Comprehensive medical terminology with definitions, clinical cases, mnemonics, and treatment guides — free for students and educators.
In genetics, "2n" denotes the diploid number of chromosomes in a cell. The symbol n represents a sin…
"2n = 46" is the notation indicating that an organism's diploid number is 46. In humans, this means …
Guanosine‑analogue NRTI used in combination antiretroviral therapy. After intracellular phosphorylat…
Synthetic analog of parathyroid hormone–related peptide (PTHrP 1–34). When given as once‑daily subcu…
Brief generalized nonconvulsive seizures (formerly petit mal) characterized by sudden staring and un…
Acetylcholine (ACh) is a neurotransmitter released by certain nerve cells in both the central and pe…
Achalasia is a motility disorder in which degeneration of the esophageal myenteric plexus causes los…
Autosomal‑dominant disorder caused by a gain‑of‑function mutation in FGFR3 that overly suppresses ch…
Most common skeletal dysplasia (genetic dwarfism) caused by an FGFR3 gene mutation (gain-of-function…
Common chronic inflammatory disease of pilosebaceous units (hair follicles and oil glands) character…
Benign Schwann cell tumor of the vestibulocochlear nerve (CN VIII), usually at the cerebellopontine …
Anterior pituitary peptide from POMC that stimulates the adrenal cortex (zona fasciculata/reticulari…
Active transport is the energy-requiring process of moving substances across a cell membrane against…
Acute inflammation of the liver due to heavy alcohol use, usually after prolonged drinking, characte…
Life-threatening infection of the meninges (protective brain/spinal cord lining) causing acute infla…
Acute inflammation of the gallbladder, usually triggered by a gallstone obstructing the cystic duct …
Rare, life-threatening complication of late pregnancy characterized by microvesicular fatty infiltra…
Acute inflammation of the liver (hepatitis lasting <6 months) due to hepatocyte injury from various …
Acute intestinal obstruction is a sudden blockage of normal intestinal flow (usually a mechanical bl…
Acute inflammation of the pancreas due to premature enzyme activation causing autodigestion of pancr…
Life-threatening acute lung injury characterized by diffuse alveolar damage, leading to increased ca…
Post-streptococcal autoimmune inflammatory disease that occurs about 2–4 weeks after untreated group…
Adaptation in biology refers to a heritable trait or characteristic that improves an organism's abil…
Group of genetic disorders with absent or reduced melanin pigment in skin, hair, and eyes due to mel…
Spectrum of liver injury due to chronic alcohol use, ranging from reversible fatty infiltration to l…
An allele is one of the different forms of a particular gene. For any given gene, an individual norm…
Allergic inflammation of the nasal mucosa caused by an IgE-mediated reaction to environmental allerg…
Allopatric speciation is the formation of a new species from populations that are geographically iso…
Inherited protease inhibitor (serpin) disorder with low or dysfunctional alpha-1 antitrypsin. Leads …
Loss of two of the four α-globin genes (either both on one chromosome cis or one on each trans). Cau…
Any acute change in a patient's mental state – encompassing altered level of consciousness, cognitio…
A developmental vision disorder where the brain fails to process input from one eye, leading to redu…
Amenorrhea is absence of menstruation in a woman of reproductive age. Primary amenorrhea is no menar…
Pathologic extracellular deposition of insoluble misfolded protein fibrils (β-pleated sheets) in tis…
Progressive degenerative motor neuron disease affecting upper and lower motor neurons, leading to mu…
A severe, life-threatening systemic hypersensitivity reaction (often IgE-mediated) characterized by …
Group of small vessel vasculitides driven by ANCA autoantibodies, causing necrotizing inflammation w…
Anencephaly is a neural tube defect where the rostral neuropore fails to close, resulting in absence…
Localized dilatation or ballooning of an artery due to a weakened vessel wall (e.g., from elastin fi…
Neurogenetic disorder caused by loss of the maternal *UBE3A* gene (15q11–13) due to genomic imprinti…
The anion gap represents the difference between measured cations (Na⁺) and measured anions (Cl⁻ + HC…
Chronic inflammatory disease of the axial skeleton, primarily involving the sacroiliac joints and sp…
*Anorexia nervosa* is an eating disorder marked by self-induced starvation and severe weight loss. P…
Autoimmune hypercoagulable disorder (primary or SLE-associated) marked by recurrent venous/arterial …
Uncommon autoimmune syndrome characterized by autoantibodies against aminoacyl-tRNA synthetases, lea…
Tear in the aortic intimal layer allowing blood to split the wall layers (forming a false lumen); cl…
Narrowing of the aortic valve opening that obstructs left ventricular outflow, most often due to age…
It's when the vermiform appendix (a small pouch off the colon) becomes acutely inflamed, usually due…
Aquaporins are integral membrane proteins that serve as channels for water transport in and out of c…
Artificial selection is the process by which humans intentionally breed plants or animals for specif…
Chronic fibrosing pneumoconiosis of the lungs caused by prolonged inhalation of asbestos fibers.…
Abnormal fluid accumulation in the peritoneal cavity; often due to portal hypertension (e.g., decomp…
Chronic inflammatory airway disease with episodes of bronchoconstriction causing wheezing, breathles…
Chronic inflammatory arterial disease marked by cholesterol-rich plaque (atheroma) buildup in medium…
Atopic dermatitis (AD), also called eczema, is a chronic, pruritic inflammatory skin disease and the…
ATP synthase is a large protein complex in the inner mitochondrial membrane (and similar membranes o…
