1500+ medical terms, defined.

Linkage disequilibrium (LD) is the non-random association of alleles at two or more loci in a population, occurring more often or less often than expected by chance given their individual allele frequencies. It is distinct from linkage,...

Carpal tunnel syndrome is compression neuropathy of the median nerve as it passes through the carpal tunnel at the wrist, causing pain, paresthesias, and weakness in the median nerve distribution (palmar thumb, index, middle, and half of...

Oligomycin is an antibiotic that inhibits ATP synthase (Complex V) of the mitochondrial electron transport chain by blocking its proton channel (F0 subunit), thereby preventing ATP synthesis. It is used experimentally to distinguish betw...

Rotenone is a naturally occurring plant-derived compound that acts as a Complex I (NADH:ubiquinone oxidoreductase) inhibitor in the mitochondrial electron transport chain. It is classically used in pharmacology/biochemistry as an experim...

Relaxin is a peptide hormone produced primarily by the corpus luteum during pregnancy (also by the placenta and decidua) that promotes remodeling of the pelvic connective tissue and uterine relaxation in preparation for parturition. It w...

Long QT syndrome (LQTS) is a cardiac channelopathy characterized by prolonged ventricular repolarization (QTc >450ms men, >470ms women), predisposing to torsades de pointes (TdP), a polymorphic ventricular tachycardia that can cause sync...

Hydrocortisone is the pharmaceutical name for cortisol, a glucocorticoid used for adrenal insufficiency replacement therapy and as an anti-inflammatory/immunosuppressive agent. It has both glucocorticoid and mineralocorticoid activity, m...

Asparagine is a non-essential amino acid synthesized from aspartate via asparagine synthetase, which converts glutamine + aspartate + ATP into asparagine, glutamate, AMP, and PPi. It is a key substrate in the urea cycle-adjacent nitrogen...

Pantothenic acid (Vitamin B5) is a water-soluble vitamin essential for the synthesis of coenzyme A (CoA) and acyl carrier protein (ACP), critical cofactors in fatty acid metabolism and the citric acid cycle. Deficiency is rare but classi...

Ventricular tachycardia (VT) is a wide-complex tachyarrhythmia originating from a ventricular ectopic focus or reentrant circuit, defined as ≥3 consecutive ventricular beats at a rate >100 bpm. It can be monomorphic (uniform QRS, often d...

Pyridoxal 5'-phosphate (PLP) is the active coenzyme form of vitamin B6, essential for amino acid metabolism including transamination, decarboxylation, and heme synthesis. It serves as a critical cofactor for enzymes like ALT, AST, and AL...

Chief cells are secretory cells found in the gastric fundic glands and in the parathyroid gland, though they serve distinct functions in each location. Gastric chief cells secrete pepsinogen and gastric lipase, while parathyroid chief ce...

Sphingolipids are membrane lipids built on a sphingosine backbone, prominent in neural tissue (myelin) and cell signaling. Their catabolism requires specific lysosomal enzymes, and deficiencies in these enzymes cause a group of inherited...

Integrase is a viral enzyme, characteristic of retroviruses like HIV, that catalyzes the insertion of reverse-transcribed viral DNA into the host cell's genome. This step is essential for viral replication and establishes latent infectio...

Malignant melanoma is a highly aggressive cancer arising from melanocytes, most commonly in the skin, driven by UV radiation exposure and genetic mutations (e.g., BRAF, NRAS). It has a strong propensity for early metastasis and is diagno...

Churg-Strauss syndrome, now called Eosinophilic Granulomatosis with Polyangiitis (EGPA), is a small-to-medium vessel vasculitis characterized by asthma, eosinophilia, and granulomatous inflammation. It classically presents in patients wi...

Antimycin A is a mitochondrial toxin that inhibits Complex III (cytochrome bc1 complex) of the electron transport chain, blocking electron transfer from cytochrome b to cytochrome c1. It is primarily used as a research tool and fish/pest...

Granulomatous inflammation is a chronic inflammatory response characterized by organized collections of activated macrophages (epithelioid cells), often with multinucleated giant cells, surrounded by lymphocytes. It occurs when the immun...

Deiodinases are selenoenzymes that remove iodine atoms from thyroid hormones, regulating the conversion of T4 to the active T3 or the inactive reverse T3 (rT3). There are three types (D1, D2, D3) with distinct tissue distributions and ro...

Pancreatic lipase is the primary enzyme responsible for digesting dietary triglycerides into free fatty acids and monoglycerides in the small intestine. It requires an activated cofactor, colipase, to function optimally, especially in th...

Innate immunity is the body's first line of defense against pathogens, providing immediate (within minutes to hours), non-specific protection without prior exposure. It includes physical barriers, phagocytic cells, and pattern recognitio...

MEN1 (Multiple Endocrine Neoplasia type 1, or Wermer syndrome) is an autosomal dominant disorder caused by mutations in the MEN1 tumor suppressor gene, leading to the classic triad of parathyroid, pancreatic, and pituitary tumors (the '3...

Vitiligo is an autoimmune condition characterized by patchy, well-demarcated depigmentation of the skin due to destruction of melanocytes. It is associated with other autoimmune diseases and can occur at any age, often with a predilectio...

The Müllerian ducts (paramesonephric ducts) are paired embryonic structures that give rise to the female internal reproductive tract: fallopian tubes, uterus, cervix, and upper vagina. Their development is driven by the absence of Müller...

The optic disc (optic nerve head) is the point where retinal ganglion cell axons converge to form the optic nerve and exit the eye, along with the central retinal artery and vein. It lacks photoreceptors, creating the physiologic blind s...

