1500+ medical terms, defined.

Diffuse large B-cell lymphoma (DLBCL) is the most common non-Hodgkin lymphoma in adults, characterized by an aggressive but potentially curable clonal proliferation of large B lymphocytes. It typically presents with a rapidly enlarging l...

The tunica vaginalis is a serous membrane covering the anterior and lateral surfaces of the testis and epididymis, derived from the processus vaginalis (an outpouching of peritoneum) during testicular descent. It has parietal and viscera...

Valsartan is an angiotensin II receptor blocker (ARB) used to treat hypertension, heart failure, and post-MI cardiac remodeling. It selectively blocks the AT1 receptor, preventing angiotensin II-mediated vasoconstriction and aldosterone...

The loop of Henle is a U-shaped segment of the renal tubule that extends from the proximal convoluted tubule into the medulla and back to the distal convoluted tubule. It establishes the medullary concentration gradient via the countercu...

The collecting tubule (collecting duct) is the final segment of the nephron responsible for fine-tuning urine concentration, volume, and electrolyte balance under hormonal control. It is regulated primarily by ADH (vasopressin) and aldos...

Cisplatin is a platinum-based alkylating-like chemotherapy agent that crosslinks DNA, causing apoptosis in rapidly dividing cancer cells. It is used to treat testicular, ovarian, bladder, and lung cancers. Its major dose-limiting toxicit...

Lipoproteins are spherical particles composed of a hydrophobic core (triglycerides and cholesterol esters) surrounded by a hydrophilic shell (phospholipids, free cholesterol, and apolipoproteins). They transport lipids through the bloods...

Spontaneous pneumothorax is the accumulation of air in the pleural space without antecedent trauma, causing partial or complete lung collapse. It is classified as primary (in patients without underlying lung disease, typically tall thin...

Galactosemia is an autosomal recessive metabolic disorder most commonly caused by deficiency of galactose-1-phosphate uridyltransferase (GALT), leading to accumulation of toxic galactose metabolites. Classic presentation includes failure...

Human papillomavirus (HPV) is a non-enveloped, double-stranded DNA virus that infects epithelial cells, causing lesions ranging from benign warts to malignant cancers. High-risk types (16, 18) are the primary cause of cervical cancer, wh...

An immune complex is a molecular structure formed by the binding of antibody to soluble antigen. Deposition of these complexes in tissues (vessel walls, glomeruli, joints) triggers complement activation and inflammation, causing Type III...

Parietal cells (oxyntic cells) are located in the gastric glands of the fundus and body of the stomach. They secrete hydrochloric acid (HCl) and intrinsic factor, both essential for digestion and vitamin B12 absorption, respectively. The...

Lymph nodes are small, encapsulated secondary lymphoid organs located along lymphatic vessels that filter lymph and serve as sites for immune cell activation. They are organized into cortex (B-cell follicles), paracortex (T-cell zone), a...

Normal anion gap (typically 8-12 mEq/L) is calculated as Na+ - (Cl- + HCO3-). A normal anion gap metabolic acidosis (NAGMA) occurs due to bicarbonate loss or impaired renal acid excretion, with chloride rising to compensate (hyperchlorem...

Phospholipase C (PLC) is a membrane-bound enzyme that hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into two second messengers: inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). It is a key effector in Gq-protein-cou...

Pyoderma gangrenosum (PG) is a rare neutrophilic dermatosis presenting as painful, rapidly enlarging ulcers with violaceous, undermined borders. It is strongly associated with inflammatory bowel disease (IBD), rheumatoid arthritis, and h...

Cobalamin (vitamin B12) is a water-soluble vitamin essential for DNA synthesis and myelin maintenance. It serves as a cofactor for methionine synthase and methylmalonyl-CoA mutase. Deficiency causes megaloblastic anemia and neurologic sy...

Actinomyces israelii is a gram-positive, anaerobic (or microaerophilic), filamentous, branching, non-acid-fast bacterium that is part of normal oral and GI flora. It causes actinomycosis, a chronic granulomatous infection characterized b...

Zone 3 refers to the perivenous/centrilobular region of the hepatic lobule, located closest to the central vein and farthest from the portal triad's oxygenated blood supply. It is the most metabolically active zone (rich in cytochrome P4...

Tyrosine kinase inhibitors (TKIs) are targeted anticancer drugs that block phosphorylation activity of tyrosine kinases, enzymes involved in signal transduction pathways controlling cell growth, proliferation, and survival. They are used...

G cells are enteroendocrine cells located primarily in the antrum of the stomach that secrete gastrin in response to stimuli such as vagal (GRP-mediated) stimulation, luminal peptides/amino acids, and gastric distention. Gastrin promotes...

Hypertrophic pyloric stenosis (HPS) is a condition of infancy caused by hypertrophy of the pyloric sphincter smooth muscle, leading to gastric outlet obstruction. It classically presents at 2-8 weeks of life with progressive, non-bilious...

The motor endplate is the specialized postsynaptic region of a skeletal muscle fiber at the neuromuscular junction (NMJ), where the motor neuron's axon terminal releases acetylcholine (ACh) to trigger muscle contraction. It contains a hi...

A molar pregnancy (hydatidiform mole) is a gestational trophoblastic disease characterized by abnormal proliferation of trophoblastic tissue, resulting in a nonviable pregnancy. It presents with markedly elevated β-hCG, vaginal bleeding,...

