3RD HEMA - PART 4 (Hemostasis, Megakaryocytopoiesis) Flashcards
Maintenance of blood flow within the vascular system.
HEMOSTASIS
Involves the following:
● Constriction of damaged blood
vessels
● Formation of platelet plugs
PRIMARY HEMOSTASIS
(2) Major participants of PRIMARY HEMOSTASIS
● Blood vessels
● Platelets
Involves the following:
● Formation of fibrin meshwork through activated coagulation
factors
● Inhibition of activated coagulation factors
SECONDARY HEMOSTASIS
Aka: thrombocytes
PLATELETS
Arise from a bone marrow cell called
megakaryocytes
● Important in both primary and
secondary hemostasis
● Described as cells with granular
cytoplasm but no clear material
PLATELETS
● __________ cluster with the RBCs near the center of the blood vessel
● _____________ move back and forth with the WBCs from the venules into the white pulp of the spleen
PLATELETS
Lifespan of the Platelets
9 days +/- 1 day
(8-10 days)
On wright-stained PBS
● Spread throughout the RBC
monolayer (7-21 cells per 100x field)
● Average diameter of 2.5um (or, 2-4 um)
PLATELETS
Aka stress platelets
RETICULATED PLATELETS
● Appear in compensation for
thrombocytopenia
● Newly released from megakaryocytes and still contain RNA
RETICULATED PLATELETS
● Potentially prothrombotic (may be associated with increased risk of cardiovascular disease)
RETICULATED PLATELETS
● Early predictor of bone marrow
recovery after chemotherapy and
transplantation
RETICULATED PLATELETS
● Markedly larger than the usual
platelets (diameter in PBS: exceeds 6um [MPV reaches 12 to 14 fL])
RETICULATED PLATELETS
● Can help differentiate bone marrow failure from peripheral destruction in thrombocytopenia
RETICULATED PLATELETS
It is believed that thrombocytes enter the ____ initially, where they remain for ____ days. After this period, thrombocytes are in either the __________ blood or in the active splenic pool
It is believed that thrombocytes enter the spleen initially, where they remain for two days. After this period, thrombocytes are in either the circulating blood or in the active splenic pool
SIZE OF THE NORMAL PLATELETS
Diameter:
2.5um (average)
Approximately __ of the total number of platelets are in the systemic circulation, while ___ of the platelets are in the spleen.
Approximately ⅔ of the total number of platelets are in the systemic circulation, while ⅓ of the platelets are in the spleen.
SIZE OF THE NORMAL PLATELETS
Mean platelet volume (MPV):
Reference range: 6.8 to 10.2 fL
_______ causes swelling of platelets (causes approximately 20% increase in MPV during the first hour)
EDTA
Should not be based on EDTA specimens that are between ___ to ___ hours old
1 to 4 hours old
If the physician is looking for the
MPV value you need to wait first for ___ hour
1 hour
According to Turgeon, if you measure the ____ right away, there might be a mistake because the platelets are still swollen.
MPV
How many platelets are to be found on a normal blood smear?
a. 7-21 platelets per 10x field
b. 7-21 platelets per 100 x field
7-21 platelets per 100 x field
What is the other name for reticulated platelet? (from rodak’s)
Stress platelets
EXAMPLES OF DISORDERS CHARACTERIZED BY SIZE
SMALL PLATELETS
(2)
- Wiskott - Aldrich Syndrome (WAS)
- TORCH infections
EXAMPLES OF DISORDERS CHARACTERIZED BY SIZE
LARGE / GIANT PLATELETS
(3)
- Bernard-Soulier Syndrome
- Gray Platelet Syndrome
- May - Hegglin Anomaly
Genetic inheritance of WISKOTT - ALDRICH SYNDROME (WAS)
X - linked recessive
Was also a White Blood Cell anomaly
WISKOTT - ALDRICH SYNDROME (WAS)
Triad of WAS: [TIE]
● Thrombocytopenia
● Immunodeficiency
● Eczema
Decreased platelet count
Thrombocytopenia
The patient also sufferers
from impaired function of
WBCs
Immunodeficiency
Genetic inheritance of BERNARD - SOULIER SYNDROME (BSS)
Autosomal Recessive (AR)
Group together due to their certain similarities, one of which is the presence of SMALL PLATELETS in the peripheral smear.