A supraventricular tachyarrhythmia caused by chaotic atrial electrical activity leading to ineffecti…
Neurodevelopmental disorder characterized by persistent deficits in social communication and interac…
Chronic, immune-mediated liver inflammation (hepatitis) caused by autoimmunity. Characterized by cir…
Rare genetic disorder of lymphocyte apoptosis failure leading to chronic nonmalignant lymphoprolifer…
Autosomal refers to the non-sex chromosomes (chromosomes 1-22 in humans). A gene or trait described …
Rare primary immunodeficiency (autosomal dominant) characterized by the triad of severe eczema, recu…
A bacterial ribosome is the ribosome found in prokaryotic cells, responsible for protein synthesis i…
Intestinal metaplasia of the distal esophagus caused by chronic acid reflux, where normal squamous l…
Malignant skin tumor of basal epidermal (keratinocyte) origin; slow-growing, locally invasive, and r…
Autoinflammatory vasculitis (variable vessel) of unknown cause, featuring recurrent oral and genital…
Disease caused by vitamin B1 (thiamine) deficiency, classically divided into dry beriberi (neurologi…
Autosomal recessive quantitative or qualitative defect of the platelet GPIb-IX-V receptor that binds…
The most severe form of β-thalassemia (homozygous β⁰ or β⁺ mutations) causing near-complete absence …
Heterozygous β-globin gene mutation causing reduced β-chain production. Results in a mild, asymptoma…
Congenital absence of both kidneys (and ureters), often referred to as classic Potter syndrome. The …
Rare, life‑threatening neuroparalytic syndrome caused by botulinum neurotoxin (usually from *Clostri…
Inflammation of the small airways (bronchioles) causing airflow obstruction. In infants it typically…
Inherited arrhythmia syndrome (sodium channelopathy) featuring a characteristic coved ST-segment ele…
Eating disorder characterized by recurrent binge eating with loss of control, followed by inappropri…
Common autoimmune blistering skin disease in older adults—IgG autoantibodies attack hemidesmosomes (…
Highly aggressive B‑cell NHL driven by MYC translocation; classic 'starry‑sky' histology.…
Deposition of calcium pyrophosphate dihydrate crystals in joint cartilage leading to inflammatory ar…
A capsid is the protein shell of a virus that encloses its genetic material (DNA or RNA). It is buil…
Rare paraneoplastic syndrome caused by metastatic serotonin-secreting neuroendocrine tumors (carcino…
Clouding of the eye's normally clear lens, leading to progressive painless vision loss (often like t…
In biology, a cell is the basic unit of life - a membrane-bound structure containing the fundamental…
The cell cycle is the ordered series of phases that a cell goes through to grow and divide into two …
The cell membrane (plasma membrane) is a thin, flexible barrier that surrounds the cell-s cytoplasm,…
The central nervous system (CNS) is the part of the nervous system consisting of the brain and spina…
Centrioles are paired barrel-shaped organelles in the cytoplasm of animal cells near the nuclear env…
The centromere is a constricted region of a chromosome where spindle fibers attach during cell divis…
A centrosome is a cellular structure involved in cell division. Before division, the centrosome dupl…
A group of permanent movement and posture disorders caused by non-progressive injury to the developi…
A channel protein is an integral membrane protein that spans a cell membrane and contains a hydrophi…
The classic trio of fever, jaundice, and right upper quadrant (RUQ) pain seen in acute ascending cho…
Rare autosomal recessive immunodeficiency characterized by partial oculocutaneous albinism, recurren…
Congenital hindbrain malformation where the cerebellar tonsils herniate downward through the foramen…
A congenital hindbrain malformation with caudal displacement of the cerebellar vermis/tonsils, brain…
Chiasmata (singular: chiasma) are the physical X-shaped junctions where homologous chromosomes have …
Presence of one or more gallstones in the common bile duct (CBD), causing partial or complete biliar…
Chromatin is a mixture of DNA and proteins that forms the chromosomes in humans and other higher org…
A chromosome is a threadlike structure made of protein and a single DNA molecule that carries genomi…
Long-standing inflammation of the gallbladder, nearly always due to gallstones causing repeated mino…
Inherited phagocyte disorder with defective NADPH oxidase. Neutrophils can't generate reactive oxyge…
Ongoing liver inflammation lasting ≥6 months (vs acute <6 months). Chronic hepatitis is a syndrome w…
Progressive loss of kidney function over ≥3 months, defined by eGFR <60 mL/min/1.73 m² or signs of k…
Indolent B-cell leukemia of older adults, characterized by chronic lymphocytosis and immune dysfunct…
Myeloproliferative neoplasm with unchecked myeloid (granulocyte) proliferation; driven by BCR-ABL fu…
A progressive lung condition characterized by persistent airflow limitation and respiratory symptoms…
Long-standing inflammation of the pancreas leading to progressive fibrosis, permanent structural dam…
The circulatory system (cardiovascular system) is the organ system that circulates blood throughout …
End-stage liver disease with irreversible fibrosis and regenerative nodules replacing normal archite…
An opening in the roof of the mouth caused by the palate tissues failing to fuse during fetal develo…
In biology, cloning is the process of creating a genetically identical copy of a biological entity. …
An antibiotic-associated infection of the colon by the spore-forming bacterium Clostridioides diffic…
Co-dominance is an inheritance pattern in which two different alleles of a gene are both fully expre…
Rare autoimmune disorder characterized by inflammation of the cornea (non-syphilitic interstitial ke…
