Chapter012

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 12

Disorders of Hemostasis

Chapter 12

Disorders of Hemostasis


HemostasisHemostasis

• Stopping blood flow

• Normal:

– Blood usually fluid

– Seals broken blood vessels

• Abnormal:

– Inappropriate clotting

– Insufficient clotting


Platelets (Thrombocytes)Platelets (Thrombocytes)

• Thrombopoietin

– Made in liver, kidney, smooth muscle, bone marrow

• Megakaryocytes formed in bone marrow

– Break apart to form many platelets

• Platelets live 8–9 days in circulation

– Many are stored in spleen

– Released when needed


Platelet StructurePlatelet Structure


QuestionQuestion

All but which of the following are true about platelets?

a. An enzyme called erythropoietin stimulates their production.

b. They are made from megakaryocytes.

c. They originate from the bone marrow.

d. They are stored in the spleen.


Answer Answer

a. An enzyme called erythropoietin stimulates their production.

Erythropoietin stimulates the production of RBCs (erythrocytes). The word literally means erythrocyte production.

Platelet formation is stimulated by thrombopoietin (thrombus/clot production).


Mediators of HemostasisMediators of Hemostasis

• Chemicals produced by platelets

• Released at an injury to:

– Start clotting by reacting with blood proteins

– Help platelets stick together

– Stimulate wound healing

– Help platelets stick to vessel wall

– Constrict blood vessels


Coagulation FactorsCoagulation Factors

• Plasma proteins

– Most are synthesized by liver

– von Willebrand factor made by endothelium

– Circulate as inactive procoagulation factors

• Calcium



Question Question

What is the effect of von Willebrand disease on the platelets?

a. Increased platelet aggregation

b. Decreased platelet aggregation

c. Increased platelet formation

d. Decreased platelet formation


Answer Answer

b. Decreased platelet aggregation

Von Willebrand disease is the most common hereditary bleeding disorder. It is caused by a deficiency or defect in vWF (which carries a clotting factor). The result of less clotting factor is an inability to clot.


Cyclooxygenase Enzymes (COX) Produce Mediators of HemostasisCyclooxygenase Enzymes (COX) Produce Mediators of Hemostasis

• Celebrex is a drug that blocks COX-2

• People taking Celebrex develop increased TXA2 levels

• What problems might they have?

COX-1 COX-2

arachidonic acid

thromboxane A2 prostacyclin


Intrinsic and Extrinsic PathwaysIntrinsic and Extrinsic Pathways


Scenario:Scenario:

A man had a stroke and the doctor gave him tissue plasminogen activator (TPA)

– Why? What is the doctor trying to accomplish?

• One of the man’s relatives wondered why they did not give him heparin or warfarin instead.

– What is the difference? Why might TPA be more appropriate?


HypercoagulabilityHypercoagulability

• Increased platelet number

• Platelet aggregation

• Endothelial damage

• Increased procoagulation factors

• Decreased anticoagulation factors


Question Question

Tell whether the following statement is true or false:

Hypercoaguability states increase the risk of thrombus formation.


Answer Answer

True

Hyper- as a prefix means over or too much. Coagulation/coaguability means clotting/the ability to clot. Hypercoaguability means increased ability to clot or form thrombi.


Scenario:Scenario:

• A woman with lupus develops breast cancer…

• She is given radiation therapy

– She begins to develop nosebleeds and bruising

– Her menstrual period is abnormally heavy

Question:

Why did this happen?


Platelet DisordersPlatelet Disorders

• Decreased platelet levels (thrombocytopenia)

– Decreased production

– Increased destruction

– Platelets used up in forming clots

• Impaired platelet function


DICDIC


Question Question

Tell whether the following statement is true or false:

Platelet disorders are bleeding disorders.


Answer Answer

True

Because the platelet’s job is to clot, platelet disorders mean that the platelets cannot do that job. An inability to clot results in bleeding/bleeding disorders.

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