Medical terms, defined.

Hospice care is comfort-focused, interdisciplinary end-of-life care for patients with a terminal illness and an estimated prognosis of ≤6 months if the disease runs its natural course. It prioritizes symptom relief, quality of life, and...

Neoadjuvant therapy is systemic or radiation treatment (chemo, radiation, endocrine, targeted, or immunotherapy) given BEFORE definitive local treatment, usually surgery. It aims to shrink or downstage the tumor, make unresectable or bor...

Induction therapy is the initial, intensive phase of treatment aimed at rapidly achieving disease control or remission. In oncology (e.g., AML, ALL) it aims for complete remission; in transplantation it means potent immunosuppression (e....

Active surveillance is a management strategy for low-risk, indolent cancers (classically low-risk prostate cancer: Gleason/Grade Group 1, PSA <10, cT1–T2a) in which the tumor is closely monitored with serial PSA, DRE, repeat MRI, and rep...

Watchful waiting (active surveillance/expectant management) is a management strategy of closely monitoring a patient without immediate intervention, with treatment started only if symptoms develop or disease progresses. It is used when t...

An advance directive is a legal document or verbal/written instruction made by a competent patient that specifies their wishes for future medical care, or designates a surrogate decision-maker, should they lose decision-making capacity....

Informed consent is the ethical and legal process in which a patient with decision-making capacity voluntarily agrees to a proposed intervention after receiving information about its nature, risks, benefits, and alternatives (including n...

Glutamic acid (glutamate, Glu, E) is an acidic, negatively charged, non-essential amino acid and the major excitatory neurotransmitter in the CNS. It is a key link between amino acid and carbohydrate metabolism (transamination to alpha-k...

Nonessential amino acids are those the body can synthesize de novo (from glycolytic/TCA intermediates or other amino acids), so they aren't required in the diet under normal conditions. They include alanine, asparagine, aspartate, glutam...

Branched-chain amino acids (BCAAs) are the essential amino acids leucine, isoleucine, and valine (mnemonic: "LIV" or "Very Important Leucine"). They are metabolized by branched-chain α-keto acid dehydrogenase (BCKD), which is deficient i...

Glucogenic amino acids are amino acids whose carbon skeletons are degraded to pyruvate or TCA cycle intermediates (α-ketoglutarate, succinyl-CoA, fumarate, oxaloacetate), which can be converted to glucose via gluconeogenesis. Purely keto...

Thymine is a pyrimidine nucleobase found in DNA (not RNA), which pairs with adenine via 2 hydrogen bonds. It is made by methylating dUMP to dTMP via thymidylate synthase, which requires N5,N10-methylene-THF; this step is targeted by 5-fl...

Ketogenic amino acids are amino acids whose catabolism yields acetyl-CoA or acetoacetate (not pyruvate or TCA intermediates), so they can form ketone bodies but cannot be used for net gluconeogenesis. The only purely ketogenic amino acid...

ATP (adenosine triphosphate) is the main energy currency of the cell, made of adenine, ribose, and three phosphate groups. Hydrolysis of the high-energy phosphoanhydride bonds (ΔG ≈ −7.3 kcal/mol) drives endergonic reactions, transport,...

AMP most commonly means adenosine monophosphate (a nucleotide; cAMP is its cyclic second-messenger form and AMP activates AMPK as a cellular energy-depletion signal). Other board-relevant uses: antimicrobial peptides (e.g., defensins), a...

GDP (guanosine diphosphate) is the "inactive" nucleotide bound to G-proteins (Gα subunit) and small GTPases (Ras, Rho, Rab). Receptor activation via a GEF exchanges GDP for GTP to turn the protein "on"; intrinsic GTPase activity hydrolyz...

UTP (uridine triphosphate) is a pyrimidine nucleotide used as an energy carrier and RNA precursor. It activates sugars for glycogen synthesis (UDP-glucose) and glucuronidation, and is made from UDP by nucleoside diphosphate kinase, with...

ADP (adenosine diphosphate) is a nucleotide formed by hydrolysis of ATP (or phosphorylation of AMP) and is the substrate for ATP regeneration via oxidative phosphorylation and substrate-level phosphorylation. Extracellular ADP released f...

