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Klippel–Trénaunay syndrome
Klippel–Trénaunay syndrome (KTS), also called angio-osteohypertrophy syndrome, is a rare congenital low-flow vascular malformation disorder with port-wine stains, venous malformations, and limb overgrowth, caused by somatic PIK3CA mutations within PROS.
Klumpke paralysis
Klumpke paralysis (Klumpke's palsy, Dejerine-Klumpke palsy): lower brachial plexus palsy of C8-T1 roots from hyperabduction traction or apical tumor compression, causing claw hand, medial hand sensory loss, and Horner syndrome.
Klüver–Bucy syndrome
Klüver–Bucy syndrome (KBS), a rare neuropsychiatric disorder from bilateral temporal lobe damage, causes hypersexuality, hyperorality, hyperphagia, visual agnosia, hypermetamorphosis, and placidity; first described in monkeys by Klüver and Bucy in 1937.
Knee
Knee: the largest human joint, a synovial hinge joining femur, tibia, and patella with ACL, PCL, collateral ligaments, and menisci; only human knee reaches full extension among compared mammals.
Koniocellular cell
Koniocellular (K) cells are the smallest relay neurons of the primate lateral geniculate nucleus, forming thin calbindin-rich layers between M and P layers; a heterogeneous third visual channel carrying blue-yellow color and other signals to V1 blobs, extrastriate cortex, and blindsight-related routes.
Korotkoff sounds
Korotkoff sounds, also known as Korotkov sounds, are pulsatile sounds heard over the brachial artery during blood pressure cuff deflation, described by Nikolai Korotkov in 1905; their onset marks systolic and their disappearance diastolic pressure.
Krabbe disease
Krabbe disease (globoid cell leukodystrophy) is a rare autosomal recessive GALC-deficiency leukodystrophy causing psychosine accumulation and demyelination; HSCT within the first weeks of life is the only disease-modifying treatment.
Kuru (disease)
Kuru is an acquired human prion disease, also called an endocannibalism-transmitted spongiform encephalopathy, once epidemic among the Fore people of Papua New Guinea; over 1,874 deaths, mean incubation 12.4 years, last case 2009.
L-type calcium channel
L-type calcium channels (Cav1.1–Cav1.4) are high-voltage-activated, dihydropyridine-sensitive voltage-gated calcium channels in muscle, heart, and neurons; Cav1.2 drives cardiac excitation-contraction coupling, and their blockers treat hypertension and angina.
Labia
Labia: the outer labia majora and inner labia minora, skin folds of the vulva protecting the urethral and vaginal openings. Highly variable in size (labia minora length roughly 20–100 mm); central to labiaplasty debates.
Labia minora
Labia minora: the inner folds of the vulva enclosing the vestibule, highly variable in size (length 5–100 mm) and richly innervated; also called nymphs, basis of labiaplasty.
Labyrinthitis
Labyrinthitis is acute inflammation of the inner-ear labyrinth, causing prolonged vertigo with sensorineural hearing loss or tinnitus, most often from viral infection and improving within weeks.
Lacrimal gland
The lacrimal gland, also called the tear gland, is an exocrine gland in the upper outer orbit that secretes the watery layer of tears and is targeted in Sjogren's syndrome.
Lacrimoauriculodentodigital syndrome
Lacrimoauriculodentodigital syndrome (LADD, Levy-Hollister syndrome) is a rare autosomal dominant disorder from FGFR2, FGFR3, or FGF10 mutations, causing lacrimal and salivary gland malformations, hearing loss, dental anomalies, and digital defects.
Laevocardia
Laevocardia (levocardia): cardiac position term for a heart lying in the left hemithorax, counterpart of dextrocardia and mesocardia; used in Van Praagh-style classification of congenital heart disease; distinct from the cockle genus Laevicardium.
