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Immunohematology > Lecture 9: Platelet > Flashcards

Lecture 9: Platelet Flashcards

1
Q

What are platelets involved in?

A

primary hemostasis
halting bleeding following vascular injury

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2
Q

What are platelets made from?

A

cellular fragments of cytoplasm from megakaryocytes in the bone marrow

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3
Q

What are the 3 zones of platelets?

A

the peripheral zone
the sol-gel zone
the organelle zone

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4
Q

Peripheral Zone

A

the stimulus receptor/transmitter region

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5
Q

Peripheral Zone components

A

Glycocalyx
Plasma membrane
open canalicular system
specialized microfilaments

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6
Q

glycocalyx

A

important component of the platelet membrane

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7
Q

What are glycoproteins responsible for?

A

blood group specificity (ABO)
tissue compatibility (human leukocyte antigen [HLA])
platelet-unique immunologic antigenicity
serve as receptors and facilitate transmission of stimuli

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8
Q

What is the purpose of the phospholipids in the Peripheral zone?

A

serves as a surface for the interaction of the plasma proteins involved in blood coagulation

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9
Q

What is also in platelet surface?

A

Coagulation factors V and VIII
participate in the formation of fibrin

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10
Q

What is the purpose development of stickiness in the peripheral zone?

A

essential for the platelet functions of adhesion and aggregation

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11
Q

Sol-Gel Zone

A

the cytoskeletal/contractile region
contains microtubules and microfilaments

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12
Q

Thrombosthenin

A

microfibrillar “contractile” protein
form the platelet’s cytoskeleton, which contracts as the platelet’s shape changes
together with microfilaments: actin and myosin

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13
Q

What is the cytoskeleton responsible for?

A

maintaining its normal discoid shape

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14
Q

Organelle Zone

A

the metabolic/organellar region
responsible for the metabolic activities of the platelet

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15
Q

platelet granules

A

most numerous organelles
heterogeneous in size and differentiated by their electron density and chemical contents

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16
Q

Types of platelet granules

A

Alpha and dense granules

17
Q

Alpha granules

A

more numerous
contain a number of different proteins
physiologic role not clearly defined; but PF 4 does neutralize the anticoagulant heparin

18
Q

Dense bodies

A

fewer in number
densely opaque granules in (TEM) preparations

19
Q

storage pool

A

intragranular concentration of ADP and ATP found in the dense bodies

20
Q

release reaction

A

contents of both the alpha granules and dense bodies are released
energy dependent
additional platelets are drawn to the site of the vascular injury- platelet aggregates

21
Q

dense tubular system (DTS)

A

another important structure present in the cytoplasm in organelle zone
Similar to sarcotubules in skeletal muscle
site of prostaglandin synthesis and sequestration of calcium

22
Q

What does the release of calcium from the DTS do?

A

triggers contraction of thrombosthenin and subsequent internal activation of platelets

23
Q

The role of platelets in hemostasis includes what?

A

(1) maintenance of vascular integrity
(2) initial arrest of bleeding by platelet plug formation
(3) stabilization of the hemostatic plug by contributing to the process of fibrin formation

24
Q

Maintenance of Vascular Integrity

A

Platelets are involved in the nurturing of endothelial cells lining the vascular system
Platelet adheres to cell, cytoplasm b/n cell and platelet decreases, platelet becomes part of cell
This process has an effect of “nurturing” or “feeding”

25
Q

How much platelets are used in maintaining vascular integrity?

A

10% in circulation

26
Q

Platelet Plug Formation: processes

A

platelet adhesion
platelet aggregation
platelet release reaction

27
Q

Platelet Plug formation: Adhesion

A

a reversible process whereby platelets stick to foreign surfaces
involves the interaction of platelet surface glycoproteins with the connective tissue elements of the subendothelium
Exposure to subendothelial connective tissue, such as collagen fibers begins process

28
Q

Adhesion of platelets to subendothelial fibers depends on a plasma protein called what?

A

on Willebrand factor (vWF)

29
Q

What does adhesion do for platelets?

A

Platelets adhere to the area of injury at the endothelial lining or to each other when injured
acting to arrest the initial episode of bleeding

30
Q

Platelet Plug Formation: Aggregation

A

injured platelet changes shape from discoid to spheric, with pseudopod formation
caused by ADP, which is released from adherent platelets or endothelial cells

31
Q

Adenosine diphosphate

A

potent initiator of aggregation
By binding specific membrane receptors
resulting in the transformation of ambient discoid platelets to reactive spiny spheres

32
Q

Aside from Adenosine diphosphate (ADP) what else is needed for aggregation?

A

Both calcium and the plasma protein fibrinogen

33
Q

Platelet Plug Formation: Platelet Release reaction

A

from dense granules involves the secretion of ADP, serotonin (a vasoactive amine), and calcium

34
Q

What does the release of ADP do?

A

further aggregation of more platelets

35
Q

Stabilization of Hemostatic Plug

A

The last stage involved in arresting bleeding after vessel damage
achieved through the formation and deposition of fibrin, the end product of coagulation

36
Q

platelets require energy in the form of ATP for what?

A

cellular movement
active transport of molecules across the membrane
biosynthetic purposes
maintenance of a hemostatic steady state

37
Q

Why is The study of ATP and ADP in platelets complicated?

A

adenine nucleotides are present in two pools

38
Q

adenine nucleotides metabolically active pool

A

participates in metabolism
found in the cytoplasm, mitochondria, and membranes

39
Q

adenine nucleotides inactive storage pool

A

found in the dense granules and plays a role in the release reaction

Immunohematology (16 decks)

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