1500+ medical terms, defined.

The labia majora are the paired, hair-bearing outer folds of skin of the vulva that form the lateral boundaries of the pudendal cleft. They are homologous to the male scrotum and develop from the labioscrotal swellings during embryogenes...

Bactericidal refers to antibiotics or antimicrobial agents that directly kill bacteria, as opposed to bacteriostatic agents which merely inhibit bacterial growth and rely on host immune defenses to clear the infection. This distinction i...

Vimentin is a class III intermediate filament protein that serves as a cytoskeletal component of cells of mesenchymal origin, including fibroblasts, endothelial cells, lymphocytes, and other connective tissue cells. It is a key immunohis...

Benzodiazepine withdrawal occurs after abrupt discontinuation or rapid dose reduction in patients with physical dependence, producing rebound CNS hyperexcitability. Symptoms include anxiety, insomnia, tremor, autonomic instability, and p...

The ureteric bud is an outgrowth of the mesonephric (Wolffian) duct that induces metanephric mesenchyme to form the kidney during embryogenesis. It gives rise to the collecting system of the kidney, including the ureter, renal pelvis, ca...

Neural folds are the paired elevations of neuroectoderm that form along the lateral edges of the neural plate during the third to fourth week of embryonic development. They rise up and fuse in the midline to form the neural tube, the pre...

Coronary Artery Bypass Grafting (CABG) is a surgical procedure that reroutes blood around narrowed or blocked coronary arteries using grafts, typically to treat severe coronary artery disease (CAD). Common grafts include the left interna...

Immune thrombocytopenic purpura (ITP) is an autoimmune disorder characterized by isolated thrombocytopenia due to antiplatelet antibodies (typically against GPIIb/IIIa) leading to peripheral platelet destruction by splenic macrophages. I...

The clitoris is an erectile female external genital organ located at the anterior junction of the labia minora, homologous to the penis. It functions solely in sexual arousal and pleasure, containing dense sensory innervation. Only the g...

Opsonins are molecules (e.g., IgG, C3b) that coat pathogens or particles, marking them for enhanced recognition and phagocytosis by macrophages and neutrophils. This process, called opsonization, is a key mechanism linking innate and ada...

Water hammer pulse (Corrigan's pulse) is a bounding pulse with rapid rise and rapid collapse, classically associated with aortic regurgitation. It reflects the wide pulse pressure seen in conditions with increased stroke volume and low d...

Transcription factors are proteins that bind specific DNA sequences (promoters/enhancers) to regulate gene expression by promoting or inhibiting RNA polymerase recruitment. Mutations in transcription factor genes cause numerous developme...

Endotoxin refers to lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria that triggers a strong innate immune response. It is released upon bacterial cell lysis and can cause fever, hypotension, and disse...

Microangiopathic hemolytic anemia (MAHA) is a form of intravascular hemolysis caused by mechanical destruction of red blood cells as they pass through narrowed or damaged small vessels containing fibrin strands or platelet microthrombi....

Isovolumetric contraction is the phase of the cardiac cycle occurring right after mitral valve closure and before aortic valve opening, during which the left ventricle contracts and pressure rises sharply, but volume remains constant bec...

Type 2 (proximal) renal tubular acidosis is caused by impaired bicarbonate reabsorption in the proximal convoluted tubule, leading to a hyperchloremic, normal anion gap metabolic acidosis with urine that can appropriately acidify (urine...

Transformation refers to the process by which bacteria take up free extracellular DNA from their environment, incorporating it into their genome. In molecular biology and oncology, the term also describes the conversion of normal cells i...

Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of the pentose phosphate pathway, catalyzing the first step that generates NADPH. G6PD deficiency is the most common human enzyme deficiency, an X-linked recessive diso...

Motilin is a peptide hormone secreted by M cells of the small intestine (duodenum/jejunum) that stimulates gastrointestinal motility, particularly triggering the migrating motor complex (MMC) during the fasting state. Motilin receptor ag...

Celiac sprue (celiac disease) is an autoimmune enteropathy triggered by gluten (gliadin) ingestion in genetically susceptible individuals, leading to small bowel villous atrophy and malabsorption. It is strongly associated with HLA-DQ2/D...

Gram-positive rods (bacilli) are bacteria that retain crystal violet stain due to a thick peptidoglycan cell wall and have a rod-shaped morphology. Key pathogenic genera include Bacillus, Clostridium, Corynebacterium, Listeria, and Actin...

Nondihydropyridine calcium channel blockers (verapamil and diltiazem) primarily target cardiac tissue, reducing heart rate, AV nodal conduction, and myocardial contractility. They are used for rate control in atrial fibrillation/flutter,...

The corpus cavernosum refers to two paired cylindrical erectile tissue structures within the penis (or clitoris) that engorge with blood during sexual arousal to produce an erection. They are surrounded by the tunica albuginea and are th...

Labioscrotal swellings are paired embryonic structures in the urogenital region that develop into the labia majora in females or fuse to form the scrotum in males, depending on the presence or absence of androgen (DHT) exposure.

Superantigens are microbial toxins (e.g., from Staphylococcus aureus and Streptococcus pyogenes) that cause massive, non-specific activation of T cells by cross-linking the T-cell receptor (V-beta region) directly to MHC class II molecul...

