Connective Tissue Notes

Connective Tissue

Connective tissue supports and connects tissues/cells to form organs.
Interstitial fluid provides metabolic support via nutrient/waste diffusion.
Main component: extracellular matrix (ECM).
ECM includes protein fibers (collagen, elastic fibers) and ground substance.
Ground substance: proteoglycans, glycosaminoglycans (GAGs), multiadhesive glycoproteins (laminin, fibronectin).
Glycoproteins stabilize ECM by binding matrix components and cell membrane integrins.
Water in ground substance facilitates nutrient/waste exchange.
Connective tissue diversity arises from variations in cells, fibers, and ground substance.
Origin: embryonic mesenchyme (from mesoderm).
Mesenchyme: viscous ground substance, few collagen fibers, undifferentiated cells.
Mesenchymal cells can differentiate into connective tissue, bone, cartilage, blood, endothelium, and muscle.
Mesenchyme-like cells in adults may be stem cell sources for repair/regeneration.

Key cells: Fibroblasts originate from mesenchymal cells and reside in connective tissue.
Macrophages, plasma cells, and mast cells from hematopoietic stem cells circulate and enter connective tissue.
Leukocytes are transient, functioning briefly before apoptosis.

Most common cells, produce/maintain ECM components.
Synthesize collagen, elastin, GAGs, proteoglycans, and glycoproteins.
Secrete ECM components with modification outside the cell.
Active fibroblasts: abundant cytoplasm, much RER, large euchromatic nucleus.
Quiescent fibroblasts (fibrocytes): smaller, less RER, darker heterochromatic nucleus.
Fibroblasts respond to growth factors influencing growth/differentiation.
Adult fibroblasts rarely divide unless stimulated by growth factors during tissue repair.
Myofibroblasts (wound healing): contractile function, enriched with actin.

Macrophages phagocytose protein fibers, apoptotic cells, debris, and particulate material.
They're abundant at inflammation sites.
Vary in size/shape based on activity.
Function in ECM fiber turnover, innate immune defense, removing debris/ invaders.
Macrophages are antigen-presenting cells for lymphocyte activation.
Stimulation leads to activated macrophages with increased phagocytosis, digestion, metabolism, and enzyme activity.
Activated macrophages secrete ECM breakdown enzymes, growth factors, and cytokines.
Stimulated macrophages may fuse into multinuclear giant cells.
Macrophages have irregular surfaces, Golgi complexes, and lysosomes.
Originate from blood monocytes that enter connective tissue and differentiate.
Mononuclear phagocyte system: macrophage-like cells in various organs.
Macrophages become activated during inflammation/tissue repair, increasing in number.
They secrete growth factors and present antigens for lymphocyte activation.

Oval/irregular cells filled with basophilic secretory granules.
Granules display metachromasia.
Mast cells release bioactive substances for inflammation, immunity, and repair.
Releases Heparin (anticoagulant), Histamine (vascular permeability, muscle contraction), Serine proteases (inflammation mediators), Eosinophil and neutrophil chemotactic factors