1500+ medical terms, defined.

UMP synthase (uridine monophosphate synthase) is a bifunctional enzyme (orotate phosphoribosyltransferase + orotidine 5'-monophosphate decarboxylase) catalyzing the final two steps of de novo pyrimidine synthesis, converting orotic acid...

Plasma cells are terminally differentiated B lymphocytes specialized for mass production and secretion of antibodies (immunoglobulins). They have a characteristic 'clock-face' (spoke-wheel) chromatin pattern, eccentric nucleus, and abund...

Vasopressin (antidiuretic hormone, ADH) is synthesized in the hypothalamus and released from the posterior pituitary in response to increased plasma osmolality or decreased blood volume/pressure. It acts on V2 receptors in the renal coll...

Diastolic heart failure, also called heart failure with preserved ejection fraction (HFpEF), occurs when the left ventricle cannot relax and fill properly despite normal contractility (EF ≥50%). It's commonly caused by conditions leading...

Chlamydophila pneumoniae (now reclassified as Chlamydia pneumoniae) is an obligate intracellular gram-negative bacterium that causes atypical ("walking") pneumonia, particularly in young adults, military recruits, and school-age children...

Alkaptonuria is a rare autosomal recessive disorder caused by a deficiency of homogentisate oxidase, leading to accumulation of homogentisic acid. Classic features include dark urine upon standing/oxidation, ochronosis (blue-black pigmen...

Free water clearance (CH2O) is the volume of plasma cleared of solute-free water per unit time, indicating the kidney's ability to dilute or concentrate urine. A positive CH2O indicates excretion of dilute urine (water excess/diuresis),...

Helicase is an enzyme that unwinds double-stranded DNA (or RNA) by breaking hydrogen bonds between base pairs, creating single-stranded templates required for replication, repair, and transcription. It moves along the DNA using ATP hydro...

Signal recognition particle (SRP) is a ribonucleoprotein complex that recognizes the signal sequence of nascent proteins being translated on free ribosomes and directs the ribosome-mRNA-protein complex to the rough endoplasmic reticulum...

Peptidoglycan is a structural polymer forming the rigid cell wall of bacteria, providing shape and protection against osmotic lysis. It is a major target of antibiotics (e.g., beta-lactams, vancomycin) and immune recognition, and differs...

Opsonization is the process by which pathogens or particles are tagged with molecules (opsonins) such as IgG antibodies or complement fragments (C3b) to enhance their recognition and phagocytosis by immune cells like macrophages and neut...

Aspergillus is a ubiquitous, septate, acute-angle branching mold that causes a spectrum of disease depending on host immune status, including allergic bronchopulmonary aspergillosis (ABPA), aspergilloma, and invasive aspergillosis. It is...

Acute cholangitis is a life-threatening infection of the biliary tree caused by obstruction (usually gallstones) leading to bile stasis and bacterial infection. It classically presents with Charcot's triad (fever, jaundice, RUQ pain), an...

Vulvovaginitis is inflammation of the vulva and vagina, commonly caused by infections (Candida, Trichomonas vaginalis, bacterial vaginosis), irritants, or atrophic changes (postmenopausal estrogen deficiency). Presentation includes disch...

Type 2 (proximal) Renal Tubular Acidosis is caused by impaired bicarbonate reabsorption in the proximal convoluted tubule, leading to a normal anion gap (hyperchloremic) metabolic acidosis with a urine pH that can be <5.5 once serum bica...

Tertiary syphilis is the late stage of untreated Treponema pallidum infection, occurring years to decades after initial infection. It is characterized by gummas, cardiovascular syphilis (aortitis), and neurosyphilis (tabes dorsalis, gene...

Cryptococcal meningitis is a fungal infection of the meninges caused by Cryptococcus neoformans (or C. gattii), classically occurring in immunocompromised patients, especially those with AIDS (CD4 <100 cells/µL). It presents subacutely w...

Gestational hypertension is new-onset hypertension (BP ≥140/90 mmHg) occurring after 20 weeks gestation in a previously normotensive woman, without proteinuria or other signs of preeclampsia. It resolves postpartum, typically within 12 w...

Edema is the abnormal accumulation of fluid in the interstitial space, resulting from disruption of Starling forces. Common causes include increased hydrostatic pressure, decreased oncotic pressure, increased vascular permeability, and l...

Weil disease is the severe icteric form of leptospirosis caused by pathogenic Leptospira interrogans, characterized by jaundice, acute kidney injury, and hemorrhage. It follows exposure to water or soil contaminated with animal urine (ra...

Alcoholic fatty liver (hepatic steatosis) is the earliest and most reversible stage of alcoholic liver disease, caused by excessive triglyceride accumulation in hepatocytes due to chronic alcohol use. It is typically asymptomatic or pres...

Chronic liver disease (CLD) refers to progressive, long-standing (>6 months) liver damage leading to fibrosis, cirrhosis, and eventual liver failure. Common causes include chronic viral hepatitis (HBV, HCV), alcohol use, non-alcoholic fa...

The oxygen-hemoglobin dissociation curve is a sigmoidal graph depicting the relationship between partial pressure of oxygen (PaO2) and hemoglobin oxygen saturation (SaO2). It reflects hemoglobin's cooperative binding of O2, with the sigm...

Gram staining is a differential staining technique used to classify bacteria into Gram-positive (purple) and Gram-negative (pink/red) based on cell wall composition. It is a first-line diagnostic tool in clinical microbiology to guide em...

Complement activation is a proteolytic cascade of plasma proteins that opsonizes pathogens, promotes inflammation, and forms the membrane attack complex (MAC) to lyse target cells. It occurs via three pathways—classical, alternative, and...

