Platelets Flashcards

*Question: What are megakaryocytes primarily responsible for producing?

A) Red blood cells

B) White blood cells

C) Platelets

D) Plasma proteins

*Answer: C) Platelets

*Question: What percentage of bone marrow cells do megakaryocytes comprise?

A) 1-2%

B) 5-10%

C) <0.5%

D) 2-3%

*Answer: C) <0.5%

*Question: What is the size range of megakaryocytes?

A) 10-20 um

B) 30-50 um

C) 2-3 um

D) 14-18 um

*Answer: B) 30-50 um

*Question: Which hormone do megakaryocytes primarily respond to?

A) Erythropoietin

B) G-CSF

C) Thrombopoietin (TPO)

D) IL-6

*Answer: C) Thrombopoietin (TPO)

*Question: Megakaryocyte differentiation is promoted by which transcription factors?

A) MYB and RUNX1

B) GATA-1 and FOG-1

C) NF-E2 and MYB

D) RUNX1 and NF-E2

*Answer: B) GATA-1 and FOG-1

*Question: Which transcription factor suppresses megakaryocyte differentiation from the common myeloid progenitor?

A) GATA-1

B) FOG-1

C) MYB

D) NF-E2

*Answer: C) MYB

*Question: Which of the following is the correct order of megakaryocyte progenitor stages?

A) CFU-Meg → BFU-Meg → LD-CFU-Meg

B) BFU-Meg → LD-CFU-Meg → CFU-Meg

C) BFU-Meg → CFU-Meg → LD-CFU-Meg

D) LD-CFU-Meg → BFU-Meg → CFU-Meg

*Answer: C) BFU-Meg → CFU-Meg → LD-CFU-Meg

*Question: What type of cell division do megakaryocytes undergo that lacks telophase and cytokinesis?

A) Mitosis

B) Meiosis

C) Endomitosis

D) Binary fission

*Answer: C) Endomitosis

*Question: Which factor mediates the switch from mitosis to endomitosis in megakaryocytes?

A) GATA-1

B) NF-E2

C) MYB

D) RUNX1

*Answer: D) RUNX1

*Question: What does RUNX1 suppress to prevent cytokinesis in megakaryocytes?

A) GATA-1 signaling

B) Rho/ROCK signaling pathway

C) NF-E2 activation

D) TPO receptor binding

*Answer: B) Rho/ROCK signaling pathway

*Question: NF-E2 allows DNA replication in megakaryocytes to reach which ploidy levels?

A) 2N, 4N, 6N

B) 4N, 8N, 12N

C) 8N, 16N, 32N

D) 16N, 32N, 64N

*Answer: C) 8N, 16N, 32N

*Question: Which terminal megakaryocyte differentiation stage is the least differentiated and cannot be reliably distinguished from myeloblasts?

A) MK-III

B) MK-II

C) MK-I

D) BFU-Meg

*Answer: C) MK-I

*Question: What is the nucleus-to-cytoplasm ratio of MK-I (megakaryoblast)?

A) 1:2

B) 1:4

C) 3:1

D) 1:1

*Answer: C) 3:1

*Question: Which MK stage has an indented nucleus and is at the 4N replication stage?

A) MK-I

B) MK-II

C) MK-III

D) BFU-Meg

*Answer: B) MK-II

*Question: MK-III (megakaryocyte) is described as having which type of cytoplasm?

A) Basophilic

B) Basophilic and granular

C) Azurophilic and granular

D) Eosinophilic

*Answer: C) Azurophilic and granular

*Question: Which terminal MK stage is the most abundant and easily recognized?

A) MK-I

B) MK-II

C) MK-III

D) CFU-Meg

*Answer: C) MK-III

*Question: What percentage of precursors does MK-III represent?

A) 20%

B) 25%

C) 40%

D) 55%

*Answer: D) 55%

*Question: How many platelets does a single megakaryocyte shed?

A) 200-400

B) 500-1000

C) 2000-4000

D) 5000-8000

*Answer: C) 2000-4000

*Question: What is the lifespan of platelets?

A) 1-2 days

B) 4-5 days

C) 8-9 days

D) 14-21 days

*Answer: C) 8-9 days

*Question: At the end of thrombocytopoiesis, what happens to naked megakaryocyte nuclei?

A) They are recycled into new megakaryocytes

B) They are consumed by marrow macrophages

C) They are released into circulation

D) They undergo apoptosis independently

*Answer: B) They are consumed by marrow macrophages

*Question: Which megakaryocyte membrane marker is the TPO receptor and is seen at all maturation stages?

A) CD34

B) CD41

C) MPL

D) CD42

*Answer: C) MPL

*Question: CD34 is described as a marker for which cells and disappears as maturation proceeds?