The outer membrane is a distinguishing structural feature of Gram-negative bacteria, located external to the peptidoglycan layer. It contains lipopolysaccharide (LPS/endotoxin), porins, and phospholipids, contributing to antibiotic resis...

Acid-fast staining (Ziehl-Neelsen or Kinyoun method) identifies bacteria with mycolic acid-rich cell walls that resist decolorization by acid-alcohol after carbolfuchsin staining. Key acid-fast organisms include Mycobacterium species (M....

Ribosomes are ribonucleoprotein complexes composed of rRNA and proteins that synthesize proteins by translating mRNA. Eukaryotic ribosomes (80S = 40S + 60S) differ from prokaryotic ribosomes (70S = 30S + 50S), a distinction exploited by...

Coagulative necrosis is a form of cell death in which tissue architecture is preserved for several days despite loss of cellular nuclei, due to denaturation of proteins including enzymes that would otherwise degrade the cell. It is the h...

The decidua basalis is the portion of the endometrium underlying the implantation site that forms the maternal component of the placenta. It contains maternal blood vessels and spiral arteries that supply the intervillous space, contribu...

Nucleic acids (DNA and RNA) are polymers of nucleotides that store, transmit, and express genetic information. DNA serves as the stable, long-term repository of genetic code, while RNA (mRNA, tRNA, rRNA, and others) mediates gene express...

PCSK9 (Proprotein Convertase Subtilisin/Kexin type 9) is a hepatic enzyme that promotes degradation of LDL receptors, thereby raising serum LDL-cholesterol levels. PCSK9 inhibitors (e.g., evolocumab, alirocumab) are monoclonal antibodies...

PCSK9 inhibitors (e.g., evolocumab, alirocumab) are monoclonal antibodies that lower LDL cholesterol by inhibiting proprotein convertase subtilisin/kexin type 9, preventing LDL receptor degradation. They are used as adjuncts to statins i...

Evolocumab is a fully human monoclonal antibody that inhibits PCSK9 (proprotein convertase subtilisin/kexin type 9), leading to increased LDL receptor recycling and significantly lower LDL cholesterol levels. It is used as an adjunct to...

Conjugation is a mechanism of horizontal gene transfer in bacteria in which genetic material (typically a plasmid) is transferred directly from a donor to a recipient cell via a pilus. It is a major driver of antibiotic resistance spread...

Fatty acid synthase (FAS) is a large multi-enzyme complex that catalyzes the synthesis of palmitate (16-carbon saturated fatty acid) from acetyl-CoA and malonyl-CoA, using NADPH as a reducing agent. It is the key enzyme of de novo lipoge...

The ductus venosus is a fetal vascular shunt that connects the umbilical vein directly to the inferior vena cava, allowing oxygenated blood from the placenta to bypass the liver. It closes shortly after birth to become the ligamentum ven...

Enoxaparin is a low-molecular-weight heparin (LMWH) that primarily inhibits Factor Xa by potentiating antithrombin III. It's used for prophylaxis and treatment of DVT/PE, and in acute coronary syndromes. Unlike unfractionated heparin, it...

Ebola virus is a filovirus causing severe viral hemorrhagic fever with high mortality rates (up to 90%). It is transmitted via direct contact with bodily fluids of infected humans or animals (fruit bats are the natural reservoir), and ou...

Premature rupture of membranes (PROM) is rupture of the amniotic sac before the onset of labor, at any gestational age. When it occurs before 37 weeks gestation, it is termed preterm PROM (PPROM). Diagnosis is confirmed by pooling of flu...

Corynebacterium diphtheriae is a gram-positive, club-shaped bacillus that causes diphtheria via an exotoxin encoded by a lysogenic bacteriophage (tox gene). It produces a characteristic gray-white pseudomembrane in the pharynx and can ca...

The glomerulus is the tuft of capillaries in the kidney where blood filtration begins, forming the initial step of urine production. It is surrounded by Bowman's capsule and filters plasma based on size and charge selectivity, producing...

Viral gastroenteritis is inflammation of the stomach and intestines caused by viral pathogens, most commonly Norovirus (all ages, common in outbreaks/cruise ships) and Rotavirus (leading cause in infants/young children). It presents with...

Hepatitis E virus (HEV) is a non-enveloped, single-stranded RNA virus (Hepeviridae family) transmitted via the fecal-oral route, primarily through contaminated water. It causes acute, typically self-limited hepatitis but is notably dange...

Ebolavirus is a filovirus causing severe viral hemorrhagic fever with high mortality rates, transmitted via direct contact with bodily fluids of infected individuals or animals. It presents with fever, severe hemorrhage, and multi-organ...

PROM (Premature Rupture of Membranes) refers to rupture of the amniochorionic membranes before the onset of labor. If it occurs before 37 weeks gestation, it is termed PPROM (Preterm Premature Rupture of Membranes). Key risks include asc...

Palliative care is specialized, interdisciplinary medical care focused on providing relief from symptoms, pain, and stress of serious illness, aiming to improve quality of life for both patient and family. It can be provided alongside cu...

Dengue fever is a mosquito-borne viral illness caused by dengue virus (a flavivirus with 4 serotypes), transmitted by Aedes aegypti mosquitoes. It presents with high fever, severe headache/retro-orbital pain, myalgias/arthralgias ('break...

Humoral immunity is the arm of adaptive immunity mediated by B lymphocytes and their secreted antibodies (immunoglobulins), which neutralize and opsonize extracellular pathogens and toxins. It works alongside complement to eliminate path...

Class switching (isotype switching) is the process by which activated B cells change the constant region of their immunoglobulin heavy chain (e.g., from IgM to IgG, IgA, or IgE) without altering antigen specificity. It requires CD40-CD40...