300+ medical terms, defined.

Papillary muscles are cone-shaped muscular projections within the left and right ventricles that anchor the chordae tendineae to prevent mitral and tricuspid valve prolapse during systole. Dysfunction leads to mitral regurgitation and is...

The baroreceptor reflex is a rapid, negative feedback mechanism that maintains blood pressure homeostasis by detecting changes in arterial pressure and adjusting heart rate and vascular tone accordingly. Increased BP → decreased HR and v...

SIADH is characterized by excessive ADH secretion leading to water retention, hyponatremia, and concentrated urine despite normal/low plasma osmolality. Classic presentation includes euvolemic hyponatremia with inappropriately concentrat...

Dead space refers to the portion of the respiratory system where gas exchange does not occur. It includes anatomical dead space (conducting airways) and physiological dead space (alveoli that are ventilated but not perfused). Normal dead...

Anatomic dead space refers to the portion of the respiratory system where no gas exchange occurs, including the conducting airways from the nose/mouth to the terminal bronchioles. It typically accounts for approximately 150 mL or 2.2 mL/...

Carcinoid tumors are well-differentiated neuroendocrine tumors arising from enterochromaffin cells, most commonly in the GI tract and lungs. They secrete serotonin and other vasoactive substances, potentially causing carcinoid syndrome w...

Tryptophan hydroxylase is the rate-limiting enzyme in serotonin biosynthesis that converts L-tryptophan to 5-hydroxytryptophan (5-HTP). It exists as two isoforms: TPH1 (peripheral tissues) and TPH2 (central nervous system). This enzyme i...

Esophageal webs are thin (< 5 mm) membranes of mucosa and submucosa extending from the anterior esophageal wall, typically in the upper esophagus. Associated with Plummer-Vinson syndrome (iron deficiency, dysphagia, increased risk of eso...

Portal hypertension is elevated pressure in the portal venous system (> 12 mmHg) caused by increased intrahepatic resistance (cirrhosis), prehepatic obstruction (portal vein thrombosis), or posthepatic obstruction (Budd-Chiari). Causes e...

Hydrogen peroxide (H2O2) is a reactive oxygen species and byproduct of cellular metabolism. It is produced by NADPH oxidase in phagocytes and other enzymes; catalase and glutathione peroxidase enzymatically break it down to prevent oxida...

The P wave on ECG represents atrial depolarization; it is normally < 120 ms wide (< 3 small squares) and < 2.5 mm tall in lead II. Absent P waves suggest atrial fibrillation; prolonged P waves indicate atrial enlargement or delay.

The bowel (intestines) includes the small intestine (duodenum, jejunum, ileum) and large intestine (colon, rectum, anal canal). The small bowel is primary site of nutrient absorption; the colon absorbs water and electrolytes.

Vitamin B2 (riboflavin) is a water-soluble B vitamin that serves as a cofactor for FAD and FMN in oxidation-reduction reactions. Deficiency causes ariboflavinosis, characterized by glossitis, cheilosis, dermatitis, and angular stomatitis.

Cheilosis (cheilitis) is inflammation and cracking of the lips, typically at the corners of the mouth (angular cheilitis). Caused by vitamin B2 deficiency, iron deficiency, or nutritional deficiencies; also seen in Plummer-Vinson syndrome.

MHCs (major histocompatibility complexes) are cell surface glycoproteins that present antigens to T cells and mediate immune recognition. HLA (human leukocyte antigen) is the human MHC system; Class I (present to CD8+ T cells) and Class...

Major histocompatibility complexes (MHCs) are cell surface molecules presenting antigens to T cells. MHC Class I (all cells, CD8+ T cells) and Class II (APCs, CD4+ T cells); essential for adaptive immunity and transplant rejection.

TCRs (T cell receptors) are antigen-recognition receptors on T lymphocytes. Composed of alpha-beta or gamma-delta chains paired with CD3 and zeta chains; each T cell has unique TCR specificity for antigen-MHC complexes.

APCs (antigen-presenting cells) are professional immune cells that process and present antigens via MHC to T cells. Main types: dendritic cells (most efficient), macrophages, and B cells; essential for initiating adaptive immune responses.

Claudication is muscle pain with exercise due to insufficient blood supply, typically in the legs (intermittent claudication from peripheral arterial disease). Caused by atherosclerosis; pain resolves with rest (ischemic pain).

Ventricular free wall rupture is a catastrophic mechanical complication of acute myocardial infarction occurring 3-7 days post-MI, caused by transmural necrosis and loss of structural integrity. Results in sudden death or cardiogenic sho...

Th2 (T helper 2) cells are CD4+ T cells producing IL-4, IL-5, and IL-13, promoting humoral immunity (antibody production) and parasitic/allergic responses. Differentiate from Th1 under IL-4 and IL-2 influence; opposite to Th1 pro-inflamm...

Uterine leiomyosarcoma is a rare, aggressive malignant smooth muscle tumor of the uterus. Presents with abnormal bleeding and pelvic mass; poor prognosis with high recurrence and metastasis rate, typically to lungs.

Systolic heart failure (HFrEF, ejection fraction ≤ 40%) is reduced cardiac contractility from cardiomyopathy (ischemic, dilated, toxic) or prolonged pressure/volume overload. Causes decreased cardiac output and pulmonary/systemic congest...

Ischemic heart disease results from atherosclerotic coronary artery stenosis causing myocardial oxygen supply-demand mismatch. Presents as angina (stable, unstable, vasospastic) or myocardial infarction; managed with antiplatelet therapy...

Structural heart disease includes organic abnormalities: valvular disease (stenosis, regurgitation), cardiomyopathy, myocarditis, pericarditis, congenital heart disease. Causes symptoms via altered hemodynamics, arrhythmias, or reduced c...

