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Hematology > Module D3 > Flashcards

Module D3 Flashcards

1
Q

Platelets have 2 main functions in hemostasis

A

Hemostatic plug formation

The activation and enhancement of other components of hemostasis

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2
Q

Hemostatic plug formation

A

Platelets are physically involved in forming the hemostatic plug

Includes the processes of platelet adhesion, aggregation and retraction

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3
Q

The activation and enhancement of other components of hemostasis

A

Platelets undergo the “release reaction” in which they release a variety of substances that enhance

Vasoconstriction
Platelet aggregation
Coagulation

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4
Q

Platelet response has 3 steps

A

Platelet adhesion
Platelet aggregation
Platelet retraction

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5
Q

Platelet adhesion

A

Platelets stick to the subendothelial collagen and basement membrane that is exposed to the blood after a vessel is injured

Requires: normal glycocalyx, adequate amounts of Von willebrands factor which is part of the factor VIII complex molecule

Requires energy

Can occur with a lot of other foreign substances besides collagen (viruses, glass)

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6
Q

Platelet aggregation

A

ADP and thrombin will attract nearby platelets, which stick to the adhering platelets

Aggregation involves platelets sticking to each other

2 phases: primary (reversible) aggregation, secondary (irreversible) aggregation

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7
Q

Primary (reversible) aggregation

A

Platelets first form a loose aggregate, which plugs up the injury (temporarily)

Requires: some ADP, normal platelet membrane glycoprotein, calcium ions and fibrinogen

Platelets can dissociate from the primary plug and resume their normal flow in the circulation (minor vessel injuries)

No products of coagulation participating in the platelet plug

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8
Q

Secondary (irreversible) aggregation

A

When injuries to vessels are sufficiently large, enough tissue thromboplastin is released to activate the extrinsic pathway of coagulation

Production of thrombin

Exposure of collagen by the injury causes more adhering platelets to release more ADP

ADP and thrombin in sufficient concentration will induce the aggregated platelets to produce thromboxane A2

Thromboxane A2 causes the platelets in the primary aggregate to do 2 things: undergo viscous metamorphis, undergo the release reaction

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9
Q

Viscous metamorphosis

A

Consists of the aggregated platelets undergoing a shape change from disc-or sphere shaped to spiny

After viscous metamorphosis, the platelets in the platelet plug can no longer disassociate from the plug

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10
Q

Release reaction

A

The platelets in the aggregate release a variety of substances, which enhance vasoconstriction and coagulation and causes more platelets to aggregate

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11
Q

Thromboxane A2 function

A

Powerful vasoconstrictor which helps sustain vasoconstriction in the injured area

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12
Q

The end product of coagulation

A

Fibrin

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13
Q

Red plug

A

Fibrin binds the platelets together and anchors the plug in place

This plug traps red blood cells in the sticky fibrin network

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14
Q

Platelet retraction

A

Platelets in the red plug contract their micro filaments

This contraction causes the retraction of the spiny extensions of the platelets in the red plug and pulls in the fibrin strands attached to the spines to form a compact, impermeable hemostatic plug

In the test tube, this phase is called clot retraction

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15
Q

The platelet response

A

Injury-exposure of collagen-platelet adhesion-produces ADP-primary aggregation-produces TxA2-viscous metamorphosis and release reaction-secondary aggregation-white plug-red plug-platelet retraction-hemostatic plug

Injury-release of tissue thromboplastin activates coagulation-produces thrombin-produces fibrin

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16
Q

Platelet factors

A

Substances found on the platelet membrane, which act to enhance coagulation

17
Q

PF-3 phospholipid

A

Most important factor

Stored in the platelet granules and released onto the platelet membrane during the release reaction

Acts as an organizational surface for specific coagulation reactions

18
Q

PF-4 anti-heparin factor

A

Inhibits the action of heparin

19
Q

PF-2 fibrinogen activating factor

A

Renders fibrinogen more sensitive to the action of thrombin

20
Q

PF-1

A

Coagulation factor v, which has been absorbed onto the platelet membrane

21
Q

Substances that affect platelet aggregation

4 groups

A

Substances that affect the level of cAMP in the platelets

NSAIDs

Chelating agents

Heparin

22
Q

Dypridamole

A

Acts as a coronary vasodilator

23
Q

Papaverine

A

Used to relieve spasms of smooth muscle

24
Q

Adenosine

A

A structural component of nucleic acids and a major molecular component of ADP and ATP

25
Q

PGD2

A

Bronchoconstrictor, platelet activating factor, has cytotoxic effects

26
Q

Prostacyclin

A

Produced in the walls of blood vessels that acts as a vasodilator and inhibits platelet aggregation

27
Q

Cyclic adensoine monophosphate (cAMP)

A

Substance found intracellularly that acts as an internal messenger

Platelets: acts to inhibit platelet aggregation, too much and it won’t

Substances that increase: Dypridamole, Papaverine, caffeine, adenosine, PGD2 and prostacyclin

Substances that decrease: epinephrine, thrombin, ADP, collagen, TxA2

28
Q

NSAIDs

A

Non steroidal anti inflammatory drugs

Inhibit platelet aggregation

Inhibits formation of TxA2

29
Q

Chelating agents

A

EDTA

Inhibit platelet aggregation

Removes calcium

30
Q

Heparin

A

Inhibits the action of thrombin

31
Q

Vascular component

A

Vasoconstriction slows blood flow, thus decreasing blood loss and enhancing platelet adhesion

Release of tissue thromboplastin activates the extrinsic pathway of coagulation

Release of tissue plasminogen activator activates the fibrinolytic system

Exposure of collagen starts platelet adhesion and activates the intrinsic pathway of coagulation

32
Q

Platelet components

A

Adhesion and release of ADP promotes aggregation and primary platelet plug formation

Primary aggregation provides a temporary, reversible seal of the injury; promotes further aggregation

Secondary aggregation-viscous metamorphosis creates and irreversible platelet plug; the release reaction liberates factors, which reinforce vasoconstriction and accelerate aggregation and coagulation

Retraction consolidates the hemostatic plug

Hematology (4 decks)

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