Coenzyme A (CoA) is a carrier of acyl groups derived from pantothenic acid (vitamin B5). Its terminal sulfhydryl (-SH) group forms high-energy thioester bonds with acyl groups (e.g., acetyl-CoA, succinyl-CoA, malonyl-CoA), activating the...

GTP (guanosine triphosphate) is a purine nucleoside triphosphate that serves as an energy source and as the key molecular switch for G-protein signaling. It is also required for protein synthesis (translation initiation/elongation), micr...

Cellulose is an unbranched polysaccharide of β-1,4-linked glucose found in plant cell walls. Humans lack the enzyme (cellulase) to hydrolyze β-1,4 linkages, so it is indigestible and functions as insoluble dietary fiber, adding stool bul...

FMN (flavin mononucleotide) is the phosphorylated, active coenzyme form of riboflavin (vitamin B2), formed by riboflavin kinase. It serves as an electron carrier (FMNH2 ↔ FMN) in redox reactions, most notably as the prosthetic group of C...

CTP (cytidine triphosphate) is a pyrimidine ribonucleotide used for RNA synthesis and phospholipid synthesis (as CDP-choline, CDP-ethanolamine, CDP-diacylglycerol). It is made from UTP by CTP synthetase (amination using glutamine and ATP...

Starch is the main dietary storage polysaccharide of plants, composed of glucose units as amylose (linear, α-1,4 linkages) and amylopectin (branched, α-1,4 with α-1,6 branches every ~24-30 residues). It is digested by salivary and pancre...

FAD (flavin adenine dinucleotide) is an electron-carrying coenzyme derived from riboflavin (vitamin B2). It accepts 2 electrons/2 H⁺ to become FADH₂, which donates them to the electron transport chain (Complex II). It is a cofactor for s...

Proteoglycans are macromolecules with a core protein covalently attached to many unbranched glycosaminoglycan (GAG) chains (~95% carbohydrate by weight). They are major ECM components that hydrate and cushion tissue, resist compression (...

Glycosaminoglycans (GAGs, formerly mucopolysaccharides) are long, unbranched, negatively charged heteropolysaccharides made of repeating disaccharide units (an amino sugar + a uronic acid, except keratan sulfate which has galactose). The...

Glycosaminoglycans (GAGs, formerly mucopolysaccharides) are long, unbranched, negatively charged heteropolysaccharides made of repeating disaccharide units (an amino sugar + a uronic acid, except keratan sulfate, which has galactose). Th...

Proteoglycans are macromolecules of a core protein covalently linked to many unbranched glycosaminoglycan (GAG) chains (~95% carbohydrate by weight). They are major components of the extracellular matrix (ECM), cartilage, and basement me...

Chondroitin sulfate is a sulfated glycosaminoglycan (GAG) made of repeating disaccharides of glucuronic acid and N-acetylgalactosamine (GalNAc). It is a major component of cartilage, bone, cornea, and aggrecan, where it provides compress...

HDL (high-density lipoprotein) is the smallest, densest lipoprotein; it mediates reverse cholesterol transport, carrying cholesterol from peripheral tissues and vessel walls back to the liver. Higher levels are epidemiologically associat...

IDL (Intermediate-Density Lipoprotein) is a transient lipoprotein formed when VLDL is hydrolyzed by lipoprotein lipase. It is either taken up by the liver (via ApoE receptors) or further converted to LDL by hepatic lipase. Elevated IDL i...

Phospholipids are amphipathic lipids with a hydrophilic phosphate-containing head and two hydrophobic fatty acid tails. They form the lipid bilayer of all cell membranes, and they are also the main component of lung surfactant (dipalmito...

Sphingolipids are membrane lipids built on a sphingosine backbone (an amino alcohol) linked to a fatty acid via an amide bond to form ceramide, the core structure. They include sphingomyelin, cerebrosides, gangliosides, and sulfatides. D...