Proarrhythmic effects are paradoxical arrhythmia induction or worsening by antiarrhythmic drugs. Caused by drug effects on action potential duration, conduction velocity, or refractoriness; includes torsades de pointes (QT prolongation)...

Class IC antiarrhythmics (flecainide, propafenone) are potent sodium channel blockers with marked slowing of conduction (increased PR and QRS duration). High proarrhythmic potential; contraindicated post-MI; use limited to refractory SVT...

β-blockers (propranolol, metoprolol, atenolol, carvedilol) competitively block β-adrenergic receptors, reducing heart rate, contractility, and blood pressure. First-line for hypertension, angina, arrhythmias, and post-MI; reduce mortalit...

Chronic tubulointerstitial nephritis (CTIN) is chronic kidney disease with tubular and interstitial inflammation/fibrosis, sparing glomeruli. Causes include NSAIDs, antibiotics, reflux, obstruction; presents with gradual loss of renal fu...

Papillary necrosis is acute necrosis of renal papillae (pyramids) causing severe flank pain, hematuria, and acute kidney injury. Associated with NSAIDs, acute pyelonephritis, sickle cell disease, and obstruction; can progress to chronic...

Hamartomatous polyps are benign growths of normal tissue in abnormal arrangement, found in hereditary polyposis syndromes (Peutz-Jeghers, Cowden, juvenile polyposis). May cause bleeding, obstruction, or serve as precursor to adenocarcino...

GBM has two meanings in medicine: (1) Glomerular basement membrane—critical for glomerular filtration barrier, damaged in anti-GBM disease (Goodpasture syndrome) causing rapidly progressive glomerulonephritis and pulmonary hemorrhage; (2...

The 4th aortic arch (pharyngeal arch artery) gives rise to the proximal aorta and arch vessels. Left 4th arch forms the aortic arch; right 4th arch forms the right subclavian artery. Abnormalities cause vascular rings and slings compress...

Arteria Lusoria (anomalous right subclavian artery) is an aberrant right subclavian artery arising from the distal aortic arch, passing behind the esophagus. Usually asymptomatic but can cause dysphagia (dysphagia lusoria) or rarely, hem...

The canalicular period (16-26 weeks gestation) is the second stage of lung development characterized by formation of respiratory bronchioles and terminal sacs. This period is critical for establishing the basic framework for gas exchange...

Type III collagen is a fibrillar collagen that provides structural support to hollow organs and blood vessels. It is the predominant collagen in early wound healing and is associated with Ehlers-Danlos syndrome type IV when defective.

The parotid gland is the largest salivary gland, located anterior to the ear, producing serous saliva via Stensen's duct. It's clinically significant for mumps infection, Sjögren's syndrome, and pleomorphic adenomas.

The nephron is the functional unit of the kidney, consisting of a glomerulus, Bowman's capsule, and tubular system. Each kidney contains approximately 1 million nephrons responsible for filtration, reabsorption, and secretion to maintain...

Surface tension is the cohesive force between liquid molecules at the air-liquid interface that creates resistance to surface expansion. In the lungs, pulmonary surfactant (primarily dipalmitoylphosphatidylcholine) reduces alveolar surfa...

V/Q scan (ventilation-perfusion scan) is a nuclear medicine imaging study that evaluates pulmonary ventilation and perfusion to diagnose pulmonary embolism. It compares airflow (ventilation) to blood flow (perfusion) in the lungs using r...

Bronchioles are small airways (<1mm diameter) distal to bronchi that lack cartilage and glands but contain smooth muscle. Terminal bronchioles are the smallest purely conducting airways, while respiratory bronchioles participate in gas e...

The anion gap is a calculated value representing unmeasured anions in serum, used to classify metabolic acidosis. Normal range is 8-12 mEq/L. An elevated anion gap (>12) indicates accumulation of organic acids and helps narrow the differ...

Carbonic anhydrase inhibitors block the enzyme carbonic anhydrase, preventing the conversion of CO2 and H2O to carbonic acid. They cause diuresis, metabolic acidosis, and are used to treat glaucoma, altitude sickness, and epilepsy. Aceta...

Pulse oximetry is a non-invasive method to measure oxygen saturation (SpO2) of hemoglobin in arterial blood using light absorption principles. Normal values are 95-100%, with readings below 90% indicating hypoxemia requiring immediate at...

Diffusion is the passive movement of molecules from areas of high concentration to low concentration across a concentration gradient, requiring no energy input. It's fundamental to gas exchange in lungs, drug absorption, and cellular tra...

Tertiary hyperparathyroidism occurs when chronic secondary hyperparathyroidism leads to autonomous parathyroid gland hyperplasia that persists even after correction of the underlying condition. It is most commonly seen in chronic kidney...

Kayser-Fleischer rings are golden-brown corneal deposits of copper seen in Wilson's disease (hepatolenticular degeneration). They appear as circular deposits at the periphery of the cornea and are virtually pathognomonic for Wilson's dis...

Clopidogrel is an irreversible P2Y12 receptor antagonist that inhibits ADP-induced platelet aggregation. It's a prodrug requiring hepatic activation via CYP2C19 and is used for secondary prevention of cardiovascular events.

The ratio of forced expiratory volume in 1 second to forced vital capacity, used to diagnose obstructive lung disease. A ratio <0.70 indicates obstruction (COPD, asthma); a normal ratio with reduced FVC suggests restriction.

Rapid ventricular response; refers to a fast ventricular rate (typically >100 bpm) during atrial fibrillation due to rapid conduction through the AV node. Hemodynamically significant and requires rate control.