vagina: A muscular tube extending between the uterus and the vestibule.

varicose veins: Distended superficial veins.

vasa recta: Long, straight capillaries that parallel the loop of Henle in juxtamedullary nephrons.

vasa vasorum: Blood vessels that supply the walls of large arteries and veins.

vascular: Pertaining to blood vessels.

vascularity: The blood vessels in a tissue.

vascular spasm: A contraction of the wall of a blood vessel at an injury site; may slow the rate of blood loss.

vasoconstriction: A reduction in the diameter of arterioles due to the contraction of smooth muscles in the tunica media; elevates peripheral resistance; may occur in response to local factors, through the action of hormones, or from the stimulation of the vasomotor center.

vasodilation: An increase in the diameter of arterioles due to the relaxation of smooth muscles in the tunica media; reduces peripheral resistance; may occur in response to local factors, through the action of hormones, or after decreased stimulation of the vasomotor center.

vasomotion: Changes in the pattern of blood flow through a capillary bed in response to changes in the local environment.

vasomotor center: The center in the medulla oblongata whose stimulation produces vasoconstriction and an elevation of peripheral resistance.

vein: A blood vessel carrying blood from a capillary bed toward the heart.

vena cava: One of the major veins delivering systemic blood to the right atrium; superior and inferior venae cavae.

ventilation: Air movement into and out of the lungs.

ventral: Pertaining to the anterior surface.

ventricle: A fluid-filled chamber; in the heart, one of the large chambers discharging blood into the pulmonary or systemic circuits; in the brain, one of four fluid-filled interior chambers.

ventricular escape: The initiation of ventricular contractions after a pause caused by impaired conduction of the contractile stimulus from the AV node.

ventricular folds: Mucosal folds in the laryngeal walls that do not play a role in sound production; the false vocal cords.

venule: Thin-walled veins that receive blood from capillaries.

vermiform appendix: A blind tube connected to the cecum of the large intestine; also called appendix.

vermis: A midsagittal band of neural cortex on the surface of the cerebellum.

vertebral canal: The passageway that encloses the spinal cord; a tunnel bounded by the neural arches of adjacent vertebrae.

vertebral column: The cervical, thoracic, and lumbar vertebrae, the sacrum, and the coccyx.

vertebrochondral ribs: Ribs 8–10; false ribs, connected to the sternum by shared cartilaginous bars.

vertebrosternal ribs: Ribs 1–7; true ribs, connected to the sternum by individual cartilaginous bars.

vertigo: Dizziness.

vesicle: A membranous sac in the cytoplasm of a cell.

vestibular complex: The utricle, saccule, and semicircular canals of the inner ear.

vestibular duct: The perilymph-filled chamber of the inner ear, superior to the vestibular membrane; pressure changes there result from distortions of the oval window; also called scala vestibuli.

vestibular membrane: The membrane that separates the cochlear duct from the vestibular duct of the inner ear.

vestibular nucleus: The processing center for sensations that arrive from the vestibular apparatus of the inner ear; located near the border between the pons and the medulla oblongata.

vestibule: A chamber; in the inner ear, the utricle and saccule.

vestibulospinal tracts: Descending tracts of the medial pathway that carry involuntary motor commands issued by the vestibular nucleus to stabilize the position of the head.

villus/villi: A slender projection of the mucous membrane of the small intestine.

virus: A noncellular pathogen.

viscera: Organs in the ventral body cavity.

visceral: Pertaining to viscera or their outer coverings.

visceral smooth muscle: A smooth muscle tissue that forms sheets or layers in the walls of visceral organs; the cells may not be innervated, and the layers often show automaticity (rhythmic contractions).

viscosity: The resistance to flow that a fluid exhibits as a result of molecular interactions within the fluid.

viscous: Thick, syrupy.

vital capacity: The maximum amount of air that can be moved into or out of the respiratory system; the sum of the inspiratory reserve, the expiratory reserve, and the tidal volume.

vitamin: An essential organic nutrient that functions as a coenzyme in vital enzymatic reactions.

vitreous humor: The gelatinous mass in the vitreous chamber of the eye.

vocal folds: Folds in the laryngeal wall that contain elastic ligaments whose tension can be voluntarily adjusted; the true vocal cords, responsible for phonation.

voluntary: Controlled by conscious thought processes.

vulva: The female pudendum (external genitalia).