mod 3

• Connective tissues provide a matrix that supports and physically connects other tissues and cells together to form the organs of the body
• Connective tissues give metabolic support to cells as the medium for diffusion of nutrients and waste products
• Functions of connective tissues include binding and packing material of other tissues, forming the structural framework of many organs, and serving as a storage area for fat
• Ground substance in connective tissues is highly hydrated, transparent, and viscous, consisting of glycosaminoglycans (GAGs), proteoglycans, and multiadhesive glycoproteins
• Glycosaminoglycans (GAGs) are mucopolysaccharides, with examples like Hyaluronan, Dermatan sulfate, Chondroitin sulfates, Keratan sulfate, and Heparan sulfate
• Proteoglycans consist of a core protein attached to sulfated GAGs, with examples like Perlecan and Aggrecan
• Multiadhesive glycoproteins are large macromolecules with branched oligosaccharide chains, such as Laminin and Fibronectin
• Interstitial fluid in connective tissue contains water with an ion composition similar to plasma, with hydrostatic pressure and colloid osmotic pressure affecting fluid movement
• Collagen is a key element of all connective tissue, with different types like fibrillar collagen, network or sheet-forming collagens, and linking/anchoring collagens
• Reticular fibers are found in delicate connective tissue of many organs, mainly consisting of Collagen Type III, and serve as supportive stroma for parenchymal secretory cells
• Elastic fibers are thinner than type I collagen fibers, allowing tissues to be stretched and return to their original shape
• Resident (fixed) cells in connective tissue include fibroblasts, fibrocytes, reticular cells, adipose cells, mast cells, and resident macrophages
• Visiting (wandering) cells in connective tissue include inflammatory macrophages, plasma cells, and leukocytes
• Fibroblasts are the most common cell in connective tissue, synthesizing and secreting collagen and elastin, while fibrocytes are quiescent cells with fewer processes
• Adipocytes are fat cells specialized for cytoplasmic storage of lipid, cushioning, and insulation
• Macrophages are phagocytic cells important for tissue repair, removal of apoptotic cells, and secretion of growth factors
• Mast cells release bioactive substances important in local inflammatory responses, innate immunity, and tissue repair
• Plasma cells are B lymphocyte-derived cells that synthesize immunoglobulin antibodies
• Leukocytes are white blood cells involved in the vascular and defensive response to injury or foreign substances
• Embryonic connective tissue originates from the embryonic mesenchyme, which develops mainly from the middle layer of the embryo (mesoderm)
• Mucoid (mucous) connective tissue is found in the fetal umbilical cord and contains hyaluronan in a gelatinous matrix with sparse collagen fibers and scattered fibroblasts
• Loose connective (areolar) tissue typically contains a viscous ground substance with few collagen fibers
• • Reticular connective tissue is characterized by abundant fibers of type III collagen forming a delicate network that supports various types of cells
• Connective Tissue:

  • Red fibroblasts are similar to the tissue found in the vitreous chambers of eyes and pulp cavities of young teeth
  • Loose connective (areolar) tissue typically contains cells, fibers, and ground substance in roughly equal parts
  • Dense regular connective tissue consists mainly of Type I collagen bundles and fibroblasts aligned in parallel
  • Dense irregular connective tissue has bundles of collagen fibers randomly interwoven with no definite orientation
• Functions of Connective Tissue:

  • Loose connective tissue forms a layer beneath the epithelial lining of many organs and fills the spaces between fibers of muscle and nerve
  • Dense regular connective tissue provides great resistance to prolonged and repeated stresses from the same direction
  • Dense irregular connective tissue protects organs and strengthens them structurally
  • Reticular connective tissue provides a framework with a specialized microenvironment for hematopoietic tissues in bone marrow and lymphoid organs
• • Adipose tissue serves as storage depots for neutral fats (triglycerides) and provides thermal insulation for the body
• White Adipose Tissue:

  • Most common type of adipose tissue that specializes in fat storage
  • Adipocytes in white adipose tissue are spherical when isolated but polyhedral when closely packed in situ
  • White adipose tissue is associated with different organs and appears histologically similar, but differences in gene expression have been observed
  • White adipocytes can store triglycerides derived from dietary fats, lipids synthesized in the liver, and free fatty acids and glycerol synthesized by the adipocytes
• Brown Adipose Tissue:

  • Cells in brown adipose tissue have multiple lipid droplets interspersed among abundant mitochondria, giving them a darker appearance
• • Adipose tissue is fat-storing cells or adipocytes that predominate
• • Brown adipocytes are polygonal and generally smaller than white adipocytes
• • Brown adipose tissue produces heat by nonshivering thermogenesis
• • Brown adipocytes have greatly upregulated levels of the transmembrane protein uncoupling protein-1 (UCP1) or thermogenin, leading to greater heat production
• • Brown adipose tissue constitutes 2-5% of newborn body weight and is mainly located at the back, neck, and shoulders
• Adipose Tissue

  
• Linking Anchoring - short collagens that link fibrillar collagens to one another and to other components of the ECM

  *Type VII, IX, XII, and XIV

  
• Fibrillar - have polypeptide subunits that aggregate to form large fibrils

  *Type I, II, III, V, and IX

  
• Network or Sheet-Forming - subunits produced by epithelial cells and major structural proteins of the external laminae and all epithelial basal laminae

  *Type IV and X

  
• Types of Fibers

  
• CATEGORIES OF RESIDENT

  
• Fibroblast - Round

  Fibrocyte - Spindle-shaped

  Macrophage - oval/kidney-bean (VARY)

  Monocyte - Horse-shoe shaped

  Mast - Oval

  Plasma - spherical

  Leukocytes - round