A) Fully mature megakaryocytes

B) Stem cells and common myeloid progenitors

C) Platelets only

D) Promegakaryocytes

*Answer: B) Stem cells and common myeloid progenitors

*Question: Which marker first appears at the CFU-Meg stage and persists through platelets?

A) MPL

B) CD34

C) CD41

D) CD42

*Answer: C) CD41

*Question: Factor VIII, vWF, and Fibrinogen are markers of which megakaryocyte stage?

A) BFU-Meg

B) MK-I

C) MK-II

D) Fully mature megakaryocyte (MK-III/PLT)

*Answer: D) Fully mature megakaryocyte (MK-III/PLT)

*Question: What is the primary source of TPO?

A) Kidney

B) Spleen

C) Liver

D) Bone marrow stromal cells

*Answer: C) Liver

*Question: TPO concentration is inversely proportional to what?

A) Red blood cell mass

B) Platelet and megakaryocyte mass

C) White blood cell count

D) Plasma fibrinogen levels

*Answer: B) Platelet and megakaryocyte mass

*Question: Which cytokine acts with TPO to induce early differentiation of stem cells?

A) IL-6

B) IL-11

C) IL-3

D) GM-CSF

*Answer: C) IL-3

*Question: Oprelvekin is an analogue of which interleukin used in chemotherapy-induced thrombocytopenia?

A) IL-3

B) IL-6

C) IL-8

D) IL-11

*Answer: D) IL-11

*Question: Which of the following inhibits megakaryocyte growth?

A) Kit ligand

B) GM-CSF

C) Platelet factor-4

D) G-CSF

*Answer: C) Platelet factor-4

*Question: What is the normal platelet count range?

A) 50-100 x10⁹/L

B) 100-200 x10⁹/L

C) 150-450 x10⁹/L

D) 200-500 x10⁹/L

*Answer: C) 150-450 x10⁹/L

*Question: What fraction of total body platelets is sequestered in the spleen?

A) 1/4

B) 1/3

C) 1/2

D) 2/3

*Answer: B) 1/3

*Question: What is the Mean Platelet Volume (MPV) of normal platelets?

A) 2-5 fL

B) 7-12 fL

C) 12-14 fL

D) 15-20 fL

*Answer: B) 7-12 fL

*Question: Platelets are described as what type of cellular structures?

A) Large nucleated cells

B) Small non-nucleated membrane-bound cellular fragments

C) Biconcave disc-shaped cells

D) Granular nucleated fragments

*Answer: B) Small non-nucleated membrane-bound cellular fragments

*Question: What is the diameter of normal platelets?

A) 5-7 um

B) 7-10 um

C) 2-3 um

D) 10-14 um

*Answer: C) 2-3 um

*Question: Reticulated/stress platelets are associated with which condition?

A) Normal platelet turnover

B) Compensation for thrombocytopenia

C) Inhibition of platelet production

D) Reduced megakaryocyte activity

*Answer: B) Compensation for thrombocytopenia

*Question: What stain is used to identify reticulated/stress platelets?

A) Wright-Giemsa

B) Prussian blue

C) Thiazole orange

D) Periodic acid-Schiff

*Answer: C) Thiazole orange

*Question: Reticulated platelets are associated with which clinical state?

A) Antithrombotic states

B) Prothrombotic states

C) Fibrinolytic states

D) Anticoagulant states

*Answer: B) Prothrombotic states

*Question: Which phospholipid in the inner platelet membrane layer supplies arachidonic acid for TXA2 synthesis?

A) Phosphatidylcholine

B) Sphingomyelin

C) Phosphatidylinositol

D) Phosphatidylethanolamine

*Answer: C) Phosphatidylinositol

*Question: Which phospholipids are found in the outer layer of the platelet plasma membrane?

A) Phosphatidylserine and phosphatidylethanolamine

B) Phosphatidylcholine and sphingomyelin

C) Phosphatidylinositol and phosphatidylserine

D) Sphingomyelin and phosphatidylinositol

*Answer: B) Phosphatidylcholine and sphingomyelin

*Question: The glycocalyx on the platelet surface is described as having which charge?

A) Positively charged

B) Neutral

C) Negatively charged

D) Alternating charge

*Answer: C) Negatively charged

*Question: What is the thickness of the platelet glycocalyx?

A) 2-5 nm

B) 10-15 nm

C) 20-30 nm

D) 50-100 nm

*Answer: C) 20-30 nm

*Question: The Surface-Connected Canalicular System (SCCS) serves which primary function?

A) Calcium sequestration

B) Storage of hemostatic proteins and environmental interaction

C) Platelet shape maintenance

D) Synthesis of thromboxane

*Answer: B) Storage of hemostatic proteins and environmental interaction

*Question: The Dense Tubular System (DTS) is a condensed remnant of which organelle?