Primary antibody immunodeficiency with hypogammaglobulinemia (low IgG plus low IgA/IgM) causing recu…
Clinical syndrome of the heart's inability to pump blood effectively, leading to inadequate perfusio…
Inflammation of the conjunctiva ("pink eye") causing red eye and discharge; usually benign and self-…
Connective tissue is a broad category of tissue that supports, connects, or separates different type…
Atherosclerotic narrowing of coronary arteries reduces blood flow to heart muscle (myocardial ischem…
The Corrected QT Interval (QTc) adjusts the measured QT interval for heart rate, allowing comparison…
Crossing over is the process during meiosis in which two homologous chromosomes exchange genetic mat…
Clinical syndrome of chronic cortisol excess (hypercortisolism); Cushing disease refers specifically…
Autosomal recessive disorder of CFTR (chloride channel) causing abnormally thick secretions in exocr…
Cytochrome c (Cyt c) is a small, soluble heme protein associated with the inner mitochondrial membra…
Ubiquitous human β-herpesvirus (HHV-5) that establishes lifelong latency; usually asymptomatic or mo…
In genetics, a deletion is a type of mutation where one or more nucleotides (bases) are removed from…
Chronic cognitive syndrome marked by progressive decline in one or more cognitive domains (memory, l…
Idiopathic autoimmune myositis characterized by symmetric proximal muscle weakness and distinctive s…
Gradual, controlled exposure to an allergen or drug to induce immune tolerance (reduced or eliminate…
Disorder of water balance causing excretion of large volumes of dilute urine due to insufficient ADH…
Chronic metabolic disorder of hyperglycemia due to insufficient insulin action. In type 1 diabetes (…
Life-threatening acute complication of diabetes mellitus characterized by hyperglycemia (glucose >25…
Microangiopathy of the retina caused by chronic hyperglycemia, leading to capillary leak and occlusi…
Increase in stool frequency and liquidity, typically defined as ≥3 loose or watery stools per day. D…
Autosomal dominant microdeletion of chromosome 22q11.2 (usually de novo) causing defective developme…
Disease of the heart muscle characterized by dilated ventricular chambers and systolic dysfunction (…
Acute infection by toxin-producing Corynebacterium diphtheriae affecting the respiratory tract (or s…
Diploid describes a cell or organism that has two complete sets of chromosomes. In a diploid cell, c…
Systemic activation of coagulation (often via tissue factor or widespread endothelial injury) produc…
Presence of outpouchings (diverticula) in the colonic wall, most often in the sigmoid colon. Diverti…
DNA is the hereditary material in nearly all living organisms. It is a double-stranded helix of nucl…
A dominant allele is one that will determine the phenotype even if only one copy is present. In othe…
A genetic condition caused by an extra copy of chromosome 21 (trisomy 21), most often due to materna…
X-linked recessive dystrophin gene mutation causing absent dystrophin protein and progressive muscle…
Congenital absence or complete closure of part of the duodenal lumen; causes neonatal intestinal obs…
Long-standing unrepaired left-to-right cardiac shunt that leads to severe pulmonary hypertension and…
Chronic destructive lung disease: permanent enlargement of airspaces distal to terminal bronchioles …
Infection of the heart's inner lining (endocardium), usually involving the valves, forming vegetatio…
The endocrine system is the body's hormone network - a collection of ductless glands that secrete ho…
Malignant tumor of the uterine endometrium (lining); usually an adenocarcinoma arising from endometr…
Presence of endometrial tissue (glands and stroma) outside the uterus; lesions are estrogen-dependen…
Arthritis associated with inflammatory bowel disease (Crohn disease or ulcerative colitis). Can mani…
Bleeding from the nose (nosebleed), usually from ruptured vessels in the nasal mucosa. Classified as…
Epithelial tissue (epithelium) consists of sheets of tightly packed cells that cover the exterior su…
Paralysis of the arm from injury to the upper trunk (C5–C6) of the brachial plexus; classically pres…
Relatively common bacterial infection of the upper dermis (usually group A Strep) causing a well-dem…
Congenital discontinuity of the esophagus (ends in a blind pouch) that prevents swallowed material f…
Dilated submucosal veins in the distal esophagus due to portal hypertension (usually from cirrhosis)…
Evolution is the change in the heritable characteristics of a population over successive generations…
Weakness or paralysis of the facial muscles due to dysfunction of CN VII (facial nerve); peripheral …
Inherited point mutation in the Factor V gene (most commonly Arg506→Gln) that makes factor V resista…
FAD (flavin adenine dinucleotide) is a redox coenzyme that can accept electrons and protons. In its …
FADH2 is the reduced form of FAD (flavin adenine dinucleotide), a coenzyme that carries electrons in…
Familial Mediterranean fever (FMF) is a hereditary autoinflammatory disorder (usually autosomal rece…
Involuntary loss of solid or liquid stool due to loss of bowel control; ranges from minor leakage (s…
Fermentation is an anaerobic metabolic process by which cells break down sugars to generate energy w…
Indolent B‑cell NHL with t(14;18) causing BCL2 overexpression and inhibited apoptosis.…
Fructose is a six-carbon monosaccharide sugar (C₆H₁₂O₆) commonly known as "fruit sugar." It is an is…
A G protein-coupled receptor (GPCR) is a cell surface receptor protein that traverses the cell membr…
G1 phase (Gap 1) is the first stage of interphase in the cell cycle, occurring right after cell divi…
G2 phase (Gap 2) is the third and final stage of interphase in the cell cycle, following S phase. Du…
Mechanical small bowel obstruction by a gallstone (passed via a biliary-enteric fistula); a rare com…
