2,701 articles
Artificial heart valve
Artificial heart valve: prosthetic replacement for diseased native valves, mechanical or biological. First commercial device was the Starr-Edwards caged ball valve, implanted by Albert Starr in 1960; TAVR now delivers tissue valves by catheter.
Ascending aorta
Ascending aorta: first aortic segment from the left ventricle to about T4, ~3.5 cm wide, coronary arteries from its sinuses; aneurysm surgery at 5.0-5.5 cm, Bentall or valve-sparing repair.
Astigmatism
Astigmatism is a refractive error in which light focuses at two perpendicular lines in the eye, causing blur. Most common refractive error, about 40% adult prevalence; corrected with cylindrical glasses, toric contact lenses, or surgery.
Astrocyte
Astrocyte: star-shaped glial cell of the CNS, named by Lenhossek in 1891; maintains brain homeostasis by clearing 80% of extracellular glutamate, feeding neurons glutamine, and reacting in disease.
Astrocytoma
Astrocytoma is a glioma that forms in star-shaped astrocyte cells of the brain and spinal cord, graded from slow-growing pilocytic tumors in children to fast-spreading glioblastoma in adults.
Astrocytoma grade 2
Astrocytoma grade 2 (diffuse astrocytoma, IDH-mutant, CNS WHO grade 2) is a slow-growing infiltrative brain glioma defined by IDH1/2 mutation, frequent ATRX/TP53 changes, no 1p/19q codeletion, and few mitoses; treated with surgery, deferred or early radiotherapy, temozolomide, or vorasidenib.
Asystole
Asystole (cardiac standstill, flatline) is the absence of cardiac electrical activity on ECG during cardiac arrest. A nonshockable rhythm with PEA; treated with CPR and early epinephrine, not defibrillation or pacing.
Ataxia
Ataxia is poor muscle control causing clumsy movement, usually from cerebellar damage; it spans hereditary forms (SCAs, Friedreich ataxia, ataxia-telangiectasia), acquired causes, and new drug approvals.
Atherectomy
Atherectomy: catheter-based removal of arterial plaque by cutting, shaving, sanding, or vaporizing; four device types (directional, rotational, orbital, laser) used in peripheral and coronary artery disease.
Atherosclerosis
Atherosclerosis: chronic inflammatory arterial disease caused by retention of apoB lipoproteins (LDL, remnants, Lp(a)) in the intima, forming plaques that rupture; statins cut events 22% per mmol/L LDL-C.
Atherosclerosis of renal artery
Atherosclerosis of the renal artery (atherosclerotic renal artery stenosis, ARAS): plaque narrowing the renal arteries, causing about 90% of renal artery stenosis and secondary hypertension; treated mainly with medical therapy, revascularization reserved for select high-risk patients.
Athletic heart syndrome
Athletic heart syndrome, or exercise-induced cardiac remodeling, is the physiological heart enlargement and electrical change from repetitive strenuous training, first described by Henschen in 1899, and distinguished from cardiomyopathy by reversibility with detraining.
Atlas (anatomy)
Atlas (C1), first cervical vertebra: a ring-shaped bone with no body or spinous process that supports the skull, articulates with the occipital condyles and axis, and provides about half of head rotation.
Atonia
Atonia is the complete loss of muscle tone, an ICD-11 symptom code (MB45.2) and a normal feature of REM sleep. Its failure causes REM sleep behavior disorder; inappropriate activation causes cataplexy in narcolepsy.
Atrial natriuretic peptide
Atrial natriuretic peptide (ANP, atrial natriuretic factor), a 28-amino-acid cardiac hormone discovered by de Bold in 1981, released on atrial stretch, acting via NPR-A and cGMP to drive natriuresis, vasodilation, and RAAS inhibition.
Atrial septal aneurysm
Atrial septal aneurysm (interatrial septal aneurysm): congenital bulging of the heart's atrial septum over 10 mm into an atrium. Found in about 2.4% of adults by echocardiography; with patent foramen ovale it raises cryptogenic stroke and recurrence risk.
Atrial tachycardia
Atrial tachycardia (AT) is a supraventricular arrhythmia with regular atrial rates above 100 bpm and P waves originating outside the sinus node, caused by automaticity, triggered activity, or microreentry; classified as focal or macroreentrant, treated with drugs and catheter ablation.
Atrioventricular node
The atrioventricular node, or AV node, is a mass of cardiac muscle at the base of the atrial septum that conducts electrical impulses from the atria to the ventricles.
Atrioventricular reentrant tachycardia
Atrioventricular reentrant tachycardia (AVRT), the reentrant arrhythmia of Wolff-Parkinson-White syndrome, uses an accessory pathway plus the AV node as a macroreentrant circuit; orthodromic forms are narrow-complex, antidromic wide-complex, and radiofrequency ablation is curative.
Atrioventricular septal defect
Atrioventricular septal defect (AVSD), also called AV canal or endocardial cushion defect, is a congenital heart defect with holes between heart chambers and a common five-leaflet AV valve, common in Down syndrome, repaired surgically in infancy.
Atrioventricular septum
Atrioventricular septum: septal heart structure between right atrium and left ventricle at the crux, partly membranous and partly muscular. Defects (AVSD) cause 0.24–0.31/1000 live-birth congenital heart disease, strongly linked to Down syndrome; repair mortality about 3%.
Atrium (heart)
Atrium (heart): the two upper heart chambers (right and left atrium) that collect incoming blood. Distinct right pectinate muscles versus smooth left walls, three-phase reservoir-conduit-booster function, and the left atrial appendage as the main AF thrombus site.
Attention, perception & psychophysics
Attention, Perception, & Psychophysics (AP&P), formerly Perception & Psychophysics (1966–2008), is the Psychonomic Society's peer-reviewed journal for sensory processes, perception, attention, and psychophysics, published by Springer, eight issues yearly, ISSN 1943-3921.
Attic perforation of tympanic membrane
Attic perforation of tympanic membrane (pars flaccida perforation, ICD-11 AB13.1) is a hole in the upper, Shrapnell's membrane segment of the eardrum; an unsafe perforation with elevated risk of cholesteatoma and mastoiditis, usually managed surgically.
Auburn hair
Auburn hair is a reddish-brown human hair color produced by reduced eumelanin with substantial pheomelanin, often linked to one loss-of-function MC1R variant; deeper and browner than copper, darker-red than chestnut.
Audiology
Audiology: healthcare profession of hearing and balance care; audiologists diagnose and treat hearing, balance, tinnitus, and auditory disorders across all ages; doctoral (Au.D.) trained; shaped by the 2022 FDA OTC hearing aid category.
Auditory cortex
The auditory cortex is the region of the temporal lobe that receives and processes sound information from the ears, with primary area A1 on Heschl's gyrus.
Auditory fatigue
Auditory fatigue is a temporary loss of hearing sensitivity after sound exposure, measured as a temporary threshold shift in decibels that recovers over minutes to days.
Auditory scene analysis
Auditory scene analysis is the framework describing how listeners group a sound mixture into separate auditory streams, established in Albert Bregman's 1990 monograph and the basis of computational sound-separation systems.
Augusto, Michaela, and Lorenzo Odone
Augusto, Michaela, and Lorenzo Odone: the family behind Lorenzo's oil, a 4:1 trioleate/trierucate mixture for adrenoleukodystrophy, the 1992 film, and the Myelin Project.