The dynamic structure of arterioles

Abstract

Arterioles are the blood vessels in the arterial side of the vascular tree that are located proximal to the capillaries and, in conjunction with the terminal arteries, provide the majority of resistance to blood flow. Consequently, arterioles are important contributors to the regulation of mean arterial pressure and tissue perfusion. Their wall consists of cellular and extracellular components that have been traditionally classified as conforming three layers: an intima containing endothelial cells sited on a basement membrane; a media made of an internal elastic lamina apposed by one or two layers of smooth muscle; and an adventitia composed mostly of collagen bundles, nerve endings and some fibroblasts. These components of the arteriolar wall are dynamically interconnected, providing a level of plasticity to the arteriolar wall that blurs the traditional boundaries of a rigid layered classification. This MiniReview focuses on the structural conformation of the arteriolar wall and shows how wall components interact spatially, functionally and temporally to control vascular diameter, regulate blood flow and maintain vascular permeability.

Figure

Schematic representation of an arteriole with tone. The wall of the vessel consists of cellular and extracellular components. Depicted are endothelial cells that run parallel to the longitudinal axis of the vessel in the luminal side and sit on a basement membrane apposed by an internal elastic lamina. Fenestrae in the internal elastic lamina allow for endothelial cells to make contact with smooth muscle cells that sit on the abluminal side of the lamina. Smooth muscle cells are spindled shaped and arranged transversal to the longitudinal axis of the vessel. Notice that smooth muscle cells have, on the luminal side, evenly distributed dense bodies that make contact with the internal elastic lamina at points where ridges on the lamina are made as the vessel is constricted. These dense bodies are connected to cytoskeletal stress fibers within the smooth muscle cells for the transmission of forces in and out of the cell. Abluminally, smooth muscle cells connect through dense bodies with extracellular components of the adventitia and external elastic lamina whenever one is present. Within the adventitia notice the presence of fibroblasts that are arranged mostly parallel to the longitudinal axis of the vessel.