Lecture 18: Clotting Cascade Flashcards
Hemostasis occurs in how many steps?
3 steps
What is primary hemostasis?
Formation of a primary plug - clumping of blood platelets at site of injury
What is secondary hemostasis?
Formation of blood clot
Secondary hemostatic plug is formed by depositing of?
Insoluble strands of fibrin on the primary plug
What occurs during the 3rd sage of hemostasis?
Fibrinolysis - removal of clot
3 characteristics of hemostasis?
1) Must be fast
2) Localized
3) Carefully controlled
Goal of fibrin clot is altering which soluble protein into which insoluble one?
Fibrinogen (soluble)—–> Fibrin (insoluble)
What is the largest plasma protein and accounts for 4% of the total plasma proteins?
Fibrinogen
What is a zymogen and how is it activated?
Inactive form of an enzyme that can be activated by proteolysis.
What are the two sites on a zymogen and their function?
1) Pre- For secretion
2) Pro- Keeps it inactive
Zymogens are made where?
Liver
Zymogen are released into blood plasma and what makes them active?
Cleavage of the Pro- site by a protease in coagulating blood
Each zymogen serves first as a ________, then as a ______?
First as a substrate, then as an enzyme
The final substrate is?
Fibrinogen
Fibrinogen (factor I) is acted on by which enzyme and becomes?
Acted on by Thrombin (IIa), becomes fibrin
What is factor II and factor IIa?
Factor II = Prothrombin
Factor IIa = Thrombin
What does fibrin form at site of injury?
Polymerizes into clot - forms insoluble crosslink dam
What is factor III?
Tissue factor (TF)
What is factor IX?
Christmas Factor
What is factor XII?
Contact Factor
What is factor XIII?
Plasma transglutimase
Factor IX deficiency causes?
Hemophilia B: Christmas disease
Prothrombin is activated to thrombin by what kind of cleavage?
Proteolytic cleavage with a serine protease (prothrombinase)
Thrombin is itself a ________ and cuts at sites with which amino acids?
Serine protease and cuts at sites with ARG-GLY
Fibrinogen is made up of which subunits, that exist as?
3 subunits (α, β, and γ), exist as dimers
Thrombin cuts and releases what from fibrinogen?
A + B fibrinopeptides
Which domains of fibrinogen interact; type of bond?
E domain binds to D domain; H-bond
Why are A + B fibrinopeptides significant?
Prevent self-aggregation
Release of A fibrinopeptide allows for what interaction to occur; forms?
E domain (A sites) interacts with D domain (γ subunit) over + over; forms a “soft” clot
Cutting off ends of B sites allow for what interaction?
B chains interact to form 3D wall
Formation of a cross-linked fibrin (hard clot) requires what kind of bond, between which amino acids?
Covalent bond between NH2 of glutamine and NH3 of lysine.
What factor is responsible or the formation of the cross-linked fibrin?
Factor XIIIa - transglutaminase
What activates transglutaminase?
Thrombin
Factor XIII ——> Factor XIIIa
Why must prothrombin be modified by post-translational modification?
Important for clot localization
What occurs during the post-translational modification of prothrombin; new charge?
Carboxylation of several glutamic acid residues - adds another charge to side R-group on amino acid
“-2” negative charge
What is the post-translational modified glutamate on prothrombin called?
γ-carboxyglutamate
How does this -2 charge help localize prothrombin to damaged vessels?
Damage vessels release Ca2+ - so modified Prothrombin (-2 charge) has perfect binding site for Ca2+
Ca2+ bound to prothrombin then binds where and unconvers?
To platelets which have exploded uncovering negatively charged phospholipids as they invert.
Modification of Prothrombin (carboxylation) requires which vitamin?
Vitamin K
Recycling of Vitamin K requires which enzyme?
Epoxide reductase
How do Warfarin (coumadin) and Dicoumerol act on epoxide reductase; do what to prothrombin levels?
Competitive inhibition; decrease prothrombin levels
Warfarin and Dicoumerol inhibit which step; classified as what kind of drugs?
