1500+ medical terms, defined.

The sphincter of Oddi is a smooth muscle valve surrounding the confluence of the common bile duct and main pancreatic duct as they empty into the second part of the duodenum at the ampulla of Vater. It regulates the flow of bile and panc...

Varicella-zoster virus (VZV), a human herpesvirus (HHV-3), causes primary infection presenting as varicella (chickenpox) in children and reactivates from dorsal root/cranial nerve ganglia later in life as herpes zoster (shingles). It is...

The pudendal nerve (S2-S4) is the main somatic nerve of the perineum, providing sensory, motor, and autonomic innervation to the external genitalia, anal sphincter, and pelvic floor muscles. It is clinically important for pudendal nerve...

Fascia is a layer of fibrous connective tissue that surrounds and separates muscles, organs, nerves, and vessels throughout the body. It provides structural support, compartmentalizes anatomical spaces, and can be a route for spread of i...

Moxifloxacin is a 4th-generation fluoroquinolone antibiotic with broad-spectrum coverage including gram-positive, gram-negative, atypical, and anaerobic organisms. It is commonly used for respiratory infections (CAP, sinusitis, bronchiti...

SGLT2 inhibitors (e.g., empagliflozin, dapagliflozin, canagliflozin) block sodium-glucose cotransporter 2 in the proximal convoluted tubule, reducing renal glucose reabsorption and causing glucosuria. Beyond glycemic control, they provid...

Coagulation factors are plasma proteins (mostly serine proteases and cofactors) that act in a sequential cascade to convert soluble fibrinogen into insoluble fibrin, stabilizing platelet plugs and forming a definitive clot. Most are synt...

Atorvastatin is a HMG-CoA reductase inhibitor (statin) used to lower LDL cholesterol and reduce cardiovascular risk. It works by competitively inhibiting the rate-limiting enzyme in hepatic cholesterol synthesis, upregulating LDL recepto...

The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve (CN X) that innervates all intrinsic muscles of the larynx except the cricothyroid muscle, providing motor function for phonation and sensory innervation below the vocal...

Thyroxine-binding globulin (TBG) is the major plasma transport protein for thyroid hormones (T4 and T3), synthesized in the liver. It binds ~70-75% of circulating T4 and T3, keeping free hormone levels low and buffering hormone availabil...

The left bundle branch (LBB) is part of the cardiac conduction system that carries electrical impulses from the bundle of His to the left ventricle, splitting into anterior and posterior fascicles. It depolarizes the interventricular sep...

A peripheral nerve is a bundle of axons (motor, sensory, and/or autonomic fibers) outside the CNS that connects the brain and spinal cord to muscles, skin, and organs. Peripheral nerves are enveloped by connective tissue layers (endoneur...

Ventral refers to the anterior (front) surface or direction in anatomical terminology, derived from Latin 'venter' meaning belly. In humans, ventral is synonymous with anterior since we stand upright; in quadrupeds, ventral refers to the...

An opening snap (OS) is a high-pitched extra heart sound heard shortly after S2, classically associated with mitral stenosis. It results from the sudden tensing of the stenotic mitral valve leaflets as they abruptly stop opening due to f...

Fetal circulation is the specialized blood flow pattern in utero that bypasses the non-functional lungs and liver using three shunts: the ductus venosus, foramen ovale, and ductus arteriosus. Oxygenated blood from the placenta reaches th...

Gemfibrozil is a fibrate class drug that lowers triglycerides by activating PPAR-alpha, which upregulates lipoprotein lipase activity. It is primarily used to treat severe hypertriglyceridemia to reduce the risk of pancreatitis. It also...

Septate uterus is the most common Müllerian duct anomaly, caused by failure of resorption of the fibrous/muscular septum that forms after the two Müllerian ducts fuse. It presents with a normal external uterine contour but a fibrous sept...

A signal peptide is a short (typically 15-30 amino acid) N-terminal sequence on nascent proteins that directs them to the endoplasmic reticulum (ER) for co-translational translocation. It is recognized by the signal recognition particle...

Type II hypersensitivity is an antibody-mediated (IgG or IgM) immune reaction in which antibodies bind directly to antigens on the surface of cells or extracellular matrix, leading to cell damage or dysfunction. Mechanisms include comple...

Diltiazem is a non-dihydropyridine calcium channel blocker (CCB) used for hypertension, angina, and rate control in atrial fibrillation/flutter. It works by blocking L-type calcium channels in cardiac and vascular smooth muscle, causing...

Propafenone is a Class IC antiarrhythmic agent used to treat supraventricular and ventricular arrhythmias, particularly atrial fibrillation in patients without structural heart disease. It works by blocking fast sodium channels, signific...

Chordae tendineae are fibrous, tendon-like cords that connect the papillary muscles of the ventricles to the leaflets of the atrioventricular (mitral and tricuspid) valves. They prevent the valve leaflets from prolapsing back into the at...

Insulin-like growth factor 1 (IGF-1) is a peptide hormone produced mainly by the liver in response to growth hormone (GH) stimulation. It mediates most of GH's anabolic and growth-promoting effects on bone, cartilage, and muscle. IGF-1 l...

Glomerulonephritides refer to a group of kidney disorders characterized by inflammation of the glomeruli, leading to hematuria, proteinuria, and varying degrees of renal dysfunction. They are broadly classified into nephritic and nephrot...

Hemorrhoids are swollen, engorged vascular cushions in the anal canal, classified as internal (above the dentate line) or external (below the dentate line). They result from increased venous pressure and straining, commonly presenting wi...

