a vessel through which blood passes from various organs or parts back to the heart, in the systemic circulation carrying blood that has given up most of its oxygen. Veins, like arteries, have three coats: an inner coat (tunica intima
), middle coat (tunica media
), and outer coat (tunica externa
); however, in veins these are less thick and collapse when the vessel is cut. Many veins, especially superficial ones, have valves formed of reduplication of their lining membrane. See Appendix 2-6 and see also Plates.
afferent v's veins that carry blood to an organ.
allantoic v's paired vessels that accompany the allantois, growing out from the primitive hindgut and entering the body stalk of the early embryo.
cardinal v's embryonic vessels that include the pre- and postcardinal veins and the ducts of Cuvier (common cardinal veins).
emissary vein one passing through a foramen of the skull and draining blood from a cerebral sinus into a vessel outside the skull. See anatomic Table of Veins in the Appendices.
postcardinal v's paired vessels in the early embryo that return blood from regions caudal to the heart.
precardinal v's paired venous trunks in the embryo cranial to the heart.
pulp v's vessels draining the venous sinuses of the spleen.
subcardinal v's paired vessels in the embryo, replacing the postcardinal veins and persisting to some degree as definitive vessels.
sublobular v's tributaries of the hepatic veins that receive the central veins of hepatic lobules.
supracardinal v's paired vessels in the embryo developing later than the subcardinal veins and persisting chiefly as the lower segment of the inferior vena cava.
thebesian v's smallest cardiac veins; see anatomic Table of Veins in the Appendices.
trabecular v's vessels coursing in splenic trabeculae, formed by tributary pulp veins.
vitelline v's veins that return the blood from the yolk sac to the primitive heart of the early embryo.
pertaining to the veins.
persistent dilatation of the vein but without necessarily any weakening of the wall or varicosity.
hepatic portal venous system
includes the veins from the alimentary tract, the portal vein, the sinusoids in the liver, the hepatic veins and then the entry into the caudal vena cava.
obstructed venous drainage
may be generalized or local; manifested by dilation, local edema.
orbital venous plexus
a plexus for venous drainage from the ophthalmic veins at the apex of the orbit; drains into the cavernous venous sinus within the cranium.
the flow of blood into the heart from the peripheral vessels.
venous return curves
relate venous return to atrial pressure; the inverse of the Starling relationship; an increase in atrial pressure decreases the venous return.
scleral venous plexus
a ring of small vessels around the corneal limbus which forms a link in the chain of vessels which drain the aqueous humor. Called also canal of Schlemm.
the bodily system of veins commencing with the venae cavae, thence through the large veins and their tributaries, and immediately subsequent to the capillaries, the venules.
the presence of a thrombus in a vein. Originates in phlebitis in most cases. It is a major problem in horses because of the high incidence of jugular phlebitis and periphlebitis as a result of injection of irritating materials. See also caudal
vena caval thrombosis.