2,701 articles
Achromatopsia
Achromatopsia (ACHM, rod monochromatism, total color blindness) is a rare autosomal recessive retinal disorder of cone photoreceptors causing color blindness, low acuity, photophobia, and nystagmus; mainly caused by CNGA3 and CNGB3 variants, with gene therapy trials underway.
Acid-Base Equilibrium
Acid-base equilibrium, or acid-base homeostasis, is the physiological steady state of hydrogen ion concentration maintained by buffers, lungs, and kidneys, analyzed via Henderson-Hasselbalch or Stewart approaches.
Acoustic reflex
Acoustic reflex: involuntary stapedius (and tensor tympani) contraction to loud sound, measured as thresholds of 85-100 dB SPL at 500-2000 Hz; used to diagnose middle-ear, cochlear, and retrocochlear disorders.
Acquired progressive lymphangioma
Acquired progressive lymphangioma, also known as benign lymphangioendothelioma, is a rare, non-cancerous, slowly growing tumor of lymphatic vessels that appears as red or bruise-like skin plaques.
Acquired stenosis of external auditory canal
Acquired stenosis of external auditory canal (ICD-11 AA40.1): post-inflammatory, postsurgical, post-traumatic, or radiation narrowing of the ear canal lateral to the tympanic membrane, causing otorrhea and conductive hearing loss; treated surgically, with restenosis the main complication.
Acromioclavicular joint
Acromioclavicular joint (ACJ, articulatio acromioclavicularis): planar synovial joint between lateral clavicle and acromion, stabilized by AC and coracoclavicular ligaments; site of common shoulder injuries graded by the Rockwood system.
Acromion
The acromion is the bony projection of the scapular spine that arches over the shoulder joint and articulates with the clavicle. Covers its ossification, Bigliani shape types, dimensions, os acromiale, and impingement relevance.
Acta neuropathologica
Acta neuropathologica (Acta Neuropathol) is a Springer peer-reviewed neuropathology journal founded in 1961 in Berlin, ISSN 0001-6322, organ of the World Federation of Neurology's neuropathology commissions, hybrid model, 2025 impact factor 10.3, with open-access sister journal Acta Neuropathologica Communications (2013).
Acute atopic conjunctivitis
Acute atopic conjunctivitis (ICD-10 H10.1, ICD-11 9A60.01; Angelucci's syndrome, spring catarrh) is a sudden IgE-mediated allergic inflammation of the conjunctiva from airborne allergens, causing itchy, red, watery eyes, usually self-limiting and treated with topical antihistamines.
Acute coronary syndrome
Acute coronary syndrome (ACS) is the umbrella term for unstable angina, NSTEMI, and STEMI, caused by sudden reduced heart blood flow from plaque rupture and thrombosis; diagnosed by ECG and troponin, treated with antiplatelets and reperfusion.
Acute epidemic conjunctivitis
Acute epidemic conjunctivitis: outbreak form of highly contagious pink eye, mainly adenoviral (EKC serotypes 8, 19, 37; PCF 3, 4, 7) or enteroviral (AHC, EV70, CA24v), self-limited, supportive care.
Acute flaccid myelitis
Acute flaccid myelitis (AFM), a polio-like spinal cord gray matter condition causing sudden limb weakness mainly in young children; linked to enterovirus D68, with US outbreaks in 2014, 2016, and 2018.
Acute limb ischaemia
Acute limb ischaemia (ALI), sudden arterial perfusion loss threatening a limb within two weeks of symptom onset; caused by embolism, thrombosis, aneurysm, dissection, or trauma; staged by Rutherford class and treated with heparin plus urgent revascularization.
Acute macular neuroretinopathy
Acute macular neuroretinopathy (AMN) is a rare retinal disorder causing sudden blind spots near central vision, with reddish-brown wedge-shaped lesions around the fovea, first described in 1975.
