Intercellular Substances in Connective Tissue
The intercellular substances in connective tissue are collectively referred to as the extracellular matrix (ECM). The ECM is the most important component of connective tissue. It is responsible for the structural, functional, and pathological diversity of this tissue type. The ECM provides structural support to cells and acts as a medium for the diffusion of nutrients and waste products.
The ECM consists of two main components:
Protein fibres: These provide strength, elasticity, and support to the tissue.
Ground substance: This is a viscous, hydrated gel that fills the space between cells and fibres, providing a medium for the exchange of nutrients and waste products.
Protein Fibres
The three main types of protein fibres found in the ECM are:
Collagen fibres: These are the most abundant protein in the human body, accounting for 30% of its dry weight. They are strong and resistant to shearing and tearing forces. There are at least 28 types of collagen, each with a unique structure and function. The most common type, type I collagen, forms large bundles called collagen fibres that are commonly found in tendons, organ capsules, and the dermis.
Reticular fibres: These are composed primarily of type III collagen and form delicate, highly glycosylated networks. They are particularly abundant in lymphoid organs and other tissues where cells need to be supported in a flexible, three-dimensional framework. Reticular fibres stain black with silver salts, a property called argyrophilia.
Elastic fibres: These are composed of the protein elastin, which gives them their characteristic stretchability and resilience. Elastic fibres are often found in tissues that need to expand and contract, such as blood vessels, lungs, and skin.