Connective Tissue

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Intro to CT - Body's Framework

  • Connective Tissue (CT): Body's framework, providing structural & metabolic support to organs and other tissues.
  • Origin: Predominantly mesodermal.
  • Key Functions:
    • Binding & Supporting (e.g., tendons, ligaments)
    • Protecting (e.g., bone, cartilage)
    • Insulating (e.g., adipose tissue)
    • Transporting substances (e.g., blood)
  • Two Main Components:
    • Cells: Diverse population (e.g., fibroblasts, adipocytes, chondrocytes, osteocytes, blood cells).
    • Extracellular Matrix (ECM): Non-living material surrounding cells, produced by them.
      • Fibers: Collagen (tensile strength), Elastic (recoil), Reticular (delicate framework).
      • Ground Substance: Hydrated, amorphous gel (proteoglycans, glycosaminoglycans (GAGs), adhesive glycoproteins like fibronectin). Components of Connective Tissue Diagram

⭐ The Extracellular Matrix (ECM), comprising fibers and ground substance, dictates the specialized physical properties of each connective tissue type (e.g., rigidity of bone, resilience of cartilage).

CT Components: Cells - The Living Units

  • Fixed Cells (Resident): 📌 FAMM
    • Fibroblasts/Fibrocytes: Most common. Synthesize ECM (collagen, elastin). Fibroblast (active, RER) vs. Fibrocyte (inactive). Myofibroblasts: wound contraction.
    • Adipocytes: Store triglycerides. Unilocular (white fat): single large droplet, signet ring. Multilocular (brown fat): multiple droplets, thermogenesis.
    • Mast Cells: Oval; granules (histamine, heparin). IgE receptors. Allergic reactions. Metachromasia.
    • Macrophages (Histiocytes): Phagocytic; antigen presentation. From monocytes. Kidney-shaped nucleus. (e.g., Kupffer).
  • Wandering Cells (Transient):
    • Plasma Cells: From B-lymphocytes. Antibody (Ig) synthesis. Eccentric "clock-face" nucleus, basophilic cytoplasm, Golgi halo.
    • Leukocytes: Neutrophils, Lymphocytes. Immune response via blood migration.

Connective Tissue Cell Lineages

⭐ Mast cell granules contain preformed mediators like histamine (vasodilator, ↑ vascular permeability) and heparin (anticoagulant).

CT Fibers & Matrix - Matrix Marvels

Fibers: The Framework

  • Collagen Fibers: Most abundant protein; tensile strength.
    • Type I: Bone, Skin, Tendon, Dentin, Cornea. (Strongest)
    • Type II: Cartilage, Vitreous body (📌 Cartwolage)
    • Type III: Reticular fibers (skin, vessels) (📌 R3ticular)
    • Type IV: Basement membrane (📌 Type 4 on the floor)
    • Vit C needed for synthesis; deficiency → Scurvy.
  • Elastic Fibers: Elastin + Fibrillin; stretch & recoil.
    • Locations: Large arteries, lungs, skin.
    • Fibrillin-1 defect → Marfan Syndrome.
  • Reticular Fibers: Type III collagen; delicate meshwork.
    • Locations: Liver, spleen, lymph nodes. Argyrophilic.

Ground Substance: The Gel

  • Amorphous, hydrated gel. Components:
    • Glycosaminoglycans (GAGs): Long unbranched polysaccharides.
      • Hyaluronic acid: Largest, non-sulfated. Synovial fluid, vitreous.
      • Sulfated GAGs: Chondroitin, Dermatan, Heparan, Keratan sulfates.
    • Proteoglycans: Core protein + GAGs (e.g., Aggrecan).
    • Multiadhesive Glycoproteins: Link cells to ECM (e.g., Fibronectin, Laminin).

⭐ Osteogenesis Imperfecta ("Brittle Bone Disease") is primarily due to defects in Type I collagen synthesis, leading to fragile bones, blue sclerae, and hearing loss.

Collagen hierarchy from molecule to tendon

Classification of CT - The Tissue Tapestry

Connective tissues are diverse, classified by cell type, fiber density, and matrix.

  • Embryonic CT:
    • Mesenchyme: Undifferentiated; gives rise to all other CT types.
    • Mucoid CT: Gelatinous; e.g., Wharton's jelly (umbilical cord).
  • CT Proper:
    • Loose CT: Fewer fibers, more ground substance. (Areolar, Adipose, Reticular)
    • Dense CT: More fibers, less ground substance. (Regular, Irregular, Elastic)
  • Specialized CT:
    • Cartilage: Avascular; (Hyaline, Elastic, Fibrocartilage).
    • Bone: Mineralized matrix; (Compact, Spongy).
    • Blood: Fluid matrix (plasma).

⭐ Wharton's jelly, a type of mucoid connective tissue, is rich in hyaluronic acid and proteoglycans, providing cushioning to umbilical cord vessels.

Histology: Epithelial, Connective, Muscle, Nervous Tissue

High‑Yield Points - ⚡ Biggest Takeaways

  • Connective tissue, derived from mesoderm, is the most abundant in the body.
  • Collagen Type I is the most common, found in bone, skin, and tendon.
  • Elastic fibers (elastin, fibrillin) provide recoil; Marfan syndrome involves fibrillin-1 defect.
  • Reticular fibers (Collagen Type III) form supportive networks in organs like liver, spleen.
  • Ground substance consists of GAGs (e.g., hyaluronic acid), proteoglycans, and glycoproteins.
  • Fibroblasts are the principal cells, responsible for ECM synthesis.
  • Mast cells contain histamine and heparin, mediating allergic and inflammatory responses.

Practice Questions: Connective Tissue

Test your understanding with these related questions

Intermediate filaments in connective tissue are which type of structural component?

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Flashcards: Connective Tissue

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What type of cartilage contains fibroblasts and chondrocytes?_____

TAP TO REVEAL ANSWER

What type of cartilage contains fibroblasts and chondrocytes?_____

Fibrocartilage

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