Medical terms, defined.

Apoptotic bodies are membrane-bound vesicles containing condensed cytoplasm, organelles, and nuclear fragments (karyorrhexis) that form when a cell undergoing apoptosis blebs and fragments. They are rapidly phagocytosed by macrophages (r...

Proton pump inhibitors (PPIs; e.g., omeprazole, esomeprazole, lansoprazole, pantoprazole, rabeprazole, dexlansoprazole) are prodrugs that irreversibly inhibit the H+/K+ ATPase on gastric parietal cell apical membranes, producing the most...

Lewy bodies are intraneuronal, eosinophilic cytoplasmic inclusions composed of misfolded alpha-synuclein. They are the pathologic hallmark of Parkinson disease (substantia nigra pars compacta), Lewy body dementia (cortical), and Parkinso...

Reed-Sternberg (RS) cells are large, binucleate (or bilobed) neoplastic B-cell-derived cells with prominent eosinophilic "owl-eye" nucleoli, pathognomonic for classic Hodgkin lymphoma. They are CD15+ and CD30+, CD45−, and typically CD20−...

Potassium-sparing diuretics act at the late distal tubule/collecting duct to promote mild natriuresis while retaining K+. Two classes: aldosterone receptor antagonists (spironolactone, eplerenone) and ENaC blockers (amiloride, triamteren...

Psammoma bodies are round, concentrically laminated, basophilic calcified structures seen microscopically in certain tumors and tissues. Classic associations: papillary thyroid carcinoma, meningioma, serous cystadenocarcinoma of the ovar...

Howell-Jolly bodies are small, round, basophilic (dark purple) nuclear remnants (DNA fragments) within RBCs on peripheral smear. They are normally removed by the spleen, so their presence indicates asplenia or hyposplenism (e.g., post-sp...

A proto-oncogene is a normal cellular gene that promotes cell growth, proliferation, and differentiation. Gain-of-function mutations, amplification, or translocation convert it into an oncogene, which drives uncontrolled growth. Only one...

Mitochondrial inheritance is non-Mendelian transmission of mtDNA-encoded traits exclusively through the mother: all offspring of an affected mother inherit the mutation (to varying degrees), while an affected father transmits it to none....

Antigen-presenting cells (APCs) process and display antigen peptides on MHC molecules to T cells. Professional APCs (dendritic cells, macrophages, B cells) express MHC class II and costimulatory molecules (B7) and activate CD4+ T cells;...

Antigen-presenting cells (APCs) process and display antigen fragments on MHC molecules to T cells. Professional APCs (dendritic cells, macrophages, B cells) express MHC class II (and class I) plus costimulatory molecules (B7/CD80-86); de...

The countercurrent multiplier is the renal mechanism in the loop of Henle that creates a hypertonic medullary interstitium (up to ~1200 mOsm/L). The thick ascending limb (TAL) actively reabsorbs NaCl via NKCC2 but is impermeable to water...

Obligate anaerobes are bacteria that cannot grow in the presence of oxygen because they lack (or have very low levels of) superoxide dismutase and catalase, so they cannot detoxify reactive oxygen species. They are found in oxygen-poor s...

Countercurrent exchange is a passive mechanism in which two fluids flow in opposite directions alongside each other, allowing transfer of heat, solutes, or gases down gradients. In the kidney, the vasa recta preserve the medullary osmoti...

An upper motor neuron (UMN) lesion is damage to motor neurons of the motor cortex or their descending corticospinal/corticobulbar tracts, above the anterior horn cell. It causes contralateral (if above the pyramidal decussation) spastic...

Pacemaker potential (phase 4 spontaneous depolarization) is the slow, spontaneous diastolic depolarization of SA node (and AV node) cells that drives automaticity until threshold is reached and an action potential fires. It is caused by...

Gram-negative cocci are spherical bacteria that stain pink/red on Gram stain (thin peptidoglycan with an outer membrane containing LPS/endotoxin). The high-yield genera are Neisseria (N. meningitidis, N. gonorrhoeae) and Moraxella catarr...