Wegener granulomatosis, now called Granulomatosis with Polyangiitis (GPA), is a small-vessel, ANCA-associated vasculitis characterized by necrotizing granulomatous inflammation affecting the upper respiratory tract, lungs, and kidneys. I...

Androstenedione is a weak endogenous androgen steroid hormone produced by the adrenal glands, gonads (testes and ovaries), and placenta. It serves as a key precursor in the biosynthesis of both testosterone and estrone, sitting at a crit...

Sex Hormone-Binding Globulin (SHBG) is a glycoprotein produced by the liver that binds testosterone and estradiol in the blood, regulating the amount of free (bioavailable) hormone. Increased SHBG lowers free testosterone, while decrease...

Osmotic demyelination syndrome (ODS), classically central pontine myelinolysis, is a demyelinating condition caused by rapid correction of chronic hyponatremia, leading to osmotic-induced damage to oligodendrocytes and myelin sheaths in...

The bundle of His is part of the cardiac conduction system that transmits electrical impulses from the atrioventricular (AV) node to the bundle branches and Purkinje fibers, coordinating ventricular contraction. It lies within the interv...

Trypsinogen is the inactive zymogen precursor of trypsin, synthesized and secreted by pancreatic acinar cells. It is activated in the duodenum by enteropeptidase (enterokinase), which cleaves it to form active trypsin. This activation st...

Rapidly Progressive Glomerulonephritis (RPGN) is a clinical syndrome characterized by acute loss of renal function over days to weeks, with histologic finding of crescents in >50% of glomeruli on biopsy. It represents a medical emergency...

Citrate synthase catalyzes the first committed step of the TCA (Krebs) cycle, condensing acetyl-CoA with oxaloacetate to form citrate. It is a rate-limiting mitochondrial matrix enzyme and is often used as a marker of mitochondrial conte...

The citric acid cycle (Krebs cycle/TCA cycle) is the central hub of aerobic metabolism, oxidizing acetyl-CoA to produce NADH, FADH2, GTP/ATP, and CO2. It occurs in the mitochondrial matrix and is essential for connecting carbohydrate, fa...

Calcium channel blockers (CCBs) inhibit L-type voltage-gated calcium channels in vascular smooth muscle and cardiac myocytes, causing vasodilation and reduced cardiac contractility/conduction. They are divided into dihydropyridines (vaso...

Diffuse proliferative glomerulonephritis (DPGN) is the most severe and common renal manifestation of systemic lupus erythematosus (Class IV lupus nephritis), characterized by immune complex deposition causing global and diffuse glomerula...

Immunofluorescence (IF) is a laboratory technique that uses fluorescently labeled antibodies to detect and localize specific antigens (proteins) in tissue samples or cells under a fluorescence microscope. It is widely used in diagnosing...

Trypsin is a serine protease secreted by pancreatic acinar cells as inactive trypsinogen, which is activated by enteropeptidase (enterokinase) in the duodenal brush border. It cleaves peptide bonds at the carboxyl side of lysine and argi...

Hemoglobin F (fetal hemoglobin) is the predominant hemoglobin in the fetus, composed of two alpha and two gamma globin chains (α2γ2). It has a higher affinity for oxygen than adult hemoglobin (HbA), facilitating oxygen transfer across th...

Samter triad (also called aspirin-exacerbated respiratory disease, AERD) is a clinical syndrome consisting of asthma, chronic rhinosinusitis with nasal polyps, and sensitivity/intolerance to aspirin and other NSAIDs. It results from dysr...

The membrane attack complex (MAC, C5b-9) is the terminal product of the complement cascade, formed by sequential binding of C5b, C6, C7, C8, and multiple C9 molecules. It creates a pore in the target cell membrane, leading to osmotic lys...

The peritoneal cavity is a potential space between the parietal and visceral peritoneum lining the abdominal wall and abdominal organs. It normally contains a thin film of serous fluid that lubricates surfaces and allows organs to move a...

Retinol is the storage/transport form of vitamin A, essential for vision (rhodopsin synthesis), epithelial cell differentiation, and immune function. Deficiency causes night blindness (nyctalopia) and xerophthalmia; toxicity causes terat...

Von Willebrand factor (vWF) is a large multimeric glycoprotein synthesized by endothelial cells and megakaryocytes that mediates platelet adhesion to damaged subendothelium and stabilizes/carries Factor VIII in circulation. It is essenti...

The endoderm is one of the three primary germ layers formed during gastrulation, giving rise to the epithelial lining of the gastrointestinal tract, respiratory tract, and associated glandular organs. It is critical for understanding emb...

An anal fissure is a linear tear in the anoderm distal to the dentate line, most commonly located posteriorly in the midline. It presents classically with severe, tearing pain during defecation followed by a dull ache, and bright red blo...

The labia minora are two thin, hairless folds of skin located medial to the labia majora, surrounding the vaginal and urethral openings. They are richly vascularized and innervated, contributing to sexual arousal, and meet anteriorly to...

Tropical sprue is a malabsorption syndrome of unclear etiology (likely infectious, possibly bacterial overgrowth) that occurs in residents or visitors of tropical regions (Caribbean, India, Southeast Asia). It causes villous atrophy pred...

Shigella is a gram-negative, non-lactose fermenting, facultative anaerobic bacillus that causes bacillary dysentery (bloody diarrhea with mucus). It is highly infectious (low infectious dose), transmitted via fecal-oral route, and is a m...

Immunoglobulins (Igs), also called antibodies, are glycoproteins produced by plasma cells (differentiated B lymphocytes) that recognize specific antigens. There are five classes—IgG, IgA, IgM, IgD, and IgE—each with distinct structure, l...