Solid calculi that form in the gallbladder or biliary tree from components of bile (cholesterol, bil…
Life-threatening necrotizing infection of muscle (myonecrosis) caused by toxin-producing *Clostridiu…
Chronic condition where gastric contents flow back into the esophagus, resulting in troublesome symp…
Congenital full-thickness abdominal wall defect (usually just right of the umbilicus) that allows in…
An anxiety disorder characterized by persistent, excessive worry about multiple everyday things (suc…
Genetic drift is a mechanism of evolution in which allele frequencies in a population change over ge…
The Cockcroft-Gault equation estimates creatinine clearance (CrCl) as a surrogate for glomerular fil…
Granulomatous large-vessel vasculitis in patients >50, typically affecting the extracranial carotid …
Benign inherited (usually autosomal recessive) condition of reduced bilirubin UDP-glucuronosyltransf…
Rare autosomal recessive platelet function disorder where platelets cannot aggregate due to an absen…
Progressive optic neuropathy, usually from elevated intraocular pressure (IOP), leading to character…
Inflammation of the kidney's glomeruli (often immune-mediated) presenting as nephritic syndrome – he…
Glucose is a six-carbon monosaccharide sugar (formula C₆H₁₂O₆) that serves as a primary energy sourc…
An inherited X-linked recessive enzyme disorder of red blood cells causing impaired NADPH production…
Glycolysis is the anaerobic breakdown of glucose (a 6-carbon sugar) into two 3-carbon pyruvate molec…
Inflammatory arthritis caused by deposition of monosodium urate crystals in joints and tissues due t…
Alloimmune complication of allogeneic transplantation where donor T cells attack the host's tissues,…
A small organized collection of immune cells (especially macrophages) that forms when the immune sys…
Gregor Mendel (1822-1884) was an Austrian monk and scientist whose experiments with pea plants estab…
Haploid describes a cell or organism that has only one set of chromosomes. In humans, the haploid nu…
The heart is a muscular organ that pumps blood through the circulatory system. In humans, the heart …
Clinical syndrome of the heart's inability to pump sufficient blood (or only able to do so at elevat…
A common spiral-shaped, urease-producing Gram-negative bacterium that colonizes the gastric mucosa; …
Presence of blood in the urine (typically ≥3 RBCs/HPF on microscopy). Gross hematuria is visible blo…
Heme is an iron-containing molecular component (a prosthetic group) found in hemoglobin and certain …
Iron overload disorder with excessive iron deposition in tissues (especially liver), leading to orga…
Three α-globin gene deletions (–/–/–/α): a severe form of α-thalassemia causing chronic hemolytic an…
Thrombotic microangiopathy with the triad of microangiopathic hemolytic anemia, thrombocytopenia, an…
Life-threatening hyperinflammatory syndrome of uncontrolled macrophage & T-cell activation (cytokine…
IgA immune complex small-vessel vasculitis in children; classic tetrad of palpable purpura, arthriti…
Spectrum of reversible neuropsychiatric abnormalities due to advanced liver dysfunction or portosyst…
Inflammation of the liver due to various causes – most often hepatitis viruses (A, B, C, D, E), but …
Primary malignancy of hepatocytes (liver cells), usually arising in a cirrhotic liver. It is the mos…
Life-threatening functional renal failure occurring in advanced liver disease (cirrhosis with ascite…
Rare autosomal dominant disorder causing deficiency or dysfunction of C1 esterase inhibitor; leads t…
Autosomal recessive inborn error of fructose metabolism due to aldolase B deficiency; fructose (or s…
Congenital absence of enteric ganglion cells in the distal colon (aganglionosis) → failure of relaxa…
B‑cell lymphoma characterized by Reed–Sternberg (CD15+, CD30+) cells and contiguous nodal spread.…
Holoprosencephaly (HPE) is a congenital forebrain malformation where the embryonic prosencephalon fa…
Homeostasis is the process by which living organisms maintain a stable internal environment despite …
A hormone is a chemical messenger produced by an endocrine gland and released into the bloodstream t…
Congenital fusion anomaly in which the two kidneys, most often at the lower poles, are joined by an …
Neuroendocrine circuit for stress: CRH (hypothalamus) → ACTH (anterior pituitary) → cortisol (adrena…
Chronic infection by HIV (a retrovirus) that destroys CD4+ T cells, causing progressive immunodefici…
A family of small, non-enveloped double-stranded DNA viruses that infect epithelial cells. Low-risk …
Complete absence of α-globin production (four-gene deletion, –/– –/–), resulting in a fetus that can…
Primary immunodeficiency where B cells cannot class-switch, leading to normal or elevated IgM but ve…
Abnormally high parathyroid hormone (PTH) levels causing disrupted calcium–phosphate homeostasis. Cl…
Inappropriate or exaggerated immune response to an antigen (allergen or self) that causes host tissu…
Cardiac changes caused by chronic high blood pressure, primarily pressure-overload–induced concentri…
State of excess thyroid hormone production (↑T3 and T4) by the thyroid gland, leading to a hypermeta…
Genetic cardiomyopathy (usually autosomal dominant) characterized by unexplained left‑ventricular hy…
A deficiency of thyroid hormone resulting in a generalized slowing of metabolism. Can be primary (th…
A decrease in intravascular extracellular fluid volume (esp. plasma volume) due to loss of salt and …
Immune complex-mediated small-vessel vasculitis confined to the skin, typically causing palpable pur…
Immune-mediated fibroinflammatory disease that can affect nearly any organ; characterized by tumefac…
The immune system is a complex network of cells, tissues, and organs that helps the body fight infec…
