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Utricle (ear)
Utricle (ear): otolith organ of the vestibular labyrinth, with the saccule; its horizontal macula, striola, and otoconial membrane sense horizontal linear acceleration and head tilt, tested clinically by oVEMP and SVV.
Uveitis
Uveitis (iritis, choroiditis) is inflammation of the uvea, the eye's middle layer (iris, ciliary body, choroid). Causes include autoimmune disease, infection, injury, and lymphoma; treated with corticosteroids and steroid-sparing immunosuppressants.
Uvula
Uvula (palatine uvula), the teardrop of tissue hanging from the soft palate; secretes saliva, seals the nasopharynx during swallowing, aids gag reflex and uvular speech sounds; found only in humans.
Vagal maneuver
Vagal maneuvers (Valsalva, carotid sinus massage, diving reflex) are first-line physical techniques that raise vagal tone to terminate AV-node-dependent supraventricular tachycardia; the modified REVERT Valsalva converts about 43% versus 17% standard.
Vagal tone
Vagal tone is the vagus nerve's parasympathetic influence on the heart, estimated from HRV indices RMSSD, pNN50, and HF power; measured via ECG, tied to respiration, and distinct from wearable PRV.
Vagina
Vagina: the elastic muscular canal of the female reproductive tract, from vulva to cervix; also called birth canal. Distinct from the vulva; about 7-10 cm unaroused; no glands, lactobacilli-dominated microbiota; vaginitis is the most common disorder.
Vaginal contraction
Vaginal contraction: tightening of vaginal and pelvic floor muscles, voluntary or reflexive, occurring in orgasm, childbirth assessment, and vaginismus; measured by manometry and sEMG.
Vaginal lubrication
Vaginal lubrication, also known as vaginal wetness or vaginal secretions, is the moistening of the vagina by fluid from blood plasma, increasing during sexual arousal to allow painless penetration.
Vagus nerve
Vagus nerve (cranial nerve X): longest cranial nerve, medulla to abdomen, sensory and parasympathetic fibers. Also covers vagus nerve stimulation, FDA-approved uses, and evidence quality.
Vagus nerve stimulation
Vagus nerve stimulation (VNS, taVNS) is electrical neuromodulation of the vagus nerve, FDA-approved since 1997 for drug-resistant epilepsy and later for depression, obesity, stroke rehabilitation, and rheumatoid arthritis, with about 46% of epilepsy patients achieving 50% seizure reduction.
Valsalva maneuver
Valsalva maneuver: forced expiration against a closed airway, first described by Antonio Maria Valsalva in 1704 for clearing the middle ear; now used in autonomic testing, murmur diagnosis, SVT treatment, and ear clearing.
Valvular heart disease
Valvular heart disease: stenosis or regurgitation of the heart valves. Also called heart valve disease. Affects ~41 million (rheumatic) to 24 million (mitral regurgitation) people; treated by SAVR, TAVR, TEER per 2025 ESC/EACTS guidelines.
VaMIS study
VaMIS (Västmanland Myocardial Infarction Study), NCT01452178, is a Swedish observational cohort of 1008 acute myocardial infarction patients with matched controls, recruited 2005–2011 in Västerås, studying type D personality, peripheral artery disease, and long-term outcomes; distinct from the VAMIS robotic surgery trial.
Variant Creutzfeldt–Jakob disease
Variant Creutzfeldt–Jakob disease (vCJD), also called human mad cow disease, is a fatal prion disease from BSE-contaminated beef, first described in the UK in 1996; 233 deaths worldwide, median age 28, transmissible by blood transfusion.
Vas deferens
Vas deferens, or ductus deferens, is a long muscular tube in men that carries mature sperm from the epididymis of each testicle to the urethra before ejaculation.
Vasa praevia
Vasa praevia (vasa previa): unprotected fetal blood vessels run through the amniotic membranes over the cervix. Types I–III; risk factors include IVF and low-lying placenta; ultrasound diagnosis and planned cesarean cut fetal mortality from over 60% to under 5%.
