1500+ medical terms, defined.

Direct oral anticoagulants (DOACs) are oral anticoagulants that directly inhibit specific clotting factors—either factor Xa (apixaban, rivaroxaban, edoxaban) or thrombin/factor IIa (dabigatran)—without requiring antithrombin as a cofacto...

Rivaroxaban is an oral direct factor Xa inhibitor used for anticoagulation, including prevention/treatment of DVT/PE, stroke prevention in nonvalvular atrial fibrillation, and VTE prophylaxis after orthopedic surgery. Unlike warfarin, it...

Transduction is a mechanism of horizontal gene transfer in bacteria in which a bacteriophage (virus) transfers DNA from one bacterium to another. It comes in two forms: generalized transduction (random bacterial DNA packaged into phage)...

Loop diuretics (e.g., furosemide, bumetanide, torsemide, ethacrynic acid) inhibit the Na+/K+/2Cl- (NKCC2) cotransporter in the thick ascending limb of the loop of Henle, causing potent natriuresis and diuresis. They are used for volume o...

Midazolam is a short-acting benzodiazepine commonly used for procedural sedation, anesthesia induction, anxiolysis, and seizure termination. It enhances GABA-A receptor activity, causing sedation, amnesia, and anxiolysis. Its rapid onset...

DDAVP (desmopressin) is a synthetic analog of antidiuretic hormone (ADH/vasopressin) that selectively acts on V2 receptors to promote water reabsorption in the renal collecting ducts. It is used to treat central diabetes insipidus, noctu...

Vitamin A (retinol) is a fat-soluble vitamin essential for vision, epithelial cell differentiation, and immune function. Deficiency causes night blindness (nyctalopia), xerophthalmia, and increased infection susceptibility, while excess...

Ribose is a five-carbon monosaccharide (aldopentose) that serves as a fundamental structural component of RNA, ATP, NADH, and other essential nucleotides. It is synthesized via the pentose phosphate pathway (PPP) from glucose-6-phosphate...

Deoxyribose is a 5-carbon sugar (pentose) that forms the backbone of DNA, differing from ribose (found in RNA) by lacking a hydroxyl group at the 2' carbon position. This structural difference contributes to DNA's greater chemical stabil...

The anterior (ventral) horn is the gray matter region in the anterior part of the spinal cord that contains lower motor neuron (LMN) cell bodies. These neurons send axons via ventral roots to innervate skeletal muscle. Damage here causes...

Upper airway obstruction refers to blockage of airflow anywhere from the nose/mouth through the larynx to the extrathoracic trachea, presenting classically with stridor (typically inspiratory), dyspnea, and use of accessory muscles. Comm...

Type 4 renal tubular acidosis (RTA) is a hyperkalemic, hyperchloremic non-anion gap metabolic acidosis caused by aldosterone deficiency or resistance in the collecting duct. It is the most common RTA seen in clinical practice, classicall...

Trisomy 21 (Down syndrome) is the most common chromosomal disorder and leading genetic cause of intellectual disability, caused by an extra copy of chromosome 21. Risk increases with advanced maternal age. Diagnosis is confirmed by karyo...

Beta blockers are drugs that antagonize β-adrenergic receptors, decreasing heart rate, contractility, and conduction velocity, thereby reducing myocardial oxygen demand and blood pressure. They are used in hypertension, angina, heart fai...

Complex IV (cytochrome c oxidase) is the terminal enzyme complex of the mitochondrial electron transport chain, catalyzing the transfer of electrons from cytochrome c to molecular oxygen, reducing O2 to water. It contains cytochromes a a...

Oxidative phosphorylation is the metabolic pathway in which ATP is generated via the electron transport chain (ETC) and ATP synthase, using energy released from electron transfer to oxygen to pump protons across the inner mitochondrial m...

Charcot triad refers to the classic combination of fever/chills, right upper quadrant (RUQ) pain, and jaundice, which is associated with ascending cholangitis. It indicates biliary obstruction complicated by infection, typically due to c...

Flecainide is a Class IC antiarrhythmic that blocks fast sodium channels, significantly slowing conduction velocity in cardiac tissue without markedly affecting action potential duration. It is used to treat supraventricular arrhythmias...

Glycine is the smallest amino acid and serves dual roles as an inhibitory neurotransmitter in the spinal cord/brainstem and as a building block for proteins, heme, purines, glutathione, and creatine. It acts on glycine receptors (Cl- cha...

Empiric antibiotic therapy refers to the initiation of antimicrobial treatment based on the most likely pathogens for a given clinical syndrome, before definitive microbiologic identification (culture/sensitivity) is available. It is gui...

Large bowel obstruction (LBO) is a mechanical or functional blockage of the colon that impairs passage of stool and gas. The most common causes are colorectal cancer, sigmoid volvulus, and diverticular strictures. Presents with abdominal...

Verapamil is a non-dihydropyridine calcium channel blocker with predominant cardiac (vs vascular) effects, used primarily for rate control in atrial fibrillation/flutter, SVT termination, and management of hypertension and angina. It has...

The carotid sinus is a dilated area at the bifurcation of the common carotid artery into internal and external branches, containing baroreceptors that detect changes in blood pressure. It plays a key role in the baroreceptor reflex, help...

Prostaglandins are lipid signaling molecules derived from arachidonic acid via the cyclooxygenase (COX) pathway. They mediate inflammation, pain, fever, platelet aggregation, uterine contraction, and protect gastric mucosa. NSAIDs and as...

