Unit 7: Platelets

Hemostasis

The process of turning free-flowing blood into a stationary clot.

Cellular elements of blood

Erythrocytes, Leukocytes, and Thrombocytes.

Platelet location in spun EDTA tube

In the buffy coat with white blood cells.

Hormone that signals platelet production

Thrombopoietin, produced mostly in the liver.

Thrombopoiesis

The process by which thrombocytes are created.

Formation of platelets

Pinched off from megakaryocytes in the bone marrow.

Lifespan of a platelet

10-14 days in peripheral blood.

Removal of old platelets

By phagocytic cells in the spleen; called 'senescence'.

Primary Hemostasis

Formation of a platelet plug to stop small bleeds.

Secondary Hemostasis

Stabilization of the clot with fibrin.

Fibrinolysis

The breakdown of the clot after healing.

Four systems involved in Hemostasis

Blood vessels, Platelets, Plasma coagulation proteins, Plasma fibrinolytic proteins.

Vascular response in primary hemostasis

Vessels constrict to reduce blood loss and create turbulence.

Key protein for platelet adhesion

Von Willebrand's Factor.

Four steps of platelet activation

Adhesion, Release, Aggregation, Contraction.

Extrinsic pathway of coagulation

Initiated by tissue factor outside the vessel; measured by PT.

Intrinsic pathway of coagulation

Initiated by factors within the blood; measured by aPTT.

Common pathway of coagulation

Final sequence where fibrin is formed from fibrinogen.

Role of Calcium in coagulation

Critical for both pathways; bound by anticoagulants like EDTA.

Final stabilizer of the fibrin clot

Factor XIII, the Fibrin Stabilizing Factor.

Breakdown products of a clot

Fibrin Degradation Products.

Test for platelet number

CBC platelet count; check smear for clumping.

Test for platelet function

Buccal Mucosal Bleeding Time.

Normal BMBT in a dog

Less than 4 minutes.

Normal BMBT in an anesthetized cat

Less than 3.3 minutes.

Prothrombin Time (PT) tests which pathway?

The extrinsic and common coagulation systems.

Activated Partial Thromboplastin Time (aPTT) tests which pathway?

The intrinsic and common coagulation systems.

Activated Clotting Time (ACT)

In-clinic test for intrinsic/common pathways; uses grey-top tube.

Normal ACT in dogs

1-2 minutes.

Normal ACT in cats

Less than 1 minute.

Prolonged PT with normal PTT indicates

A problem in the extrinsic pathway.

Clinical sign of a capillary clotting disorder

Petechiae on skin or mucous membranes.

Other clinical signs of coagulation issues

Epistaxis, melena, bruising.

Major factor evaluated by PT

Factor VII, which has the shortest half-life.

Purpose of the fibrinolytic system

To break down clots and prevent vessel clogging.

Primary vs. Secondary Hemostasis analogy

Primary is the "bandaid", secondary is the "cement".

What initiates the extrinsic pathway?

Tissue damage and release of tissue factor.

What initiates the intrinsic pathway?

Activation of clotting factors inside the vessel.

Why is Vitamin K important for coagulation?

Essential for producing clotting factors; inhibited by rodenticides.