TORCH INFECTIONS
TORCH stands for
● TOXOPLASMA
● OTHER AGENTS
● RUBELLA
● CYTOMEGALOVIRUS
● HERPESVIRUS
What is the letter T in TORCH infections?
○ TOXOPLASMA
● Presence of Giant platelets
● Thrombocytopenia
BERNARD - SOULIER SYNDROME (BSS)
BERNARD - SOULIER SYNDROME (BSS)
Receptor that combine with
your platelets
Gp1b/IXb/V complex deficiency
Genetic inheritance of GRAY PLATELET SYNDROME (GPS)
Autosomal Recessive (AR)
GRAY PLATELET SYNDROME (GPS)
One of the storage pool defects
Alpha Granules deficiency
● Presence of Large Gray platelets
● Mild bleeding tendencies
● Thrombocytopenia
● Fibrosis of the marrow
GRAY PLATELET SYNDROME (GPS)
Genetic inheritance of MAY - HEGGLIN ANOMALY (MHA)
Autosomal Dominant
MYH9 MUTATIONS
Kinds
All presents
Large platelets
(4)
● Fechtner syndrome
● Sebastian syndrome
● Epstein syndrome
● MHA (May - Hegglin Anomaly)
● Variable thrombocytopenia
● Presence of spindle shaped
inclusions in WBC’s
○ Döhle-body like inclusions
MAY - HEGGLIN ANOMALY (MHA)
All of the following exhibits large platelets except:
a. Flechtner syndrome
b. Epstein syndrome
c. GPS
d. WAS
d. WAS
● Also a WBC disorder
● Presence of Döhle body like
inclusions
● Presence of Giant platelets
● Leukopenia
○ Low WBC count
MAY - HEGGLIN ANOMALY (MHA)
SHAPE OF PLATELETS
● Shape varies/state whether active or resting
● Bicon_______ - Red Blood Cell
● Bicon_______ - Platelets
● Biconcave - Red Blood Cell
● Biconvex - Platelets
All of the following are characterized by small platelets except:
a. WAS
b. Cytomegalovirus infection
c. Herpesvirus infection
d. BSS
d. BSS
Biconvex shape or
disk-shaped (small plates)
Resting and Circulating
platelets
Spherical with pseudopods
(Projections)
Activated platelets
CYTOPLASM OF PLATELETS
On a Wright Stained PBS, platelets appear
Lavender and Granular
● Chromomere and Hyalomere are two major parts of the cytoplasm
Light Microscope
Platelets are only 2-4 um
Light Microscope
● Centrally-located
● Granular
Chromomere (aka. Granulomere)
To see other minute structures of platelets like cytoskeleton and
dense tubular system
Electron Microscope
aka. Granulomere
Chromomere
● Peripherally located
● Non-granular
Hyalomere
● Size: 30-50 um
● Has a multilobated nucleus and
abundant granular cytoplasm
MEGAKARYOCYTES
Aka. Megakaryopoiesis
MEGAKARYOCYTOPOIESIS
● Process by which megakaryocytes develop in the bone marrow
● Platelets are products of Megakaryocytes
MEGAKARYOCYTOPOIESIS
Largest Cells in bone marrow
MEGAKARYOCYTES
● Less than 0.5% of all bone marrow
● On normal bone marrow smear: 2 to 4 per 10x LPF (LPO)
MEGAKARYOCYTES
In a normal bone marrow smear, how many megakaryocytes are seen?