Aquaporins (AQPs) are transmembrane water channel proteins that allow rapid, selective transport of water across cell membranes down osmotic gradients. AQP2 in the renal collecting duct is the key clinically relevant isoform, regulated b...

Hirschsprung disease is a congenital disorder caused by failure of neural crest cell migration, resulting in an aganglionic segment of the distal colon that lacks both Meissner's and Auerbach's plexuses. This leads to functional obstruct...

Tumor suppressor genes encode proteins that normally inhibit cell proliferation, promote apoptosis, or repair DNA damage, thereby preventing cancer. Loss-of-function mutations in both alleles (following Knudson's two-hit hypothesis) lead...

Closed-angle (angle-closure) glaucoma occurs when the iris bulges forward and obstructs the trabecular meshwork/anterior chamber angle, blocking aqueous humor outflow and causing a rapid rise in intraocular pressure (IOP). It presents as...

Biofilm is a structured community of bacteria embedded in a self-produced extracellular polymeric matrix that adheres to living or non-living surfaces. It confers resistance to antibiotics and host immune defenses, making infections diff...

Naloxone is a competitive opioid receptor antagonist used to rapidly reverse opioid overdose, particularly respiratory depression. It has a short half-life (~30-90 min) compared to many opioids, so repeat dosing or continuous infusion ma...

Naltrexone is a competitive opioid receptor antagonist (primarily mu-opioid receptor) used to treat alcohol use disorder and opioid use disorder (for relapse prevention, not acute detox). It blocks the euphoric and reinforcing effects of...

The alveolar period is the final stage of lung development, occurring from about 36 weeks gestation to 8 years of age (with the majority of alveoli forming postnatally). During this stage, primitive saccules are subdivided by secondary s...

Alveoli are the terminal air sacs of the lungs where gas exchange (O2 and CO2) occurs across a thin respiratory membrane. They are surrounded by pulmonary capillaries and lined by type I and type II pneumocytes, providing an enormous sur...

Phosphofructokinase-1 (PFK-1) is the rate-limiting enzyme of glycolysis, catalyzing the irreversible conversion of fructose-6-phosphate to fructose-1,6-bisphosphate using ATP. It is the primary regulatory control point of glycolysis, act...

Cilostazol is a phosphodiesterase III (PDE3) inhibitor used primarily for the treatment of intermittent claudication in peripheral arterial disease (PAD). It works by increasing cAMP levels, leading to vasodilation and inhibition of plat...

Alkylating agents are chemotherapeutic drugs that add alkyl groups to DNA (especially guanine N7), causing DNA cross-linking and strand breaks that trigger apoptosis. They are cell cycle-nonspecific and used in various cancers. Key examp...

Biotin (Vitamin B7) is a water-soluble vitamin that acts as an essential cofactor for carboxylase enzymes involved in gluconeogenesis, fatty acid synthesis, and amino acid catabolism. Deficiency is rare but classically caused by excessiv...

Wrist drop is the inability to extend the wrist and fingers at the metacarpophalangeal joints, causing the hand to hang limply in flexion. It is classically caused by radial nerve injury, most often due to compression at the mid-humeral...

Telomerase is a ribonucleoprotein enzyme with reverse transcriptase activity that adds TTAGGG repeats to the 3' ends of chromosomes, preventing telomere shortening during DNA replication. It is highly active in stem cells, germ cells, an...

Viral myocarditis is inflammation of the myocardium most commonly caused by Coxsackievirus B (an enterovirus), leading to myocyte necrosis and potential cardiac dysfunction. It classically presents in young patients with prior flu-like i...

A point mutation is a change in a single nucleotide base pair in DNA. It can be classified as silent, missense, or nonsense, depending on its effect on the resulting protein. Point mutations are a fundamental mechanism of genetic variati...

The afferent arteriole is the small vessel that carries blood from the interlobular (cortical radiate) artery into the glomerulus of the nephron. It delivers blood at high pressure to the glomerular capillaries to enable filtration and i...

The efferent arteriole is the vessel that carries blood away from the glomerulus after filtration, before feeding into the peritubular capillaries or vasa recta. Its resistance is critical in regulating glomerular filtration rate (GFR) a...

Prostate cancer is the most common non-cutaneous cancer in men, typically arising in the peripheral zone of the prostate and often diagnosed via elevated PSA and/or abnormal DRE (asymmetric, nodular, indurated gland). Most cases are aden...

Mitosis is the process by which a single somatic cell divides to produce two genetically identical daughter cells, each with the same diploid (2n) chromosome number as the parent cell. It consists of four main phases—prophase, metaphase,...

Pepsinogen is the inactive zymogen precursor of pepsin, secreted by chief cells in the gastric fundic glands. It is activated to pepsin by exposure to gastric acid (HCl) or existing pepsin in a positive feedback loop. Pepsin functions as...

Chest X-ray (CXR) is a plain radiograph of the thorax used to evaluate the lungs, heart, mediastinum, and bony structures. It is a first-line imaging modality for cardiopulmonary complaints, trauma, and routine screening. Standard views...

Heinz bodies are denatured, precipitated hemoglobin inclusions within red blood cells, formed due to oxidative damage to hemoglobin. They are classically seen in G6PD deficiency after oxidative stress and are removed by splenic macrophag...

Nephroblastoma (Wilms tumor) is the most common pediatric renal malignancy, typically presenting in children ages 2-5 years as a large, unilateral, palpable abdominal mass. It arises from remnants of embryonal nephrogenic tissue (metanep...