Acute mastoiditis
Acute mastoiditis (ICD-11 AB11.0) is a rapid-onset bacterial infection of the mastoid air cells behind the ear, usually complicating acute otitis media in young children; treated with IV antibiotics, myringotomy, or mastoidectomy.
Acute myringitis
Acute myringitis is a recent-onset inflammation of the tympanic membrane, or eardrum, either in the membrane itself or secondary to adjacent external or middle ear inflammation.
Acute otitis media
Acute otitis media (AOM), middle ear infection, acute middle ear infection: rapid-onset infection with middle ear effusion in young children, causing ear pain and fever; most cases resolve in about 3 days without antibiotics, which give small benefits and cause adverse events.
Acute pericarditis
Acute pericarditis is inflammation of the pericardial sac, causing pleuritic chest pain; mostly idiopathic or viral, diagnosed by 2 of 4 criteria, treated with NSAIDs plus colchicine, recurring in 20-30%.
Acute septic splenitis
Acute septic splenitis (septic spleen), ICD-11 3B81.70, is acute bacterial infection of the spleen seen in septicaemia; historically called acute splenic tumour, related to splenic abscess, treated with antibiotics, drainage, or splenectomy.
Acute suppurative otitis media
Acute suppurative otitis media is a rapid-onset middle ear infection behind the eardrum that produces pus, mainly affecting young children and often improving within 3 days without antibiotics.
Adam's apple
Adam's apple: the laryngeal prominence of the thyroid cartilage, larger in males (about 90° fusion angle vs 120° in females) after pubertal testosterone growth; reduced surgically by chondrolaryngoplasty.
Adaptive immune system
Adaptive immune system: vertebrate immunity mediated by T and B lymphocytes with somatically rearranged antigen receptors, clonal selection (Burnet), 10^8 receptor specificities, 4-7 day response delay, immunological memory, and bidirectional crosstalk with innate immunity.
Adductor magnus muscle
Adductor magnus (musculus adductor magnus), largest medial thigh muscle, with adductor and ischiocondylar parts, dual obturator and sciatic innervation, and a design favoring hip extension over adduction.
Adductor muscles of the hip
Hip adductors (medial thigh muscles): adductor longus, brevis, magnus, gracilis, pectineus. Five muscles adducting the thigh, mostly obturator nerve (L2-L4); adductor magnus largest with dual innervation; common site of athletic groin strain.
Adenoid
Adenoid (pharyngeal tonsil, nasopharyngeal tonsil): lymphoid tissue behind the nasal passage, part of Waldeyer's ring, largest ages 3-5 and gone by adulthood; hypertrophy causes obstruction, and adenoidectomy shows no benefit for recurrent URIs versus watchful waiting.
Adolescence
Adolescence: the developmental phase between childhood and adulthood, WHO-defined as ages 10-19, marked by puberty, brain maturation into the mid-to-late 20s, and rising mental health burden.
Adrenal cortex
Adrenal cortex: outer steroid-secreting region of the adrenal (suprarenal) gland, about 90% of its mass. Three zones: glomerulosa (aldosterone), fasciculata (cortisol), reticularis (DHEA and androgens), regulated by ACTH and angiotensin II.
Adrenal gland
Adrenal gland: paired endocrine glands atop the kidneys; cortex makes cortisol, aldosterone, and androgen precursors, medulla makes epinephrine and norepinephrine. First described by Eustachio in 1564; cortisone work won the 1950 Nobel Prize.
Adrenal medulla
Adrenal medulla: inner, chromaffin-cell portion of the adrenal gland, neural crest derived, secreting epinephrine and norepinephrine under splanchnic nerve control; distinct from the steroid-producing adrenal cortex, with pheochromocytoma as its main disorder.
Adrenarche
Adrenarche is the childhood rise in adrenal androgen production, mainly DHEA and DHEAS, from the zona reticularis, beginning around age 6-8, independent of puberty, causing pubic hair, and occurring only in humans and some Old World primates.