300+ medical terms, defined.

Carbonic anhydrase inhibitors are diuretics that block the enzyme carbonic anhydrase, primarily in the proximal tubule of the kidney. They cause mild diuresis, metabolic acidosis, and are mainly used for glaucoma, altitude sickness, and...

BRCA1 is a tumor suppressor gene that produces a protein involved in DNA repair via homologous recombination. Germline mutations in BRCA1 significantly increase the risk of hereditary breast and ovarian cancers, with lifetime breast canc...

Arachidonic acid is a 20-carbon polyunsaturated fatty acid that serves as the precursor to important inflammatory mediators including prostaglandins, leukotrienes, and thromboxanes. It is released from membrane phospholipids by phospholi...

Anaphylactic shock is a severe, life-threatening systemic allergic reaction characterized by rapid onset of cardiovascular collapse, respiratory distress, and multi-organ dysfunction. It results from massive mast cell and basophil degran...

The pleural space is a potential space between the visceral and parietal pleura containing a thin layer of pleural fluid (~10-15 mL) that lubricates pleural surfaces and maintains negative pressure for lung expansion. Pathological accumu...

Respiratory failure is the inability of the respiratory system to maintain adequate gas exchange, defined as PaO2 <60 mmHg (Type I/hypoxemic) or PaCO2 >50 mmHg with pH <7.35 (Type II/hypercapnic). It represents a life-threatening conditi...

Flavin adenine dinucleotide (FAD) is a crucial coenzyme derived from riboflavin (vitamin B2) that serves as an electron acceptor in cellular respiration and metabolism. It alternates between oxidized (FAD) and reduced (FADH2) forms, play...

Incomplete penetrance occurs when individuals with a disease-causing genotype do not express the expected phenotype. This means that not all people who carry a pathogenic mutation will develop the associated disease or trait, even with i...

Hypoxic vasoconstriction is the physiological response where blood vessels constrict in response to low oxygen levels. Most notably occurs in pulmonary vessels (hypoxic pulmonary vasoconstriction) to redirect blood flow away from poorly...

Endothelin is a potent vasoconstrictor peptide produced primarily by vascular endothelial cells. ET-1 is the most clinically significant isoform, playing crucial roles in vascular tone regulation, and is implicated in hypertension, heart...

Acute cholecystitis is inflammation of the gallbladder wall, most commonly caused by gallstone obstruction of the cystic artery (95% of cases). It presents with RUQ pain, fever, and positive Murphy's sign, and can progress to gangrene, p...

The brain is the central command organ of the nervous system, weighing ~1.4 kg and consuming 20% of total body glucose and oxygen despite being only 2% of body weight. It consists of cerebrum, cerebellum, and brainstem, protected by the...

Mechanical ventilation is artificial respiratory support that assists or replaces spontaneous breathing using positive pressure to deliver oxygen and remove carbon dioxide. It's indicated for respiratory failure, airway protection, or du...

Cerebral edema is the accumulation of excess fluid in brain tissue, leading to increased intracranial pressure (ICP). It can be classified as vasogenic (blood-brain barrier breakdown), cytotoxic (cellular swelling), or interstitial (CSF...

Giemsa stain is a Romanowsky-type stain used primarily for blood smears and bone marrow examination. It differentially stains cellular components, making nuclei appear blue-purple and cytoplasm pink-red, essential for identifying blood c...

NADH dehydrogenase (Complex I) is the first and largest enzyme complex of the electron transport chain, catalyzing the transfer of electrons from NADH to coenzyme Q while pumping protons across the inner mitochondrial membrane. Deficienc...

The electron transport chain (ETC) is a series of protein complexes in the inner mitochondrial membrane that transfers electrons from NADH and FADH2 to oxygen, generating ATP through oxidative phosphorylation. This process produces appro...

Caspases are cysteine-aspartic proteases that serve as the central executioners of programmed cell death (apoptosis). They exist as inactive precursors and are activated through proteolytic cleavage in response to apoptotic signals, lead...

Obesity is defined as a BMI ≥30 kg/m² and represents excessive body fat accumulation that increases health risks. It's a major risk factor for cardiovascular disease, type 2 diabetes, and metabolic syndrome. Central obesity (increased wa...

The splenic vein is a major portal venous tributary that drains blood from the spleen, pancreatic tail, and left side of the greater curvature of the stomach. It joins with the superior mesenteric vein to form the hepatic portal vein, ma...

Amlodipine is a long-acting dihydropyridine calcium channel blocker used primarily for hypertension and angina. It selectively blocks L-type calcium channels in vascular smooth muscle, causing vasodilation and reduced blood pressure with...

Oxygen saturation (SaO2 or SpO2) measures the percentage of hemoglobin molecules bound to oxygen. Normal values are 95-100%, with values <90% indicating hypoxemia requiring immediate attention. Pulse oximetry provides non-invasive contin...

Growth Hormone-Releasing Hormone (GHRH) is a hypothalamic peptide hormone that stimulates growth hormone (GH) release from anterior pituitary somatotrophs. It acts via cAMP pathway and is essential for normal growth and development. GHRH...

Serum osmolality measures the concentration of solute particles per kilogram of water in blood serum, normally 280-295 mOsm/kg. It reflects the body's water balance and is primarily determined by sodium, glucose, and urea concentrations....

The genital tubercle is an embryonic structure that appears around week 4 of gestation and gives rise to external genitalia in both males and females. It differentiates into the penis/clitoris under hormonal influence, with testosterone/...

