Haemostasis and Blood Groups Flashcards
What are 2-4 in diameter, have amoeboid movement (little feet), and are 130,000 to 400,000 per litre?
Platelets
Small fragments of megakaryocyte cytoplasm are?
Platelets
What can secrete chemicals (clotting factors, factors for endothelial repair & vasoconstrictors in broken vessels), form temporary platelet plugs, dissolve old blood clots and attract leukocytes to sites of inflammation to phagocyte bacteria?
Platelets
A balanced interaction of blood cells, vasculature, plasma proteins and low molecular weight substances is…
homeostasis
Perfect haemostasis means:
No bleeding and no thrombosis (clotting)
What occurs to effectively close breaks in small vessels?
Haemostasis (the control of bleeding)
What is primary haemostasis?
Temporary Platelet Plug
What is secondary haemostasis?
Coagulation then stable clot
What is the first step in haemostasis?
Vascular spasm
Vascular spasm is the prompt constriction of a broken vessel. What 3 things is this triggered by?
Pain receptors (this lasts for a few minutes)
Injury to smooth muscle (this provides longer lasting constriction)
The release of serotonin from platelets
What other 2 mechanisms are given time to work whilst vascular spasm takes place in haemostasis?
Platelet plug formation and blood clotting
What is the second stage of haemostasis?
Platelet plug formation
Outline how platelet plug formation works:
After the injury there is immediate vasoconstriction.
Within seconds there is platelet adhesion, and minutes there is platelet aggregation.
As there is a broken vessel, there is a rough surface and exposed collagen. Platelets stick to that and other platelets too, and release substances like ADP. This is a positive feedback cycle.
What type of feedback mechanism is used in haemostasis?
Positive Feedback
What is exposed that platelets stick to when a vessel breaks?
Collagen
In a major break, would platelet plug formation work?
No
What is the third step in haemostasis?
Coagulation.
There are inactive clotting factors in the plasma. What produces these?
The liver
How does coagulation work?
Fibrinogen combines with thrombin to make insoluble fibrin - this forms a tight mesh for red blood cells to stick to
There are 2 pathways in coagulation. What are they?
Extrinsic (fast)
Intrinsic
Which coagulation pathway is started by the damaged tissue releasing thromboplastin?
Extrinsic - this happens fast when blood vessel is first damaged
Which coagulation pathway occurs once the temporary platelet plug releases a chemical into the blood?
Intrinsic
The 2 coagulation pathways occur together and converge to make a common pathway. What is required for them to be effective?
Calcium
Damaged perivascular tissues release thrombin factor 3, which activates another factor then another factor until FACTOR X is activated. Which pathway is this?
Extrinisic
What is it called when one factor activates the next in coagulation?
Reaction Cascade
Once factor X has been produced, the common pathway in coagulation starts to form a sturdy clot. List this pathway (there are 5 steps)
Factor X activates prothrombin activator
Prothrombin activator activates prothrombin factor 2
Prothrombin factor 2 activate thrombin
Thrombin activates more prothrombin but also combines with fibrinogen to make fibrin
Fibrin makes a fibrin polymer/clot
Fibrinogen is soluble and thrombin is an enzyme. What does thrombin do to fibrinogen?
It makes it into fibrin which is insoluble
Factor VIII is needed for blood clotting. For people who don’t have this, what do they have?
Haemophilia
Blood coagulation has a positive feedback mechanism. So how does clotting eventually stop?
The platelets produce chemicals to inhibit clotting and other substances in the blood (WBCs) inhibit it too
The clot also dissolves (fibrinolysis) due to plasmin - which dissolves fibrin
We don’t form clots all the time as platelets do not stick to the smooth vessel wall and we have natural anticoagulants in the blood (antithrombin in the liver and heparin in WBCs).
What other reason also usually prevents this, but without it we can get a DVT?
Rapid blood flow dilutes clotting factors.
Slow blood flow = DVT
Name 2 anticoagulants in the blood and where they are produced
Antithrombin - liver
Heparin - basophils and mast cells (leukocytes)
How does heparin act as an anticoagulant?
It stops thrombin from converting fibrinogen to insoluble fibrin
What 4 things can be measured to test haemostatic function?
Blood count (platelet count) to check in normal range
Blood film (for thrombocytopenia, a common cause of abnormal bleeding)
Bleeding time (for abnormal platelet function if have normal levels)
INR (international normalised ratio = how quick stop bleeding)
What are the 4 blood groups/types?
A
B
AB
O
Glycoproteins on the RBC membrane can be inherited. They are known as antigens. What are these antigens?
A and B
Where are antigens A and B found?
RBC membrane
We all have antibodies in our plasma that can do what in mismatched blood transfusions? Why?
They can cause agglutination/clumping - because they can react with antigens on the RBCs.
What antigens do Blood Group O people have?
None
What antigens do Blood Group AB people have?
A and B
What antigens do Blood Group B people have?
B
What antigens do Blood group A people have?
A
What antibodies do people have with Blood Group A?
anti-B
What antibodies doe people have with Blood Group B?
anti-A
What antibodies do people have with blood group AB?
None
What antibodies do people have with blood group O?
Anti-A and Anti-B
If you gave AB blood to someone with O blood, would this be ok?
NO - there would be A and B antigens in the AB blood, which would mean the anti-A and Anti-B antibodies in the O group person would react against them
If you gave O group blood to someone with AB blood, would this be ok?
Yes. The AB person has no antibodies in their blood, so it won’t bother them if you give them blood with no antigens
(You could also give them A or B group blood)
All blood groups can (but don’t always) have one type of antigen. What is is?
Antigen D
If you give someone the wrong kind of blood, what happens?
The RBCs in the new blood have antigens on them, which form complexes with the antibodies in the persons plasma.
One antibody can react with multiple antigens and form complexes
What does Rh+ mean?
Rhesus positive - it means you have the D antigen on your RBCs
If someone was an O Blood group and rhesus positive, what antigens do they have?
Antigen D
If a person is AB blood group and rhesus positive, what antigens do they have on their RBCs?
A, B and D
When could an AntiD antibody form?
After pregnancy or a transfusion. If a person is rhesus negative (has no D antigens) and is then exposed to rhesus positive blood, the plasma can form a D antibody.
What 4 things should you observe for to see if you may have given someone the wrong blood?
Increase in Temp/BP
Rash
Pain
Kidney Problems (due to blocked vessels)
Agglutination (blockage of vessels) and haemolysis (free haemoglobin can block kidney tubules and cause death) are reactions of what?
Mismatched blood transfusion
What type of blood can be given to any blood group person??
O negative
O has no antigens at all, no D antigen either as negative
Can you give rhesus positive blood to someone who is rhesus negative?
No - as someone who is rhesus negative may then from D antibodies
Can you give rhesus negative blood to someone who is rhesus positive?
Yes - as the rhesus positive person has d antigens on their red blood cells but the rhesus negative blood has no antibodies
How can haemolytic disease of newborns occur?
A rhesus negative mother gives birth to a rhesus positive child.
If the placenta tears, the rhesus positive blood could get into her blood.
This could then cause her to develop D antibodies.
If she then has a second child who is rhesus positive, the antibodies could attack the baby
This results in severe anaemia and toxic brain syndrome
How do we prevent haemolytic disease in newborns?
If a woman is rhesus negative you give her Anti-D antibodies during pregnancy, after delivery and within 3 days after birth.
This means if she is exposed to rhesus positive blood from the child, the vaccine kills the antibodies she develops
How many times a year can you give blood, and how much can you give?
3 times and 1 unit (500ml)