A) Golgi apparatus

B) Smooth ER

C) Rough ER (RER)

D) Mitochondria

*Answer: C) Rough ER (RER)

*Question: Which enzymes are contained within the Dense Tubular System?

A) Thrombin and fibrin

B) PLA2, COX, and thromboxane synthase

C) Plasminogen and plasmin

D) Factor V and Factor VIII

*Answer: B) PLA2, COX, and thromboxane synthase

*Question: What is the role of microtubules in resting platelets?

A) Release of dense granules

B) Maintenance of discoid shape

C) Production of thromboxane

D) Binding to vWF

*Answer: B) Maintenance of discoid shape

*Question: How many alpha-granules are found per platelet?

A) 2-7

B) 10-20

C) 50-80

D) 100-200

*Answer: C) 50-80

*Question: Alpha-granules stain which color under electron microscopy?

A) Black (opaque)

B) Medium gray

C) White

D) Dark purple

*Answer: B) Medium gray

*Question: Which protein found exclusively in platelet alpha-granules is used as a platelet-specific marker?

A) Fibrinogen

B) Fibronectin

C) Beta-thromboglobulin

D) vWF

*Answer: C) Beta-thromboglobulin

*Question: Alpha-granule contents are released via which system?

A) Dense tubular system

B) Surface-connected canalicular system (SCCS)

C) Lysosomal pathway

D) Direct plasma membrane fusion

*Answer: B) Surface-connected canalicular system (SCCS)

*Question: How many dense granules are found per platelet?

A) 2-7

B) 50-80

C) 10-20

D) 100+

*Answer: A) 2-7

*Question: Dense granules stain which color under electron microscopy?

A) Medium gray

B) White

C) Black (opaque)

D) Red

*Answer: C) Black (opaque)

*Question: Which small molecule in dense granules is a vasoconstrictor that binds endothelial cells?

A) ADP

B) ATP

C) Serotonin

D) Calcium

*Answer: C) Serotonin

*Question: ADP in dense granules supports platelet aggregation by binding to which receptors?

A) PAR1 and PAR4

B) P2Y1 and P2Y12

C) TPα and TPβ

D) IP and EP3

*Answer: B) P2Y1 and P2Y12

*Question: What is the role of platelet lysosomes?

A) Storage of coagulation factors

B) Release of vasoconstrictors

C) Digestion of vessel wall matrix components during aggregation

D) Synthesis of thromboxane

*Answer: C) Digestion of vessel wall matrix components during aggregation

*Question: GPIb/IX/V belongs to which receptor family?

A) CAM integrin family

B) Seven-transmembrane receptor family

C) CAM leucine-rich repeat family

D) CAM immunoglobulin gene family

*Answer: C) CAM leucine-rich repeat family

*Question: GPIIb/IIIa (integrin αIIbβ3) binds which ligand to mediate platelet aggregation?

A) vWF

B) Collagen

C) Fibrinogen

D) Thrombospondin

*Answer: C) Fibrinogen

*Question: GPVI binds to which type of collagen to trigger TXA2 and ADP release?

A) Type II fibrillar collagen

B) Type IV collagen

C) Type I fibrillar collagen

D) Type III collagen

*Answer: C) Type I fibrillar collagen

*Question: Which receptor mediates platelet tethering via vWF binding to GPIbα?

A) GPIIb/IIIa

B) GPIb/IX/V

C) GPVI

D) GPIa/IIa

*Answer: B) GPIb/IX/V

*Question: Thrombin binds to which seven-transmembrane receptors on platelets?

A) P2Y1 and P2Y12

B) TPα and TPβ

C) PAR1 and PAR4

D) IP and EP3

*Answer: C) PAR1 and PAR4

*Question: P2Y1 ADP receptor activation leads to which effect?

A) Irreversible platelet aggregation

B) Decreased intracellular calcium

C) Increased intracellular calcium and reversible platelet aggregation

D) Inhibition of platelet shape change

*Answer: C) Increased intracellular calcium and reversible platelet aggregation

*Question: P2Y12 ADP receptor activation leads to which effect?

A) Reversible platelet aggregation via increased cAMP

B) Irreversible platelet aggregation via decreased cAMP

C) Platelet inhibition via increased cAMP

D) Shape change without aggregation

*Answer: B) Irreversible platelet aggregation via decreased cAMP

*Question: Prostacyclin (PGI2) binding to the IP receptor leads to which effect on platelets?

A) Platelet activation

B) Increased intracellular calcium

C) Increased cAMP, inhibiting platelet activation

D) Shape change to pseudopods

*Answer: C) Increased cAMP, inhibiting platelet activation

*Question: FCγRIIa (CD32) plays a role in which clinical condition?