Addition of carboxylic acid groups to prothrombin; anti-clotting drugs
Safe and effective tx for Warfarin reversal?
IV Vitamin K
Why must patients on Warfarin be watched carefully?
Warfarin is a rodenticide: rat poison
Clotting cascase is an enzyme cascade of what type of proteases?
Serine
What are the two pathways of the clotting cascade; lead to?
Intrinsic (workhorse) and extrinsic (starts process); common pathway
Which pathway does not require a protein outside of blood to be activated?
Intrinsic pathway
A broken vessel will release contact factors and activate?
Factor XII —-> XIIa
What must be in the presence of XIIa to activate XI—->XIa?
Ca2+
XIa activates IX in the presence of ?
PF3: platelet factor 3: phospholipids
Where is PF3 located?
Interior platelets, become exposed when platelet disrupted
Function of FVIII; activated by?
Helper protein (co-factor); activated by thrombin
VIIIa complexes with and forms?
IXa to form IXa-VIIIa complex (tenase)
Tenase in the presence of what activates?
In presence of PF3, Ca2+ will activate X—->Xa
Xa complexes with to form?
Va to form Xa-Va complex (prothrombinase)
V —-> Va requires?
Thrombin
The Xa-Va complex activates; requires?
Prothrombin ——> Thrombin; PF3, Ca2+
Hemophilia A and B are caused by issues with which factors?
A (Factor VIII)
B (Factor IX)
How does a small signal get a large response in the cascade?
Amplification
i.e., activation of handful of Factor XII activates hundreds of Factor XI which activates thousands of IX
What does the extrinsic pathway require than the intrinsic doesn’t and where is it found?
Tissue Factor (FIII) - found on surface of cells lining blood vessles
Extrinsic pathway is activated by contact of; forms?
Factor VII with tissue factor (FIII); forms VIIa-TF complex
What is the major pathway?
Extrinsic
Where does the thrombin come from that is necessary for the earlier steps?
- 1% of FVII circulates as FVIIa, which joins with TF when damage occurs, activates FX.
- Platelets have some activated FVa, so FXa-FVa (prothrombinase) complex forms and you get thrombin burst
The thrombin spark to get the intrinsic pathway (workhorse) going, comes from?
Extrinsic pathway (why it’s so important/major player)
What other factors require addition of carboxyl and are vitamin K dependent?
X, IX, and VII
Rate of clotting is greatly accelerated by?
Positive feedback
Reference range from partial thromboplastin time (PTT)
20-35 seconds
Partial thromboplastin time (PTT) measures the time between, which pathways involved?
Factor XII to Fibrin clot (intrinsic and common pathways)
Prothrombin time (PT) is time between, which pathways involved?
Factor VII to Fibrin clot (extrinsic and common pathways)
What is the normal range for prothrombin time (PT)?
12-14 seconds
Initiating component for clotting in vivo?
TF
Clotting in vivo does not include which factor?
Factor XII
What is the phone number to remember steps for clotting in vivo?
379-8105
Thrombin can bind what to regulate clotting cascade?
Binds fibrin - inactivates fibrin
Thrombin can cut and inactivate which factors?
FVIIIA —> FVIIIi
Xa —> Xi
Va –> Vi
Prothrombin —> inactive form
Thrombin complexes with thrombomodulin to create TTM complex, which cleaves and creates?
Protein C into active Protein Ca
Activated Protein Ca plus other proteins inactivate which factors and cause a decrease in?
FVa and FVIIIa - decreases production of thrombin
Why do activated Protein Ca’s localize to platelet areas with PF3?
Decorated with γ-carboxyglutamate
Which common drug protects platelet integrity?
Aspirin
What does Heparin do?
Activates antithrombin III - binds to Thrombin and Xa - inactivates
What dissolves clot - fibrinolysis?
Tissue plasminogen factor (TPA)
Calcium chelating agents have what affect on Ca2+ and what affect on clotting?
Decrease Ca2+ and this has an anti-clotting affect.
