Dictionary

vena cava syndrome, superior See superior vena cava syndrome.

vena cava, superior The large vein that returns blood to the right atrium of the heart from the head, neck, and both upper limbs. The superior vena cava is located in the middle of the chest and is surrounded by rigid structures and lymph nodes. Structures bordering the superior vena cava include the trachea, aorta,…

vena cava, inferior The large vein that receives blood from the lower extremities, pelvis, and abdomen and then empties that blood into the right atrium of the heart.

velvet ant A parasitic wasp that is common in most parts of the world, including the southern and southwestern US. Velvet ant stings can trigger allergic reactions that vary greatly in severity. Avoidance and prompt treatment are essential. In selected cases, allergy injection therapy is highly effective.

vein A blood vessel that carries blood that is low in oxygen content from the body back to the heart. The deoxygenated form of hemoglobin (deoxyhemoglobin) in venous blood makes it appear dark. Veins are part of the afferent wing of the circulatory system, which returns blood to the heart. In contrast, an artery is…

VEG-F Vascular endothelial growth factor.

vector In medicine, a carrier of disease or of medication. For example, in malaria a mosquito is the vector that carries and transfers the infectious agent. In molecular biology, a vector may be a virus or a plasmid that carries a piece of foreign DNA to a host cell.

VDRL test Venereal Disease Research Laboratory test, a blood test for syphilis. A negative (nonreactive) VDRL test is compatible with a person not having syphilis. However, a person may have a negative VDRL and still have syphilis because in the early stages of the disease, the VDRL often gives false negative results. The VDRL test…

VBAC Vaginal birth after caesarean section. See caesarean section, vaginal birth after.

vasovagal syncope The temporary loss of consciousness in a particular kind of situation (situational syncope, or fainting) due to a vasovagal reaction. See also syncope.

vasovagal reaction A reflex of the involuntary nervous system that causes the heart to slow down and, at the same time, affects the nerves to the blood vessels in the legs, permitting those vessels to dilate (widen). As a result, the heart puts out less blood, the blood pressure drops, and the blood that is…

vasovagal attack See vasovagal reaction.