A) Bernard-Soulier syndrome

B) Glanzmann thrombasthenia

C) Heparin-induced thrombocytopenia

D) Immune thrombocytopenic purpura

*Answer: C) Heparin-induced thrombocytopenia

*Question: PECAM-1 (CD31) mediates adhesion between platelets and which cell types?

A) Red blood cells and neutrophils

B) WBCs and endothelial cells

C) Monocytes and basophils

D) Mast cells and fibroblasts

*Answer: B) WBCs and endothelial cells

*Question: What is the first step in primary hemostasis following vessel injury?

A) Platelet aggregation

B) Fibrin polymerization

C) Exposure of collagen and release of vWF

D) Thrombin generation

*Answer: C) Exposure of collagen and release of vWF

*Question: During platelet adhesion, vWF binds to which platelet glycoprotein to tether platelets to the injury site?

A) GPIIb/IIIa

B) GPIbα

C) GPVI

D) GPIa

*Answer: B) GPIbα

*Question: What shape change do platelets undergo upon activation?

A) Discoid to biconcave

B) Discoid to round with pseudopods

C) Round to elongated

D) Biconcave to biconvex

*Answer: B) Discoid to round with pseudopods

*Question: The endpoint of platelet aggregation in arteries produces which type of clot?

A) Red clot (fibrin-rich)

B) Mixed clot

C) White clot (platelet-rich)

D) Fibrin clot only

*Answer: C) White clot (platelet-rich)

*Question: Alpha-granule contents are primarily used for which phase of hemostasis?

A) Primary hemostasis

B) Secondary hemostasis

C) Fibrinolysis

D) Vasoconstriction

*Answer: B) Secondary hemostasis

*Question: Dense granule contents (vasoconstrictors and platelet agonists) amplify which phase of hemostasis?

A) Secondary hemostasis

B) Fibrinolysis

C) Primary hemostasis

D) Anticoagulation

*Answer: C) Primary hemostasis

*Question: In the eicosanoid synthesis pathway, what does phosphatidylinositol supply for TXA2 synthesis?

A) Thromboxane synthase

B) Arachidonic acid

C) Cyclooxygenase-1

D) Phospholipase A2

*Answer: B) Arachidonic acid

*Question: What is the half-life of TXA2?

A) 5 minutes

B) 2 minutes

C) 30 seconds

D) 10 seconds

*Answer: C) 30 seconds

*Question: TXA2 is spontaneously reduced to which stable metabolite?

A) Prostacyclin (PGI2)

B) Thromboxane B2

C) PGG2

D) PGH2

*Answer: B) Thromboxane B2

*Question: In the IP3-DAG pathway, IP3 signals the release of which ion from the ER?

A) Sodium

B) Potassium

C) Calcium

D) Magnesium

*Answer: C) Calcium

*Question: DAG in the IP3-DAG pathway activates which enzyme?

A) Phospholipase A2

B) Cyclooxygenase

C) Adenylate cyclase

D) Protein kinase C

*Answer: D) Protein kinase C

*Question: G-proteins are αβγ heterotrimers that bind GDP when in which state?

A) Active

B) Inactive

C) Phosphorylated

D) Membrane-bound

*Answer: B) Inactive

*Question: Platelet factor 4 (PF4) found in alpha-granules serves which function?

A) Promotes fibrinolysis

B) Heparin neutralization and suppresses megakaryocytopoiesis

C) Supports platelet adhesion

D) Activates thrombin

*Answer: B) Heparin neutralization and suppresses megakaryocytopoiesis

*Question: What is the demarcation membrane system (DMS) in megakaryocytes?

A) The outer cell membrane of the megakaryocyte

B) Membrane-lined channels that subdivide the cytoplasm

C) The nuclear envelope of the megakaryocyte

D) Membrane surrounding alpha-granules

*Answer: B) Membrane-lined channels that subdivide the cytoplasm

*Question: Which synthetic TPO agents are used clinically?

A) Darbepoetin and epoetin

B) Filgrastim and pegfilgrastim

C) Avatrombopag, eltrombopag, lusutrombopag, romiplostim

D) Oprelvekin and sargramostim

*Answer: C) Avatrombopag, eltrombopag, lusutrombopag, romiplostim

*Question: P-selectin (CD62) on platelets facilitates binding to which cell types?

A) Red blood cells and platelets only

B) Endothelial cells, leukocytes, and other platelets

C) Megakaryocytes and stem cells

D) Mast cells and basophils

*Answer: B) Endothelial cells, leukocytes, and other platelets

*Question: Which cytokine acts with TPO to enhance endomitosis, megakaryocyte maturation, and thrombocytopoiesis?

A) IL-3

B) IL-6 and IL-11

C) GM-CSF

D) G-CSF

*Answer: B) IL-6 and IL-11