Acid-fast bacilli (AFB) are rod-shaped bacteria whose cell walls contain long-chain mycolic acids, so they resist decolorization by acid-alcohol after staining with carbol fuchsin (Ziehl-Neelsen/Kinyoun). The classic AFB are Mycobacteriu...

Starling forces are the hydrostatic and oncotic (colloid osmotic) pressures across a capillary wall that determine net fluid movement between plasma and interstitium. Net filtration occurs at the arteriolar end and reabsorption at the ve...

A lower motor neuron (LMN) is a motor neuron whose cell body lies in the anterior horn of the spinal cord gray matter or in cranial nerve motor nuclei of the brainstem. Its axon travels via the peripheral nerve to directly innervate skel...

A lower motor neuron (LMN) lesion is damage to the anterior horn cell, spinal nerve root, plexus, peripheral nerve, or cranial nerve motor nuclei/fibers. It causes flaccid weakness, hyporeflexia/areflexia, hypotonia, muscle atrophy, and...

The circle of Willis is an anastomotic arterial ring at the base of the brain that connects the anterior (internal carotid) and posterior (vertebrobasilar) circulations. It provides collateral flow if one vessel is occluded, and it is th...

The middle cerebral artery (MCA) is the largest terminal branch of the internal carotid artery and the most commonly occluded cerebral vessel in stroke. It supplies the lateral convex surface of the cerebral hemisphere, including the pri...

Weber syndrome is a midbrain (ventral/basal) stroke syndrome caused by occlusion of paramedian branches of the posterior cerebral artery (or basilar bifurcation). It presents with ipsilateral CN III palsy (down-and-out eye, ptosis, dilat...

Wallenberg syndrome (lateral medullary syndrome) is an ischemic stroke of the lateral medulla, most often from vertebral artery occlusion (or PICA). It causes ipsilateral facial pain/temperature loss, Horner syndrome, dysphagia/hoarsenes...

The posterior cerebral artery (PCA) is a terminal branch of the basilar artery (vertebrobasilar/posterior circulation) that supplies the occipital lobe (primary visual cortex), inferomedial temporal lobe, thalamus, and midbrain. PCA stro...

Brown-Séquard syndrome is a hemisection of the spinal cord causing ipsilateral loss of motor function (UMN signs below the lesion), proprioception/vibration/fine touch, and contralateral loss of pain and temperature beginning 1-2 levels...

A broad-spectrum antibiotic is active against a wide range of bacteria, typically both gram-positive and gram-negative organisms (and sometimes anaerobes or atypicals). It is used for empiric therapy when the pathogen is unknown or infec...

Nonselective beta blockers antagonize both β1 (heart) and β2 (bronchial/vascular smooth muscle, liver, metabolic) receptors. Examples: propranolol, nadolol, timolol, pindolol (with ISA), carvedilol and labetalol (also α1 block), sotalol....

Selective (cardioselective) beta blockers preferentially antagonize β1-adrenergic receptors in the heart, lowering heart rate, contractility, and renin release with less β2 blockade (bronchospasm, peripheral vasoconstriction, masking of...

A narrow-spectrum antibiotic is active against a limited range of bacteria, typically either mainly gram-positive or mainly gram-negative organisms (or a specific pathogen). It is preferred when the pathogen is known, since it limits dis...

Bacteriostatic agents inhibit bacterial growth and replication without directly killing the organisms, relying on the host immune system to clear the infection. Most are protein synthesis inhibitors that bind the 30S or 50S ribosomal sub...

Factor Xa inhibitors (rivaroxaban, apixaban, edoxaban; betrixaban discontinued) are oral direct anticoagulants that bind factor Xa directly, blocking conversion of prothrombin (II) to thrombin (IIa). They are used for stroke prevention i...

Direct thrombin inhibitors (DTIs) bind thrombin (factor IIa) directly, independent of antithrombin, inhibiting both free and clot-bound thrombin. Examples: argatroban, bivalirudin (parenteral), lepirudin/desirudin (hirudin analogs), and...

