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Pathological Processes > Session 5: Haemostasis > Flashcards

Session 5: Haemostasis Flashcards

1
Q

Define haemostasis.

A

The stopping of haemorrhage. A physiological response to a damaged blood vessel.

Haem = blood
Stasis = halt
Halting of blood

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2
Q

What is the main difference between fibrinogen and fibrin filaments?

A

Fibrinogen is soluble and therefore travel in the blood freely.
Fibrin filaments are insoluble and will therefore trap red blood cells forming a clot.

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3
Q

Outline the three steps of haemostasis. (In a severed artery e.g.)

A
  1. The artery contracts
  2. Primary haemostat plug of activated platelets forms at the hole of injury. It sticks to the injured vessel and the connective tissue outside of it.
  3. Secondary haemostatic plug forms as fibrin filaments stabilise the friable platelet plug into a blood clot. Forms in around 30 minutes.
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4
Q

Why does the artery contract in haemostasis? How does this differ from severing a vein?

A

To decrease the pressure downstream. This doesn’t occur in veins as the blood pressure is already much lower.

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5
Q

What are the three main players in haemostasis?

A

Platelets, the process of blood clotting and the vascular wall.

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6
Q

What are platelets activated by?

A

Collagen surfaces within extravascular areas.
ADP
Thromboxane A2
Thrombin

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7
Q

What is ADP released by in the activation of platelets?

A

From already activated platelets and also by injured red blood cells which will amplify the platelet response.

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8
Q

What is thromboxane A2 released by?

A

By already activated platelets

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9
Q

Explain what happens in the clotting process after the platelets are activated?

A

They start sticking to the exposed basement membrane or collagen via von Willebrand factor which is concentrated on the basement membrane. The von Willebrand factor helps in adhesion.

The platelets starts to aggregated with other platelets via cross linking. This forms a plug. Also fibrinogen starts to bind to the platelets and sticks them together.

Swelling of the clot starts to occur and it changes into a sticky, spiny sphere.

The platelet granules will start to secrete factors like fibrinogen, ADP and thromboxane A2 in order to increase the platelet plug’s size and aid in clotting. This is an example of positive feedback.

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10
Q

What is the mechanism of aspirin?

A

Irreversibly inactivates cyclooxygenase which is one of the enzymes responsible for production of thromboxane A2. This means that platelet aggregation will be decreased.

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11
Q

Give the most important factors of blood clotting.

A 
Platelets
Von Willebrand Factor
Fibrinogen
Collagen
ADP
Thromboxane A2
Thrombin
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12
Q

What is the role of thrombin?

A

To cleave circulating plasma protein fibrinogen into the insoluble fibrin.

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13
Q

Why doesn’t thrombin keep activating fibrinogen in the blood?

A

Because it needs to be activated in order to start cleaving fibrinogen.

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14
Q

What activates thrombin?

A

In short it is Factor Xa but it is a long pathway to get there with multiple factors.

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15
Q

What is required in the synthesis of the factors for blood clotting?

A

Vitamin K.

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16
Q

What other important co-factors are needed for effective clotting?

A

Phospholipids and calcium.

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17
Q

What is the difference between the intrinsic and the extrinsic pathways of clotting?

A

The intrinsic pathway involves factors which are all contain within the blood. It is triggered by a negatively charged surface and no vessels needs to be broken open for it to occur.

The extrinsic pathway involves factors which are not contained within the blood. It relies on a tissue factor called thromboplastin (formerly Factor III) which is present outside of the blood. The thromboplastin is released from damaged cells adjacent to the area of haemorrhage.

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18
Q

How does the vascular wall play a role in haemostasis?

A

The arterial wall contracts.
The subendothelium traps platelets with the help of von Willebrand factor.
The endothelium also release tissue factor (thromboplastin) to help in blood clotting.

