1500+ medical terms, defined.

The prostatic urethra is the proximal segment of the male urethra (~3-4 cm) that passes through the prostate gland, connecting the bladder neck to the membranous urethra. It contains the urethral crest and seminal colliculus, where ejacu...

The epididymis is a coiled tubular structure attached to the posterior surface of the testis that stores, matures, and transports sperm from the testis to the vas deferens. It is divided into head, body, and tail regions and is lined by...

Jugular venous pressure (JVP) is a clinical estimate of right atrial pressure, assessed by observing the height of pulsations in the internal jugular vein with the patient reclined at 30-45 degrees. Normal JVP is ≤8 cm H2O (or ≤3-4 cm ab...

Exocytosis is the cellular process by which membrane-bound vesicles fuse with the plasma membrane to release their contents into the extracellular space. It is essential for secretion of hormones, neurotransmitters, and enzymes, and requ...

Cat scratch disease is a self-limited infection caused by Bartonella henselae, transmitted via cat scratch or bite (often from kittens). It classically presents with regional lymphadenopathy near the inoculation site, often with a preced...

Hepatic adenoma is a benign liver tumor strongly associated with oral contraceptive use and anabolic steroids, predominantly occurring in women of reproductive age. It carries risk of hemorrhage and rare malignant transformation to hepat...

Certolizumab pegol is a PEGylated Fab' fragment of a humanized monoclonal antibody that binds and neutralizes TNF-α. It is used to treat autoimmune inflammatory conditions such as rheumatoid arthritis, Crohn's disease, psoriatic arthriti...

Muscarinic antagonists (anticholinergics) competitively block muscarinic acetylcholine receptors (M1-M5), inhibiting parasympathetic nervous system effects. Classic examples include atropine, scopolamine, ipratropium/tiotropium, oxybutyn...

Erectile dysfunction (ED) is the persistent inability to achieve or maintain an erection sufficient for satisfactory sexual performance. It is commonly vascular in etiology (endothelial dysfunction), especially in older men, and is an im...

Nitric oxide synthase (NOS) is an enzyme that catalyzes the conversion of L-arginine to nitric oxide (NO) and L-citrulline, using NADPH and O2 as cofactors. There are three isoforms: eNOS (endothelial), nNOS (neuronal), and iNOS (inducib...

An ovarian cyst is a fluid-filled sac within or on the surface of the ovary, most commonly a benign functional cyst (follicular or corpus luteum) related to the menstrual cycle. Most are asymptomatic and resolve spontaneously within 8-12...

Autoimmune gastritis (Type A gastritis) is a chronic autoimmune condition targeting parietal cells of the gastric fundus/body, leading to achlorhydria, loss of intrinsic factor, and vitamin B12 deficiency causing pernicious anemia. It is...

The substantia nigra is a midbrain structure rich in dopaminergic neurons, critical for motor control via the nigrostriatal pathway. Its degeneration is the hallmark pathology of Parkinson's disease, causing bradykinesia, rigidity, resti...

Beck triad is a classic clinical finding associated with cardiac tamponade, consisting of hypotension, jugular venous distension (JVD), and muffled/distant heart sounds. It reflects impaired cardiac filling due to fluid accumulation in t...

Beta oxidation is the metabolic pathway that breaks down fatty acids into acetyl-CoA units within the mitochondrial matrix, generating NADH and FADH2 for ATP production via the electron transport chain. It is a key energy source during f...

Cysteine is a semi-essential, sulfur-containing amino acid notable for its thiol (-SH) group, which allows disulfide bond formation critical for protein tertiary structure. It is a precursor for glutathione, taurine, and coenzyme A, and...

Bipolar disorder is a mood disorder characterized by episodes of mania or hypomania, often alternating with episodes of major depression. Bipolar I requires at least one manic episode; Bipolar II requires at least one hypomanic episode p...

Teriparatide is a recombinant form of human parathyroid hormone (PTH 1-34) used to treat severe osteoporosis. Unlike continuous PTH exposure, which causes bone resorption, intermittent daily dosing paradoxically stimulates osteoblast act...

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the GI tract, arising from the interstitial cells of Cajal (the GI pacemaker cells). Most cases are driven by gain-of-function mutations in the c-KIT (CD117) o...

The vena cavae are the two large veins that return deoxygenated blood to the right atrium of the heart. The superior vena cava (SVC) drains blood from the head, neck, upper extremities, and thorax, while the inferior vena cava (IVC) drai...

The neural plate is a thickened, specialized region of ectoderm that forms during the third week of embryogenesis in response to signals from the underlying notochord. It is the precursor structure to the entire central nervous system, g...

Golimumab is a human monoclonal antibody that inhibits tumor necrosis factor-alpha (TNF-α), used to treat autoimmune inflammatory conditions such as rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, and ulcerative coliti...

A 'left shift' refers to an increase in the proportion of immature neutrophils (bands) and sometimes earlier precursors (metamyelocytes, myelocytes) in peripheral blood, typically indicating acute bacterial infection or another cause of...

Transthoracic echocardiogram (TTE) is a non-invasive ultrasound imaging technique that assesses cardiac structure and function by placing a probe on the chest wall. It is the first-line imaging modality for evaluating ejection fraction,...

Pulmonary atresia is a cyanotic congenital heart defect in which there is complete obstruction of the right ventricular outflow tract, with no communication between the right ventricle and pulmonary artery. Pulmonary blood flow is entire...

