Vöðvalagið

Vöðvalagið refers to the muscular layer of the walls of hollow organs, most commonly the tunica muscularis of the gastrointestinal tract and the tunica media of blood vessels. It consists mainly of smooth muscle cells and lies between the mucosa (and submucosa) and the outer connective tissue coat. The vöðvalagið is responsible for contractions that regulate movement and shape of the lumen.

In the gastrointestinal tract, vöðvalagið typically comprises two layers: an inner circular layer and an outer longitudinal layer. In the stomach, an additional oblique layer is present, which together with the other layers contributes to churning and propulsion of contents. The coordinated activity of these layers enables peristalsis, segmentation, and the function of sphincters formed by thickening of the muscular coat.

In blood vessels, the term corresponds to the tunica media, the middle coat of arteries and arterioles. This layer is rich in smooth muscle cells and elastic fibers and plays a central role in regulating vessel diameter. Contraction increases vascular resistance and blood pressure, while relaxation reduces resistance and flow. The tunica media is controlled by the autonomic nervous system and local mediators.

Development and innervation: smooth muscle cells of the vöðvalagið arise from mesodermal tissue and are innervated by the autonomic nervous system. In the GI tract, the enteric nervous system, including the myenteric (Auerbach) and submucosal (Meissner) plexuses, modulates muscular activity.

Clinical relevance: disorders of the vöðvalagið can affect motility, as in ileus or gastroparesis, or alter vascular tone, contributing to hypertension or vascular diseases. Diagnosis and treatment often target smooth muscle function and its neural regulation.