The extrinsic pathway is one of two routes that initiate the coagulation cascade, triggered by tissue factor (Factor III) release from damaged endothelium/subendothelial tissue. It rapidly activates Factor VII, leading to the common path...

Periodic acid-Schiff (PAS) stain highlights carbohydrates such as glycogen, mucopolysaccharides, and glycoproteins, staining them magenta/pink. It is widely used to detect fungal cell walls, basement membrane thickening, and glycogen sto...

An S4 gallop is a low-frequency heart sound heard just before S1 (late diastole/atrial contraction), produced by blood being forcefully ejected into a stiff, noncompliant left ventricle. It is best heard with the bell of the stethoscope...

Adaptive immunity is the antigen-specific arm of the immune system mediated by T and B lymphocytes, characterized by specificity, diversity, memory, and self/non-self recognition. It develops over days to weeks after antigen exposure but...

Thermogenin, also known as uncoupling protein 1 (UCP1), is a mitochondrial inner membrane protein found in brown adipose tissue. It dissipates the proton gradient generated by the electron transport chain, uncoupling oxidative phosphoryl...

Influenza virus is a segmented, negative-sense, single-stranded RNA virus of the Orthomyxoviridae family, causing seasonal respiratory illness (fever, myalgia, cough, sore throat). Types A, B, and C exist, with Influenza A being responsi...

Helper T cells (CD4+ T cells) are immune cells that coordinate the adaptive immune response by activating B cells, cytotoxic T cells, and macrophages through cytokine secretion and direct interaction. They recognize antigen presented on...

Heparan sulfate is a sulfated glycosaminoglycan (GAG) found covalently attached to core proteins as heparan sulfate proteoglycans (HSPGs), a major component of the basement membrane (e.g., glomerular basement membrane) and cell surfaces....

The azygos vein is a right-sided venous structure that drains the posterior thoracic, abdominal, and lumbar walls, ultimately emptying into the superior vena cava (SVC). It serves as a critical collateral pathway connecting the superior...

The thoracic duct is the largest lymphatic vessel in the body, draining lymph from the lower body, left upper body, left thorax, left arm, and left head/neck into the left venous system at the junction of the left subclavian and internal...

Levofloxacin is a fluoroquinolone antibiotic that inhibits bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, preventing DNA replication. It has broad-spectrum activity against gram-negative rods, atypical organisms, and enhan...

Maltose is a disaccharide composed of two glucose molecules joined by an α-1,4-glycosidic bond. It is produced during digestion of starch by salivary and pancreatic amylase and is subsequently cleaved by intestinal brush-border enzymes (...

Vitamin B1 (thiamine) is a water-soluble vitamin that serves as a cofactor for key enzymes in carbohydrate metabolism, including pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, transketolase, and branched-chain ketoacid dehydr...

Adrenal adenoma is a benign, usually small (<4 cm), well-circumscribed tumor of the adrenal cortex. Most are nonfunctional and discovered incidentally on imaging ("adrenal incidentaloma"), but some secrete hormones causing endocrine synd...

Western blot is a laboratory technique used to detect specific proteins in a sample by separating them based on molecular weight and identifying them with labeled antibodies. It is classically known as a confirmatory test for HIV infecti...

Duodenal ulcers are the most common type of peptic ulcer disease, typically caused by H. pylori infection or NSAID use. Classic presentation is epigastric pain that improves with eating and recurs 2-3 hours postprandially, often waking p...

Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTIs) are antiretroviral drugs used in HIV treatment that inhibit the viral reverse transcriptase enzyme, blocking conversion of viral RNA to DNA. Examples include tenofovir, emtri...

Nucleic acids are biological macromolecules (DNA and RNA) composed of nucleotide subunits that store and transmit genetic information. Each nucleotide consists of a nitrogenous base (purine or pyrimidine), a pentose sugar (deoxyribose or...

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder caused by antibodies against presynaptic voltage-gated calcium channels (VGCC) at the neuromuscular junction, leading to decreased acetylcholine release. It causes proxim...

Paracentesis is a percutaneous procedure to aspirate fluid from the peritoneal cavity, used both diagnostically (to characterize ascitic fluid) and therapeutically (to relieve symptoms of large-volume ascites). It's essential in the work...

Sulfamethoxazole is a sulfonamide antibiotic that inhibits bacterial folate synthesis by blocking dihydropteroate synthase, preventing conversion of PABA to dihydrofolate. It is almost always combined with trimethoprim (TMP-SMX/co-trimox...

Murphy sign is a clinical finding for acute cholecystitis: the examiner palpates under the right costal margin at the midclavicular line while the patient inspires deeply, causing pain and inspiratory arrest as the inflamed gallbladder d...

Gangliosides are glycosphingolipids containing sialic acid (N-acetylneuraminic acid) that are highly concentrated in neuronal cell membranes, especially at synapses. They play roles in cell signaling, membrane stability, and cell recogni...

A brain abscess is a focal, encapsulated collection of pus within the brain parenchyma, typically arising from contiguous spread (otitis media, sinusitis, dental infection), hematogenous spread (endocarditis, IV drug use), or direct inoc...

Thyroid cancer includes several histologic subtypes: papillary (most common, ~80%, excellent prognosis, associated with RET/PTC and BRAF mutations, spreads via lymphatics), follicular (hematogenous spread, associated with RAS mutations),...

Multiple endocrine neoplasia (MEN) syndromes are autosomal dominant disorders causing hyperplasia and tumors in multiple endocrine glands. MEN1 involves the pituitary, parathyroid, and pancreas (3 P's); MEN2A involves parathyroid, medull...