Chapter 10 Alterations in Hemostasis

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Chapter 10Alterations in Hemostasis


Hemostasis

• Stopping blood flow• Normal:

– Blood usually fluid– Seals broken blood vessels

• Abnormal:– Inappropriate clotting– Insufficient clotting


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


Question

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

a. An enzyme called erythropoietin stimulates their production.

Rationale: Erythropoietin stimulates the production of RBCs (erythrocytes). The word literally means erythrocyte production. Platelet formation is stimulated by thrombopoietin (thrombus/clot production).


Mediators 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 Factors

• Plasma proteins – Most are synthesized by liver– von Willebrand factor made by endothelium– Circulate as inactive procoagulation factors

• Calcium


Question

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

a. Increased platelet aggregationb. Decreased platelet aggregationc. Increased platelet formationd. Decreased platelet formation


Answer

b. Decreased platelet aggregationRationale: 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.


Vessel Spasm


Cyclooxygenase 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 Pathways


Fibrinogen Fibrin


ScenarioA 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?


Hypercoagulability• Increased platelet number• Platelet aggregation• Endothelial damage• Increased procoagulation factors• Decreased anticoagulation factors


Question

Tell whether the following statement is true or false.Hypercoagulability states increase the risk of thrombus

formation.


Answer

TrueRationale: Hyper- as a prefix means “over” or “too much.”

Coagulation/coagulability means “clotting/the ability to clot.” Hypercoagulability means “increased ability to clot or form thrombi.”


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 Disorders

• Decreased platelet levels (thrombocytopenia)– Decreased production– Increased destruction– Platelets used up in forming clots

• Impaired platelet function


Question

Tell whether the following statement is true or false.Platelet disorders are bleeding disorders.


Answer

TrueRationale: 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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Chapter 10 Alterations in Hemostasis