Idiopathic inflammatory myopathy of older adults characterized by progressive muscle weakness and ri…
Incomplete dominance is a pattern of inheritance in which a heterozygote's phenotype is intermediate…
Inflammatory bowel disease (IBD) is a chronic immune-mediated inflammatory disease of the gastrointe…
Influenza, or "the flu," is a highly contagious respiratory illness caused by influenza viruses (Ort…
Protrusion of intra-abdominal contents through a weakness in the anterior abdominal wall of the groi…
An insertion is a mutation in which one or more nucleotides are added into a DNA sequence. Like dele…
Congenital anomaly of intestinal rotation and fixation resulting in abnormal bowel positioning; pred…
An inversion is a chromosome mutation in which a segment of DNA breaks off and reattaches in the opp…
A chronic functional gastrointestinal disorder (disorder of gut–brain interaction) characterized by …
Congenital obstruction of the small intestine (jejunum or ileum) due to an in‑utero vascular acciden…
Chronic childhood arthritis (onset before age 16, duration ≥6 weeks) of unknown cause, encompassing …
Acute vasculitis of childhood (usually <5 years) involving medium-sized arteries (especially coronar…
A kidney is one of two bean-shaped organs that filter the blood to remove waste products and excess …
A kinetochore is a protein structure assembled on the centromere of a chromosome that serves as the …
Genetic condition in which a phenotypic male has an extra X chromosome (47,XXY), leading to primary …
Injury of the lower brachial plexus (C8-T1 roots) causing paralysis of intrinsic hand muscles ('claw…
The Krebs cycle (citric acid cycle) is a series of enzyme-driven reactions in the mitochondrial matr…
Severe protein malnutrition in children characterized by bilateral pitting edema and fatty liver (di…
Elevated blood lactate (usually >4 mmol/L) causing an anion gap metabolic acidosis (arterial pH <7.3…
Autoimmune disorder of the neuromuscular junction (presynaptic) where antibodies target voltage-gate…
The law of independent assortment states that genes for different traits are sorted into gametes ind…
The law of segregation is Mendel's principle that the two alleles for a single trait separate (segre…
Severe childhood-onset epileptic encephalopathy with multiple refractory seizures, cognitive impairm…
Atherosclerotic occlusion at the aortic bifurcation (distal aorta or common iliac arteries) causing …
X‑linked recessive HGPRT enzyme deficiency that blocks purine salvage, causing hyperuricemia (↑uric …
Malignant proliferation of hematopoietic cells with primary involvement of bone marrow and blood.…
Abnormally high white blood cell count (typically >11,000/µL in adults).…
Chronic T-cell mediated inflammatory disease of the skin and mucous membranes, featuring intensely p…
A ligand-gated channel is a type of ion channel that opens or closes in response to the binding of a…
A lipid bilayer is a double-layered sheet of phospholipid molecules that forms the core structure of…
The liver is the largest internal organ of the body and a vital metabolic center. Located in the upp…
Disorder of ventricular repolarization (congenital or acquired) causing a prolonged QT interval on E…
The lungs are a pair of spongy, air-filled organs in the chest that serve as the primary organs of r…
Group of lung tumors arising from neuroendocrine cells, ranging from indolent carcinoid tumors (typi…
Immune complex–mediated inflammation of blood vessels occurring as a complication of systemic lupus …
Malignant neoplasms of lymphoid tissue (nodes or extranodal) subdivided into Hodgkin and non‑Hodgkin…
A lysosome is a membrane-bound organelle in eukaryotic cells that contains digestive enzymes. It fun…
Anemia with macrocytosis (MCV > 100 fL). Subclassified into megaloblastic (impaired DNA synthesis, e…
A common mood disorder characterized by at least two weeks of pervasive depressed mood and/or loss o…
Aggressive malignancy of the mesothelial lining of serous cavities (pleura >> peritoneum), usually d…
B‑cell NHL with t(11;14) → cyclin D1 (CCND1) overexpression; typically older men; often disseminated…
Form of severe acute malnutrition from overall calorie deficiency, leading to extreme wasting (loss …
Clonal mast cell proliferation (often driven by a KIT D816V mutation) causing mast cell accumulation…
Injury to the median nerve (often at the elbow or wrist) leading to characteristic deficits; patient…
A group of autosomal dominant tubulointerstitial nephropathies characterized by slowly progressive c…
The MELD (Model for End-Stage Liver Disease) Score predicts 3-month mortality in patients with end-s…
Meniere disease (idiopathic endolymphatic hydrops) is an inner ear disorder caused by excess endolym…
Meningocele is a congenital neural tube defect (spina bifida) in which only the meninges (with CSF) …
Permanent cessation of menses due to loss of ovarian follicular function, confirmed after 12 months …
Primary acid–base disturbance characterized by a reduction in serum HCO₃⁻ (bicarbonate), usually wit…
Elevated blood pH (>7.45) due to a primary increase in bicarbonate (HCO₃⁻).…
Necrotizing small-vessel vasculitis (pauci-immune) affecting capillaries (esp. in kidneys & lungs); …
Mitochondria are double-membraned organelles known as the "powerhouses" of the cell. They generate m…
Mitochondrial ribosomes are the protein synthesis machinery inside mitochondria. They are similar to…
Bulging (prolapse) of one or both mitral valve leaflets into the left atrium during systole, due to …
Messenger RNA is a single-stranded RNA copy of a gene that serves as a template for protein synthesi…
Congenital malformation of a kidney in which multiple noncommunicating cysts replace normal renal ti…
Autoimmune demyelinating disease of the CNS causing episodes of neurologic dysfunction separated in …
