Connective Tissue Overview and Components

Connective Tissue Overview

• Connective tissue is a diverse and abundant tissue providing structural support, tensile strength, and binding tissues together. It also plays roles in immune defense, metabolism, energy storage, and cushioning.
• Examples include bone, cartilage, blood, adipose tissue, and lymphatic tissue.

Components of Connective Tissue

• Cells: Various cell types, including fibroblasts (main cell in non-specialized tissue, producing and maintaining the extracellular matrix), fibrocytes (inactive fibroblasts), adipocytes (fat cells), macrophages (phagocytic immune cells), plasma cells (antibody producers), eosinophils (immune response), neutrophils (phagocytic), lymphocytes (B and T cells), mast cells (involved in inflammatory reactions), chondroblasts, osteoblasts, and odontoblasts in specialized tissues (cartilage, bone, and dentin respectively).
• Extracellular Matrix: A complex structure surrounding the cells, consisting of:
  • Ground Substance: A viscous substance filling spaces between cells, hydrophilic, and composed of water, glycosaminoglycans (GAGs), and proteoglycans. Its high water content and negative charge make it strong and resilient, resisting compressive forces and facilitating diffusion.
  • Fibres: Embedded in the ground substance, they include:
    • Collagen: The most abundant protein, providing high tensile strength, supporting flexibility, and arranged in various types (Type I in bone, Type II in cartilage).
    • Elastin: Thin, branched, providing elasticity allowing stretching (found in skin, ears, arteries, lungs, and bladder). Secreted as tropoelastin and polymerizes into elastin.
    • Reticular: Delicate, thin, forming frameworks for organs, glands, and blood vessels.

Classification of Connective Tissue Proper

• Density of Tissue:

  • Loose: Many cells, abundant ground substance, loosely arranged fibers. Functions in binding structures and facilitating diffusion. (e.g., lamina propria).
  • Dense: Fewer cells, less ground substance, more fibers. Subtypes based on fiber arrangement:
    • Regular: Fibers organized in parallel, providing tensile strength in a single direction (e.g., tendons, ligaments).
    • Irregular: Fibers arranged randomly, withstanding pressure from multiple directions (e.g., dermis).

• Adipose Tissue: Connective tissue specializing in energy storage.

  • White Adipose: Unilocular, stores fat in a single large droplet, most common in adults.
  • Brown Adipose: Multilocular, with smaller lipid droplets, mostly in newborns, specialized for thermogenesis (heat production).

Genetic Mutations and Connective Tissue

• Some genetic mutations affect the production of specific collagen types (e.g., Type I, II, III, and V), causing conditions like:
  • Osteogenesis Imperfecta: Brittle bone syndrome due to Type I collagen deficiencies.
  • Chondrodysplasia: Cartilage defects due to Type II collagen deficiencies.
  • Ehlers-Danlos Syndrome: Fragile, hyper-elastic skin and joint hypermobility due to defects in Type I, III or V collagen or fibrillin.
  • Marfan Syndrome: Affects tissues rich in elastic fibers, notably the aorta, increasing risk of aneurysms, skeletal defects, and hypermobile joints along with arachnodactyly.