A. 2-4 megakaryocytes/100x field
B. 2-4 megakaryocytes/10x field
B. 2-4 megakaryocytes/10x field
● Hormone that acts a platelet
production
● Major regulator of platelet production
THROMBOPOIETIN (TPO)
THROMBOPOIETIN (TPO) is primarily produced by the ________
Liver
● Possesses 23% homology with
erythropoietin (EPO)
THROMBOPOIETIN (TPO)
THROMBOPOIETIN (TPO) weight (w/unit)
70,000 dalton molecule
Coagulation factor also
produced by the _____
Liver
Concentration in plasma
● Thrombopoietin concentration in the plasma is ___________ proportional to platelet and megakaryocyte mass, suggesting that membrane binding and consequent removal of TPO by
thrombocytes is the primary platelet count control mechanism
● Thrombopoietin concentration in the plasma is inversely proportional to platelet and megakaryocyte mass, suggesting that membrane binding and consequent removal of TPO by
thrombocytes is the primary platelet count control mechanism
● Stimulates megakaryocytopoiesis (Some of the cytokines that function with it to stimulate this process include IL-3, IL-6, AND IL-11)
THROMBOPOIETIN (TPO)
● Induces the proliferation and
maturation of megakaryocytes
● Induces thrombocytopoiesis
THROMBOPOIETIN (TPO)
○ TPO receptor site present at all
maturation stages
○ From BRU-Meg to PLTs
MPL - myeloproliferative leukemia virus
How many is the megakaryocyte lineage-committed progenitor stage
3
● Least Mature
● Participate in normal mitosis
Burst-forming unit (BFU-Meg)
● Participate in normal mitosis
Colony-forming unit (CFU-Meg)
● Most Mature
● Loses its capacity to divide through normal mitosis
● Perform Endomitosis
Light-density CFU (LD-CFU-Meg)
All of these progenitors resemble:
Lymphocytes
○ Process involving nuclear and cytoplasmic division.
○ It divides forming 2 daughter cells
○ BFU-Meg and CFU-Meg
Normal Mitosis
○ Nuclear division without cytoplasmic division
○ LD-CFU-Meg
Endomitosis
Terminal Megakaryocyte Differentiation Stages
stages wherein the observers are able to recognize the unique Wright-stained morphology of the cells in bone marrow smears or H and E - stained bone marrow biopsy sections
● least differentiated
● cannot be reliably distinguished
from myeloblasts or pronormoblasts (light microscopy)
MK-I STAGE aka Megakaryoblast
● identified by the appearance of
nuclear lobularity
MK-II STAGE aka Promegakaryocyte
● begins to develop MOST of its
cytoplasmic ultrastructure (including α-granules, dense granules, and the demarcation
system (DMS))
MK-I STAGE aka Megakaryoblast
● most abundant
● easily recognized at 10X magnification
○ (basis is size: 30 to 160 μm)
MK-III STAGE
aka Megakaryocyte
● largest cell in the bone marrow
● At the full maturation of the cell, platelet shedding proceeds.
MK-III STAGE
aka Megakaryocyte
Which of the following performs platelet shedding?
a. Megakaryoblast
b. Promegakaryocyte
c. Immature megakaryocyte
d. Mature megakaryocyte
d. Mature megakaryocyte
● One megakaryocyte may shed
________-________ platelets.
2000-4000 platelets
● One megakaryocyte may shed
2000-4000 platelets.
MK-III STAGE
aka Megakaryocyte
Platelet shedding – aka:
Thrombocytopoiesis or Thrombopoiesis
○ aka Platelet Production
● ⅔ platelets from the bone marrow travels to the blood
● ⅓ platelets goes to the spleen
MK-III STAGE aka Megakaryocyte
According to Rodaks, at full maturity of the cell, a single megakaryocyte sheds about ____ to _______ platelets all in all
2000 to 4000
Nucleus
MK-I MK-II MK-III
Round - Indented - Multilobed
Nucleoli
MK-I MK-II MK-III
2 to 6 - Variable - Not visible
Chromatin
MK-I MK-II MK-III
Homogenous
Moderately condensed
Deeply and variably condensed
N:C ratio
MK-I MK-II MK-III
3:1 - 1:2 - 1:4
Mitosis
MK-I MK-II MK-III
Absent - Absent - Absent
Endomitosis
MK-I MK-II MK-III
Present - Ends - Absent
Cytoplasm
MK-I MK-II MK-III
Basophilic
Basophilic and granular
Azurophilic and granular
Demarcation System
MK-I MK-II MK-III
Present - Present - Present
Of the three, which are the precursors?