Ipilimumab is a monoclonal antibody that blocks CTLA-4, an inhibitory checkpoint on T cells, thereby enhancing T-cell activation and antitumor immune response. It is used primarily in metastatic melanoma. Key toxicity is immune-related a...

Follicular thyroid carcinoma (FTC) is the second most common thyroid cancer, arising from follicular epithelial cells. It spreads hematogenously (bone, lung) rather than via lymphatics, distinguishing it from papillary carcinoma. Diagnos...

Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder caused by mutations in the LYST gene, leading to defective lysosomal trafficking and giant granules in cells. Clinically, it presents with recurrent pyogenic infection...

Nonproliferative diabetic retinopathy (NPDR) is the earlier, more common stage of diabetic retinopathy characterized by damage to retinal microvasculature without neovascularization. It presents with microaneurysms, dot-blot hemorrhages,...

Enterohepatic circulation is the cycling of substances (bile acids, drugs, bilirubin) between the liver, bile, small intestine, and back to the liver via portal blood. Bile acids are the classic example: ~95% are reabsorbed in the termin...

The rough endoplasmic reticulum (RER) is a cytoplasmic organelle studded with ribosomes that synthesizes and processes secretory and membrane-bound proteins. It is prominent in cells with high secretory activity, such as plasma cells, he...

The common bile duct (CBD) is formed by the union of the cystic duct and common hepatic duct, and it delivers bile from the liver and gallbladder into the second part of the duodenum via the ampulla of Vater. It passes posterior to the f...

The bulbus cordis is an embryonic structure derived from the primitive heart tube that gives rise to portions of the ventricles and outflow tract of the heart. It contributes to the smooth parts (outflow tracts) of the right and left ven...

Meningococcemia is a life-threatening bloodstream infection caused by Neisseria meningitidae, a gram-negative diplococcus. It classically presents with fever, hypotension, and a petechial/purpuric rash, and can rapidly progress to septic...

Gilbert syndrome is a common, benign hereditary disorder caused by reduced activity of UDP-glucuronosyltransferase (UGT1A1), leading to mild unconjugated (indirect) hyperbilirubinemia. It is typically discovered incidentally and worsened...

Trinucleotide repeat disorders are genetic diseases caused by expansion of three-nucleotide DNA sequences beyond a normal threshold, leading to unstable, expandable repeats. Many demonstrate genetic anticipation—increased repeat number a...

Class switching (isotype switching) is a process in which activated B cells change the antibody isotype they produce (e.g., from IgM to IgG, IgA, or IgE) while retaining antigen specificity. It occurs in germinal centers of secondary lym...

Stop codons (UAA, UAG, UGA) are mRNA sequences that signal the ribosome to terminate protein synthesis, as no tRNA anticodon matches them. Release factors recognize stop codons and trigger release of the completed polypeptide from the ri...

ACE inhibitors (e.g., lisinopril, enalapril, captopril) block angiotensin-converting enzyme, preventing conversion of angiotensin I to angiotensin II. They are first-line agents for hypertension, heart failure, diabetic nephropathy, and...

The Romberg sign is a positive test when a patient loses balance upon standing with feet together and eyes closed, indicating impaired proprioception (dorsal column dysfunction) rather than a cerebellar problem. It is used to distinguish...

Non-small cell lung cancer (NSCLC) accounts for ~85% of lung cancers and includes adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. It is strongly associated with smoking (though adenocarcinoma is most common in non-smok...

External hemorrhoids are dilated vascular cushions arising from the inferior rectal venous plexus, located below the dentate line and covered by squamous epithelium. They are innervated by somatic nerves, making them painful, especially...

The renal vein drains venous blood from the kidney into the inferior vena cava (IVC). The left renal vein is longer than the right and passes anterior to the aorta, coursing between the superior mesenteric artery (SMA) and aorta, making...

Prothrombin time (PT) measures the extrinsic and common coagulation pathways (Factors I, II, V, VII, X). It is prolonged by deficiencies or inhibition of these factors and is used to monitor warfarin therapy via the INR (International No...

PEPCK (phosphoenolpyruvate carboxykinase) is a key rate-limiting enzyme in gluconeogenesis, catalyzing conversion of oxaloacetate to phosphoenolpyruvate. It exists in cytosolic and mitochondrial isoforms and is highly regulated by hormon...

Type I collagen is the most abundant collagen in the body, providing tensile strength to bone, skin, tendons, and ligaments. It is composed of two α1 chains and one α2 chain forming a triple helix, requiring vitamin C-dependent hydroxyla...

Partial thromboplastin time (PTT), also called activated PTT (aPTT), measures the intrinsic coagulation pathway (factors XII, XI, IX, VIII, X, V, prothrombin/II, and fibrinogen). It is used to monitor unfractionated heparin therapy and t...

The vestibule is the central chamber of the bony labyrinth of the inner ear, located between the cochlea and the semicircular canals. It houses the utricle and saccule, which contain sensory maculae responsible for detecting linear accel...

Crescentic glomerulonephritis (CrGN), or rapidly progressive glomerulonephritis (RPGN), is a severe pattern of glomerular injury characterized by cellular crescents in Bowman's space on histology, leading to rapid loss of renal function...

Prednisone is a synthetic corticosteroid prodrug converted by the liver to prednisolone, its active form. It has potent anti-inflammatory and immunosuppressive effects, used to treat autoimmune diseases, inflammatory conditions, allergic...