CHAPTER 12

DISORDERS OF HEMOSTASIS

Essentials of Pathophysiology

PRE LECTURE QUIZ (TRUE/FALSE)

Platelets are also known as leukocytes. Idiopathic thrombocytopenic purpura (ITP) is

an autoimmune disorder that affects the normal function and formation of platelets.

Disseminated intravascular coagulation is a condition that results in massive systemic bleeding, but coagulation function remains normal.

The use of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) has been identified as a cause of impaired platelet function.

Bleeding can occur as a result of a decrease in the number of circulating platelets or because of impaired platelet function.

F

T

T

T

T

PRE LECTURE QUIZ _________________ is the orderly, stepwise

process for stopping bleeding that involves vasospasm, formation of a platelet plug, and development of a fibrin clot.

A decrease in the number of circulating platelets is known as _________________________.

Hemophilia A is an X-linked recessive disorder that involves a deficiency of factor _________________.

________________ disorders are caused by defects associated with platelets, coagulation factors, and vessel integrity.

Vitamin _______________, a fat-soluble vitamin that is continuously being synthesized by intestinal bacteria, is necessary for normal activity of factors VII, IX, and X and prothrombin.

Bleeding 

K 

Hemostasis 

thrombocytopenia

VIII 

  

  

  

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

PLATELET STRUCTURE

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).

CLOTTING CASCADE

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

Given to block inflamation

People taking Celebrex develop increased TXA2 levels

What problems might they have?

COX-1 COX-2

arachidonic acid

thromboxane A 2 ProstacyclinMacrophage Activation & Inflamation mediationNSAIDs inhibit both COX 1 &2

COX 1 is needed for intestinal mucosaProblems here?

INTRINSIC AND EXTRINSIC PATHWAYS

Common Pathway

PLATELETS

Platelet aggregate with fibrin threads

Activated plateletsNon activated platelet

FIBRINOGEN FIBRIN

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?

HYPERCOAGULABILITY

Increased platelet number Platelet aggregation Endothelial damage Increased procoagulation

factors Decreased anticoagulation

factors

QUESTION

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

DIC

QUESTION

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.