1500+ medical terms, defined.

Meningoencephalitis is simultaneous inflammation of both the meninges and brain parenchyma, presenting with signs of meningitis (fever, headache, nuchal rigidity) plus encephalitis (altered mental status, seizures, focal neurologic defic...

Acanthamoeba is a free-living amoeba found in soil, dust, and water that causes two major diseases: Acanthamoeba keratitis (associated with contact lens use, especially with poor hygiene or exposure to contaminated water) and granulomato...

Enfuvirtide (T-20) is an HIV fusion inhibitor that blocks viral entry into CD4+ T cells by binding gp41, preventing membrane fusion. It is administered subcutaneously and used as part of salvage therapy in treatment-experienced patients...

α4-integrin (CD49d) is a cell adhesion molecule expressed on leukocytes that pairs with β1 (VLA-4) or β7 integrin subunits to mediate adhesion to VCAM-1 and MAdCAM-1, facilitating leukocyte trafficking into tissues including the CNS and...

Enfuvirtide is a fusion inhibitor antiretroviral drug used in HIV treatment, particularly in multidrug-resistant cases. It is a synthetic peptide that blocks HIV entry into CD4+ T cells by inhibiting gp41-mediated membrane fusion. It is...

HAART (Highly Active Antiretroviral Therapy) is combination drug therapy for HIV infection, typically using ≥3 drugs from ≥2 different classes to maximally suppress viral replication and prevent resistance. It reduces HIV viral load to u...

Schizonts are a multinucleated intracellular stage in the malaria parasite (Plasmodium spp.) life cycle, formed during asexual replication within red blood cells or hepatocytes. They rupture to release merozoites, causing hemolysis and t...

Sporozoites are the infective, motile sporozoan stage of parasites like Plasmodium species, injected into the human host by the bite of a female Anopheles mosquito. They travel through the bloodstream to the liver, where they invade hepa...

Plasmodium is a genus of protozoan parasites transmitted by female Anopheles mosquitoes that cause malaria. The major species affecting humans are P. falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi, each with distinct clinic...

Coxiella burnetii is an obligate intracellular, gram-negative bacterium that causes Q fever, a zoonotic disease typically acquired via inhalation of aerosolized particles from infected animal products (especially parturition materials of...

Merozoites are the invasive, asexual daughter forms produced during the erythrocytic (and pre-erythrocytic) stages of Plasmodium and other apicomplexan parasites (e.g., Babesia). They are released from infected hepatocytes or red blood c...

MCV (Mean Corpuscular Volume) is a red blood cell index that measures the average volume of red blood cells, used to classify anemias as microcytic (<80 fL), normocytic (80-100 fL), or macrocytic (>100 fL). It is a key first step in the...

Mean corpuscular volume (MCV) is a red blood cell index that measures the average volume of red blood cells, expressed in femtoliters (fL). It is calculated by dividing the hematocrit by the RBC count and is the primary parameter used to...

Procalcitonin (PCT) is a peptide precursor of calcitonin that rises significantly during bacterial infections, especially severe systemic bacterial infections like sepsis. It is used clinically to help differentiate bacterial from viral/...

Indole is a metabolic byproduct formed from bacterial breakdown of tryptophan via the enzyme tryptophanase. Detection of indole production is a key biochemical test used to identify and differentiate Gram-negative bacteria, especially wi...

CD3 is a T-cell surface marker complex composed of multiple invariant polypeptide chains (γ, δ, ε, ζ) associated with the T-cell receptor (TCR). It is essential for TCR signal transduction and is used clinically as a pan-T-cell marker fo...

FOXP3 (Forkhead box P3) is a transcription factor essential for the development and function of regulatory T cells (Tregs), which suppress immune responses and maintain self-tolerance. Mutations in FOXP3 cause IPEX syndrome (Immune dysre...

Ventriculomegaly refers to abnormal dilation of the cerebral ventricles, most commonly diagnosed prenatally on ultrasound when the atrial diameter of the lateral ventricle exceeds 10 mm. It can be an isolated finding or associated with u...

Esophagitis is inflammation of the esophageal mucosa, most commonly caused by GERD, infections (Candida, HSV, CMV) in immunocompromised patients, eosinophilic infiltration (allergic), or pill-induced injury. Presents with odynophagia, dy...

HHV-5 is the taxonomic name for Cytomegalovirus (CMV), a member of the Herpesviridae family (beta-herpesvirus subfamily). It causes congenital infection, mononucleosis-like illness in immunocompetent hosts, and severe opportunistic disea...

TNF-α (Tumor Necrosis Factor-alpha) is a pro-inflammatory cytokine produced mainly by activated macrophages, playing a key role in systemic inflammation, immune regulation, and apoptosis. It is central to septic shock pathophysiology and...

Beclomethasone is an inhaled corticosteroid (ICS) used as first-line controller therapy for persistent asthma and also available as a nasal spray for allergic rhinitis. It reduces airway inflammation by suppressing cytokine production, e...

Budesonide is a corticosteroid available in inhaled, oral (enteric-coated capsule), and rectal formulations, characterized by high first-pass hepatic metabolism (~90%) that limits systemic side effects. It is commonly used for asthma, CO...

Fluticasone is a synthetic corticosteroid used in inhaled form for asthma/COPD maintenance, intranasal form for allergic rhinitis, and topical form for dermatologic conditions. It works by reducing airway or mucosal inflammation and is a...

Babesia is a tick-borne intraerythrocytic protozoan parasite transmitted by Ixodes scapularis, causing babesiosis, a malaria-like illness endemic to the Northeast and upper Midwest US. It classically causes hemolytic anemia, fever, and i...

