1500+ medical terms, defined.

Resting membrane potential (RMP) is the electrical charge difference across a cell membrane at rest, typically around -70 mV in neurons and -90 mV in cardiac/skeletal muscle. It is primarily determined by K+ efflux through leak channels,...

Type 1 diabetes mellitus (T1DM) is an autoimmune disease resulting in destruction of pancreatic beta cells, leading to absolute insulin deficiency. It typically presents in childhood/adolescence with polyuria, polydipsia, polyphagia, and...

The ligamentum teres hepatis is the fibrous remnant of the fetal umbilical vein, running in the free edge of the falciform ligament from the umbilicus to the liver. It marks the division between the medial and lateral segments of the lef...

The portal vein is a large vessel formed by the union of the splenic vein and superior mesenteric vein, delivering nutrient-rich, deoxygenated blood from the GI tract, spleen, and pancreas to the liver. It supplies ~75% of hepatic blood...

Bile acid sequestrants (e.g., cholestyramine, colestipol, colesevelam) are non-absorbable resins that bind bile acids in the gut, preventing their reabsorption and increasing their fecal excretion. This upregulates hepatic LDL receptors,...

Rosuvastatin is a synthetic, high-potency HMG-CoA reductase inhibitor (statin) used to lower LDL cholesterol and reduce cardiovascular risk. It is one of the most potent statins, effective at lower doses than atorvastatin or simvastatin.

Retinoic acid is the biologically active metabolite of vitamin A (retinol), acting as a ligand for nuclear retinoic acid receptors (RAR/RXR) to regulate gene transcription. It is critical for epithelial cell differentiation, vision (as r...

Leydig cells are testosterone-producing interstitial cells located in the testes, adjacent to the seminiferous tubules. They respond to luteinizing hormone (LH) from the anterior pituitary to synthesize testosterone from cholesterol. The...

Ranitidine is a histamine H2-receptor antagonist previously used to treat peptic ulcer disease, GERD, and acid-related disorders by decreasing gastric acid secretion. It was withdrawn from the market in 2020 due to contamination with N-n...

Superoxide dismutase (SOD) is an antioxidant enzyme that catalyzes the dismutation of superoxide radical (O2•−) into hydrogen peroxide (H2O2) and oxygen (O2), protecting cells from oxidative damage. It is a key component of the cellular...

Genomic imprinting is an epigenetic phenomenon in which genes are expressed in a parent-of-origin-specific manner, meaning only the allele inherited from one parent (maternal or paternal) is active, while the other is silenced via DNA me...

Becker muscular dystrophy (BMD) is an X-linked recessive dystrophinopathy caused by partial-function mutations in the DMD gene, leading to a milder, later-onset form of muscular dystrophy compared to Duchenne. It presents with proximal m...

Chiari malformations are congenital or acquired structural defects in which the cerebellum (and sometimes brainstem) herniates through the foramen magnum into the spinal canal. Type I involves cerebellar tonsillar herniation ≥5mm below t...

High-output heart failure occurs when cardiac output is normal or elevated but still insufficient to meet the body's excessive metabolic or circulatory demands, leading to signs of heart failure. Common causes include anemia, thyrotoxico...

Lactic acid is a metabolic byproduct of anaerobic glycolysis, formed when pyruvate is reduced by lactate dehydrogenase (LDH) under conditions of insufficient oxygen or mitochondrial dysfunction. Elevated serum lactate (lactic acidosis) i...

Type 1 (distal) renal tubular acidosis is caused by failure of the alpha-intercalated cells in the distal tubule to secrete H+, leading to inability to acidify urine. It results in normal anion gap (hyperchloremic) metabolic acidosis wit...

Purines are nitrogen-containing heterocyclic compounds (adenine and guanine) that serve as building blocks of DNA, RNA, ATP, GTP, and cofactors like NAD+ and CoA. They are synthesized de novo or via salvage pathways and are catabolized t...

Alpha-1 antitrypsin (A1AT) deficiency is an autosomal codominant genetic disorder caused by mutations in the SERPINA1 gene, leading to reduced or dysfunctional A1AT protein. This results in unopposed neutrophil elastase activity causing...

Sertoli cells are somatic support cells within the seminiferous tubules of the testes that nurture developing sperm and form the blood-testis barrier. They are regulated by FSH and produce inhibin B, which provides negative feedback on F...

The zona glomerulosa is the outermost layer of the adrenal cortex, responsible for producing mineralocorticoids, primarily aldosterone. It is regulated mainly by the renin-angiotensin-aldosterone system (RAAS) and plasma potassium levels...

Aortic coarctation is a congenital narrowing of the aorta, most commonly located just distal to the origin of the left subclavian artery near the ligamentum arteriosum (juxtaductal). It causes upper extremity hypertension with weaker, de...

An indirect inguinal hernia occurs when abdominal contents protrude through the internal (deep) inguinal ring, lateral to the inferior epigastric vessels, following the path of the spermatic cord through the inguinal canal. It results fr...

A codon is a sequence of three nucleotides in mRNA that codes for a specific amino acid or a stop signal during protein synthesis. There are 64 possible codons (61 sense codons + 3 stop codons) encoding 20 amino acids, making the genetic...

Axial refers to the central axis of the body—the head, neck, and trunk (spine, thorax, abdomen, pelvis)—as opposed to the appendicular skeleton (limbs). It is also used in imaging to describe a transverse cross-sectional plane that divid...

The parathyroid glands are four small endocrine glands located posterior to the thyroid gland that secrete parathyroid hormone (PTH), the primary regulator of serum calcium levels. PTH increases blood calcium by stimulating bone resorpti...

