Blood Clotting, Hemostasis, and Platelet Disorders: Key Concepts for Biology

Platelets function

Help in blood clotting and stop bleeding

Platelets formation

Formed from megakaryocytes in bone marrow

Platelet structure

Small cell fragments, no nucleus, contain granules

Hemostasis steps in order

Vascular spasm → Platelet plug → Coagulation

Vascular spasm

Blood vessel constricts to reduce blood flow

Platelet plug

Platelets stick together to block injury

Coagulation

Fibrin forms to stabilize the clot

Intrinsic pathway

Activated by damage inside blood vessel, slower

Extrinsic pathway

Activated by external trauma, faster

Common pathway

Both pathways meet and form fibrin clot

Clot removal

Fibrinolysis breaks down clot using plasmin

Thrombus

Blood clot that forms and stays in one place

Embolus

Clot that travels through bloodstream

Why thrombus is dangerous

Blocks blood flow where it forms

Why embolus is dangerous

Can travel and block vital organs like lungs or brain

Thrombocytopenia

Low platelet count

Cause of thrombocytopenia 1

Bone marrow disease

Cause of thrombocytopenia 2

Increased platelet destruction (autoimmune)