Platelets

These flashcards cover key vocabulary and concepts regarding platelets and their role in hemostasis, relevant disorders, and associated physiological processes.

Platelets

Also known as thrombocytes, they are small cell fragments involved in hemostasis.

Thrombocytosis

Elevated platelet count (>450,000/uL), which can cause thrombosis or bleeding.

Thrombopoietin (TPO)

A hormone that stimulates platelet production and binds to platelets.

Megakaryocytes

Large bone marrow cells that produce platelets through a process called thrombopoiesis.

Endomitosis

A process during megakaryocyte maturation where cells undergo interrupted mitosis to become polyploid.

Adenosine diphosphate (ADP)

A platelet activator released at sites of vascular injury, important for platelet activation.

Glycoprotein Ib-IX complex

A receptor on platelets that binds to von Willebrand factor for adhesion.

Integrin αIIbβ3 (GP IIb/IIIa)

A receptor on activated platelets that binds fibrinogen to promote aggregation.

α Granules

Platelet granules containing proteins such as fibrinogen and von Willebrand factor.

Dense Bodies

Platelet granules that contain calcium, serotonin, and ADP/ATP.

Degranulation

The release of granule contents from activated platelets.

von Willebrand factor (vWF)

A blood glycoprotein that facilitates platelet adhesion to the vessel wall.

Coagulation cascade

A series of events that leads to blood clotting, strengthening the platelet plug.

Primary hemostasis

The initial formation of a platelet plug following vascular injury.

Hemostasis

The process that prevents and stops bleeding, involving platelet activation and coagulation.

Emperipolesis

Normal phenomenon where marrow cells appear to pass through the demarcation membrane of megakaryocytes.

Blood flow shear forces

Forces that affect platelet contact and activation, related to the size of blood vessels.

Thromboxane A2 (TXA2)

A lipid compound produced by activated platelets that promotes vasoconstriction and platelet aggregation.

Serotonin

A neurotransmitter that is stored in platelets and involved in vasoconstriction.

Petechiae

Small bleeding marks on the skin, typically less than 2mm.

Purpura

Larger bleeding spots on the skin, generally greater than 2mm.

Isolated thrombocytosis

Elevated platelet count without other accompanying blood abnormalities.

Secondary hemostasis

The stabilization of the platelet plug through the formation of a fibrous clot.

Hemagglutination

The clumping of cells, such as platelets, that occurs during aggregation.

Defects of Platelet Adhesion

Conditions such as von Willebrand disease that impair platelet adherence to the vessel wall.

Defects of Platelet Aggregation

Conditions such as Glanzmann’s thrombasthenia that prevent platelets from clumping.

Iron deficiency

A condition affecting platelet production and leading to thrombocytosis.

Acetylsalicylic acid

A medication used to prevent clot formation by inhibiting platelet aggregation.

Clopidogrel

A medication that acts as a P2Y12 receptor inhibitor, preventing platelet activation.

Uremic platelet dysfunction

Platelet dysfunction associated with kidney failure, leading to increased bleeding risk.

Thrombocytopenia

A condition characterized by low platelet counts, leading to increased bleeding risk.

Kinetics of platelet production

Refers to the rate of platelet production and turnover in the body.

Calcium's role in platelets

Calcium ions are essential for various steps in platelet activation and aggregation.

Mucocutaneous bleeding

Bleeding that occurs in mucous membranes or the skin, often associated with platelet disorders.

Bone marrow biopsy findings

Diagnostic procedure used to visualize megakaryocytes and assess platelet production.

Bone marrow megakaryocyte

The precursor cell responsible for the production of platelets.

Net platelet production

Daily production of platelets typically estimated at 1 x 10^11 in healthy adults.

Short half-life of platelets

Platelets have a lifespan of about 10 days in circulation.

ADP receptor P2Y12

A receptor on platelets that, when activated, promotes aggregation.

Active platelet plug

The stage of platelet aggregation where a stable plug forms to prevent bleeding.

Collagen exposure

A key trigger for platelet activation and aggregation following vascular injury.

Thrombospondin

A glycoprotein released by platelets that plays a role in coagulation.

PGI2

Prostaglandin I2, released by endothelial cells, which inhibits platelet activation.

Vasoconstriction

Narrowing of blood vessels which reduces blood flow and assists in hemostasis.

Reactive thrombocytosis

Thrombocytosis due to secondary causes such as inflammation or infection.

Essential thrombocythemia

A myeloproliferative disorder characterized by high platelet counts.

Hemostatic factors

Substances released by platelets that promote clot formation and stability.

Clinical presentation of thrombocytosis

Asymptomatic until high counts create risk for thrombosis or bleeding.

Scotty's syndrome

A platelet disorder resulting from a defect in coagulation activity.