpal) (sternum, iliac crest) FLAT (skull) IRREGULAR (vertebra) Trabeculae (Spongy bone)  Bone Tissue Components and Function Cells: osteoprogenitors → osteoblasts → osteocytes, osteoclasts (bone-marrow) Extracellular matrix: collagen I, proteoglycans, glycoproteins Mineralization of the extracellular matrix by calcium and phosphorus: hydroxyapatite crystals Ca10(PO4)6(OH)2 Function: support (skeleton), protect (skull) and store (calcium and phosphate)  Osteoblasts mesenchyme (osteoprogenitor cells) osteoid osteocyte in lacuna calcified bone matrix  Osteocyte (TEM) (one per lacuna) canaliculi Dried Bone (mineralized)  Osteoclasts clear zone → ← ruffled border  Bone Resorption/Remodeling 1. Decalcification 2. Lysosomal hydrolysis of Parathormone the organic component (parathyroid) raises low blood calcium and stimulates osteoclasts (increases calcium absorption in the gut and decreases calcium loss by the kidney) Calcitonin (thyroid C cells) lowers elevated blood calcium and inhibits osteoclasts (increases kidney loss of calcium)  Osteon or Haversian System Concentric lamellae (major vessels/nerves) (osteoprogenitors) (osteoprogenitors) (single a/v/n) Osteon (inset) (surrounds each osteon)  Clinical Correlations Paget’s disease: uncontrolled osteoclast and osteoblast activity leads to larger but disorganized bones prone to fractures. Osteoporosis: resorption by osteoclasts exceeds deposition by osteoblasts, which leads to bone fractures and vertebrae compressions. Rickets: insufficient calcium (or vitamin D needed for calcium absorption in the gut) during growth or adulthood (osteomalacia) leads to abnormal calcification of the bone matrix. Scurvy: vitamin C deficiency results in non-calcifiable collagen of the bone matrix. Intramembranous (blastema) Ossification (in a lacuna) Endochondral Ossification Endochondral Ossification Endochondral Ossification Endochondral Ossification  Bone Repair (spongy) (intramembranous) (endochondral) (compact) Joints (hyaline, no perichondrium) Synovial Membrane (synovial fluid, dialysate of plasma) lubrication nutrition phago- cytosis