Connective Tissue Overview

Connective Tissue

• Connective tissues are diverse tissues with multiple functions, including binding & supporting, protection, insulation, storage, and transport.
• Four main types: connective tissue proper, cartilage, bone, and blood.
• Originate from mesenchyme (embryonic tissue).
• Vary in vascularity.
• All have an extracellular matrix separating living cells, providing resistance to stress.
• Comprised of three main components: ground substance, fibres, and cells.

Ground Substance

• Unstructured material filling spaces between cells.
• Contains interstitial fluid, cell adhesion proteins (e.g., holding cells to the matrix), and proteoglycans.
• Proteoglycans have a protein core with glycosaminoglycans (GAGs).
• GAGs are negatively charged, trapping water, increasing viscosity (e.g., hyaluronic acid).

Fibres

• Provide support to structures.
• Collagen: Strongest and most common, most abundant animal protein. Forms bundles, cross-links for high tensile strength. Types differ in structure and location.
  • Type I: skin, tendons, bone, ligaments, dentin
  • Type II: cartilage, vitreous humor
  • Type III: skin, muscle, blood vessels
  • Type IV: basal laminae
  • Type IX: cartilage, vitreous humor
• Elastic: Long, thin, branching network. Allow stretch (elastin) limited by collagen. Return to original shape when relaxed. Found in skin, lungs, blood vessels.
• Reticular: Continuous, branched network of collagen fibers. Provides support around blood vessels and soft tissues.

Cartilage

• Resists tension and compression.
• Density falls between connective tissue and bone.
• Lacks nerves and blood vessels (repair slow).
• Calcifies (turns to bone) with age.
• Types:
  • Hyaline: Most common; supports, reinforces. Found in ends of long bones, nose, larynx, trachea.
  • Elastic: Similar to hyaline but with more elastic fibers. Maintains shape while flexible; found in ear (pinna), epiglottis.
  • Fibrocartilage: Less dense than hyaline. Compressible and resists tension; absorbs compressive shock, withstands pressure. Found in intervertebral discs, knee.

Bone

• Also called osseous tissue, provides support and protection.
• Contains cavities for fat storage & blood cell synthesis.
• Matrix similar to cartilage but denser.
• Contains calcium salts (bone salts).
• Has central canals with blood vessels and nerves.

Bone Functions

• Anchorage: Attachment site for skeletal muscles. Forms levers.
• Production: Haematopoiesis (blood formation) in bone marrow.
• Hormones: Influences insulin secretion, glucose homeostasis, and energy use.
• Storage: Triglycerides (energy store), calcium, and phosphates (blood ions replenishment).

Skeleton

• Two groups:
  • Axial: Forms central axis of the body (skull, vertebral column, ribcage). Provides protection and support.
  • Appendicular: Includes upper and lower limbs, and girdles (shoulders and hips). Primarily for locomotion and movement.