Anaplasma phagocytophilum is a gram-negative, obligate intracellular bacterium transmitted by Ixodes ticks that causes human granulocytic anaplasmosis (HGA). It infects and replicates within neutrophils, forming characteristic morulae, a...

Flaviviridae is a family of enveloped, positive-sense single-stranded RNA viruses transmitted primarily by arthropod vectors (mosquitoes, ticks). Key members include Dengue, Zika, Yellow Fever, West Nile, and Hepatitis C viruses. These v...

Matonaviridae is a viral family that includes Rubella virus, the causative agent of German measles (rubella) and congenital rubella syndrome. It is a positive-sense, single-stranded RNA, enveloped virus, previously classified under Togav...

Human parainfluenza virus (HPIV) is a paramyxovirus (enveloped, negative-sense, single-stranded RNA) that is the leading cause of croup (laryngotracheobronchitis) in young children, and can also cause bronchiolitis, pneumonia, and common...

Paramyxoviridae is a family of enveloped, single-stranded negative-sense RNA viruses that includes measles, mumps, parainfluenza virus, and respiratory syncytial virus (RSV). These viruses cause respiratory and systemic infections and ar...

H1 receptor antagonists are antihistamines that block histamine H1 receptors, used to treat allergic reactions, urticaria, motion sickness, and insomnia. They are classified as first-generation (sedating, cross blood-brain barrier) and s...

HBsAg (Hepatitis B surface antigen) is the first serologic marker to appear after Hepatitis B virus (HBV) infection, indicating active infection (acute or chronic). Its presence for more than 6 months defines chronic HBV infection. It is...

GPI (glycosylphosphatidylinositol) is a glycolipid anchor that attaches proteins to the outer leaflet of the plasma membrane. It is most high-yield in the context of Paroxysmal Nocturnal Hemoglobinuria (PNH), where an acquired mutation i...

RAG (Recombination Activating Gene) refers to RAG1 and RAG2, enzymes essential for V(D)J recombination during B- and T-lymphocyte development. Mutations in RAG1/RAG2 cause a form of severe combined immunodeficiency (SCID) characterized b...

Reticulocytes are immature, anucleate red blood cells released from the bone marrow that still contain residual ribosomal RNA. They typically mature into erythrocytes within 1-2 days in circulation. The reticulocyte count/index is used c...

Corticosteroids are steroid hormones (glucocorticoids and mineralocorticoids) produced by the adrenal cortex or synthesized as drugs, used for anti-inflammatory, immunosuppressive, and metabolic effects. They act via intracellular recept...

Ptosis is the drooping or abnormal downward positioning of the upper eyelid, resulting from weakness/dysfunction of the levator palpebrae superioris muscle or its sympathetic (Müller's muscle) or CN III innervation. It can be congenital...

Proerythroblasts are the earliest morphologically identifiable precursor cells committed to the erythroid lineage in the bone marrow, arising from the erythroid progenitor cells (BFU-E and CFU-E) under the influence of erythropoietin. Th...

Weibel-Palade bodies are rod-shaped, membrane-bound secretory organelles found in vascular endothelial cells. They store von Willebrand factor (vWF) and P-selectin, releasing them in response to endothelial injury or activating stimuli (...

Pica is the compulsive eating of non-nutritive substances (e.g., dirt/geophagia, ice/pagophagia, starch/amylophagia, hair/trichophagia) for at least one month, inappropriate to developmental level. It is classically associated with iron...

Koilonychia refers to 'spoon-shaped' nails characterized by thinning and concave upward curvature of the nail plate, such that a drop of water would pool on the nail surface. It is a classic sign of chronic iron deficiency anemia. It can...

Ferroxidase is an enzyme that oxidizes ferrous iron (Fe2+) to ferric iron (Fe3+), a critical step for safe iron transport and storage in the body. The two major examples tested are ceruloplasmin and hephaestin, both of which enable iron...

Ferroportin is the only known cellular iron exporter in humans, responsible for transporting iron from enterocytes, macrophages, and hepatocytes into the bloodstream. It is negatively regulated by hepcidin, the master regulator of system...

Porphobilinogen (PBG) is a monopyrrole intermediate in heme biosynthesis, formed by ALA dehydratase from two molecules of aminolevulinic acid (ALA). Elevated urinary PBG is the classic diagnostic marker for acute intermittent porphyria (...

Hematopoietic stem cells (HSCs) are multipotent, self-renewing cells residing primarily in the bone marrow that give rise to all blood cell lineages—myeloid and lymphoid. They express CD34 surface marker and are the basis for bone marrow...

ALA dehydratase (ALAD) is the second enzyme in heme synthesis, converting two molecules of δ-aminolevulinic acid (ALA) into porphobilinogen. It occurs in the cytoplasm and is exquisitely sensitive to lead poisoning, making it a key link...

Ferrochelatase is the terminal enzyme in heme biosynthesis, catalyzing the insertion of Fe2+ into protoporphyrin IX to form heme. It is located on the inner mitochondrial membrane. Deficiency causes erythropoietic protoporphyria, and inh...

Normocytic refers to red blood cells (RBCs) of normal size, typically defined by a mean corpuscular volume (MCV) of 80–100 fL. Normocytic anemia is caused by conditions involving either decreased RBC production or increased RBC destructi...

Microcytic anemia is defined by low hemoglobin with a mean corpuscular volume (MCV) < 80 fL, indicating small red blood cells. The four classic causes (mnemonic 'TAILS'): Thalassemia, Anemia of chronic disease, Iron deficiency, and Lead...

6-Mercaptopurine (6-MP) is a purine analog chemotherapy and immunosuppressive agent used primarily for acute lymphoblastic leukemia (ALL) maintenance therapy and inflammatory bowel disease (IBD). It requires metabolic activation by HGPRT...