1500+ medical terms, defined.

The fallopian tubes (uterine tubes/oviducts) are paired muscular ducts connecting the ovaries to the uterus, serving as the site of fertilization. They are lined by ciliated columnar epithelium that helps transport the ovum toward the ut...

The broad ligament is a peritoneal fold that drapes over the uterus, fallopian tubes, and ovaries, connecting them to the lateral pelvic walls. It provides structural support and serves as a conduit for vessels, nerves, and ligaments of...

Eosinophils are granulocytic white blood cells involved in defense against parasitic infections and mediation of allergic reactions. They are identified histologically by bright red-orange cytoplasmic granules on H&E stain and typically...

The corpus spongiosum is one of three erectile tissue columns in the penis, surrounding the urethra ventrally. It maintains urethral patency during erection, preventing compression that would occur from the two corpora cavernosa alone, a...

Serine is a nonessential, hydroxyl-containing amino acid that serves as a key building block for other biomolecules and as a catalytic residue in serine proteases. It plays central roles in one-carbon metabolism, phospholipid/sphingolipi...

Fibroblasts are the most common cells of connective tissue, responsible for synthesizing extracellular matrix components including collagen, elastin, glycosaminoglycans, and glycoproteins. They play a central role in wound healing, tissu...

Jod-Basedow phenomenon is thyrotoxicosis induced by iodine exposure in a patient with an underlying thyroid abnormality, such as multinodular goiter or latent Graves' disease. It occurs because autonomous thyroid tissue is no longer subj...

The embryonic period spans weeks 3–8 of human development, during which the three germ layers (ectoderm, mesoderm, endoderm) form and differentiate into the primordia of all major organ systems. This is the most critical window for terat...

A femoral hernia occurs when abdominal or pelvic contents protrude through the femoral canal, below the inguinal ligament. It is more common in women (due to a wider femoral canal) but overall less common than inguinal hernias. Femoral h...

Cystathionine β-synthase (CBS) is a vitamin B6-dependent enzyme that converts homocysteine to cystathionine in the transsulfuration pathway, the first committed step in cysteine synthesis. Deficiency causes homocystinuria, characterized...

Cardiac catheterization is an invasive procedure involving insertion of a catheter into the heart chambers or coronary arteries (via femoral or radial access) to measure pressures, oxygen saturations, and cardiac output, and to visualize...

Thyroid-stimulating hormone (TSH) is a glycoprotein hormone secreted by anterior pituitary thyrotrophs that stimulates the thyroid gland to produce T3 and T4. It is the most sensitive marker for assessing thyroid function and is regulate...

Whipple disease is a rare, chronic multisystem infectious disease caused by the gram-positive bacillus Tropheryma whipplei. It classically presents with malabsorption, weight loss, diarrhea, arthralgias, and CNS/cardiac involvement, most...

Proline is a unique, non-essential amino acid with a cyclic secondary amine structure (imino acid) that introduces kinks into polypeptide chains and disrupts alpha-helix formation. It is a major component of collagen, where it is hydroxy...

Schistocytes are fragmented red blood cells with irregular, jagged shapes (helmet cells, triangle cells) seen on peripheral blood smear. They form when RBCs are mechanically sheared while passing through damaged or occluded microvasculat...

Thyroxine (T4) is the primary hormone secreted by the thyroid gland, synthesized from iodine and tyrosine via thyroglobulin. It is converted peripherally to the more active triiodothyronine (T3) and regulates basal metabolic rate, growth...

The sella turcica ('Turkish saddle') is a bony saddle-shaped depression in the sphenoid bone at the base of the skull that houses the pituitary gland (hypophysis). It is a key landmark for imaging pituitary pathology, especially pituitar...

Tumor markers are biomolecules (proteins, hormones, enzymes, or antigens) produced by tumor cells or the body in response to malignancy, used to aid diagnosis, monitor treatment response, detect recurrence, and assess prognosis. They are...

Amyloid nephropathy is renal damage caused by deposition of misfolded amyloid fibrils (typically AL or AA type) in the glomeruli, leading to nephrotic-range proteinuria and progressive kidney dysfunction. It is a major cause of nephrotic...

Primary hypothyroidism is thyroid hormone deficiency caused by dysfunction of the thyroid gland itself, resulting in low T3/T4 with compensatory elevated TSH. The most common cause worldwide is iodine deficiency, while Hashimoto's thyroi...

A nucleoside is a molecule composed of a nitrogenous base (purine or pyrimidine) covalently linked to a pentose sugar (ribose or deoxyribose) via an N-glycosidic bond, but lacking a phosphate group. Nucleosides are precursors to nucleoti...

Courvoisier sign refers to a palpable, non-tender, distended gallbladder in a patient with painless jaundice, classically associated with malignant obstruction of the common bile duct (often pancreatic head cancer or cholangiocarcinoma)...

Melatonin is a hormone secreted by the pineal gland that regulates circadian rhythm and sleep-wake cycles. Its secretion is stimulated by darkness and suppressed by light, peaking at night. It is synthesized from tryptophan via serotonin.

An aponeurosis is a broad, flat sheet of dense fibrous connective tissue that connects muscle to bone or other muscle, functioning similarly to a tendon but with a wider, sheet-like structure. Common examples include the epicranial (gale...

Carboplatin is a second-generation platinum-based chemotherapeutic agent that causes DNA crosslinking (intrastrand and interstrand), leading to inhibition of DNA replication and transcription, ultimately triggering apoptosis in rapidly d...

