Veins

A vein () is a blood vessel in the circulatory system of humans and most other animals that carries blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are those of the pulmonary and fetal circulations which carry oxygenated blood to the heart. In the systemic circulation, arteries carry oxygenated blood away from the heart, and veins return deoxygenated blood to the heart, in the deep veins.

medication administered into a vein

large veins (venous trunks) that return deoxygenated blood from the body into the heart

A venule is a very small vein in the microcirculation that allows blood to return from the capillary beds to drain into the venous system via increasingly larger veins. Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50 μm they can incorporate smooth muscle and are known as muscular venules. Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. Many venules unite to form a vein.

veins draining blood from the pelvis and lower limbs

vein running from the placenta to the fetus

Vein in the human fetus

veins deep in the body; contrasted with superficial veins

anatomical feature

veins close to the surface of the body

outer layer of blood vessel

rounded or irregular muscular columns which project from the inner surface of the right and left ventricles of the heart

technique of biometric identification

thumb|500px|Phleboliths (seen as punctiform calcifications) in the scrotum of an individual with varicocoele.A phlebolith is a small, focal, usually rounded, calcified thrombus within a vein. They are very common in the veins of the lower pelvis; however, phleboliths can also occur outside the pelvic region, including in the oral and maxillofacial (OMF) area. Phleboliths are often incidental findings and are most commonly detected on X-ray and CT imaging. They have distinct radiologic features that help distinguish them from other types of calcifications.

collection of skeletal muscles

medical test to determine the competency of the valves in the superficial and deep veins of the legs

Congregation of multiple veins

a network of valveless veins in the human body that connect the deep pelvic veins and thoracic veins to the internal vertebral venous plexuses