CONNECTIVE TISSUE

• The hair follicle is a tube-shaped structure in the skin that produces hair and is made up of:

  • The outer root sheath (L): a layer of connective tissue surrounding the hair follicle
  • The inner root sheath (D): a layer of epithelial cells surrounding the hair shaft
  • The hair shaft: the central part of the hair follicle made up of keratinized cells

  
• Areolar connective tissue is the most common type of connective tissue found in many parts of the body, including the skin, muscles, and organs

  
• Areolar connective tissue is made up of a network of collagen and elastin fibers surrounded by a gel-like substance called ground substance, which contains water, salts, and other nutrients
• Functions of connective tissue include:

  • Attachment of one tissue to another (e.g., ligaments, tendons)
  • Transport of fluids and materials (e.g., blood)
  • Defending the body from invading microorganisms (important in the immune system)
  • Storage of materials (e.g., fat)
  • Establishing a structural framework for the body (e.g., bones)
• Components of connective tissue:

  • Cells
  • Ground Substance
  • Fibers
• Cells of connective tissue include:

  • Fibroblasts: major cells that synthesize and secrete most components of the extracellular matrix
  • Fibrocytes: inactive form of fibroblasts
  • Adipocytes: specialized for storage of triglycerides
  • Mesenchymal cells: capable of differentiation into all supporting tissue cell types
• Macrophages are phagocytic cells that differentiate in connective tissue from precursor cells called monocytes and function in ECM turnover, phagocytosis, antigen presentation, and secretion of growth factors and cytokines
• Mast cells originate from blood cell precursors and release vasoactive agents and substances during inflammatory and allergic reactions
• Plasma cells differentiate from B lymphocytes and secrete specific antibodies called immunoglobulins
• Leukocytes provide surveillance against bacterial invaders, stimulate tissue repair, and include white blood cells and wandering cells like macrophages, mast cells, and plasma cells
• Ground substance in connective tissue is an amorphous transparent material with water-binding ability, composed of glycoproteins, complex carbohydrates, and:

  • Glycosaminoglycans (GAGs/Mucopolysaccharides)
  • Proteoglycans
  • Structural Glycoproteins
• The hair follicle is a tube-shaped structure in the skin that produces hair and is made up of:

  • The outer root sheath (a layer of connective tissue)
  • The inner root sheath (a layer of epithelial cells)
  • The hair shaft (central part made up of keratinized cells)

  
• Areolar connective tissue is made up of a network of collagen and elastin fibers surrounded by a gel-like substance called ground substance, containing water, salts, and other nutrients
• Areolar connective tissue is strong and flexible, supporting and protecting the organs and tissues of the body
• Types of connective tissue:

  • Loose connective tissue (areolar tissue) has relatively more ground substance than collagen, surrounds small blood vessels, and is flexible
  • Dense connective tissue has fewer cells, mostly fibroblasts, and a predominance of bundled type I collagen fibers over ground substance, protecting and strengthening organs structurally
• Reticular tissue consists of delicate networks of type III collagen, abundant in certain lymphoid organs where the fibers form attachment sites for immune cells
• Mucoid tissue is a gel-like connective tissue with few cells found around blood vessels, with abundant ground substance (Hyaluronan) and sparse collagen fibers
• Connective tissue originates from embryonic mesenchyme
• EXTRACELLULAR MATERIAL

  • Large Protein Fibers: elastic, collagen, reticular
  • Non-fibrous areas of unstained ground substance rich in Glycosaminoglycans and water
• Extracellular Matrix: Ground Substance + Large protein fibers
• FIBROBLAST has a more abundant and irregularly branched cytoplasm, containing much rough endoplasmic reticulum (RER) and a well- developed Golgi apparatus, with a large, ovoid, euchromatic nucleus and a prominent nucleolus.
• FIBROBLAST

  • the major cells of connective tissue proper
  • involved in wound healing, sometimes called myofibroblasts
  • are elongated, irregularly shaped cells with oval nuclei that synthesize and secrete most components of the ECM.
  • targets of many families of proteins called growth factors that influence cell growth and differentiation
• FIBROCYTE (QUIESCENT CELL)

  • Inactive form of Fibroblast

  • Smaller than the active fibroblast, is usually spindle-shaped with fewer processes, much less RER, and a darker, more heterochromatic nucleus
• ADIPOCYTES (FAT CELLS)

  • Very large cells specialized for storage of triglycerides

  • They predominate in a specialized form of connective tissue called adipose tissue
• MESENCHYMAL CELLS

  • Mesenchyme is the embryological tissue from which all types of supporting/connective tissue are derived.

  • are relatively unspecialized and are capable of differentiation into all supporting tissue cell types.
• MESENCHYMAL CELLS

  • have an irregular, star (stellate) or spindle (fusiform)shape, with delicate branching cytoplasmic extensions which form an interlacing network throughout the tissue.

  • nuclei have dispersed chromatin and visible nucleoli.

  • The matrix consists almost exclusively of blue-staining ground substance without mature fibers, facilitating diffusion of metabolites to and from developing tissues.
• MACROPHAGES

  • Phagocytic cells

  • short-lived cells that differentiate in connective tissue from precursor cells called monocytes.

  • function in ECM turnover, phagocytosis of dead cells and debris, and antigen presentation to lymphocytes; secretion of growth factors, cytokines, and other agents

  • “Histiocytes” are macrophages present in the connective tissue.
• MONONUCLEAR PHAGOCYTE SYSTEM

  • Monocyte- found in Blood and Precursor of macrophages
  • MACROPHAGE- found in Connective tissue, lymphoid organs, lungs, bone marrow, pleural and peritoneal cavities. It is responsible for the production of cytokines, chemotactic factors, and several other molecules that participate in inflammation(defense), antigen processing, and presentation
  • KUPFFER CELL- found in Liver(perisinusoidal); Same as macrophages
  • MICROGLIAL CELL- found Central Nervous System; Same as macrophages
• MONONUCLEAR PHAGOCYTE SYSTEM

  • LANGERHANS CELL - found in the Epidermis of skin; Antigen processing and presentation
  • DENDRITIC CELL- Lymph nodes, spleen Antigen processing and presentation
  • OSTEOCLAST (FROM FUSION OF SEVERAL MACROPHAGES) - found in Bone; Localized digestion of bone matrix
  • MULTINUCLEAR GIANT CELL (SEVERAL FUSED MACROPHAGES)- found in connective tissue under various pathological conditions; Segregation and digestion of foreign bodies