Hemostasis I

Question 1

Define 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 platelets at the site of vessel results in soft clotformation2. Coagulation: formation of fibrin polymers within the platelet that produces a hard clot3. 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 adhesion2. Platelet aggregation

Question 4

Explain platelet adhesion

Answer 4

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

What is this?

Answer 5

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

Question 6

Explain what do we observed on western blot of plasma proteins with respect of VWF?

Answer 6

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 7

Explain the synthesis of Von Willebrand factor.

Answer 7

Made by 2 cell types:1. Endothelial cells, where it is stored in Wiebel palade bodies2. 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 metalloprotease in the plasma called the ADAMTS-13, which breaks them down into usable sizes

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 spontaneous 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, hence stabilizing factor VIII.

Question 10

Explain the process of 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 is the extrinsic pathway?

Answer 11

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 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 12

What does factor X do

Answer 12

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

Question 13

Explain the instrinsic pathway.

Answer 13

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 14

What are some exmaples of platelet agonists

Answer 14

1. Adenosine Diphosphate2. Collagen3. Thrombin4. Thromboxane5. Epinephrine

Question 15

Explain fibrin clotformation

Answer 15

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

Question 16

How do you form thrombin

Answer 16

There are 3 principle pathways:1. Intrinsic pathway2. Extrinsic pathway3. Common pathway

Question 17

Explain the formation of tenase complex and prothrombinase complex

Answer 17

Following platelet activation, PS flip flops from the inner leaflet to the outer leaflet of the platelet plasma membrane. This flip-flop allows the assembly of the tenase complex and prothrombinase complex.

Question 18

Explain fibrin polymerization and how does thrombin work

Answer 18

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 bonds are made between 2 D domains by Factor XIIIa

Question 19

Explain fibrinolysis

Answer 19

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 clotinto small fragment which are then cleared away by the blood.Plasminogen is made by the liver.

Question 20

What causes hemophilia A

Answer 20

Deficiency in Factor VIIIa”Hemophilia a(eight)”

Question 21

What is the role of Factor XIIIa

Answer 21

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

Question 22

What are the proteins that are dependent upon vitamin K?

Answer 22

Factor II, VII, IX and XThese are procoagulentsAnticoagulents are protein C and S

Question 23

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

Answer 23

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 membraneIn this process vitamin K is converted from its active form to its inactive form. Warfarin acts to inhibit the conversion of Vitamin K from its inactive form to its active formby inhibiting vitamin k epoxide reductase

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 blood clot?

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