Contagious viral illness (a paramyxovirus) causing painful swelling of the salivary glands (parotiti…
Muscle tissue is a type of tissue composed of cells (muscle fibers) that have the ability to contrac…
A mutation is a change or error in the DNA sequence of an organism. Mutations can range from a singl…
Autoimmune neuromuscular junction disorder characterized by fatigable skeletal muscle weakness (wors…
Necrosis of heart muscle due to prolonged ischemia from an acute loss of coronary blood flow (usuall…
Inflammation of the heart muscle (myocardium) that injures cardiac myocytes; most often triggered by…
Autosomal dominant muscular dystrophies (DM1 & DM2) caused by unstable repeat expansions; defined by…
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in all living cells that acts as an ele…
NADH is the reduced form of the coenzyme NAD- (nicotinamide adenine dinucleotide). It carries high-e…
Malignancy of the nasopharynx epithelium (usually an undifferentiated squamous cell carcinoma) stron…
Natural selection is the process by which individuals with traits that confer an advantage in a give…
Life‑threatening, rapidly progressive infection of the fascia and deep soft tissues ("flesh‑eating" …
Inflammation of the glomeruli causing hematuria (blood and RBC casts in urine), usually mild protein…
A nephron is the microscopic functional unit of the kidney responsible for filtering blood and formi…
Kidney disorder with nephrotic-range proteinuria (>3.5 g/day) causing hypoalbuminemia, generalized e…
Nervous tissue is the tissue type that makes up the nervous system, composed of nerve cells (neurons…
Embryonal tumor of the sympathetic nervous system (neural crest origin), usually arising in the adre…
Urinary bladder dysfunction caused by injury or disease of the nervous system that impairs bladder c…
A neuron is a nerve cell - the basic functional unit of the nervous system specialized to receive an…
A non-coding RNA (ncRNA) is an RNA molecule that is transcribed from DNA but not translated into a p…
Heterogeneous group of mostly B‑cell lymphomas (also T/NK) with non‑contiguous spread and frequent e…
Metabolic liver disease characterized by ≥5% hepatic steatosis not due to significant alcohol use; e…
Noonan syndrome is an autosomal dominant RASopathy marked by short stature, characteristic facies, c…
Nuclear pores are large protein-lined channels in the nuclear envelope that regulate exchange of mat…
Involuntary, rhythmic oscillation of the eyes (rapid jerking or drifting movements) typically caused…
Obesity is a chronic disease of excess body fat. Adults: BMI ≥30 kg/m². Children/adolescents: BMI-fo…
Sleep disorder of repetitive upper airway collapse causing reduced or paused breathing (apneas/hypop…
Obstructive uropathy is a structural or functional blockage of urinary flow, causing a back-up of ur…
Congenital midline abdominal wall defect at the base of the umbilical cord, where abdominal organs (…
Osmosis is the passive movement of water molecules across a selectively permeable membrane from a re…
Chronic focal disorder of bone remodeling characterized by excessive bone resorption followed by cha…
Chronic degenerative joint disease caused by wear-and-tear cartilage loss, resulting in bone spurs (…
Group of disorders in growing children involving temporary loss of blood supply to bone (usually at …
Group of heritable connective tissue disorders causing fragile bones that fracture with minimal trau…
Rare hereditary bone disorder where osteoclasts cannot resorb bone, leading to abnormally dense, bri…
Systemic skeletal disease characterized by low bone mass and deterioration of bone microarchitecture…
Abnormal bony remodeling of the otic capsule (especially around the stapes footplate) leading to fix…
Malignant tumor arising from ovarian tissue. Epithelial ovarian carcinoma is by far the most common …
Two distinct disorders: one is a focal bone remodeling disease (excessive osteoclast and chaotic ost…
A benign childhood focal epilepsy (also called early-onset occipital epilepsy) characterized by seiz…
The parasympathetic nervous system is one of the two divisions of the autonomic nervous system, resp…
Progressive neurodegenerative movement disorder caused by loss of dopaminergic neurons in the substa…
Systemic disease caused by niacin (vitamin B3) deficiency, classically characterized by the "4 D's" …
Life-threatening autoimmune blistering disease of skin and mucous membranes, characterized by acanth…
Break in the gastric or duodenal mucosa extending through the muscularis mucosa into deeper layers, …
Peripatric speciation is a specific type of allopatric speciation that happens when a small populati…
Atherosclerotic narrowing of peripheral arteries (usually legs) causing reduced blood flow and ische…
The peripheral nervous system (PNS) is the part of the nervous system outside the brain and spinal c…
Inflammation of the peritoneum (the serous lining of the abdominal cavity), most often due to a bact…
A peroxisome is a small, single-membrane organelle containing enzymes that catalyze oxidative reacti…
A phospholipid is a lipid molecule composed of a glycerol backbone attached to two fatty acid tails …
Photosynthesis is the process by which certain organisms (plants, algae, and cyanobacteria) convert …
A plasmid is a small, circular DNA molecule found in bacteria (and some other microorganisms) that i…
Infection of the lung alveoli leading to inflammation and consolidation (air spaces fill with pus/fl…
Air in the pleural space leading to partial or complete lung collapse. Types include spontaneous (wi…
Systemic necrotizing vasculitis of medium-sized muscular arteries causing ischemia and infarction in…
Genetic disorders characterized by numerous fluid-filled cysts in the kidneys. Autosomal dominant PK…