Hepatic lipase (HL) is an enzyme on the surface of hepatic sinusoidal endothelium that hydrolyzes triglycerides and phospholipids in IDL and HDL (and chylomicron remnants). It converts IDL to LDL and HDL2 to smaller HDL3, and also promot...

Deoxyadenosylcobalamin (5'-deoxyadenosylcobalamin, adenosylcobalamin) is an active coenzyme form of vitamin B12 (cobalamin) and is the cofactor for methylmalonyl-CoA mutase in mitochondria. This enzyme converts L-methylmalonyl-CoA to suc...

N5-methyltetrahydrofolate (5-MTHF) is the main circulating, biologically active form of folate. It donates a methyl group to homocysteine to form methionine via methionine synthase (B12-dependent), and this is the "methyl folate trap" st...

LDL (low-density lipoprotein) is the main cholesterol-carrying lipoprotein in blood, derived from VLDL → IDL metabolism, with ApoB-100 as its structural protein. It delivers cholesterol to peripheral tissues via LDL receptor–mediated end...

Enolase is a glycolytic enzyme that converts 2-phosphoglycerate to phosphoenolpyruvate (PEP) by dehydration (a lyase reaction). It is inhibited by fluoride (which is why fluoride is added to blood-glucose collection tubes). Neuron-specif...

Water-soluble vitamins are the B-complex vitamins (B1, B2, B3, B5, B6, B7, B9, B12) and vitamin C. They are not stored in significant amounts (except B12, which the liver stores for years), are excreted renally, and rarely cause toxicity...

NAD+/NADH is a niacin (vitamin B3)-derived coenzyme that acts as the major electron carrier in catabolic redox reactions (glycolysis, TCA cycle, fatty acid β-oxidation, ethanol metabolism). NAD+ is the oxidized form (accepts hydride, bec...

ALT (alanine aminotransferase, formerly SGPT) is a liver enzyme that catalyzes transfer of an amino group from alanine to α-ketoglutarate, producing pyruvate and glutamate (requires vitamin B6/PLP). It is more specific for hepatocellular...

Aspartate aminotransferase (AST, formerly SGOT) is a pyridoxal phosphate (vitamin B6)-dependent enzyme that transfers an amino group from aspartate to alpha-ketoglutarate, yielding oxaloacetate and glutamate. It is found in liver, cardia...

Malate dehydrogenase (MDH) is an NAD+-dependent oxidoreductase that reversibly converts malate to oxaloacetate, generating NADH. It catalyzes the final step of the TCA (Krebs) cycle in the mitochondrial matrix (MDH2) and is a key compone...

Carnitine palmitoyltransferase (CPT) is a two-enzyme system (CPT-I on the outer mitochondrial membrane, CPT-II on the inner membrane) that shuttles long-chain fatty acids into the mitochondrial matrix for β-oxidation. CPT-I is the rate-l...

GGT (gamma-glutamyl transferase) is a membrane-bound enzyme found in hepatocytes and biliary epithelium (also kidney, pancreas, intestine) that is a sensitive marker of hepatobiliary disease and alcohol use. Elevated GGT alongside elevat...

Gamma-glutamyl transferase (GGT) is a membrane-bound enzyme found in hepatobiliary epithelium, kidney, pancreas, and other tissues that transfers gamma-glutamyl groups (key to glutathione metabolism). Serum GGT is a sensitive marker of h...

AST (aspartate aminotransferase, formerly SGOT) is an intracellular enzyme found in liver, cardiac muscle, skeletal muscle, kidney, and RBCs that catalyzes transfer of an amino group from aspartate to α-ketoglutarate, forming oxaloacetat...

Carbamoyl phosphate synthetase I (CPS I) is the mitochondrial rate-limiting enzyme of the urea cycle. It combines NH3 (ammonia), CO2 (as HCO3⁻), and 2 ATP to form carbamoyl phosphate, and it is allosterically activated by N-acetylglutama...

Lipoxygenase (LOX) is a family of iron-containing enzymes that convert arachidonic acid into leukotrienes and other lipoxygenase products (HPETEs, HETEs, lipoxins). 5-Lipoxygenase (5-LOX) generates leukotrienes (LTB4, LTC4, LTD4, LTE4),...