Question 1

From where are additional platelets first derived when the circulating count decreases?&#10;A)bone marrow&#10;B)stem cells&#10;C)cells marginated on vessel endothelial cells&#10;D)spleen

Accepted Answer

When the circulating platelet count decreases,platelets are first derived from those sequestered or stored in the spleen (normally one third of those available).

Question 2

Platelet agonists are substances that&#10;A)bind to phospholipid in the platelet membrane.&#10;B)promote apoptosis.&#10;C)activate platelets.&#10;D)enhance megakaryocyte proliferation.

Accepted Answer

Platelet agonists include thromboxane A₂ (TXA₂),ADP,and thrombin.Each of them binds to its transmembrane receptor,and platelet activation is the result.

Question 3

How are platelets released into peripheral circulation from the bone marrow?&#10;A)Mature platelets squeeze between sinusoid endothelial cells.&#10;B)Megakaryocyte cytoplasmic fragments extend through the endothelial cells, lining the sinusoids, into blood and then shed platelets.&#10;C)Platelets adhere to white cells and exit with them.&#10;D)Megakaryocytes exit the marrow with white cells, and then platelets fragment off once they reach the blood.

Accepted Answer

Cytoplasmic extensions elongate and pierce between the endothelial cells that line the marrow sinuses;then they extend into venous blood.These extensions release platelets once they enter blood.The cytoplasmic extensions are called proplatelet processes.

Question 4

How many circulating platelets are produced from a single megakaryocyte?&#10;A)200-400&#10;B)2000-4000&#10;C)6000-8000&#10;D)10,000-12,000

Accepted Answer

A single megakaryocyte sheds approximately 2000 to 4000 platelets with a total turnover in 8 to 9 days.

Question 5

What system is the &#34;control center&#34; for platelet activation?&#10;A)eicosanoid (prostaglandin) pathway&#10;B)surface connect canalicular system&#10;C)membrane glycoproteins&#10;D)dense tubular system

Accepted Answer

The dense tubular system is a condensed remnant of the rough endoplasmic reticulum.It sequesters Ca⁺⁺ and bears a series of enzymes that support platelet activation.It is the control center for platelet activation.

Question 6

Which of the following is the liver-secreted plasma enzyme that digests &#34;unused VWF&#34;?&#10;A)ADP&#10;B)TXA2&#10;C)ADAMTS-13&#10;D)GPIb

Accepted Answer

ADAMTS-13 is a VWF-cleaving protease.ADP and TXA₂ are platelet activators.GPIb is a receptor for adhesion.

Question 7

Which of the following is not a function of the platelet surface-connected canalicular system (SCCS)?&#10;A)produces energy for the cell&#10;B)delivers granule contents to the surface&#10;C)connects the internal contents to the surface&#10;D)stores hemostatic proteins

Accepted Answer

Granule contents are delivered to the surface of the platelet and released through the SCCS.It twists throughout the platelet,providing a large system in which additional plasma coagulation proteins are found in the glycocalyx.Because this is part of the platelet membrane,it connects the internal contents to the surface.It does not produce energy.

Question 8

Which of the following is true of megakaryocytes as they mature?&#10;A)nucleus becomes polyploid&#10;B)cytoplasmic basophilia becomes more pronounced&#10;C)size decreases&#10;D)nucleoli become more prominent

Accepted Answer

As the megakaryocyte matures,it undergoes endomitosis.Deoxyribonucleic acid (DNA)synthesis normally proceeds to 8N,16N,or 32N,but no cell division occurs.The nucleus is thus polyploid.Basophilia in the cytoplasm diminishes,but the cytoplasmic volume increases along with the nuclear size so that the cell becomes the largest cell in the bone marrow.The chromatin gradually clumps,and nucleoli become less prominent and eventually cannot be detected.

Question 9

Identify the platelet receptor and plasma protein required for normal platelet aggregation.
Platelet receptorPlasma protein

A)GP IIb/IIIa fibrinogen
B)GP IV factor VIII
C)GP Ib/IX/V VWF
D)PF4 factor V

Accepted Answer

The answer of Identify the platelet receptor and plasma protein...

Question 10

Phospholipids in the platelet membrane are important for all of the following functions except&#10;A)supply of arachidonic acid.&#10;B)receptor for plasma fibrinogen.&#10;C)receptor for plasma coagulation enzymes.&#10;D)forms part of the platelet glycocalyx.

Accepted Answer

Fibrinogen binds to the receptor GP IIb/IIIa.Membrane phospholipids supply arachidonic acid,which becomes converted to thromboxane during platelet activation.They form part of the platelet glycocalyx,which is the platelet surface.Many of the coagulation enzymes bind to platelet phospholipids,including factors V,VIII,IX,and X.

Question 11

A platelet histogram can be generated using automated hematology analyzers,where frequency is plotted versus platelet volume.When a platelet histogram from a normal patient is examined,which of the following is true?

A)Distribution is gaussian.
B)Mean platelet volume (MPV) is 14 fL.
C)Distribution is log normal with a small population of large platelets.
D)MPV is 5 fL.

Accepted Answer

The answer of A platelet histogram can be generated using...

Question 12

Which of the following substances is stored in dense granules?&#10;A)serotonin&#10;B)platelet factor 4&#10;C)fibronectin&#10;D)protein C inhibitor

Accepted Answer

The answer of Which of the following substances is stored...

Question 13

Identify the platelet receptor and plasma protein required for normal platelet adhesion.
Platelet receptorPlasma protein

A)glycoprotein (GP) IV factor VIII
B)platelet factor 4 (PF4) factor V
C)gp IIb/IIIa fibrinogen
D)gp Ib/IX/V von Willebrand factor (VWF)

Accepted Answer

The answer of Identify the platelet receptor and plasma protein...

Question 14

Which of the following accurately describes reticulated (stress)platelets?&#10;A)They appear in compensation for thrombocytopenia.&#10;B)They are smaller than mature circulating platelets.&#10;C)Their diameter exceeds 6 &#181;m.&#10;D)Both a and c are true.

Accepted Answer

The answer of Which of the following accurately describes reticulated...

Question 15

Which of the following megakaryocyte membrane markers disappears as differentiation proceeds?&#10;A)CD34&#10;B)CD41&#10;C)CD42&#10;D)CD61

Accepted Answer

The answer of Which of the following megakaryocyte membrane markers...

Deck 13: Platelet Production, Structure, and Function