Common endocrine disorder in reproductive-age women defined by hyperandrogenism, ovulatory dysfuncti…
Polymerase Chain Reaction (PCR) is a laboratory technique used to rapidly make millions of copies of…
Inflammatory rheumatic syndrome of older adults (age >50) causing bilateral shoulder and hip girdle …
Idiopathic inflammatory muscle disease causing symmetric proximal muscle weakness due to T-cell–medi…
Pathologically elevated pressure in the portal venous system (normal portal pressure ~5 mm Hg; clini…
Rare genetic imprinting disorder (loss of paternal 15q11.2–q13) causing infantile hypotonia with poo…
Autoimmune destruction of small intrahepatic bile ducts leading to chronic cholestasis (bile stasis)…
Group of extranodal B-cell non-Hodgkin lymphomas originating in and confined to the skin (no systemi…
Unregulated overproduction of parathyroid hormone by the parathyroid glands, causing hypercalcemia. …
Episodes of chest pain (angina) caused by transient coronary vasospasm, typically occurring at rest …
Medications that profoundly reduce gastric acid secretion by irreversibly inhibiting the H⁺/K⁺-ATPas…
Chronic immune-mediated inflammatory skin disorder characterized by clearly defined, erythematous an…
Inflammatory arthritis associated with psoriasis. Typically seronegative and can involve peripheral …
Blockage of one or more pulmonary arteries (usually by a blood clot from a leg DVT) that impairs lun…
Progressive scarring of the lung interstitium (fibrosis) leading to restrictive lung disease and imp…
The pyruvate shunt is the transitional step that converts pyruvate (the end product of glycolysis) i…
Injury or compression of the radial nerve (C5–T1, branch of the posterior cord) causing weakness or …
Episodic vasospasm of small arteries (usually in the fingers/toes) triggered by cold or stress, caus…
Post-infectious inflammatory arthritis that typically occurs 1–4 weeks after a gastrointestinal or g…
In genetics, "recessive" describes an allele or trait that is only expressed when an individual has …
Recombinant DNA is DNA that has been artificially created by combining genetic material from multipl…
Protrusion of rectal tissue through the anus. Can involve the full thickness of the rectum (complete…
Rare systemic autoimmune disease with recurrent inflammation and progressive destruction of cartilag…
Inability of the respiratory system to maintain gas exchange, leading to inadequate oxygenation and/…
Rare pediatric acute encephalopathy with microvesicular fatty liver failure (non-inflammatory), clas…
Immune-mediated hemolysis in a fetus or newborn, typically caused by maternal anti-Rh(D) IgG antibod…
Chronic systemic autoimmune disease causing symmetric inflammatory polyarthritis (synovitis) of smal…
Inflammation of the nasal cavity and paranasal sinuses ("sinus infection"). Acute cases last 12 week…
A ribosome is a cellular structure composed of RNA and proteins that serves as the site of protein s…
Defective mineralization of the growth plates (in children) leading to soft, deformed bones; most of…
RNA is a nucleic acid similar to DNA but usually single-stranded. It contains ribose sugar (instead …
The rough endoplasmic reticulum (rough ER) is a series of flattened membrane sacs studded with ribos…
Contagious rubella virus infection ("German measles") causing a mild 3-day rash and fever. Congenita…
S phase (Synthesis phase) is the part of the cell cycle during which DNA replication occurs. In S ph…
Systemic inflammatory disease of unknown cause characterized by noncaseating granulomas (non-necroti…
A sarcomere is the fundamental contractile unit of striated muscle fibers. It is the segment of a my…
A chronic psychiatric disorder characterized by episodes of psychosis – including delusions, halluci…
Lateral curvature of the spine >10° (Cobb angle) with accompanying vertebral rotation.…
Disease caused by prolonged vitamin C (ascorbic acid) deficiency, leading to defective collagen synt…
Secondary active transport is a form of active transport in which one substance is moved against its…
Excess PTH production secondary to chronic hypocalcemia (or hyperphosphatemia). Typically caused by …
Transient episodes of abnormal, excessive, synchronous neuronal activity in the brain, often causing…
A group of rare inherited immunodeficiencies characterized by profound T- and B-cell dysfunction, le…
A sex-linked trait results from a gene located on a sex chromosome (in humans, either the X or Y chr…
Life-threatening syndrome of inadequate tissue perfusion leading to cellular hypoxia and organ dysfu…
An autosomal recessive hemoglobinopathy caused by a point mutation (Glu→Val) in the β-globin gene, l…
Systemic autoimmune disease targeting exocrine glands (especially lacrimal and salivary), causing dr…
The smooth endoplasmic reticulum (smooth ER) is a network of membranous tubules in the cell, continu…
Sodium (Na⁺) is the major extracellular cation and the primary determinant of plasma osmolality. It …
Speciation is the evolutionary process by which one ancestral species splits into two or more new sp…
Mildest form of spina bifida (a neural tube defect) where the bony vertebral arches fail to fuse, le…
Group of autosomal recessive motor neuron disorders (SMN1 gene deletion on 5q) causing degeneration …
Family of inflammatory arthritides characterized by axial skeletal involvement (sacroiliac joints, s…
Malignancy arising from squamous epithelium (e.g. skin, mucosa) characterized by keratinizing malign…
Chest discomfort (or anginal equivalent like dyspnea) from transient myocardial ischemia due to a fi…
Spectrum of liver disease characterized by hepatic steatosis (fat >5% of liver weight) associated wi…
Misalignment of the eyes such that they do not properly align on the same target. In other words, on…
