Histology · Connective tissue, cartilage and bone

Extracellular matrix: collagen types, elastin, ground substance !

Topic

The extracellular matrix is the material between cells: fibres that give strength and stretch, and a gel that holds water.

Updated 2026-11-01

See it in 3D: Skin · Femur

What it is

The extracellular matrix is made of fibres (collagen, reticular and elastic) and ground substance (glycosaminoglycans, proteoglycans and glycoproteins such as fibronectin and laminin). Fibroblasts make most of it. Its make-up explains the strength of tendon, the recoil of the aorta and several inherited connective tissue diseases.

Structure

On H&E collagen appears as pink, wavy, cell-poor bundles; elastic and reticular fibres are hard to tell apart.
Reticular fibres are black with silver and PAS positive; elastic fibres black with Verhoeff; ground substance barely stains (it is lost in processing).
Elastin is laid down on a fibrillin-1 scaffold; it is abundant in the aorta, lung and skin.

Step by step

In the fibroblast's RER, alpha chains are made with the repeating glycine-X-Y sequence.
Proline and lysine are hydroxylated; the enzyme needs vitamin C.
Three chains wind into a triple helix (procollagen) and are secreted.
Outside the cell the ends are cut off, forming tropocollagen.
Lysyl oxidase, which needs copper, forms cross-links and the molecules gather into fibrils and fibres.

Collagen types

Type	Where	Feature	Disease
Type I	Bone, skin, tendon, dentin, cornea, mature scar	Most abundant; high tensile strength	Osteogenesis imperfecta (COL1A1, COL1A2)
Type II	Hyaline and elastic cartilage, vitreous humour, nucleus pulposus	Fine fibrils	Skeletal dysplasias from COL2A1
Type III	Reticular fibres of liver, spleen and lymph node; vessels; granulation tissue	Argyrophilic with silver	Vascular Ehlers-Danlos (COL3A1)
Type IV	Basal lamina	Forms a mesh, not fibrils	Alport syndrome; Goodpasture syndrome
Type V	Alongside type I in skin and tendon	Regulates fibril diameter	Classical Ehlers-Danlos (COL5A1, COL5A2)

Clinical notes

Scurvy: without vitamin C hydroxylation fails; bleeding gums, perifollicular haemorrhages and poor wound healing.
Marfan syndrome: faulty fibrillin-1; aortic dilatation, lens dislocation and tall stature.
Emphysema from alpha-1 antitrypsin deficiency: elastase destroys alveolar elastin.
Menkes disease: copper transport fails and lysyl oxidase cannot form cross-links.

Test yourself

Think of the answer, then tap the question to see it.

Which collagen type forms the basal lamina?

Type IV collagen, which forms a mesh instead of fibrils.

Why does vitamin C deficiency affect collagen?

It is needed to hydroxylate proline and lysine; without it the triple helix is unstable and connective tissue weakens.

Which collagen is altered in osteogenesis imperfecta?

Type I collagen, through variants in COL1A1 or COL1A2.

Which protein fails in Marfan syndrome?

Fibrillin-1, the scaffold on which elastic fibres are built.

Add to my cards (4)

See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of histology

Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: 4.3 Connective Tissue Supports and Protects (OpenStax (Rice University), 2022); Osteogenesis imperfecta (MedlinePlus Genetics (U.S. National Library of Medicine), 2024); Ehlers-Danlos syndrome (MedlinePlus Genetics (U.S. National Library of Medicine), 2024).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.