Vascular disease
Vascular disease covers conditions affecting arteries, veins, capillaries, and lymphatics, including atherosclerosis, aneurysm, PAD, and venous thrombosis; diagnosed by ABI and imaging, treated with lifestyle change, medicines, angioplasty, or surgery.
Vascular resistance
Vascular resistance: opposition of blood vessels to flow, R = (P1−P2)/Q. Covers systemic (SVR) and pulmonary (PVR) resistance, Poiseuille radius dependence, Wood units, and the >2 WU pulmonary hypertension threshold.
Vascular ring
Vascular ring: congenital aortic arch anomaly, mainly double aortic arch or right arch with aberrant left subclavian artery, encircling and compressing the trachea and esophagus; about 1% of congenital cardiac anomalies, treated surgically when symptomatic.
Vascular surgery
Vascular surgery: surgical specialty treating arteries, veins, and lymphatics via open operations (carotid endarterectomy, aneurysm repair) and catheter-based endovascular techniques; rooted in Carrel's 1902 anastomosis and transformed by Dotter's 1964 angioplasty and EVAR.
Vasoconstriction
Vasoconstriction is narrowing of blood vessels by smooth muscle contraction, controlled by sympathetic vasomotor nerves and hormones such as angiotensin, vasopressin, epinephrine, and norepinephrine; it conserves heat, limits bleeding, raises blood pressure, and was discovered in 1851-1852 by Bernard and Brown-Séquard.
Vasodilation
Vasodilation is widening of blood vessels from smooth muscle relaxation, lowering vascular resistance and blood pressure while increasing flow. Key mechanisms: NO–sGC–cGMP signaling, K+ channel hyperpolarization; quantified by flow-mediated dilation (~6.4% healthy).
Vasodilator-Heart Failure Trials
The Vasodilator-Heart Failure Trials (V-HeFT I and II) were 1986 and 1991 Veterans Affairs trials showing hydralazine plus isosorbide dinitrate reduced mortality in chronic heart failure.
Vasopressin
Vasopressin (antidiuretic hormone, ADH, arginine vasopressin) is a hypothalamic nonapeptide released by the posterior pituitary that drives renal water reabsorption via V2 receptors, vasoconstriction via V1a, and ACTH release via V1b; synthesized by du Vigneaud (1955 Nobel Prize).
Vasoproliferative tumor of the retina
Vasoproliferative tumor of the retina (RVPT), also called retinal vasoproliferative tumor, is a rare benign retinal vascular growth, typically in the peripheral retina, causing vision loss and floaters.
Vastus lateralis muscle
Vastus lateralis, the largest quadriceps femoris muscle of the lateral thigh, extends the knee, is innervated by the femoral nerve (L2–L4), supplied by the lateral circumflex femoral artery, and is the standard muscle biopsy site in research.
Vastus medialis
Vastus medialis, also vastus medialis obliquus (VMO), medial quadriceps muscle of the thigh extending the knee; femoral nerve L2-L4; disputed VMO/VML subdivision; ultrasound validated against MRI for its size.
Vein
Vein: blood vessel returning blood to the heart; pulmonary veins carry oxygen-rich blood. Holds about 70-75% of blood volume, has one-way valves, thin three-layered walls, and was central to Harvey's 1628 circulation discovery.
Vein of Galen aneurysmal malformations
Vein of Galen aneurysmal malformation (VGAM, vein of Galen malformation) is a rare congenital cerebral arteriovenous fistula draining into a persistent embryonic median prosencephalic vein, presenting with neonatal heart failure or infant hydrocephalus and treated mainly by transarterial embolization.
Velamentous cord insertion
Velamentous cord insertion (VCI): umbilical cord attaches to fetal membranes rather than the placenta, leaving vessels unprotected by Wharton's jelly; affects about 1.4% of singletons, more in twins and IVF, and raises risks of stillbirth, preterm birth, and vasa previa.