Acute loss of brain function due to disrupted blood flow—usually from an arterial blockage (ischemic…
Bleeding into the subarachnoid space (between the arachnoid and pia mater), usually due to a rupture…
The sympathetic nervous system is the division of the autonomic nervous system that triggers the "fi…
Sympatric speciation occurs when new species arise from a single ancestral species while inhabiting …
A synapse is the junction between two nerve cells (neurons), or between a neuron and another target …
Transient loss of consciousness ("fainting") caused by global cerebral hypoperfusion, typically with…
Inappropriate, continued ADH release (from pituitary or ectopic source) leading to excess water reab…
Chronic multi-organ autoimmune disease where nuclear autoantibodies form immune complexes that damag…
T-tubules (transverse tubules) are deep invaginations of a muscle fiber's plasma membrane (sarcolemm…
Granulomatous large-vessel vasculitis affecting the aorta and its major branches, typically in young…
Small, dilated blood vessels visible on the skin or mucous membranes, often appearing as fine red or…
A tendon is a tough, fibrous connective tissue band that attaches a muscle to a bone. Tendons transm…
Autonomous hypersecretion of PTH after long-standing secondary hyperparathyroidism. The parathyroid …
Life-threatening neurologic illness caused by *Clostridium tetani* exotoxin (tetanospasmin), charact…
Conotruncal heart defect with four anomalies: VSD, subpulmonic pulmonary stenosis (RV outflow obstru…
Group of inherited microcytic, hemolytic anemias caused by decreased production of α- or β-globin ch…
Life-threatening thrombotic microangiopathy caused by severe ADAMTS13 deficiency (usually autoimmune…
Tidal Volume (TV or VT) is the volume of air moved in or out of the lungs during a single normal bre…
Inflammation of the palatine tonsils (lymphoid tissue in the throat), usually due to infection by co…
A group of congenital infections in pregnancy that are often benign or mild in the mother but cause …
Neurodevelopmental tic disorder characterized by multiple motor tics and at least one vocal tic, per…
Rare, life‑threatening shock syndrome caused by superantigen‑producing Staph aureus (TSST‑1 toxin) o…
Infection caused by the protozoan *Toxoplasma gondii*. Typically asymptomatic in healthy people, but…
Transcription is the process of making an RNA copy of a gene's DNA sequence. In transcription, an en…
Translation is the process by which the information encoded in messenger RNA (mRNA) directs the asse…
Transfer RNA is a small RNA molecule that helps build proteins by carrying amino acids to the riboso…
Contagious airborne infection by Mycobacterium tuberculosis that usually affects the lungs (pulmonar…
Turner syndrome is a sex chromosome disorder in phenotypic females caused by complete or partial abs…
Injury or compression of the ulnar nerve (C8–T1) often at the elbow (cubital tunnel) or wrist (Guyon…
A spondyloarthritis picture that doesn't yet meet criteria for a specific subtype (AS, PsA, etc.). P…
An acute coronary syndrome marked by new or worsening chest pain (angina) at rest or with minimal ex…
Qualitative platelet defect in advanced kidney failure due to circulating uremic toxins and altered …
Pruritic, circumscribed wheals (hives) due to transient dermal edema from mast cell histamine releas…
Inflammation of the uveal tract (iris, ciliary body, choroid). Anterior uveitis (iritis/iridocycliti…
Inflammation of the uveal tract (iris, ciliary body, choroid) leading to an intraocular inflammatory…
A vaccine is a biological preparation that teaches the immune system to recognize and fight a specif…
A vacuole is a membrane-bound sac within a cell that functions in storage and transport of substance…
A herpesvirus (DNA) also known as human herpesvirus-3 (HHV-3), which causes varicella (chickenpox) a…
Abnormal enlargement (varicosity) of the pampiniform plexus (scrotal veins); essentially varicose ve…
Inflammation of blood vessel walls leading to vessel wall damage, thickening, narrowing/occlusion, a…
Retrograde flow of urine from the bladder into the ureters and kidneys due to incompetent ureteroves…
Acute inflammation of the vestibular (balance) portion of CN VIII causing sudden, prolonged vertigo …
Inflammation of the brain (encephalitis) and meninges (meningitis) due to viral infection of the cen…
A virus is a tiny infectious particle consisting of genetic material (DNA or RNA) enclosed in a prot…
Vitiligo is a common acquired disorder of pigmentation characterized by well-defined depigmented (wh…
A voltage-gated channel is an ion channel that opens or closes in response to changes in the electri…
Twisting of a loop of intestine around its mesentery, creating a closed-loop obstruction with risk o…
Common inherited bleeding disorder due to quantitative or qualitative defects of von Willebrand fact…
Age-specific epilepsy of infancy defined by a triad: clusters of infantile spasms, an abnormal inter…
Most common pediatric renal malignancy (nephroblastoma) occurring in young children (<5 yo); maligna…
Rare autosomal recessive copper metabolism disorder (*ATP7B* mutation) causing toxic copper accumula…
Winter's formula predicts the expected PCO₂ in a patient with metabolic acidosis if respiratory comp…
Cardiac preexcitation syndrome caused by an accessory atrioventricular pathway (Bundle of Kent) that…
X-linked describes genes or traits located on the X chromosome. Because females have two X chromosom…
X-linked recessive immunodeficiency caused by a BTK gene mutation, resulting in failure of B cell ma…
Y-linked traits are determined by genes on the Y chromosome. These traits are passed exclusively fro…
Syndrome caused by a gastrin-secreting tumor (gastrinoma) leading to excessive gastric acid hypersec…
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