However the vascular wall and endothelium in particular doesn’t only promote blood clotting but also the opposite.
Endothelium release plasminogen activator which will in its turn activate fibrinolysis which dissolves a clot. Endothelium also release protein C which interferes with the clotting cascade as an anticoagulant.

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19
Q

Give examples of factors that oppose clotting. What happens if these are not present?

A

Antithrombin III
Protein C
Protein S

If any of these lack a person might experience repeated episodes of thrombosis.

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20
Q

Explain fibrinolysis.

A

The clotting cascade sets fibrinolysis in motion because fibrin increases the activity of tissue plasminogen activator. tPA activates plasminogen into plasmin. Plasmin will then break down the fibrin into fibrin degradation products also called FDPs or D-dimers.

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21
Q

There are other plasminogen activators. Which?

A

Urokinase found in urine.

Streptokinase obtained from streptococci.

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22
Q

D-dimers are increased in certain conditions like?

A

Where there is thrombosis.

DIC, DVT and pulmonary embolism.

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23
Q

What happens to fibrinolysis after surgery?

A

The activity drops and remains low for about 7-10 days. Increased risk of thrombosis because of this.

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24
Q

Explain the extrinsic pathway of clotting.

A

Endothelial cell injury leads to release of thromboplastin. This tissue factor turns factor VII into factor VIIa (activated).
Factor VIIa activates factor X into factor Xa.
Factor Xa turns prothrombin into thrombin.
Thrombin cleaves fibrinogen into fibrin.

