Coagulation and Fibrinolysis

Question 1

Hemostasis

Answer 1

The cellular and noncellular process that prevents blood loss following blood vessel injury

Question 2

Explain the process of hemostasis

Answer 2

It happens in 3 steps:

1. Platelet plug formation: clumping of platerlets at the site of vessel results in soft cloth formation
2. Coagulation: formation of fibrin polymers within the platelet that produces a hard cloth
3. Fibrinolysis: breakdown of fiber polymers by an enzyme called plasmin, this occurs simultaneously with wound healing

Question 3

Platelet plug formation

Answer 3

This is a two step process:

1. Platelet adhesion
2. Platelet aggregation

Question 4

Platelet Adhesion

Answer 4

Platelet Adhesion: the goal here is to form a monolayer of platelets, there are 3 proteins involved here. Von Willbred Factor, Collagen and Glycoprotein 1B-5-9

Von Willbrand factor is like a glue that attaches to collagen, causes a monolayer of itself to form which then allows the platelets to stick to them using their trans glycoprotein 1B-5-9

Question 5

Von Willebrand factor

Answer 5

Made by 2 cell types:

1. Endothelial cells, where it is stored in Wiebel palade bodies
2. Platelets (stored in alpha granules)

Its structure is a single polypeptide chain which can form multimers, these are linked by disulfide bonds. When endothelial cells make them they are secreted in very large sizes and then they are processed by a metalloptrotease in the plasma called the ADAMTS-13, which breaks them down into usable sizes

Question 6

Answer 6

Alpha granules, one of the proteins stored here is the Von Willebrand factor

Question 7

What is this

Answer 7

This is a western blot of the plasma proteins and the endothelial supernatant. As we go upwards there is an increase in molecular weight of the VWF, at the top are ultra large VWF that are made by the endothelial cells

Question 8

Why are ultra large WVF pathologic

Answer 8

In people that have a deficiency of ADAMTS-13 enzyme, these ultra large vwf can cause spontaneou agglutination of platelets inside the vessels. This disease is called Thrombotic thrombocytopenia purpura

Question 9

What is the second most important function of vwf

Answer 9

It is a carrier of procoagulent protein factor VIII, increasing its half life, stabilizing the factor VIII

Question 10

Platelet Aggregation

Answer 10

Monmeric platelets form polymer platelets by platelet agonist.

There are receptors on the surface of the platelets for fibrinogen called the Glycoprotein IIB-IIIA. This is activated by platelet agonists which then results in fibrinogen binding to these receptors causing platelet aggregation

Question 11

What are some exmaples of platelet agonists

Answer 11

1. Adenosine Diphosphate
2. Collagen
3. Thrombin
4. Thromboxane
5. Epinephrine

Question 12

Fibrin Cloth formation

Answer 12

There is a coagulation cascade. The final enzyme is thrombin which causes the solouble fibrinogen to insolouble fiber which polymerize to form the fibrin cloth formation

Question 13

How do you form thrombin

Answer 13

There are 3 principle pathways:

1. Intrinsic pathway
2. Extrinsic pathway
3. Common pathway

Question 14

Extrinsic pathway

Answer 14

It all starts with a tissue factor which is a transmembrane protein that is found in platelets, endothelial cells or fibroblasts. When any of these cells get damaged the tissue factor on the membrane is activated which causes an the tissue factor to bind to enzyme VIIa, which is now more active (it is an allosteric activator).

Factor VIIa works to activate factor X.

Factor VIIa needs phosphotylserine and Ca for function

Question 15

What does factor X do

Answer 15

It is activated by cofactors PS, Ca and Factor Va to act on prothombin to thrombin - this is the common pathway

Question 16

Instrinsic pathway

Answer 16

This works in highly charged surfaces such as glass. Factor 12 is converted to factor 12a. This converts factor XI to XIa. XIa converts factor IX to IXa. Factor IX then needs cofactors for activation, one of them is FVIIIa, the rest are PS and Ca

Question 17

What causes hemophilia A

Answer 17

Deficiency in FVIIIa

Question 18

What is the role of Factor XIIIa

Answer 18

It forms the covalent bonds between the fibrin polymers to form high tensile strength polymers

Question 19

What are the proteins that are dependent upon vitamin K

Answer 19

Factor II, VII, IX and X

These are procoagulents

Anticoagulents are protein C and S

Question 20

What does vitamin K do and what is the role of warfarin

Answer 20

It allows the glutamic acid to have a carboxylate added (by vitmain carboxylase) to it to form 2- charge which can then bind with Ca which allows the protein to have conformational changes and insert itself to the membrane

In this process vitamin K is converted from its active form to its inactive form. Warfarin acts to inhibit this step

Question 21

Tenase complex and prothrombinase complex

Answer 21

Question 22

Fibrin polymerization or how does thrombin work

Answer 22

The structure of fibrinogen is an E domain surrounded by 2 D domains with fibrinopeptides A and B. Thrombin clips the fibrinopeptides A and B to allow the fibrinogen to come in close apposition which each other.

The D domain then now interacts with E domian to form fibrin polymer. Peptide binds are made between 2 D domains by Factor XIIIa

Question 23

Fibrinolysis

Answer 23

It starts with the protein t-PA (tissue plasmogen activator). Once healing starts to take place endothelial cells release t-PA in a coordinated fashion. t-PA converts the zymogen enzyme plasminogen to plasmin which starts to break down the cloth into small fragment which are then cleared away by the blood.

Plasminogen is made by the liver

Question 24

What are plasmin and t-PA inhibitors

Answer 24

t-PAI-1 and 2 that is present in the blood and the extracellular fluid respectively whereas for plasmin it is Alpha 2-Anti Plasmin (Alpha2-AP) which is made by the liver

Question 25

How does plasmin breaks apart the cloth

Answer 25

It breaks down the links between E and D, except the peptide bond formed between D. These form D dimers which can be measured clinically to check for fibrinolysis