vein science definition

1. Any of the blood vessels that carry blood toward the heart from the body's cells, tissues, and organs. Veins are thin-walled and contain valves that prevent the backflow of blood. All veins except the pulmonary vein carry blood with low levels of oxygen.
2. One of the narrow, usually branching tubes or supporting parts forming the framework of an insect's wing or a leaf. Veins in insect wings carry hemolymph and contain a nerve. Veins in leaves contain vascular tissue, with the xylem usually occurring on the upper side of the vein (bringing in water and nutrients) and the phloem on the lower side (carrying away food). See more at leaf, venation.
3. A long, narrow deposit of mineral or rock that fills the void formed by a fracture or fault in another rock. The mineralogy of the host rock surrounding the vein is often altered where it is in contact with the vein because of chemical reactions between the two rock types.

Related Forms:

• venous venous adjective