Lagophthalmos
Lagophthalmos is incomplete eyelid closure, mainly from facial nerve paralysis (Bell's palsy), scarring, or sleep (nocturnal lagophthalmos), causing exposure keratopathy treated with lubricants, taping, tarsorrhaphy, or lid weights.
Lanugo
Lanugo is the fine, soft, unpigmented fetal hair, the first human hair type, anchoring vernix caseosa and shed around 33-36 weeks. In adults it signals anorexia, malnutrition, or rarely paraneoplastic hypertrichosis lanuginosa.
Large intestine
The large intestine (colon, bowel) is the terminal digestive tract organ, about 5 feet long, comprising cecum, colon, rectum, and anal canal; it absorbs water, electrolytes, and vitamins K and B, forms stool, and houses the gut microbiota.
Larynx
Larynx (voice box): cartilaginous organ at C3-C6 connecting pharynx to trachea; divided into supraglottis, glottis, subglottis; protects the airway, enables phonation; cricoid is the only complete airway ring; innervated by vagus branches.
Laser Corneal Surgery
Laser corneal surgery (LASIK, PRK/TransPRK, SMILE) reshapes the cornea with excimer or femtosecond lasers to correct myopia, hyperopia, and astigmatism; evidence shows comparable efficacy and predictability across modern techniques.
LASIK
LASIK (Laser-Assisted In Situ Keratomileusis) is eye surgery in which a hinged corneal flap is folded back and an excimer laser reshapes the cornea to treat refractive errors.
Lateral geniculate nucleus
Lateral geniculate nucleus (LGN), also lateral geniculate body: thalamic relay nucleus of the visual pathway, with six magnocellular, parvocellular, and koniocellular layers, sending optic radiations to primary visual cortex.
Lateral grey column
Lateral grey column (lateral horn, columna grisea lateralis medullae spinalis): small lateral projection of spinal cord grey matter at T1–L2/L3 containing preganglionic sympathetic neurons (intermediolateral cell column), with axons reaching the sympathetic trunk via white rami communicantes.
Lateral medullary syndrome
Lateral medullary syndrome, also called Wallenberg syndrome or PICA syndrome, is a brainstem stroke from blockage of the vertebral artery or PICA, causing vertigo, hoarseness, and difficulty swallowing.
Lateral pterygoid muscle
Lateral pterygoid muscle (musculus pterygoideus lateralis), a two-headed muscle of mastication in the infratemporal fossa; innervated by the lateral pterygoid nerve (CN V3), protrudes and depresses the mandible, and varies from one to four heads in about a quarter of people.
Laterality
Laterality: the scientific study of left-right asymmetries in brain, behavior, and cognition, from human handedness and language dominance to animal lateralization; also the name of the interdisciplinary journal founded in 1996 by Bryden, Corballis, and McManus.
Lateralization of brain function
Lateralization of brain function: task-specific hemispheric biases, with left-hemisphere language dominance in about 95% of right-handers and right-hemisphere spatial and face-processing advantages, distinct from the debunked left-brained versus right-brained personality myth.
Latissimus dorsi muscle
Latissimus dorsi, the broad flat back muscle (lats) spanning T6 to S5 and inserting on the humerus; thoracodorsal nerve and vessels; widely used as a flap in reconstructive surgery and for rotator cuff tendon transfer.
Lattice corneal dystrophy type I
Lattice corneal dystrophy type I (LCD1, Biber-Haab-Dimmer, classic lattice corneal dystrophy) is a rare autosomal dominant TGFBI (5q31, R124C) amyloid stromal corneal dystrophy causing lattice lines, erosions, and vision loss from the first decade, treated with PTK or keratoplasty.
Laurence Auzière-Jourdan
Laurence Auzière-Jourdan (born Laurence Auzière, 1977) is a French cardiologist in Nogent-sur-Marne, daughter of Brigitte Macron and stepdaughter of President Emmanuel Macron; married to radiologist Guillaume Jourdan, she keeps a low public profile.