Blood physiology - Blood groups + haemostasis Flashcards
Draw out the ABO system
Explain the meaning of the terms Universal Donor and Universal Recipient.
Universal donor is O-. Type O negative blood lacks both A and B antigens on the surface of red blood cells and also lacks the Rh factor so can be transfused into individuals with any blood type without causing agglutination.
Universal recipient is AB+. Type AB+ blood lacks antibodies against A, B, or Rh antigens, individuals with this blood type can safely receive transfusions of blood from any other blood type without causing agglutination.
Define agglutination and haemolysis.
Agglutination - if donors antigens match recipients antibodies it causes red blood cells to clump together
Haemolysis - instead of antibodies causing agglutination they activate the complement system releasing proteolytic enzymes causing the red blood cells to rupture
Define the term haemostasis and list its four stages.
Haemostasis is the physiological process by which the body stops bleeding at the site of injury, thereby maintaining blood within the circulatory system and preventing excessive blood loss.
1 - vascular spasm
2 - platelet plug formation
3 - coagulation
4 - clot retraction
Describe the process vascular spasm.
Vasoconstriction
Nervous reflexes
Myogenic contraction
Factors from damaged tissues and activated platelets
Helps minimise blood loss
Describe the process of platelet plug formation.
- Platelets, small cell fragments found in the blood, adhere to the site of injury and become activated.
- They release chemical signals that attract more platelets to the area, forming a temporary plug that helps seal the damaged blood vessel
- Platelets are activated by contact with - von Willebrand factor, thrombin, negatively charged surface, collagen
- Activated platelets release ADP, thromboxane A2 and serotonin
Describe the process of coagulation
Set of reactions where blood is transformed from a liquid to a gel
Follows intrinsic, extrinsic and common pathways
Extrinsic and intrinsic pathways produce thromboplastin which acts via the common pathway
Describe the process of clot breakdown.
Fibrinolysis
Damaged tissues release tissue plasminogen activator (t-Pa)
t-Pa activates plasminogen in plasma
Plasminogen activates enzyme plasmin
Plasmin dissolves fibrin strands
Distinguish between bleeding and clotting time.
Bleeding time - duration of bleeding after controlled puncture of earlobe or forearm
Measures capillary and platelet function
Clotting time - time required for blood in a glass tube to coagulate
Reflects the time required for generation of thrombin
Draw out the Rhesus system.
Describe the potential difficulty of a Rhesus negative mother bearing the child of a Rhesus positive father
Erythroblastosis Fetalis
Occurs when rhesus negative mother has a second child’s who is rhesus positive
Anti-D antibodies cross the placenta and as mother has built up immunity a secondary immune response is produced
Causes agglutination of foetal red blood cells
Explain the consequences of infusing incompatible blood
Acute Hemolytic Transfusion Reaction - recipient’s immune system attacks and destroys the donor red blood cells
Delayed Hemolytic Transfusion Reaction - gradual decline of Hb
What is hyper coagulation and how is it caused?
Increased tendency for blood clot formation within the blood vessels.
Endothelial damage
Slowly flowing or static blood
Embolism - clot that travels from site where it was formed
Thrombus - blood clot that forms in a vessel
Caused by
Deficiency of platelet factors
Deficiency of vitamin-K
Deficiency of coagulation factors
Describe the extrinsic pathway of coagulation.
Tissue factors released from damaged endothelia/ tissue cells
Tissue factor + calcium + factor VII produces thromboplastin
Faster than intrinsic pathway
Describe the common pathway of coagulation.
Thromboplastin activates factor X
Factor X converts prothrombin to thrombin
Thrombin converts fibrinogen to fibrin