Streptokinase is a bacterial enzyme derived from group C β-hemolytic streptococci that acts as a thrombolytic agent by converting plasminogen to plasmin, thereby dissolving blood clots. It was historically used for acute myocardial infar...

The left anterior descending artery (LAD) is the main branch of the left coronary artery that supplies the anterior wall of the left ventricle and anterior interventricular septum. Often called the 'widow maker' due to high mortality fro...

Propylthiouracil (PTU) is an antithyroid medication that inhibits thyroid hormone synthesis by blocking thyroid peroxidase and peripheral conversion of T4 to T3. It is primarily used to treat hyperthyroidism, particularly in pregnancy an...

Vitamins are essential organic compounds required in small amounts for normal metabolism, growth, and physiological function. They cannot be synthesized by the body in adequate quantities and must be obtained from dietary sources. Defici...

The superior mesenteric artery (SMA) is a major unpaired branch of the abdominal aorta that supplies blood to the midgut derivatives, including the small intestine (except proximal duodenum) and proximal large intestine up to the splenic...

Crigler-Najjar syndrome is a rare autosomal recessive disorder caused by deficiency or absence of UDP-glucuronosyltransferase (UGT1A1), leading to severe unconjugated hyperbilirubinemia. Type I is more severe with complete enzyme absence...

Clara cells (now called club cells) are non-ciliated, dome-shaped epithelial cells found in terminal and respiratory bronchioles. They secrete surfactant protein and Clara cell secretory protein (CCSP), serving as progenitor cells for br...

Alveolar air refers to the gas mixture present in the alveoli of the lungs, which has a different composition than atmospheric air due to gas exchange with pulmonary capillary blood. It contains less oxygen (~14%) and more carbon dioxide...

Disseminated intravascular coagulation (DIC) is a life-threatening coagulopathy characterized by systemic activation of the coagulation cascade, leading to simultaneous thrombosis and hemorrhage. It is always secondary to an underlying c...

Neonatal respiratory distress syndrome (NRDS) is a condition in premature infants caused by surfactant deficiency, leading to alveolar collapse and impaired gas exchange. It primarily affects infants born before 34 weeks gestation and is...

Amniocentesis is a prenatal diagnostic procedure involving transabdominal needle insertion into the amniotic sac to extract amniotic fluid for genetic and chromosomal analysis. Typically performed between 15-20 weeks gestation, it carrie...

Dexamethasone is a potent synthetic glucocorticoid with strong anti-inflammatory and immunosuppressive effects. It has minimal mineralocorticoid activity and a long half-life (36-54 hours), making it useful for conditions requiring susta...

Hemorrhage is the escape of blood from blood vessels, classified as external (visible) or internal (concealed). It can be arterial (bright red, pulsatile), venous (dark red, steady flow), or capillary (oozing). Severity ranges from minor...

PEEP (Positive End-Expiratory Pressure) is a ventilator setting that maintains positive airway pressure at the end of expiration to prevent alveolar collapse. It improves oxygenation by increasing functional residual capacity and reducin...

Alport syndrome is an X-linked hereditary nephritis caused by mutations in genes encoding type IV collagen (COL4A5), leading to progressive glomerulonephritis, sensorineural hearing loss, and ocular abnormalities. It primarily affects ma...

Tachycardia is defined as a heart rate >100 beats per minute in adults. It can be physiological (exercise, fever, anxiety) or pathological (arrhythmias, heart failure, hyperthyroidism). Classification includes supraventricular (SVT) and...

Ischemia is inadequate blood flow to tissues resulting in oxygen and nutrient deprivation. It can be acute or chronic and may lead to tissue dysfunction or death (infarction) if prolonged. Common causes include thrombosis, embolism, vaso...

Osmotic diuretics are agents that increase urine output by creating an osmotic gradient in the nephron tubules, preventing water reabsorption. Mannitol is the prototype, used primarily for reducing intracranial pressure and treating cere...

Osmotic diuretics are substances that increase urine output by creating an osmotic gradient in the renal tubules, preventing water reabsorption. Mannitol is the prototype drug, primarily working in the proximal tubule and descending limb...

Hereditary hemochromatosis is an autosomal recessive disorder of iron metabolism caused by mutations in the HFE gene (most commonly C282Y homozygosity). It leads to excessive iron absorption in the duodenum, resulting in iron overload wi...

Positive feedback is a physiological control mechanism where the response amplifies or enhances the original stimulus, creating a self-reinforcing cycle. Unlike negative feedback (which maintains homeostasis), positive feedback drives pr...

The proximal convoluted tubule (PCT) is the first segment of the nephron tubule where approximately 65-70% of filtered sodium, water, and other solutes are reabsorbed. It's the primary site for reabsorption of glucose, amino acids, and b...

The pentose phosphate pathway (PPP) is an alternative glucose oxidation pathway that generates NADPH for reductive biosynthesis and ribose-5-phosphate for nucleotide synthesis. It's critical for maintaining reduced glutathione levels and...

Secondary hyperaldosteronism is excessive aldosterone production due to activation of the renin-angiotensin-aldosterone system (RAAS) by factors outside the adrenal glands. Unlike primary hyperaldosteronism, renin levels are elevated. Co...

Clearance is the volume of plasma from which a substance is completely removed by an organ per unit time, typically expressed in mL/min. It's a fundamental concept in pharmacokinetics and renal physiology, with creatinine clearance being...