A loss-of-function (LOF) mutation reduces or eliminates the normal activity of a gene product, often resulting in a null (amorphic) or hypomorphic allele. These mutations are typically recessive in inheritance (one normal allele can comp...

C cells (parafollicular cells) are neuroendocrine cells located in the thyroid gland, adjacent to but distinct from thyroid follicles. They secrete calcitonin in response to elevated serum calcium levels, which acts to lower blood calciu...

The dentate (pectinate) line is the junction in the anal canal marking the transition from hindgut-derived to ectoderm-derived tissue. It has critical implications for blood supply, innervation, lymphatic drainage, and the type of pathol...

Invasive aspergillosis is a life-threatening fungal infection caused by Aspergillus species (most commonly A. fumigatus) that invades pulmonary vasculature and disseminates in immunocompromised hosts, especially neutropenic patients and...

Rhizopus is a genus of fast-growing, filamentous fungi (molds) belonging to the order Mucorales, notable as a leading cause of mucormycosis, an aggressive angioinvasive infection primarily seen in immunocompromised hosts, especially thos...

Voriconazole is a second-generation triazole antifungal that inhibits fungal cytochrome P450-dependent 14α-demethylase, blocking ergosterol synthesis. It is the first-line treatment for invasive aspergillosis and is also used for candidi...

The 5' cap is a modified guanine nucleotide (7-methylguanosine) added to the 5' end of eukaryotic pre-mRNA during transcription. It protects mRNA from degradation, aids nuclear export, and is essential for ribosome recognition during tra...

Introns are non-coding sequences within a gene that are transcribed into pre-mRNA but removed via splicing before translation, leaving only exons to form mature mRNA. Alternative splicing of exons (facilitated by intron removal) allows a...

The Shine-Dalgarno sequence is a purine-rich ribosomal binding site (consensus AGGAGG) found in prokaryotic mRNA, located 6-10 base pairs upstream of the start codon (AUG). It base-pairs with a complementary sequence on the 16S rRNA of t...

The Kozak sequence is a nucleotide consensus sequence (GCCRCCATGG) surrounding the start codon (AUG) in eukaryotic mRNA that facilitates efficient recognition and initiation of translation by the ribosome. It plays a key role in determin...

Hematopoietic stem cells (HSCs) are multipotent, self-renewing cells residing primarily in the bone marrow that give rise to all blood cell lineages—erythrocytes, leukocytes, and platelets. They express the surface marker CD34, which is...

Erythrocyte sedimentation rate (ESR) is a nonspecific marker of inflammation measuring how quickly RBCs settle in a vertical tube over one hour. Elevated fibrinogen and other acute-phase proteins cause RBCs to aggregate (rouleaux formati...

Acinetobacter baumannii is a strictly aerobic, gram-negative coccobacillus notorious for causing multidrug-resistant nosocomial infections, particularly ventilator-associated pneumonia and infections in ICU/burn patients. It thrives on e...

The intrinsic pathway is one of two initial pathways of the coagulation cascade, activated by exposure of blood to subendothelial collagen or negatively charged surfaces (e.g., in vitro contact activation). It involves factors XII, XI, I...

Pulseless electrical activity (PEA) is a cardiac arrest rhythm characterized by organized electrical activity on ECG (not VF/VT) without a palpable pulse or detectable blood pressure. It is treated with high-quality CPR and epinephrine,...

Fungal meningitis is a subacute-to-chronic infection of the meninges most commonly caused by Cryptococcus neoformans, particularly in immunocompromised patients (e.g., HIV/AIDS with CD4 <100). It presents with headache, fever, and altere...

Cavernous sinus thrombosis (CST) is a rare, life-threatening condition caused by infection or clot formation within the cavernous sinus, most often secondary to spread of facial or sinus infections (the 'danger triangle'). It classically...

A hapten is a small molecule that is not immunogenic by itself but can become antigenic when it covalently binds to a larger carrier protein. This hapten-carrier complex can then trigger an immune response, including antibody production...

Violaceous refers to a purple or violet discoloration of skin or tissue, often indicating vascular congestion, inflammation, ischemia, or infiltration. It's a key descriptive term in dermatology and used to characterize lesions in variou...

Haptens are small molecules that are not immunogenic by themselves but can become immunogenic when covalently bound to a larger carrier protein. They can then elicit an antibody-mediated or T-cell-mediated immune response directed agains...

Chronic mucocutaneous candidiasis (CMC) is a group of immunodeficiency disorders characterized by persistent, recurrent Candida albicans infections of the skin, nails, and mucous membranes without invasive systemic disease. It results fr...

Roth spots are retinal hemorrhages with pale, white centers composed of fibrin-platelet aggregates, classically associated with infective endocarditis. They result from immune-complex-mediated vasculitis and septic microemboli affecting...

PD-L1 (Programmed Death-Ligand 1) is a cell surface protein that binds PD-1 receptors on T cells, delivering an inhibitory signal that suppresses T-cell activation and promotes immune tolerance. Many tumors overexpress PD-L1 to evade imm...

Janeway lesions are non-tender, erythematous or hemorrhagic macules/papules found on the palms and soles, classically associated with infective endocarditis. They result from septic microemboli lodging in small vessels of the skin. Their...

Osler nodes are tender, raised, erythematous-to-violaceous nodules found on the pads of the fingers and toes, classically associated with infective endocarditis. They are caused by immune complex deposition and are one of the minor Duke...