CorpusHuman Anatomy
Cells & TissuesTissue

Connective tissue

Textus connectivus

Also known as: connective tissue proper, supporting connective tissue, stroma

The most abundant and diverse tissue: relatively few cells scattered in an abundant extracellular matrix of fibres and ground substance, which binds, supports, protects, stores energy and transports.

Overview

All connective tissues develop from embryonic mesenchyme and consist of cells plus extracellular matrix (ECM) — protein fibres (collagen, reticular, elastic) and ground substance (glycosaminoglycans, proteoglycans, adhesive glycoproteins and tissue fluid). Unlike epithelium, connective tissue is defined by its matrix, which determines its properties: fluid in blood, gel-like in areolar tissue, firm in cartilage, mineralised in bone. Most connective tissues are well vascularised; cartilage is avascular and dense regular connective tissue poorly vascularised.

Resident cells include fibroblasts (the main matrix-producing cell), adipocytes, macrophages (histiocytes), mast cells and mesenchymal stem cells; transient (wandering) cells — neutrophils, eosinophils, lymphocytes, plasma cells, monocytes — enter from the blood, especially during inflammation. Specialised connective tissues have their own cells: chondroblasts/chondrocytes, osteoblasts/osteocytes/osteoclasts and blood cells.

Classification: (1) embryonic — mesenchyme and mucous connective tissue (Wharton jelly of the umbilical cord); (2) connective tissue proper — loose (areolar, adipose, reticular) and dense (dense regular, dense irregular, elastic); (3) supporting — cartilage (hyaline, elastic, fibrocartilage) and bone; (4) fluid — blood and lymph.

Parts & subdivisions

  1. Areolar (loose) tissue
    Loosely arranged fibres, many cell types.
  2. Adipose tissue
    Fat storage, insulation, endocrine.
  3. Reticular tissue
    Type III collagen stroma of lymphoid organs and marrow.
  4. Dense regular
    Parallel collagen — tendons, ligaments.
  5. Dense irregular
    Interwoven collagen — dermis, capsules.
  6. Elastic tissue
    Elastic fibres — large arteries, ligamenta flava.
  7. Cartilage
    Hyaline, elastic, fibrocartilage.
  8. Bone
    Mineralised connective tissue.
  9. Blood
    Fluid connective tissue.
  10. Extracellular matrix
    Fibres + ground substance.

Anatomy

Development

Derived from mesenchyme, which arises chiefly from mesoderm (paraxial, lateral plate) and, in the head and neck, from neural crest (ectomesenchyme).

Function

  • Binding and structural support (tendons, ligaments, capsules, stroma).
  • Protection (bone, cartilage, fat pads) and immune defence (macrophages, mast cells, lymphocytes).
  • Energy storage and thermal insulation (adipose tissue).
  • Transport of nutrients, gases, hormones and wastes (blood) and fluid reservoir (ground substance).
  • Repair — scar formation by fibroblasts.

Clinical significance

Heritable disorders of connective tissue

Marfan syndrome (FBN1, fibrillin-1), Ehlers–Danlos syndromes (collagen types I, III, V and processing enzymes), osteogenesis imperfecta (COL1A1/COL1A2), Loeys–Dietz syndrome (TGF-β receptor).

"Connective tissue diseases"

A clinical group of autoimmune disorders with inflammation of connective tissues and vessels: SLE, systemic sclerosis (excess collagen deposition, fibrosis), dermatomyositis, Sjögren syndrome, mixed connective tissue disease.

Oedema

Interstitial fluid accumulates in the ground substance of loose connective tissue when capillary filtration exceeds lymphatic drainage (raised venous pressure, low plasma albumin, lymphatic obstruction).

Compiled from standard anatomy and physiology references — see the Cells & Tissues sources. For education only; not medical advice.