Platelets and Hemostasis Quiz

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Questions and Answers

Which of the following cytokines is NOT mentioned as working synergistically with TPO?

GM-CSF

IL-10 (correct)

KIT ligand

G-CSF

Platelet Factor 4 (PF4) is known to enhance megakaryocyte growth.

False

Name one transcription factor that influences the maturation of megakaryocytes.

GATA-1

KIT ligand is also known as the ___________ growth factor.

mast cell Signup and view all the answers

Match the following factors with their effects on megakaryocyte growth:

PF4 = Inhibits megakaryocyte growth β-thromboglobulin = Inhibits megakaryocyte growth MYB = Suppresses megakaryocyte differentiation GATA-1 = Stimulates megakaryocyte differentiation Signup and view all the answers

What is the normal platelet count range in adults?

150-450 x 10^9/L Signup and view all the answers

Platelets are produced from megakaryocytes in the bone marrow.

True Signup and view all the answers

What hormone is primarily responsible for regulating platelet production?

Thrombopoietin (TPO) Signup and view all the answers

The average diameter of normal platelets is ______.

2.5 µm Signup and view all the answers

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

810 fL Signup and view all the answers

Match the following platelet types with their characteristics:

Normal Platelets = 2.5 µm, 810 fL Reticulated Platelets = > 6 µm, 12-14 fL Thrombocytopenia = Lower platelet count than normal Megakaryocytes = Largest cells in bone marrow Signup and view all the answers

Synthetic TPO mimetics are used to decrease platelet production in patients with cancer.

False Signup and view all the answers

What is the role of MPL in relation to thrombopoietin?

MPL is the receptor that binds thrombopoietin (TPO). Signup and view all the answers

Which of the following TPO mimetics is a nonimmunogenic oligopeptide?

Romiplostim Signup and view all the answers

Eltrombopag is effective in treating only chronic immune thrombocytopenic purpura (ITP).

False Signup and view all the answers

What role does TPO play in thrombocytopoiesis?

TPO induces differentiation of stem cells into megakaryocyte progenitors and promotes the proliferation and maturation of megakaryocytes. Signup and view all the answers

IL-3 acts in synergy with TPO to induce the early differentiation of ______.

stem cells Signup and view all the answers

Match the following cytokines with their roles in megakaryocytopoiesis:

TPO = Induces thrombocytopoiesis IL-3 = Enhances early differentiation of stem cells IL-6 = Enhances endomitosis and megakaryocyte maturation Oprelvekin = Stimulates platelet production in chemotherapy-induced thrombocytopenia Signup and view all the answers

What is the primary use of oprelvekin?

To stimulate platelet production in chemotherapy-induced thrombocytopenia Signup and view all the answers

IL-6 and IL-11 work independently of TPO to promote megakaryocyte maturation.

False Signup and view all the answers

What is the mechanism by which TPO induces the differentiation of megakaryocyte progenitors?

TPO induces differentiation of megakaryocyte progenitors into megakaryoblasts and further into megakaryocytes. Signup and view all the answers

Study Notes

Platelets (Thrombocytes)

Trigger primary hemostasis upon exposure to subendothelial collagen and inflammatory proteins during blood vessel injury.
Derived from megakaryocytes, which are the largest cells in bone marrow, characterized by multiple chromosome copies.
Normal platelets are nonnucleated, biconvex cells with an average diameter of 2.5 µm and a mean platelet volume (MPV) of 810 fL.
Typical platelet count ranges from 150-450 x 10^9/L, with women generally having higher counts; two-thirds circulate while one-third is sequestered in the spleen.
Reticulated (stress) platelets appear as a compensatory response to thrombocytopenia and are larger than normal platelets (> 6 µm) with an MPV of 12-14 fL.

Thrombopoietin (TPO)

TPO is a glycoprotein growth factor, weighing 70,000 Daltons, with 23% homology to erythropoietin.
It is primarily synthesized in the liver, kidneys, stromal cells, and smooth muscle; it circulates in plasma as a hormone.
TPO binds to the MPL receptor on megakaryocytes and platelets, where decreased plasma TPO concentration signals an increase in platelet mass.
Synthetic TPO analogs such as romiplostim (MPL receptor agonist) and eltrombopag (separately binding MPL site) enhance platelet production, particularly in conditions like chronic immune thrombocytopenic purpura (ITP).

Mechanisms of TPO Action

TPO plays a crucial role in the differentiation of stem cells into megakaryocyte progenitors, megakaryocyte precursor cells, and ultimately mature megakaryocytes.
It also promotes the maturation and proliferation of megakaryocytes, driving thrombocytopoiesis (platelet production).

Synergistic Cytokines

IL-3 works alongside TPO to induce early differentiation of stem cells.
IL-6 and IL-11, in the presence of TPO, enhance endomitosis and megakaryocyte maturation; oprelvekin (an IL-11 analog) is used to increase platelets in chemotherapy-induced thrombocytopenia.
Other synergistic factors include:
- KIT ligand (stem cell factor)
- GM-CSF (granulocyte-macrophage colony-stimulating factor)
- G-CSF (granulocyte colony-stimulating factor)
- Acetylcholinesterase-derived megakaryocyte growth stimulating peptide.

Inhibition of Megakaryocytopoiesis

Factors that inhibit megakaryocyte growth in vitro include:
- Platelet Factor 4 (PF4)
- β-thromboglobulin
- Neutrophil-activating peptide 2
- IL-8
Transcription factors such as GATA-1, FOG1, and NF-E2 are vital in regulating megakaryocyte maturation, with deficiencies leading to reduced megakaryocytopoiesis.

Regulatory Mechanisms

An inverse relationship exists between TPO levels and platelet/megakaryocyte mass, indicating that platelet-bound TPO regulates overall platelet count.
Elevated TPO levels signal a high production demand for platelets, influencing the binding capacity to MPL receptors on megakaryocytes.

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Description

Test your knowledge on platelets or thrombocytes and their role in primary hemostasis. This quiz covers their origin from megakaryocytes, normal platelet characteristics, and their functions during blood vessel injury. Perfect for students studying hematology or related fields.