Connective Tissue

Keeping it all together

Of the major tissue types, the connective tissue group plays a unique and vital role in defining the body’s form, maintaining the integrity and placement of organs, and providing cohesion and support throughout its internal components.

All connective tissues are composed of three elements: extracellular fibers; a gel-like material known as ground substance; and a complement of stationary and migrating cells. The relative proportions of these components found in a given part of the body depend on the structural requirements of that site.

Connective tissue can be separated into two subtypes: connective tissue proper and special connective tissue.

• Connective tissue proper varies only by its compositional balance:
  • Loose connective tissue contains more ground substance and relatively little fibrous material
  • Dense connective tissue (such as that found in ligaments and tendons) is more fibrous, surrounded by a minimal amount of ground substance matrix.
• Special connective tissue includes tissue types more specific to location and function:
  • Reticular connective tissue (fine-meshed networks around cell groups)
  • Adipose (fat) tissue
  • Cartilage
  • Bone
  • Blood and lymph (“liquid connective tissues” not always grouped with others in the special tissue subtype)

The cellular connection

Cells themselves are an integral component of connective tissue and are subdivided according to their capacity for movement, or not.

• Stationary cells include:
  • Fibroblasts – Elongate, spindle-shaped cells responsible for secreting constituents of the ground substance; believed to play a role in scar formation to protect wounded tissue
  • Adipose (fat) cells – Involved in the synthesis and storage of the body’s nutrient reserves, converting glucose and fatty acids into lipid

• Migrating cells are able to move throughout the extracellular spaces within loose connective tissue, and include:
  • Mast cells – Histamine and heparin-containing cells that influence vascular permeability and inhibit blood clotting; instrumental in inflammation and swelling reactions
  • Eosinophils – A type of leukocyte (white blood cell) that enters connective tissue through capillary walls; produce hydrolytic enzymes that break down antigen-antibody complexes
  • Macrophages – vital to tissue repair and defense against bacterial invasion; engulf bacterial cells, debris, other foreign substances and digest them in a process called phagocytosis.