1500+ medical terms, defined.

mTOR (mechanistic target of rapamycin) is a serine/threonine kinase that integrates nutrient, energy, and growth factor signals to regulate cell growth, proliferation, and metabolism. It exists in two complexes, mTORC1 and mTORC2, and is...

DNA-dependent RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template, catalyzing transcription in both prokaryotes and eukaryotes. In eukaryotes, three distinct polymerases (I, II, III) transcribe different cla...

Schistocytes are fragmented red blood cells seen on peripheral blood smear, classically appearing as helmet cells or triangular/crescent-shaped fragments. They are a hallmark finding of microangiopathic hemolytic anemia (MAHA) and mechan...

Dysentery is a type of gastroenteritis characterized by bloody diarrhea with mucus, abdominal cramping, and tenesmus, caused by invasive pathogens that damage the colonic mucosa. Classic causes include Shigella, Entamoeba histolytica, Ca...

Microangiopathic hemolytic anemia (MAHA) is a Coombs-negative hemolytic anemia caused by mechanical destruction of red blood cells as they pass through narrowed or damaged small vessels containing fibrin strands or platelet microthrombi....

Hemolytic Uremic Syndrome (HUS) is a triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. It most commonly occurs in children following infection with Shiga toxin-producing E. coli (STEC), particularly s...

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening microangiopathy caused by deficiency or inhibition of ADAMTS13, leading to accumulation of ultra-large vWF multimers and platelet microthrombi. It classically presents with...

Thrombotic Thrombocytopenic Purpura (TTP) is a thrombotic microangiopathy caused by deficiency or inhibition of ADAMTS13, leading to large vWF multimers that cause platelet microthrombi, hemolysis, and organ ischemia. It classically pres...

GPIb (Glycoprotein Ib) is a platelet surface receptor that binds von Willebrand factor (vWF), mediating platelet adhesion to exposed subendothelial collagen at sites of vascular injury. It is the key receptor in primary hemostasis's init...

Ecchymoses are larger (>1 cm) areas of skin discoloration caused by extravasation of blood into subcutaneous tissue, commonly known as bruises. They differ from petechiae (<3mm) and purpura (3mm-1cm) by size, with all three representing...

GPIIb/IIIa (integrin αIIbβ3) is a platelet surface glycoprotein receptor that binds fibrinogen, linking platelets together to form the platelet aggregation plug during primary hemostasis. It is activated following platelet adhesion and A...

The ristocetin cofactor assay (and related ristocetin-induced platelet aggregation, RIPA) measures von Willebrand factor (vWF) function by assessing its ability to bind platelet GPIb receptors in the presence of the antibiotic ristocetin...

GPIb (glycoprotein Ib) is a platelet surface receptor that binds von Willebrand factor (vWF), mediating platelet adhesion to the subendothelial matrix at sites of vascular injury. It is essential for the initial step of primary hemostasi...

vWF metalloprotease, also known as ADAMTS13, cleaves large von Willebrand factor (vWF) multimers into smaller, less active forms. Deficiency or inhibition of ADAMTS13 leads to accumulation of ultra-large vWF multimers, causing excessive...

P2Y12 is a Gi-protein-coupled ADP receptor on platelet surfaces that promotes platelet activation and aggregation upon binding ADP. It is the pharmacologic target of antiplatelet drugs like clopidogrel, prasugrel, and ticagrelor used in...

GPIIb/IIIa (integrin αIIbβ3) is a platelet surface receptor that binds fibrinogen and von Willebrand factor, mediating platelet-platelet aggregation—the final common pathway of primary hemostasis. Congenital deficiency causes Glanzmann t...

Dactylitis, also called 'sausage digit,' refers to diffuse swelling of an entire finger or toe due to inflammation of the digit including the tendons, joints, and soft tissue. It is a hallmark finding of seronegative spondyloarthropathie...

Enteritis refers to inflammation of the small intestine, commonly caused by infectious agents (viral, bacterial, or parasitic) and presenting with diarrhea, abdominal pain, nausea, and vomiting. It is often used alongside 'gastroenteriti...

Sprue refers to malabsorptive disorders causing chronic diarrhea, steatorrhea, and nutrient deficiencies due to small bowel mucosal damage. The two main types are celiac sprue (gluten-sensitive enteropathy) and tropical sprue (associated...

Trendelenburg gait is an abnormal, waddling gait pattern caused by weakness of the hip abductor muscles (gluteus medius and minimus), resulting in pelvic drop on the contralateral side during the stance phase of the affected limb. It is...

The Trendelenburg sign is a clinical finding indicating weakness of the hip abductor muscles (gluteus medius and minimus) or superior gluteal nerve dysfunction. When standing on the affected leg, the contralateral pelvis drops instead of...

The sartorius is the longest muscle in the body, a thin, strap-like muscle that runs obliquely across the anterior thigh from the anterior superior iliac spine (ASIS) to the medial proximal tibia. It flexes, abducts, and laterally rotate...

The pectineus is a flat, quadrangular muscle in the anteromedial thigh that acts as both a hip flexor and adductor. It belongs to the medial (adductor) compartment but is unique in receiving dual innervation from both the femoral and obt...

Anucleate refers to a cell that lacks a nucleus. Key examples in humans include mature red blood cells (erythrocytes) and the cells of the lens (lens fibers), which extrude their nuclei during terminal differentiation to optimize function.

Leishmania is a genus of protozoan parasites transmitted by the bite of female sandflies (Phlebotomus in Old World, Lutzomyia in New World), causing cutaneous, mucocutaneous, or visceral leishmaniasis. Visceral leishmaniasis (kala-azar),...

Megakaryocytes are large, polyploid bone marrow cells responsible for producing platelets (thrombocytes) through cytoplasmic fragmentation. They are regulated primarily by thrombopoietin (TPO), produced mainly in the liver. Each megakary...

Megakaryocytes are large, polyploid bone marrow cells responsible for platelet production. Each megakaryocyte can produce thousands of platelets via cytoplasmic fragmentation. They are derived from hematopoietic stem cells under the infl...