what are the three stages of the traditional hemostasis model?
(1) Primary stage= hemostatic plug (platelet and coag activation) platelet plug (2) Secondary- "cascade" (see pic at top) --> stable cross-linked fibrin clot (3) Fibrinolysis
walkthrough of what happens with traditional hemostasis
injury to endothelium, expose tissue underneath, which exposes collagen, Von Willebrand factor, tissue factor (3 main triggers for coag), also these 3 things cause BV contraction (squeeze BV to slow blood flow), then coag factors bind to the tissue factors, and platelets binding to exposed vWF and collagen. Platelets come along, initially recognize damaged tissue and stick to it, once bound they become ACTIVE platelets. Active platelets attract MORE platelets, then they start to produce some of the coag factors, which causes loose platelet plug, and get a loose aggregation of fibrin since a little fibrin has been produced to help keep platelet plug in place. Then gradually start to get more fibrin, more RBC, more platelets to make a nice plug. then eventually get an actual clot when fibrin is organized into cross linked organized strands which are very strong and wont go away for a while (require specific enzymatic degradation- which is where D-dimers come from) So that is the INITAL plug!
3 main triggers for coag
collagen, Von Willebrand factor, tissue factor
what are the 3 main steps of primary hemostasis? What are required for this to be triggered? what happens once the platelets are triggered?
Plt adhesion, activation, aggregation are 3 main parts of primary hemostasis. Need Collagen/vWF to trigger. Once platelets see vWF/collagen they bind and there are MEMBRANE ALTERATIONS (change of shape, surface composition), different receptors are expressed on the surface of the platelets, release more granules and factors (ADP, serotonin, TXA2, PAF, Ca++ release), attract more platelets, which gives us just that little bit of thrombin and fibrin to start.
What is the "cascade" part of the clotting path?
Have extrinsic path (7), intrinsic path( 12, 11, 9, 8 ), and common pathway (10, 5, 2, 1). But they aren't separate pathways- they have lots of key interactions. Like, factor 7 doesnt stay on one side
how is factor 7 a flipper-flopper?
both key for extrinsic path and key for START of intrinsic pathway. (in real life, intrinsic path never starts with factor 12, always starts with 7!)
what is THE initiator of coaf in the body?
factor 2 aka
There is a lot of feedback in the cascade. explain a bit
like once we start to make factor 2 (thrombin) that feeds back on the rest of the system and energizes/ pushes a lot of those reactions faster.
what do we know about factor 12?
it is essentially unimportant for coag system.
why are (activated platelet) membranes important for coag?
many factors work WAY better if they are on a membrane that is active. If not on a membrane surface, they are really slow. So if have thrombocytopenia pt, less active platelet membranes, this cascade works way slower.
what are the avantages of using the cascade "Y" model?
Accurately describes proteolytic reactions required for clot formation (like explain how we test coag in test tubes) , Actual components which can be tested for, or acted upon (explain PT, PTT tests, etc), Correlates well w/ many dx tests
problems with the cascade model?
Does not adequately explain some clinical conditions and observations ( Factor deficiency correlation to bleeding) , is Protein-centric (doesn't focus on membranes on which these reactions occur) (Localization of reactions? (do they occur on blood or on surfaces?), Control and regulation of reactions?)
how can membrane surfaces affect coag? what parts of membrane matter?
Can significantly contribute to or inhibit coagulation reactions-- what is in/what composes the membrane matters. So-- the KIND of phospholipid it is made of (remember phospholipid bilayer), what we are expressing matters (TF expression, anti-coag molecules expressed, other surface receptors)
explain the variations of surface phospholipids in the cell membranes and how it affects coag
there are several diff kinds, some neg charged, come neutrally charged, and depending on charge and which ones are there, it strongly affects which proteins are allowed to be expressed on which side of that membrane. and the inside and outside are not the same-- diff polarities. Thats part of how cell knows when to put receptor on outside or inside, part of how it knows when to put enzymes towards the outside of the cell. (so phospholipids affect Protein binding and alignment, and Enzyme kinetics)
explain a procoag membrane
normal resting membrane is very polarized. Basically no charge on outside and neg charge on inside. Procoag membrane has a lot more neg charges moved to outside. Much less polarity, everything is allowed to shift around, so starting to express a lot more on the outside.
what are the two molecules which help keep resting membrane in position where mostly neutral charge outside and mostly neg inside? what happens if there is a signal to turn membrane to pro-coag membrane?
flippase (moves neg phospholipids from outside to inside) and floppase (moves neutral phopholipids from inside to outside) --> so both keep the outside neutral. If there is a stim to change membrane to pro-coagulant, basically turn off flippase, so stop moving neg charged ones in. and then bring up 3rd enzyme called scrambalase, which doesnt really care what phospholipid is, it just shuffles when around (which tends to move more neg charge to outside and more neutral charge to inside bc of how polarity was in the first place.) --> THIS RESULTS IN PRO-COAG MEMBRANE which is important in knowing for how cells help coag to happen.
