Rough spot forms on the lining of the vessel (lining is simple squamous epithelium).
Platelets break up as they pass over the injured area – releasing platelet factors that make the platelets sticky and they stick to the wound. (In small vessels the platelet plug is all that is necessary to stop the bleeding).
Platelet factors combine with prothrombin (protein manufacture in the liver), calcium and other substances to form thrombin (an enzyme).
Thrombin reacts with fibrinogen (a blood protein) to change it into fibrin that forms a fibrous gel in the area of the wound. Fibrin is like a web of fine threads that traps RBCs and form a barrier across the vessel.
Clot retraction – fibrin threads pull the edges of the break in the vessel together.
Note: vitamin K (produced in the colon) stimulates the production of prothrombin by the liver.
Embolus – blood clot that moves
Thrombus – stationary blood clot
Arrest of bleeding
Events preventing excessive blood loss:
Vascular spasm : Vasoconstriction of damaged blood vessels
Platelet plug formation
Coagulation or blood clotting
Platelet Plug Formation
SEM of a clot with platelet, fibrin mesh, rbc’s
Clot dissolved by activity of plasmin, an enzyme which hydrolyzes fibrin
ABO Blood Group
4 blood types – A, B, AB, O
Types are identified by antigens located on the RBC surface.
Antigens – protein substances that can stimulate the body to make antibodies.
Antibody – proteins made by the body in response to stimulation by an antigen – causes clumping or agglutination in the case of RBCs.
Determined by antigens ( agglutinogens ) on surface of RBCs
Antibodies ( agglutinins ) can bind to RBC antigens, resulting in agglutination ( clumping ) or hemolysis ( rupture ) of RBCs
ABO and Rh
A person with Type A blood has A antigens on their RBC and a person with Type B blood has B antigens. What antigens does a person with type AB blood have? type O?
Natural antibodies are also present in the plasma: A person with type A blood has anti-B antibodies and a person with type B blood has anti A antibodies. What antibodies do people with type AB or type O blood have?
ABO Blood Groups
Typing and cross-matching – process by which blood type is identified and donor blood is tested for possible transfusion.
Type O is a “universal donor”, i.e.can give blood to anyone.
Type AB is the “universal recipient”, i.e. can receive blood from anyone.
Type A can receive type A or type O blood
Type B can receive type B or type O blood
Type AB can receive type B, A, AB, or O
Type O can receive type ??? Blood.
Rh factor – another antigen which may be present (Rh +) or absent (Rh -) on RBCs.
Rh negative (-) do not have natural antibodies to the Rh antigen. If they receive blood that is Rh positive (+) antibodies form but not a problem. The second exposure can produce a transfusion reaction (hemolysis and possible kidney damage).
Rh Blood Group
First studied in rhesus monkeys
Rh positive : Have these antigens present on surface of RBCs
Rh negative : Do not have these antigens present
Hemolytic disease of the newborn ( HDN)
Mother produces anti-Rh antibodies that cross placenta and cause agglutination and hemolysis of fetal RBCs