interdigitations

Interdigitations are interlocking, finger-like projections that extend from two adjacent structures and nestle together at their boundary. The term, derived from Latin for “between fingers,” describes a pattern in which two tissues or cells interlock rather than meet as a simple edge. This arrangement increases the contact surface area and strengthens adhesion, facilitating mechanical stability and efficient exchange of nutrients, signals, or electrical impulses.

In biology and medicine, interdigitations occur at several interfaces, where close apposition of surfaces improves interaction. The interlocking process is supported by cell–cell junctions such as desmosomes and gap junctions, along with extracellular matrix components that reinforce the boundary.

notable examples

- Skin: at the dermal–epidermal junction, the epidermis forms rete ridges that interdigitate with dermal papillae. This interlocking increases bond strength, helps distribute mechanical stress, and enhances nutrient diffusion to the epidermis.

- Heart: cardiac muscle cells exhibit interdigitating folds at intercalated discs. The resulting interlocks, containing desmosomes and gap junctions, promote coordinated electrical propagation and synchronized contraction.

- Teeth: the dentinoenamel junction shows interdigitations between enamel and dentin, contributing to the integrity of the enamel–dentin boundary.

Clinical and developmental relevance

Interdigitations can change with aging or disease, potentially altering boundary strength or signaling. For example, thinning or flattening of dermal–epidermal interdigitations can accompany aging, while disruption of intercalated disc interlocks can affect myocardial function in certain cardiomyopathies. In development, increasing interdigitation at tissue interfaces often accompanies tissue maturation and improved mechanical integration.