1500+ medical terms, defined.

Esophageal adenocarcinoma is the most common type of esophageal cancer in the US, typically arising in the distal 1/3 of the esophagus from Barrett's esophagus (intestinal metaplasia due to chronic GERD). Risk factors include GERD, obesi...

A gain-of-function mutation causes a gene product to acquire a new or enhanced activity, rather than losing its normal function. These mutations are typically dominant and can lead to disease through overactive signaling, toxic protein a...

A partial agonist is a drug that binds to a receptor but produces a submaximal response even at full receptor occupancy, compared to a full agonist. It can act as either an agonist or antagonist depending on the presence of a full agonist.

Kimmelstiel-Wilson nodules are round, eosinophilic, PAS-positive nodules of mesangial matrix expansion found in the glomeruli of patients with diabetic nephropathy. They represent nodular glomerulosclerosis and are a hallmark histologic...

The submucosal plexus (Meissner's plexus) is part of the enteric nervous system located in the submucosa of the GI tract. It primarily regulates local blood flow, glandular secretions, and mucosal ion transport. It is one of two major en...

Alcoholic liver disease (ALD) represents a spectrum of liver damage from chronic alcohol use, progressing from reversible hepatic steatosis (fatty liver) to alcoholic hepatitis to irreversible cirrhosis. It is a major cause of liver-rela...

SGLT (Sodium-Glucose Linked Transporter) proteins mediate active transport of glucose across cell membranes coupled with sodium reabsorption. SGLT2 is located in the proximal convoluted tubule (S1 segment) and reabsorbs ~90% of filtered...

Cell-mediated immunity refers to the arm of adaptive immunity driven by T lymphocytes rather than antibodies, involving CD4+ helper T cells, CD8+ cytotoxic T cells, macrophages, and NK cells. It is critical for combating intracellular pa...

The lesser omentum is a double-layered peritoneal fold connecting the lesser curvature of the stomach and the proximal duodenum to the liver. It consists of the hepatogastric ligament and hepatoduodenal ligament, the latter containing th...

Bronchitis is inflammation of the bronchial airways, presenting as a persistent cough, often with sputum production. It can be acute (usually viral, self-limited) or chronic (defined clinically as productive cough for ≥3 months in 2 cons...

Tubular reabsorption is the process by which the renal tubules move water and solutes from the filtrate back into the peritubular capillary blood, conserving substances the body needs. It occurs throughout the nephron (PCT, loop of Henle...

Autonomic neuropathy is damage to the autonomic nerve fibers controlling involuntary functions such as heart rate, blood pressure, digestion, bladder function, and sweating. It is most commonly caused by long-standing diabetes mellitus b...

Mycophenolate mofetil (MMF) is an immunosuppressant that inhibits inosine monophosphate dehydrogenase (IMPDH), blocking de novo purine synthesis selectively in lymphocytes. It is commonly used to prevent solid organ transplant rejection...

Thiazide diuretics (e.g., hydrochlorothiazide, chlorthalidone) inhibit the Na+/Cl- symporter in the distal convoluted tubule, reducing sodium reabsorption and increasing diuresis. They are first-line agents for hypertension and are also...

The Jarisch-Herxheimer reaction is an acute febrile illness with headache, myalgias, chills, and rigors that occurs within 24 hours after starting antibiotic treatment for spirochetal infections, most notably syphilis. It is caused by th...

Reactive oxygen species (ROS) are highly reactive molecules derived from oxygen, including superoxide (O2•−), hydrogen peroxide (H2O2), and hydroxyl radical (•OH). They cause cellular injury via lipid peroxidation, protein denaturation,...

An umbilical hernia is a protrusion of abdominal contents (typically omentum or bowel) through a weakness or incomplete closure of the umbilical ring. It is common in infants (especially African-American and premature infants) and often...

Protein kinase C (PKC) is a family of serine/threonine kinases activated by diacylglycerol (DAG) and calcium in the Gq-coupled signal transduction pathway. It phosphorylates target proteins to mediate cellular responses to hormones, neur...

The start codon is the mRNA sequence (usually AUG) that initiates protein synthesis and codes for methionine (or N-formylmethionine in prokaryotes). It sets the reading frame for translation, determining how subsequent codons are grouped...

Hypertriglyceridemia is defined as fasting serum triglyceride levels >150 mg/dL (severe if >500-1000 mg/dL). It is a major independent risk factor for acute pancreatitis (especially >1000 mg/dL) and contributes to atherosclerotic cardiov...

Proliferative diabetic retinopathy (PDR) is an advanced complication of diabetes mellitus characterized by retinal neovascularization due to chronic hypoxia. It represents the most severe form of diabetic retinopathy and can lead to vitr...

Henoch-Schönlein purpura (HSP), now termed IgA vasculitis, is the most common childhood vasculitis, characterized by IgA immune complex deposition in small vessels. Classic tetrad: palpable purpura (buttocks/legs), arthralgia, abdominal...

Urogenital folds are paired embryonic swellings that form during the indifferent stage of external genitalia development. They arise from the cloacal folds and, depending on the presence or absence of androgens, differentiate into either...

Anticipation is a phenomenon seen in certain genetic disorders where disease severity increases and age of onset decreases in successive generations. This is caused by expansion of unstable trinucleotide repeat sequences during meiosis....

Parathyroid adenoma is a benign neoplasm of one parathyroid gland (usually a single gland) that autonomously secretes excess PTH, causing primary hyperparathyroidism. It is the most common cause of primary hyperparathyroidism (~85% of ca...

