einstülpung

Einstülpung is the German term for the inward folding of a sheet of cells or tissue, producing an internal cavity, pouch, or tube. In English, the process is commonly referred to as invagination. The term is used primarily in embryology and anatomy to describe how an epithelium folds inward during development, although related inward movements are also described with terms such as involution in different contexts.

In developmental biology, Einstülpung drives the formation of body plans and organs. During gastrulation, for example, an epithelial layer invaginates to form the archenteron, giving rise to the gut and related structures. In vertebrates, neurulation involves the folding and infolding of the neural plate to generate the neural tube. The cellular basis often involves apical constriction, changes in cell adhesion, rearrangements of neighboring cells, and remodeling of the extracellular matrix, collectively shaping tissue curvature and tube formation.

Pathologically, invagination can occur abnormally, most notably as intussusception, where a segment of intestine telescopes into an adjacent segment, causing obstruction and potentially cutting off blood supply. Such invaginations can arise from developmental errors, altered peristalsis, or other intestinal disturbances. In other organs and after injury, localized evaginations or invaginations may contribute to scar formation or ductal remodeling.

Etymology: from ein- “in” and Stülpung “folding,” reflecting inward folding. In clinical and anatomical writing, einstülpung is often used as the German equivalent of invagination.