Summary
Platelets and fibrin form a clot to seal damaged vessels.
In depth
Damaged vessels constrict; platelets form a plug; clotting factors convert prothrombin to thrombin, which makes fibrinogen into fibrin mesh. Haemophilia lacks factor VIII or IX. Anticoagulants such as warfarin and heparin prevent clots.
Clotting needs vitamin K, calcium and platelets. Excess clotting causes thrombosis. Aspirin inhibits platelet aggregation.
Key idea: haemostasis stops bleeding by plug, coagulation and clot retraction.
The process has three stages: vascular spasm, platelet plug (adhesion by von Willebrand factor, activation, aggregation) and coagulation. Thrombin converts soluble fibrinogen to insoluble fibrin strands that trap red cells. Factor XIII cross-links fibrin. Vitamin K is needed to make factors II, VII, IX and X in the liver, so warfarin (a vitamin K antagonist) is an anticoagulant. Fibrinolysis by plasmin dissolves clots later.
Haemophilia A (factor VIII) and B (factor IX) are X-linked, and von Willebrand disease is the most common inherited bleeding disorder. Abnormal clotting causes thrombosis, deep vein thrombosis, stroke and heart attack. Aspirin inhibits platelet aggregation by blocking thromboxane.
Remember: clotting is a cascade with amplification, with feedback to ensure rapid response.
Frequently asked questions
What is Blood Clotting?
Platelets and fibrin form a clot to seal damaged vessels.
Which area of biology covers Blood Clotting, and how advanced is it?
Blood Clotting is one of the 51 topics in Human Physiology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Hemostasis Cascade, Cardiovascular Disease Mechanisms, Blood Components.
Can you give an example of Blood Clotting?
Vitamin K is required for clotting factors.
What should I learn before Blood Clotting?
Work through the Beginner topics in Human Physiology first, such as Homeostasis, Tissues and Organs, Skeletal System, then return to Blood Clotting. Intermediate topics assume the Beginner vocabulary.
What topics are related to Blood Clotting?
The closest topics to Blood Clotting are Hemostasis Cascade, Cardiovascular Disease Mechanisms, Blood Components, Renin-Angiotensin-Aldosterone System. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Blood Clotting?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Blood Clotting. To practise the whole of Human Physiology, use the Human Physiology quiz.
How is Blood Clotting different from Hemostasis Cascade?
Blood Clotting: Platelets and fibrin form a clot to seal damaged vessels. Hemostasis Cascade: Intrinsic and extrinsic coagulation pathways converge to convert fibrinogen to fibrin. Read both side by side and note what each one explains.
How should I study Blood Clotting step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Hemostasis Cascade and explain the difference aloud. Finally, take the Human Physiology quiz and come back to this page for any question you miss.