Overview
This lecture covers hemostasis (the process of stopping bleeding), blood clotting mechanisms, blood grouping, transfusions, and various diagnostic blood tests.
Hemostasis and Bleeding Control
- Hemostasis is the body's process to stop bleeding, both externally and internally.
- Three main stages: vascular spasm, platelet plug formation, and coagulation.
- Vascular spasm: blood vessel constriction due to endothelin and thromboxanes.
- Platelet plug formation: platelets adhere to exposed collagen with von Willebrand factor and aggregate via fibrinogen bridges.
- Coagulation: cascade involving clotting factors forms a fibrin mesh, trapping blood cells and debris.
Clotting Pathways and Control
- Clotting factors are proteins (indicated by Roman numerals) activated via extrinsic (tissue damage) or intrinsic (contact with collagen) pathways.
- Both pathways converge at Factor X, leading to the conversion of prothrombin to thrombin, and then fibrinogen to fibrin.
- Vitamin K is essential for synthesizing several clotting factors.
- The body controls clot formation using anti-coagulants such as antithrombin, heparin, prostacyclin, and drugs like warfarin.
- Clot retraction involves actin and myosin to close vessel edges; clot dissolution (fibrinolysis) breaks down fibrin.
Blood Grouping and Transfusions
- Blood types (A, B, AB, O) are determined by surface antigens on red blood cells.
- Type A has anti-B antibodies, type B has anti-A antibodies, type AB has no antibodies, and type O has both anti-A and anti-B antibodies.
- Type O is the universal donor; type AB is the universal recipient.
- Rh factor (D antigen) determines positive or negative blood type—Rh-negative individuals can only receive Rh-negative blood.
- Hemolytic disease of the newborn can occur if an Rh-negative mother carries an Rh-positive fetus; prevented with RhoGAM injections.
Diagnostic Blood Tests and Disorders
- Cross-matching tests ensure compatibility before transfusion to prevent agglutination (clumping).
- Complete blood count (CBC) measures red and white blood cells, hemoglobin, and hematocrit.
- Anemia, leukemia, clotting disorders (like von Willebrand disease and hemophilia), and infections can be diagnosed using blood tests.
- Platelet count and prothrombin time assess clotting function.
- Blood chemistry tests measure dissolved and suspended substances in plasma.
Key Terms & Definitions
- Hemostasis — process of stopping bleeding.
- Vascular spasm — blood vessel constriction to reduce blood flow.
- Platelet plug — aggregation of platelets sealing small vessel breaks.
- Coagulation — formation of a fibrin blood clot.
- Clotting factors — proteins involved in the clotting cascade.
- Vitamin K — vitamin crucial for synthesizing clotting factors.
- Anticoagulants — substances preventing blood clot formation.
- Agglutination — clumping of red blood cells due to incompatible blood mixing.
- Rh factor — protein determining positive or negative blood type.
- CBC (complete blood count) — analysis of blood cells and components.
Action Items / Next Steps
- Review end-of-chapter summary and bullet points.
- Complete practice questions on Blackboard.
- Study blood grouping compatibility and clotting pathways for exams.