The saccular period is a stage of fetal lung development occurring from about 24 to 38 weeks gestation, during which terminal bronchioles give rise to saccules with thinning epithelium and increased capillary contact, enabling gas exchan...

Cervical dysplasia refers to abnormal, premalignant epithelial changes in the cervix, most commonly caused by persistent high-risk HPV infection (especially types 16 and 18). It is classified histologically as cervical intraepithelial ne...

Keratitis is inflammation of the cornea, most commonly caused by infection (bacterial, viral, fungal, or protozoal) or contact lens-related trauma. It presents with eye pain, photophobia, redness, tearing, and blurred vision, and is an o...

Henoch-Schönlein purpura (HSP), now termed IgA vasculitis, is the most common childhood systemic vasculitis, characterized by IgA immune complex deposition causing a classic tetrad: palpable purpura (buttocks/legs), arthralgia, abdominal...

Silver stain is a histochemical technique that deposits metallic silver onto tissue structures, used to visualize fungi, certain bacteria, and reticulin/basement membrane components. Common examples include GMS (Gomori methenamine silver...

Malignant hypertension is a hypertensive emergency defined as severely elevated blood pressure (typically >180/120 mmHg) associated with acute end-organ damage, most notably papilledema and other signs of target organ injury. It is a med...

Itraconazole is a triazole antifungal that inhibits fungal cytochrome P450 enzyme lanosterol 14-α-demethylase, blocking ergosterol synthesis and disrupting fungal cell membrane integrity. It has a broad spectrum including dimorphic fungi...

Protamine sulfate is a strongly cationic (positively charged) protein derived from fish sperm that binds and neutralizes the anticoagulant effects of unfractionated heparin, which is strongly anionic (negatively charged). It is used clin...

Pulmonary hemorrhage refers to bleeding into the alveolar spaces of the lungs, presenting classically with hemoptysis, dyspnea, anemia, and diffuse alveolar infiltrates on imaging. It can be caused by autoimmune (e.g., Goodpasture syndro...

Spherocytes are small, round, densely staining red blood cells lacking central pallor, formed due to loss of membrane surface area relative to cell volume. They are classically seen in hereditary spherocytosis and autoimmune hemolytic an...

The complement system is a group of >30 plasma and cell-surface proteins that act as part of the innate immune system to opsonize pathogens, recruit inflammatory cells, and directly lyse target cells via the membrane attack complex (MAC)...

Type III hypersensitivity is an immune complex-mediated reaction in which antigen-antibody complexes (typically IgG or IgM) deposit in tissues, activate complement, and recruit neutrophils, causing local tissue damage. Classic examples i...

A myeloid progenitor (common myeloid progenitor, CMP) is a hematopoietic stem cell-derived precursor that gives rise to erythrocytes, platelets (via megakaryocytes), granulocytes (neutrophils, eosinophils, basophils), monocytes, and mast...

The indirect Coombs test (indirect antiglobulin test) detects antibodies in a patient's serum that react against foreign/donor RBCs, without those antibodies bound in vivo. It is used for antibody screening in pregnancy and pre-transfusi...

Globulins are a class of serum proteins distinct from albumin, including alpha, beta, and gamma fractions. Gamma globulins are primarily immunoglobulins (antibodies), while alpha and beta globulins include transport proteins, complement,...

Hemoglobin A (HbA) is the predominant form of hemoglobin in normal adult red blood cells, comprising ~95-98% of total hemoglobin. It consists of two alpha and two beta globin chains (α2β2). Defects in beta-globin synthesis or structure u...

BNP (B-type natriuretic peptide) is a hormone secreted primarily by ventricular myocytes in response to increased wall stress/volume overload. It promotes natriuresis, diuresis, and vasodilation, counteracting the RAAS system. Elevated B...

Ventricular apical ballooning is the hallmark echocardiographic/angiographic finding of Takotsubo cardiomyopathy (stress-induced cardiomyopathy), characterized by transient systolic dysfunction with akinesis/dyskinesis of the left ventri...

Right-sided heart failure occurs when the right ventricle cannot effectively pump blood to the lungs, causing systemic venous congestion. The most common cause is left-sided heart failure; other causes include cor pulmonale, pulmonary hy...

A competitive antagonist binds reversibly to the same receptor site as the agonist, competing for occupancy without activating the receptor. It shifts the agonist dose-response curve to the right (increases EC50) but does not change the...

The pancreatic duct (duct of Wirsung) is the main excretory duct of the pancreas that transports digestive enzymes and bicarbonate-rich fluid from acinar and ductal cells to the duodenum. It typically joins the common bile duct at the am...

Dehydroepiandrosterone (DHEA) is a weak androgen steroid hormone produced primarily by the zona reticularis of the adrenal cortex, serving as a precursor for both androgens and estrogens. It is the most abundant circulating steroid hormo...

Dehydroepiandrosterone (DHEA) is a weak androgen steroid hormone produced primarily by the zona reticularis of the adrenal cortex, with additional production in the gonads and brain. It serves as a precursor for peripheral synthesis of m...

The locus coeruleus (LC) is the primary site of norepinephrine (NE) synthesis in the brain, located in the pontine tegmentum. It regulates arousal, attention, sleep-wake cycles, and the stress/fight-or-flight response. It is also implica...

Rostral is a directional/anatomical term meaning 'toward the front (nose/beak) end' of the body or, more commonly in neuroanatomy, 'toward the anterior/front of the brain or brainstem.' It is often contrasted with 'caudal' (toward the ta...