HEMA 2 - LESSON 2: Megakaryocytopoiesis & Platelets

Alternative name for Platelets

Thrombocytes

Characteristic of Thrombocytes

Non-nucleated blood cells

Size of Platelets

2.5 um

Normal value of Platelets

150 - 400x10^9 fL

Normal volume of Platelets (MPV)

8 - 10 fL

Location of platelets in the body

* 30% in Spleen
* 60% in blood circulation

Origin of Platelets

Megakaryocytes

Largest cell in the bone marrow

Megakaryocytes

Size of Megakaryocytes

30-50 um

Term for the production and development of megakaryocytes

Megakaryocytopoiesis

Where does Megakaryocytopoiesis occur?

Bone marrow

What is the origin of blood cells?

Hematopoietic Stem Cell

Unique characteristic of Hematopoietic Stem Cell

Can undergo self-renewal, differentiation, or apoptosis

Major growth factor of Megakaryocytopoiesis

Thrombopoietin

Enumerate the 3 phase of Megakaryocytes

1. Proliferative phase
2. Terminal differentiation
3. Platelet shedding

Proliferative phase AKA

Progenitors

Terminal differentiation AKA

Morphologically Identifiable Stage

Platelet shedding AKA

Thrombocytopoiesis

What does GEMM stand for?

* Granulocyte
* Erythrocyte
* Monocyte
* Megakaryocyte

Form of mitosis that lacks telophase and cytokinesis

Endomitosis

Enumerate the major progenitor stages of Proliferative phase

1. BFU-Meg
2. CFU-Meg
3. LD-CFU-Meg

BFU-Meg (Least Mature)

Burst Forming Unit-Megakaryocyte

CFU-Meg

Colony Forming Unit-Megakaryocyte

LD-CFU-Meg (Most Mature)

Low Density-Colony Forming Unit-Megakaryocyte

Methods of Identification for Progenitors

* Immunologic tests
* Cytochemical stains

Immunologic tests AKA

Flow Cytometry

What does MK 1 (I) Stand for in Terminal Differentiation?

Megakaryoblast

What does MK 2 (II) Stand for in Terminal Differentiation?

Promegakaryocyte

What does MK 3 (III) Stand for in Terminal Differentiation?

Megakaryocyte

What stage does Endomitosis end?

MK-II or Promegakaryocyte

How many Platelets can MK-III produce?

2000-4000

Megakaryocyte marker that is present in all the stages of Megakaryocytopoiesis

MPL

What hormone induces stem cell differentiation?

Thrombopoietin

Which Cytokine/Hormones can be used for Therapy

TPO, IL-11 (Interleukin 11)

Maturation time of Megakaryocytes in the Bone Marrow

5 days

Survival/Lifespan of Platelets in circulation

8-9 days

Appearance of Platelets

Biconvex

What platelets carry free ribosomes and fragments of rough ER?

Stress Platelets

Alternative name for Stress platelets

Reticulated platelets

Size of Stress platelets

6 um

Normal volume of Stress platelets

12-14 fL

Unique characteristic of Stress platelets

Constains residual RNA

Method of detection of Stress platelets

Flow cytometry

Dye used in Flow cytometry for identification of Stress platelets

Thiazole orange

Composition of Plasma membrane of PLT

Proteins, Lipids

Platelet's outer membrane surface

Glycocalyx

Thickness of Glycocalyx

20-30 nm

Electric charge of Glycocalyx

Negative (-)

Mode of absorption of albumin, fibrinogen and transports them to storage organelles in Platelets

Endocytosis

Unique characteristic of Glycocalyx

Adhesive

What system maintains a direct communication with the extracellular environment?

Surface-Connected Canalicular System (SCCS)

What is the site for arachidonic acid metabolism within platelet?

Dense Tubular System

Control center for platelet activation

Dense Tubular System

Cytoskeleton that maintains the platelet shape

Microtubules

Composition of Microtubules

Tubulin

Cytoskeleton responsible for clot retraction

Microfilaments

Composition of Microfilaments

Actin, Myosin

What is the cause of platelet contraction?

Actin

Enumerate Platelet Granules

1. Alpha granules
2. Dense granules
3. Lysosomes

What platelet granule is present in the numbers between 50-80?

Alpha granules

Color of alpha granule in osmium dye

Gray

What is the disorder called when alpha granule contents are absent?

Gray platelet syndrome

Enumerate the ALPHA granule content

1. Fibrinogen
2. Von Willebrand Factor (vWF)
3. Factor 4 & 8
4. Platelet Factor 4

What alpha granule content neutralizes heparin?

Platelet factor 4

What platelet granule is present in the numbers between 2-7?

Dense granules

Color of Dense granule in osmium dye?

Black

Disorder for diminished Dense granule contents

Storage pool disorder

Organelle that contains enzymes needed for cellular cleaning and recycling of platelets

Lysosomes

What does Lysosomes stain positive with?

1. Arylsulfatase
2. B-glucuronidase
3. Acid phosphatase
4. Catalase

Functions of Lysosomes

1. Digest vessel wall matrix components during in vivo aggregation
2. Digest autophagic debris