title: The structure of the suprarenal venous system and its possible functional significance.
abstract: The structure of the suprarenal venous system of 25 human suprarenal glands has been studied. From a structural point of view, four portions of the suprarenal vein have been distinguished: the proximal section, the hilus section, the section of the prehilus collaterals, and the distal section. In the hilus section and the section of the prehilus collaterals, the structure of the tunica media is more complex. In the hilus section, spiral fibres are found besides the longitudinal muscle fibres. Three strata of fibres can be observed in the section of the prehilus collaterals at the point where these veins drain into the central vein: two longitudinal strata, external and internal, and a third intermediate stratum corresponding to the looped fibres. The spiral and looped fibres, on contracting, can function as a sphincter. The longitudinal fibres, by means of the traction they exert on the stroma and connective capsule of the suprarenal, increase the intraglandular pressure while decreasing the periglandular pressure. A sympathetic stimulus provokes an increase in the secretion of adrenalin, and, at the same time, a contraction of the muscle fibres of the suprarenal venous system. Under these conditions, the venous return makes use of the emissary veins; and in this way, the secreted adrenalin establishes a close contact with the cortico-suprarenal parenchyma.
mesh_terms: D000311:Adrenal Glands / Q000033:anatomy & histology / Q000098:blood supply*; D003097:Collateral Circulation; D006801:Humans; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000033:anatomy & histology; D012039:Regional Blood Flow; D014680:Veins / Q000033:anatomy & histology* / Q000502:physiology