Direct oral anticoagulants (DOACs) are oral drugs that directly inhibit a single clotting factor, either factor Xa or thrombin (factor IIa). Factor Xa inhibitors are rivaroxaban, apixaban, edoxaban, and betrixaban (the "-xaban" drugs). T...

Cardioselective beta blockers preferentially antagonize β1-adrenergic receptors (heart, JG cells of kidney) over β2 receptors (bronchial/vascular smooth muscle). Mnemonic for the main agents: "A BEAM" – Acebutolol, Betaxolol, Bisoprolol,...

First-generation cephalosporins (cefazolin, cephalexin, cefadroxil) are beta-lactam antibiotics with excellent gram-positive coverage (MSSA, streptococci) and limited gram-negative activity (PEK: Proteus mirabilis, E. coli, Klebsiella pn...

Second-generation cephalosporins (cefaclor, cefoxitin, cefotetan, cefuroxime, cefprozil) are beta-lactam antibiotics with increased gram-negative coverage (H. influenzae, Enterobacter aerogenes, Neisseria, Proteus, E. coli, Klebsiella, S...

Fourth-generation cephalosporin = cefepime (the only one in routine US use). It has broad gram-positive coverage (including MSSA) plus gram-negative coverage including Pseudomonas aeruginosa, and it resists many chromosomal AmpC beta-lac...

Third-generation cephalosporins (ceftriaxone, cefotaxime, ceftazidime, cefdinir, cefixime, cefpodoxime) are beta-lactam antibiotics with enhanced gram-negative coverage and CNS penetration but reduced gram-positive activity compared with...

Typical (first-generation) antipsychotics are dopamine D2 receptor antagonists used mainly to treat positive symptoms of schizophrenia (hallucinations, delusions). They are divided into high-potency (haloperidol, fluphenazine, trifluoper...

First-generation (typical) antipsychotics are dopamine D2 receptor antagonists used mainly for positive symptoms of schizophrenia (hallucinations, delusions). They are divided into high-potency (haloperidol, fluphenazine, trifluoperazine...

Sulfonylureas are oral antidiabetic drugs that close pancreatic beta-cell ATP-sensitive K+ channels (SUR1 subunit of K-ATP/Kir6.2), causing depolarization, Ca2+ influx, and insulin exocytosis. They work only if functional beta cells rema...

Second-generation (atypical) antipsychotics are D2 and 5-HT2A receptor antagonists used for schizophrenia, bipolar disorder, and adjunctive treatment of depression. Compared with first-generation agents, they cause fewer extrapyramidal s...

DPP-4 inhibitors (gliptins: sitagliptin, saxagliptin, linagliptin, alogliptin, vildagliptin) block the enzyme dipeptidyl peptidase-4, which degrades incretins (GLP-1 and GIP). This raises active incretin levels, increasing glucose-depend...

Thiazolidinediones (TZDs; pioglitazone, rosiglitazone) are oral antidiabetic drugs that act as PPAR-γ agonists, increasing insulin sensitivity in adipose tissue, muscle, and liver. Key adverse effects are fluid retention/edema, heart fai...

SGLT2 inhibitors (-gliflozins: empagliflozin, dapagliflozin, canagliflozin, ertugliflozin) block sodium-glucose cotransporter 2 in the proximal convoluted tubule, causing glucosuria and lowering blood glucose independent of insulin. Beyo...

GLP-1 receptor agonists (e.g., semaglutide, liraglutide, dulaglutide, exenatide, tirzepatide [dual GIP/GLP-1]) mimic incretin GLP-1 to increase glucose-dependent insulin secretion, suppress glucagon, slow gastric emptying, and promote sa...

GLP-1 receptor agonists (e.g., exenatide, liraglutide, semaglutide, dulaglutide) mimic incretin GLP-1, increasing glucose-dependent insulin secretion, suppressing glucagon, slowing gastric emptying, and promoting satiety. They are used f...

Calcineurin inhibitors (cyclosporine, tacrolimus) are immunosuppressants that block calcineurin, a calcium-dependent phosphatase, preventing NFAT dephosphorylation and IL-2 transcription, which suppresses T-cell activation. They are used...