The renal pelvis is a funnel-shaped structure formed by the convergence of the major calyces at the renal hilum, serving as the collecting point for urine before it drains into the ureter. It is lined by transitional epithelium (urotheli...

Transitional cell carcinoma (TCC), also known as urothelial carcinoma, is the most common malignancy of the urinary tract, arising from the transitional epithelium lining the renal pelvis, ureters, bladder, and urethra. The bladder is th...

Podocyte foot processes are interdigitating extensions of glomerular epithelial cells that wrap around glomerular capillaries, forming the final filtration barrier along with the fenestrated endothelium and glomerular basement membrane (...

Focal nodular hyperplasia (FNH) is the second most common benign liver tumor (after hemangioma), typically found incidentally in women of reproductive age. It is characterized by a central stellate fibrous scar and is not associated with...

The bronchi are the main air-conducting passages that branch from the trachea into the lungs, dividing progressively into smaller bronchi and eventually bronchioles. They are lined by pseudostratified ciliated columnar epithelium with go...

Type IV hypersensitivity is a delayed, T-cell-mediated (not antibody-mediated) immune reaction that develops 48-72 hours after antigen exposure. It involves CD4+ Th1 cells activating macrophages or CD8+ cytotoxic T cells directly killing...

Vitamin B6 (pyridoxine) is a water-soluble vitamin that serves as a cofactor (as pyridoxal 5'-phosphate, PLP) for transamination, decarboxylation, and glycogen phosphorylase reactions. Deficiency classically causes sideroblastic anemia,...

The amniotic cavity is a fluid-filled space that forms between the embryonic disc and the overlying amnion during the second week of development. It contains amniotic fluid, which cushions the embryo/fetus, allows fetal movement, and pla...

A sliding hiatal hernia occurs when the gastroesophageal junction and part of the stomach slide upward through the diaphragmatic esophageal hiatus into the thorax. It accounts for ~95% of hiatal hernias and is a major risk factor for GER...

Anti-Müllerian hormone (AMH) is a glycoprotein produced by Sertoli cells in males that causes regression of the paramesonephric (Müllerian) ducts during embryogenesis, preventing development of female internal reproductive structures. In...

Nivolumab is a human IgG4 monoclonal antibody that inhibits PD-1 (programmed cell death protein 1), an immune checkpoint receptor on activated T cells. By blocking PD-1's interaction with PD-L1/PD-L2 on tumor cells, it restores T-cell me...

The adrenal glands are paired endocrine organs sitting atop the kidneys, each divided into a cortex (producing steroid hormones) and medulla (producing catecholamines). The cortex has three zones—glomerulosa (aldosterone), fasciculata (c...

Mucor is a genus of fast-growing, ubiquitous saprophytic molds belonging to the order Mucorales, causing mucormycosis, an angioinvasive fungal infection primarily affecting immunocompromised hosts (uncontrolled diabetics with DKA, neutro...

Maintenance therapy refers to long-term treatment given to sustain remission, control chronic disease, or prevent relapse after initial induction/consolidation therapy has achieved a desired clinical response. It is common in oncology, i...

Troponin (cardiac troponin I and T) is a regulatory protein complex found in cardiac muscle that is released into the blood following myocardial injury. It is the most sensitive and specific biomarker for diagnosing acute myocardial infa...

The pericardial space is the potential space between the visceral and parietal layers of the serous pericardium, normally containing 15-50 mL of lubricating fluid. Excess fluid accumulation (pericardial effusion) can lead to cardiac tamp...

Carbamoyl phosphate synthetase I (CPS1) is a mitochondrial matrix enzyme that catalyzes the first, rate-limiting step of the urea cycle: combining ammonia (NH3), CO2, and ATP to form carbamoyl phosphate. It requires N-acetylglutamate (NA...

The intercostal muscles are layers of muscle situated between the ribs that aid in respiration. The external intercostals elevate the ribs during inspiration, while the internal intercostals depress the ribs during forced expiration. The...

Urokinase is a serine protease that directly converts plasminogen to plasmin, promoting fibrinolysis. It is used therapeutically as a thrombolytic agent, though it has largely been replaced by tissue plasminogen activator (tPA) derivativ...

The juxtaglomerular apparatus (JGA) is a specialized structure in the kidney composed of juxtaglomerular cells, macula densa cells, and extraglomerular mesangial cells, located where the afferent arteriole meets the distal convoluted tub...

Erythrocytes (red blood cells, RBCs) are anucleate, biconcave discoid cells that transport oxygen from the lungs to tissues and carbon dioxide back to the lungs, primarily via hemoglobin. They have a lifespan of ~120 days and are produce...

Threonine is an essential amino acid required in the diet, meaning the body cannot synthesize it de novo and it must be obtained from protein sources. It is used in protein synthesis, mucin production, and collagen/elastin formation, and...

Purkinje fibers are specialized cardiac conduction cells located in the subendocardium that rapidly transmit electrical impulses from the bundle branches to the ventricular myocardium, ensuring coordinated ventricular contraction. They h...

Aspergillosis refers to a spectrum of diseases caused by Aspergillus species (most commonly A. fumigatus), a ubiquitous septate mold with acute-angle branching hyphae. Clinical presentation depends on host immune status, ranging from all...

The femoral artery is the major arterial supply to the lower limb, arising as a continuation of the external iliac artery just distal to the inguinal ligament. It lies within the femoral triangle, lateral to the femoral vein and nerve (V...