Aminoglycosides (e.g., gentamicin, tobramycin, amikacin, streptomycin, neomycin) are bactericidal antibiotics that inhibit bacterial protein synthesis by binding the 30S ribosomal subunit, causing misreading of mRNA. They are primarily u...

The vagus nerve (CN X) is the longest cranial nerve, providing parasympathetic innervation to the heart, lungs, and GI tract (up to the splenic flexure), and carrying sensory, motor, and autonomic fibers. It plays key roles in heart rate...

Chorionic villi are finger-like projections of the chorion (fetal-derived tissue) that extend into the maternal endometrium, forming the functional unit of the placenta. They mediate nutrient, gas, and waste exchange between maternal and...

Adenocarcinoma of the lung is the most common type of lung cancer overall and the most common in non-smokers, particularly women. It arises from mucus-producing glandular cells, typically in the peripheral regions of the lung, and often...

The ampulla of Vater is the dilated duct formed by the union of the common bile duct and the main pancreatic duct (duct of Wirsung), which empties into the second (descending) part of the duodenum at the major duodenal papilla. It is sur...

The inferior mesenteric artery (IMA) is one of three unpaired anterior branches of the abdominal aorta, arising at L3 to supply the hindgut. It perfuses the distal third of the transverse colon through the upper rectum, including the des...

Colectomy is the surgical resection of all or part of the colon, performed for conditions such as colorectal cancer, inflammatory bowel disease, diverticulitis, or bowel obstruction/perforation. Types include right/left hemicolectomy, si...

Repolarization is the phase of the cardiac (or neuronal) action potential during which the membrane potential returns to its resting negative value after depolarization, primarily via efflux of potassium ions. In the heart, ventricular r...

Cystine stones are radiopaque (though less so than calcium stones), hexagonal-shaped kidney stones caused by cystinuria, an autosomal recessive disorder of defective renal tubular reabsorption of cystine, ornithine, lysine, and arginine...

Cephalosporins are beta-lactam antibiotics that inhibit bacterial cell wall synthesis by binding penicillin-binding proteins (PBPs) and disrupting transpeptidase cross-linking. They are classified into five generations, with increasing g...

Rapidly progressive glomerulonephritis (RPGN) is a clinical syndrome characterized by acute kidney injury with rapid loss of renal function over days to weeks, associated with nephritic sediment (hematuria, RBC casts, proteinuria). Histo...

Obligate intracellular organisms are pathogens (mainly certain bacteria and all viruses) that cannot replicate outside a host cell, as they depend on the host's ATP and/or metabolic machinery. Classic examples include Rickettsia, Chlamyd...

A spore is a metabolically dormant, highly resistant structure formed by certain bacteria (e.g., Bacillus, Clostridium) in response to nutrient deprivation or environmental stress. Spores resist heat, desiccation, radiation, and chemical...

Bicarbonate (HCO3-) is the primary buffer in extracellular fluid, maintaining acid-base homeostasis via the bicarbonate buffer system (CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-). It is regulated by the kidneys (reabsorption/generation) and reflects...

ELISA (Enzyme-Linked Immunosorbent Assay) is a laboratory technique used to detect and quantify antigens or antibodies in a sample using enzyme-linked reactions producing a measurable color change. It is widely used for infectious diseas...

Virulence factors are molecules or structures produced by pathogens that enhance their ability to infect, damage, or evade the host immune system. Examples include toxins, capsules, adhesins, and enzymes. Understanding these is high-yiel...

Amniotic fluid is the protective liquid surrounding the fetus within the amniotic sac, essential for fetal cushioning, temperature regulation, and lung development. Its volume and composition change throughout pregnancy, and abnormalitie...

The carotid arteries are major paired vessels supplying blood to the brain, face, and neck. The common carotid artery bifurcates into the internal carotid artery (supplies the brain via the anterior circulation) and external carotid arte...

Tumor markers are biomolecules (proteins, hormones, enzymes, or antigens) produced by cancer cells or by the body in response to cancer, used for screening, diagnosis, prognosis, monitoring treatment response, and detecting recurrence. T...

Hemoglobin electrophoresis is a laboratory technique that separates hemoglobin variants based on their charge and mobility in an electric field, used primarily to diagnose hemoglobinopathies such as sickle cell disease and thalassemias....

Granulosa cells are somatic epithelial cells within the ovarian follicle that surround the oocyte, produce estrogen (via aromatization of androgens from theca cells), and secrete inhibin B. They proliferate under FSH stimulation and are...

Acute myeloid leukemia (AML) is a clonal malignancy of myeloid precursor cells characterized by ≥20% blasts in bone marrow or blood, leading to bone marrow failure. It predominantly affects adults (median age ~65) and presents with fatig...

Apolipoprotein B (ApoB) is the primary structural protein of LDL, VLDL, IDL, and chylomicrons, existing as ApoB-100 (liver-derived, found in LDL/VLDL/IDL) and ApoB-48 (intestine-derived, found in chylomicrons). ApoB-100 serves as the lig...

The cerebral cortex is the outer layer of gray matter covering the cerebral hemispheres, responsible for higher-order functions including cognition, sensory perception, voluntary motor control, language, and executive function. It is org...

Diffuse Proliferative Glomerulonephritis (DPGN) is the most severe and common renal manifestation of systemic lupus erythematosus (SLE), classified as WHO/ISN-RPS Class IV lupus nephritis. It presents with hematuria, proteinuria (often n...

The vestibular system, located in the inner ear, detects head position, motion, and acceleration to maintain balance, posture, and gaze stability. It comprises the semicircular canals (angular/rotational acceleration), utricle and saccul...