Gonadotropin-releasing hormone (GnRH) is a hypothalamic decapeptide that stimulates the anterior pituitary to release FSH and LH, which regulate gonadal function. It is secreted in a pulsatile manner, which is essential for its stimulato...

Tetrahydrobiopterin (BH4) is an essential cofactor for phenylalanine hydroxylase, tyrosine hydroxylase, tryptophan hydroxylase, and nitric oxide synthase. It is critical for the synthesis of monoamine neurotransmitters (dopamine, norepin...

The hepatic artery is a branch of the celiac trunk that supplies oxygenated blood to the liver, accounting for ~25% of hepatic blood flow while the portal vein supplies the remaining ~75% (nutrient-rich, deoxygenated blood). It is a crit...

The cecum is a pouch-like structure marking the beginning of the large intestine, located in the right lower quadrant of the abdomen, connecting the ileum to the ascending colon. It receives chyme from the terminal ileum via the ileoceca...

Lipogenesis is the metabolic pathway that synthesizes fatty acids from acetyl-CoA (derived from excess glucose, amino acids, or ethanol) and stores them as triglycerides. It occurs primarily in the liver and adipose tissue and is upregul...

Adalimumab is a fully human monoclonal antibody that binds and neutralizes TNF-α, blocking its inflammatory effects. It is used to treat autoimmune conditions such as rheumatoid arthritis, ankylosing spondylitis, psoriasis/psoriatic arth...

Hepatic veins are the terminal branches of the venous drainage of the liver, carrying deoxygenated blood from hepatic sinusoids into the inferior vena cava (IVC). There are typically three major hepatic veins (right, middle, left) that d...

Sore throat (pharyngitis) is inflammation of the pharynx, most commonly caused by viral infection, though group A Streptococcus (GAS) is the key bacterial cause to identify due to risk of complications. Clinical evaluation focuses on dis...

The abdominal aorta is the continuation of the thoracic aorta below the diaphragm (T12) to its bifurcation into the common iliac arteries at L4. It supplies blood to the abdominal organs, gastrointestinal tract, kidneys, and lower limbs...

Isovolumetric relaxation is the phase of the cardiac cycle occurring immediately after ventricular systole, during which the ventricles relax and pressure drops sharply while ventricular volume remains constant. It occurs after the aorti...

Monoamine oxidase (MAO) is a mitochondrial enzyme that catalyzes oxidative deamination of monoamine neurotransmitters (serotonin, norepinephrine, dopamine) and dietary amines (tyramine). It exists as two isoforms, MAO-A and MAO-B, and is...

Group B Streptococcus (Streptococcus agalactiae) is a gram-positive, catalase-negative, beta-hemolytic diplococcus that is bacitracin-resistant and hippurate-hydrolysis positive. It colonizes the vaginal/rectal tract of ~10-30% of pregna...

Amphetamine is a sympathomimetic amine that increases release and blocks reuptake of catecholamines (dopamine, norepinephrine) in the CNS, producing stimulant effects. It is used therapeutically for ADHD and narcolepsy but has high abuse...

Methylphenidate is a CNS stimulant that blocks dopamine and norepinephrine reuptake, used first-line for ADHD and narcolepsy. It increases synaptic catecholamine levels, improving attention and reducing hyperactivity/impulsivity. Common...

MHC class II molecules present exogenous antigens to CD4+ helper T cells, playing a central role in initiating adaptive immune responses. They are expressed on professional antigen-presenting cells (APCs) including dendritic cells, macro...

Ubiquinone (Coenzyme Q10) is a lipid-soluble electron carrier in the inner mitochondrial membrane that shuttles electrons from Complex I and Complex II to Complex III in the electron transport chain. It is essential for oxidative phospho...

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is an autosomal recessive disorder of mitochondrial fatty acid β-oxidation, caused by mutations in the ACADM gene. It presents in infancy/childhood with hypoketotic hypoglycemia, vomi...

MHC molecules present antigens to T cells and are critical for immune recognition and self/non-self discrimination. MHC class I (HLA-A, -B, -C) presents to CD8+ T cells and is found on all nucleated cells, while MHC class II (HLA-DP, -DQ...

Renal clearance is the volume of plasma from which a substance is completely removed by the kidneys per unit time (mL/min). It is calculated as Clearance = (Urine concentration × Urine flow rate) / Plasma concentration. It's used to esti...

Schistosoma is a genus of parasitic blood flukes (trematodes) causing schistosomiasis, transmitted via freshwater snails. Major species include S. haematobium (bladder, associated with squamous cell carcinoma of bladder), S. mansoni and...

The tonsils are lymphoid tissue components of Waldeyer's ring located at the oropharynx, serving as immune surveillance sites for inhaled and ingested antigens. The palatine tonsils are the most clinically relevant, commonly involved in...

The cystic duct connects the gallbladder to the common hepatic duct, forming the common bile duct. It contains the spiral valves of Heister, which regulate bile flow into and out of the gallbladder. Obstruction of the cystic duct (typica...

The Philadelphia chromosome is a reciprocal translocation t(9;22)(q34;q11) that creates the BCR-ABL1 fusion gene, producing a constitutively active tyrosine kinase. It is the hallmark genetic abnormality of chronic myelogenous leukemia (...

A facultative anaerobe is an organism that primarily uses aerobic respiration when oxygen is available but can switch to anaerobic respiration or fermentation in its absence. This metabolic flexibility allows survival across a wide range...

Viral infections occur when obligate intracellular pathogens (viruses) invade host cells, hijack cellular machinery for replication, and trigger immune responses. Clinical presentations range from asymptomatic to life-threatening dependi...