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25
Explain the intrinsic pathway.
A negatively charged surface turns Factor XII into Factor XIIa. This turns Factor XI into factor XIa Factor XIa turns factor IX into factor IXa. Factor IXa with the help of Factor VIIIa then turns factor X into Factor Xa.
26
How can we measure clotting?
``` By: Platelet count PT (prothrombin time) APTT (activated partial thromboplastin time) Thrombin time Fibrinogen levels Bleeding time ``` We can also by factor assays measure the levels of factors such as VIII and IX. Can also measure D-dimers
27
What does PT measure?
The extrinsic and common pathway: | VII, V, X and prothrombin and fibrinogen.
28
What does APTT measure?
The intrinsic and common pathway: | VIII, IX, XI, XII, V and X. Also prothrombin and fibrinogen.
29
Give examples of inherited bleeding disorders.
``` Haemophilia A Haemophilia B (Christmas disease) Von Willebrand's disease Ehlers Danlos Hereditary Haemorrhagic Telangiectasia (HHT) ```
30
What step in haemostasis is impaired in Haemophilia A and B?
Step 3 in secondary plug formation.
31
What is haemophilia A?
An X-linked recessive disease where there is a decreased amount or decreased activity of factor VIII and therefore part of the intrinsic pathway.
32
How do patients with haemophilia A clinically present?
Easy bruising Massive haemorrhage after surgery or trauma Swollen joints due to haemorrhage into the joints Spontaneous bleeding due to minor trauma
33
``` How will the following tests present in haemophilia A? Platelet count Bleeding time PT APTT Factor assay (VIII, IX) ```
``` Platelets will be normal Bleeding time will be normal PT will be normal APTT will be prolonged as it measures factor VIII Factor VIII levels will be low. Factor IX levels will be normal. ```
34
How does haemophilia B differ to A in clinical manifestations?
They are clinically indistinguishable.
35
Explain how haemophilia B works.
Haemophilia B is a lack of factor IX in the intrinsic pathway. Therefore it will have the same symptoms as haemophilia A.
36
``` How will the following tests present in haemophilia B? Platelet count Bleeding time PT APTT Factor assay (VIII, IX) ```
``` Platelets will be normal Bleeding time will be normal PT will be normal APTT will be prolonged as it measures factor IX Factor VIII levels will be normal Factor IX levels will be low. ```
37
What Von Willebrand disease?
An (usually) autosomal dominant disease. | Comes from either a decrease in number or reduced activity/function of von Willebrand factor.
38
What clinical features of von willebrand disease?
Skin and mucosal bleeding like epistaxis (nose bleeding), gum bleeding and bruising. Prolonged bleeding after trauma like menorrhagia (heavy bleeding during menstruation) bleeding after surgery and bleeding after dental extractions.
39
``` How will the following tests present in Von Willebrand disease? Platelet count Bleeding time PT APTT Factor assay (VIII, IX) ```
``` Platelet count will be normal Bleeding time can be raised APTT can be raised PT should be normal Factor VIII levels can be decreased Factor IX levels should be normal ```
40
Normal platelet count.
150-400 x 10^9/L
41
What is thrombocytopenia?
Low platelet count
42
What is the count of platelets in thrombocytopenia?
Less than 100 x 10^9/L
43
What happens at 20 x 10^9/L in platelet count?
Spontaneous bleeding.
44
How will the following tests present in thrombocytopenia? Bleeding time PT APTT
Bleeding time will be prolonged PT normal APTT normal
45
Why is PT and APTT normal in thrombocytopenia?
Because they assess clotting cascade and not the function of the platelets. Functions leading up to the step where platelets will start to matter will be normal.
46
Where will you see spontaneous bleeding in thrombocytopenia?
Small vessels in places such as the skin, GI tract, genitourinary tract. Also intracerebral bleeding can occur.
47
What will the bleeding appear as?
Petechiae
48
What can the causes of thrombocytopenia be classified as?
``` Decreased production of platelets Decreased platelet survival Increased platelet consumption Sequestration Dilutional ```
49
Explain causes of decreased production of platelets.
Bone marrow infiltration by malignancy Drugs like cytotoxic drugs Infections like measles and HIV B12 and folate deficiency which are needed for platelet production
50
Explain causes of decreased platelet survival.
Immunologic destruction like in immune thrombocytopenic purpura Non-immunologic destruction like in DIC
51
Explain causes of sequestration.
Hypersplenism (pooling)
52
Explain dilution thrombocytopenia.
Due to massive blood transfusion. When blood is stored for more than 24 hours the blood will not contain any platelets.
53
What is DIC?
Thrombohaemorrhagic disorder
54
Causes of DIC.
``` It is always secondary to a condition. Conditions like: Sepsis Severe trauma Extensive burns Complications of childbirth Snake bite ```
55
What kind of sepsis is more likely to lead to DIC?
Gram negative sepsis such as bacteria that produce endotoxin that activates clotting
56
What kind of trauma is more likely to lead to DIC and why?
To brain as the brain contains large amounts of thromboplastin
57
Explain DIC.
In DIC an activator of clotting gets into the blood and microthrombi will form throughout the entire circulation. This process consumes platelets, fibrin and coagulation factors but also activates fibrinolysis. In DIC the platelets will eventually be used up completely leaving you with microthrombi in the blood as well as haemorrhage.
58
Treatment of DIC.
Transfusions of platelets Fresh frozen plasma Cryoprecipitates (with factor VIII, fibrinogen, von Willebrand factor and factor XIII) Red blood cell transfusion Also additional treatment with heparin can be required.
59
What can microvascular thrombosis result in?
``` Neurological impairment Gangrene of the skin Renal failure Respiratory distress And GI ulceration ```
60
What can the haemorrhagic component of DIC result in?
``` Intracerebral bleeding Petechiae Haematuria Epistaxis GI bleeding ```
61
What can be measured in DIC in blood?
FDP is activated such as D-dimer which are released in large numbers.
62
How can DIC lead to microangiopathic haemolytic anaemia?
The microthrombi can cause red blood cells to become fragmented when they try to squeeze past. This will lead to anaemia.
63
Complications of thrombophilia.
Predisposition to thrombosis such as deep vein thrombosis.
64
Causes of thrombophilia.
Factor V Leiden Antithrombin deficiency Protein C or Protein S deficiency Antiphospholipid syndrome

Pathological Processes (14 decks)

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