(membranes/cells) Tissue factor expression is really important. If dont have it, what happens?
if no TF, then not gonna start coag, bc THAT is what factor 7 responds to (and 7 is the initiator of all things). Main cells which dont regularly express tissue factor are endothelial cells bc dont want clotting randomly starting in vessels. All other tissues have it inherently on their surface so if exposed to blood, can get factor 7 going. So TF is an integral membrane protein which is mostly outside of the vasculature and is the primary initiator of coag.
where do anti-coag molecules like to hang out? what do they help with? 3 examples?
usually on surface of normal cells, esp in vessels, bc don't want clot to extend farther than it has to past the site of damage. 3 examples of these are: Thrombomodulin (TM), Heparin sulfates proteoglycans (HSPGs), Tissue factor pathway inhibitor (TFPI)
what are the "cell based" models of coag basically doing?
these say we need to incorporate lipid surfaces. Need to think about active platelet surface! These models are still mostly coagulation-- if think about 4 boxes model, still haven't moved out of first box. And they arent replacing the cascade, either. Still talking about enzymes, just shuffling them around a bit.
What are the 3 (+/-) basic categories in the cell/membrane model of coag?
(1) Initiation (2) amplification (3) propagation (+/-4) termination <--all we know about this is that the clot doesnt spread throughout the body
***cell/membrane model--> what is initiation? What is happening? what 3 things result?
There is TF (tissue factor) exposure, which binds Factor 7, which turns it into ACTIVATED factor 7 (VII-->VIIa). then activated 7 interacts with a bunch of enzymes and the end result is get: (1) a little bit of activated ten (Xa) (ten stays at site) (2) a little bit of activated 2 (IIa) (stays at site AND moves away) (3) a little bit of activated 9 (IXa) (moves away)
what happens if Xa tries to move away from the site of initiation?
Xa is supposted to stay at the site! plasma proteins bind it up and get rid of it-- antithrombin III and tissue factor pathway inhibitor come in for this. They stop the pathway from causing coag in the bloodstream
what does factor ten do/ interact with on the cell membrane surface?
10 (X) binds to surface, and brings factor 5(V) in, and what is what gives us your thrombin (IIa) generating machines!!!
so what is the basic machinery which makes thrombin (IIa)?
When there is Tissue factor (TF) exposed, which attracts 7a (activated VII), which makes some IIa and IX which moves away, as well as Xa which stays and binds and attracts Va which 10+5= machinery for thrombin. So these make factor IIa...but on a normal cell membrane, they can only make a little IIa/ it is slow.
explain the 3 products made from 7 binding to TF and making activated 7/ what these 3 things do/go?
(1) Xa- remains localized and complexes with factor V to make Va (2) II acts locally and diffuses, participates in amplification (3) IXa- ddiffuses away from the site, participates in propogation
which 2 factors leave the area?
9 and 2
What is the "idling" theory?
VII, X, II are small enough to escape vasculature in small quantities. Theory is that you are always a little bit primed for clotting because of this low grade interaction, but without really being able to bring in platelets it just is super low grade. So you are ready, but wont happen on a large scale till exposed to platelets, membranes, and other factors.
So remember 7 crosses over and goes where?
so 7 of course does its normal extrinsic pathway but also crosses over to intrinsic to 9, and we get a littttle bit of thrombin (IIa).
(this is the animation slide. he said the key things he wants us to know are in the summary slides) So once initiation has taken place, there is a little bit of factor IIa....and a platelet comes along. What happens now?
Platelet comes in and recognizes factor IIa, which will activate a couple membrane surface proteins + platelet activation receptors, and some vW-type receptor complexes which sends intracellular signaling which means the platelet is pro-coag now. Bc as soon as it sees that 2 it wants to participate in coag. So scramblase comes along and changes the polarity of the cell membrane (polarize it), once membrane polarized, gonna release dark and light granules (release some of the intracellular factors up to the surface) and platelet is completely changing morphologically. Now its an active membrane, which can partially activate a lot of the factors. So Va becomes partially activated, and once it sees the little but of IIa that's there, it is full activated. Then we can bring factor 8 in which gets activated, and basically end up with pro-coag membrane with two primed factors which are ready to produce more substances
***at the end of the amplification process, you are left with what factors where? What do they wanna do?
Now have Va and VIIIa at plt surface---Primed and ready to form “tenase” and “prothrombinase” complexes
WHAT DO Va and VIIIa (5a and 8a) Do???
(now have activated platelet with an activated membrane) Primed and ready to form “tenase” and “prothrombinase” complexes
**what is the main thing happening in the propagation phase? how is this accomplished?
Large scale thrombin generation--> Accomplished by enzyme complexes: (1) Tenase: VIIIa & IXa --> Xa (2) Prothrombinase: Va & Xa --> IIa. ALSO Where we get all the fibrin and cross-linking where actual clot happens
*what IS tenase? what does it do?
it's a complex of 8a an 9a --- it makes a lot of 10a (very efficient system for activating factor 10)
so tenase makes a bunch of activated 10-- then what does it do?
binds with activated 5--> makes prothrombinase
*what is prothrombinase?
activated 5 and activated ten together which is the prothrombin making machine which just cranks out thrombin (IIa)
(animation) So now you have Va and VIIIa sitting on an activated membrane...wat now?
the IXa which floated away during the initiation stage comes back and binds to VIIIa and XI is going to do the same. End up with an VIIIa+IXa complex.
9a and 8a makes the tenase, 10a and 5a makes the prothrombinase, which results in LOTS of thrombin
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