What is the stopping of bleeding?
What are the 3 mechanisms of hemostasis (stoppage of bleeding)?
- Vascular spasm
- Platelet plug formation
What is vascular spasm?
one of the mechanisms of hemostasis, when smooth muscles that are present in the blood vessel walls constrict (vasospasm)
What is platelet plug formation?
- one of the mechanisms of hemostasis
- thrombocytes are usually sequestered on the lumens of blood vessels but go through 3 phases when vessels are lacerated.
- 1. Platelet adhesion
- 2. Platelet release reaction
- 3.Platelet aggregation
What is platelet adhesion?
- Platelet adhesion is the first phase of platelet plug formation
- Thrombocytes accumulate in great numbers at the hemorrhage site and adhere to parts of the damaged vessel
What is platelet release reaction?
Platelet release reaction is the second phase of platelet plug formation
the platelets undergo changes and release substances that cause the smooth muscles of the vessels to further contract to decrease blood flowhe platelets become extremely sticky and clump with each other at the site of vascular damage.
What is platelet aggregation?
Platelet aggregation is the 3rd phase of platelet plug formation
thrombocytes are reinforced by fibrin threads and trap other platelets and formed elements to creat a mass called a platelet plug
What is coagulation?
- One of the 3 mechanisms of hemostasis
- it is the process by which a blood clot is formed
- complex involving a cascade effects which includes coagulation factors (12 main factors identified by Roman numerals)
- Each factor stimulates the formation of the next
Are coagulation factors in any particular order? How many main factors are there?
There are 12 main coagulation (clotting) factors that are in no particular order
How many pathways are there that lead to the activation of thrombin? What are the pathways?
2 pathways lead to the activation of thrombin
Extrinsic pathway - initiated by chemicals outside the blood
Intrinsic pathway - initiated by platelets and plasma coagulation factors inside the blood vessels
Explain the extrinsic pathway to activation of thrombin leading to coagulation of blood.
Tissue thromboplastin (tissue factor - TF) is released from the tissues surrounding the blood vessels when they are damaged.
TF in the presence of coagulation factor X (Stuart factor) converts to prothrombin. Then calcium (always in blood) causes soluble prothrombin to change to insoluble thrombin.
damaged tissue = tissue thromboplastin +coagulation factor X= prothrombin + calcium = thrombin
Explain the intrinsic pathway which leads to activation of thrombin
the intrinsic pathway is initiated by platelets and plasma coagulation factors inside the blood vessels
the platelets and plasma release prothrombin which in the presence of several factors (all requiring vitamin K) are converted into thrombin
prothrombin + several factors + Vit K = thrombin
What is the final stage in clot formation?
The thrombin in the presence of calcium coverts with soluble fibrinogen into a strong meshwork of insoluble fibrin threads. Factor XIII (fibrin stabilizing factor) is essential for this final conversion.
Once formed blood cells become entrapped in the mesh of fibrin threads, threads contract pulling the clot and rupture site together - syneresis. Serum is then squeezed out.
Once tissue is sufficiently repaired and the scab (eschar) is no longer needed what happens?
It is dissolved by an enzyme called plasmin in a process called fibrolysis.
What produces Vitamin K and what process is it important in?
Vitamin K is produced by intestinal bacteria and is absorbed when bile is present in the intestinal tract.
It is important in the intrinsic pathway (which leads to the activation of thrombin necessary for coagulation). It is required by several factors which all need it to convert prothrombin into thrombin.
If blood of 2 individuals is mixed safely and no adverse reaction occurs, then the individuals are said to be
When incompatible blood is mixed what occurs?
- agglutination between the red cells
- agglutination results from red cells sticking to each other forming clumps
In agglutination what happens?
The antibodies of the plasma (agglutinins) bind with the antigens (agglutinogens) on the surface of the red cells.
antigens - agglutinogens - on the surface of the cells
antibodies - agglutinins - in the plasma
In the ABO system what determines the blood group for each person?
The antigen of the red blood cell.
If a person is group A, what antigen is present on their red blood cells? What antibody are they born with?
What AB antigen are present in O blood? What antibodies?
No AB antigens in O blood
O is considered universal donor because of the lack of antigens, but they must receive O blood because of the AB antibodies.
What AB antigens are present in AB blood? What antibodies?
Antigens A and B
AB is considered a universal recipient because of the lack of antibodies, but they can only give blood to someone who is AB also.
What is the most common blood type?
O - 45%
What is the rarest blood type?
AB - 4%
Are Rh- people born with Rh antibodies (Rh agglutinins)?
No, they will produce them if given Rh positive blood.
What is hemolytic disease of the newborn?
- Fetus is Rh+ and mom is Rh-
- fetal blood leaks across the placenta at birth causing mom to produce Rh antibodies
- usually causes problems with later pregnancies, not the first
- the maternal antibodies cross the placenta and cause the fetal RBCs to rupture (hemolyze). Fetus usually dies unless the blood is completely replaced at birth
RhoGAM injection at birth can prevent the formation of anti-Rh antibodies
What is always done to avoid the possibility of adverse transfusion reactions from blood incompatibility?
crossmatching - mixing of blood in vitro (in the glass) prior to in vivo (in the body) transfusion
Done in addition to blood typing and Rh compatibility
Are there other antigens and antibodies in blood in addition to those associated with the ABO and Rh systems?
Yes, that is why in practice, terms like "universal" are misleading due to other possible incompatible blood systems.
That is why blood is always crossmatched.
What is the difference between plasma and lymph/interstitial fluid?
Lymph and interstitial fluid are practically identical, lymph originates as interstitial fluid
- They have
- less protein than plasma
- variable # of WBCs
- Do not contain RBC or platelets
lack of intrinsic factor needed for the absorption of vitamin B-12 which is needed for RBC production.
caused by loss of blood
- can be the cause of hemorrhagic anemia
- hidden blood loss often occurring in the gut
- can be cause of hemorrhagic anemia
- gross external blood loss
Fragile RBCs easily rupture
- destruction of bone marrow
- caused by radiation or chemical exposure
caused by abnormally shaped RBCs that are incompetent in transporting gases
- abnormal increase in the number of RBCs
- causes increase in viscosity of blood
- causes rise in BP and contributes to blood clots and hemorrhage
- Epstein-Barr virus
- high percentage of lymphocytes
- malignant disease of blood
- numerous immature and nonfunctional white blood cells
What is clotting in an unbroken vessel called? What is it called when it moves from it's site of origin?
What is a thrombolytic agent?
chemical substances injected into the body to help dissolve blood clots
ex. Streptokinase (enzyme)
What is an anticoagulant? Does it thin the blood? What are some examples?
- they help prevent clot formation by inhibiting coagulation
- they are not blood thinners
- heparin and Coumadin are examples