MK-I, MK-II
○ ultimately delineates individual platelets during thrombocytopoiesis
○ Though present in all megakaryocyte precursors, only one performs thrombopoiesis which is MK-III
Demarcation System
Hematopoietic cells capable of endomitosis
LD-CFU-MEG, MK-I, MK-II
The megakaryocyte progenitor that undergoes endomitosis is?
a. MK-I (Precursor)
b. BFU-MEG
c. CFU-MEG
d. LD-CFU-MEG
d. LD-CFU-MEG
studied using scanning and transmission electron microscopy, flow cytometry, and molecular sequencing
PLATELET ULTRASTRUCTURE
● selectively permeable
● provides phospholipids that support platelet activation internally and plasma coagulation externally
PLATELET PLASMA MEMBRANE
● anchored within the membrane are glycoproteins and proteoglycans
PLATELET PLASMA MEMBRANE
found in the outer, plasma layer
Neutral phospholipids
● phosphatidylcholine and
● sphingomyelin
Neutral phospholipids
support platelet activation by supplying arachidonic acid
phosphatidylinositol
found in the inner, cytoplasmic layer
Anionic or polar
phospholipids
(3) Found in the inner, cytoplasmic layer
● phosphatidylinositol
● phosphatidylethanolamine
● phosphatidylserine
flips to the outer surface upon
activation and is the charged phospholipid surface on which 2
coagulation pathway complexes assemble
phosphatidylserine
The 2 complexes are the:
TENASE complex and
PROTHROMBINASE complex
● the platelet membrane surface
● cellular ultrastructural component unique to the platelet
GLYCOCALYX
● absorbs albumin, fibrinogen, and other plasma proteins through endocytosis
GLYCOCALYX
A.k.a GP RECEPTORS
GLYCOPROTEIN PLATELET MEMBRANE RECEPTORS
Four (4) Kinds of GP Receptors:
○ GP Ia/IIa (1a, 2a)
○ GP VI (6)
○ GP Ib/IX/V (1b, 9, 5)
○ GP IIb/IIIa (2b, 3a)
vWF specific site
GP Iba
Bernard Soulier Syndrome
Thrombin cleaves a site on
GP V (5)
- Large platelets
- Autosomal Recessive
- GPIb/IX/V complex
Bernard Soulier Syndrome (BSS)
GP IIb/IIIa
Glanzmann’s thrombasthenia
A molecule that binds to another molecule
Ligand
○ Used especially to refer to a small molecule that specifically binds to a larger molecule
○ Molecules that bind to the receptor
Ligand
CAM means
Cell Adhesion Molecule
STR means
Seven- Transmembrane Repeat
Activation of Platelets
Thrombin
PAR 1
PAR 4
Activation of Platelets
Adenosine diphosphate (ADP)
P2Y1
P2Y12
Activation of Platelets
Thromboxane A2 (TXA2):
TPα and TPβ
Activation of Platelets
Epinephrine (Adrenaline)
α2-adrenergic
A product of eicosanoids pathway of the platelets
● Activates the platelets
Thromboxane A2 (TXA2)
Also called as prostacyclin
Prostaglandin I2 (PGI2)
● A product of eicosanoids pathway of the blood vessels
● Inhibitor of platelet aggregation
● Strong vasodilator
Prostaglandin I2 (PGI2)
● A low-affinity receptor for the immunoglobulin Fc portion (has a role in a perilous condition known as heparin-induced
thrombocytopenia [HIT])
FcγIIA (CD32)
Part of the platelets that receive ligand
Receptor
has a role in a perilous condition
known as
heparin-induced thrombocytopenia [HIT]
Inhibitor of Platelets
Prostaglandin I2 (PGI2)
IP
● During the platelet shape change, it also reassembles in long parallel bundles to provide rigidity to the pseudopods.
○ It must be firm/hard to prevent
the platelets from breaking apart.
MICROTUBULES
quantification by flow cytometry is a means for measuring in vivo platelet activation
P-selectin (CD 62)
● An integrin that helps platelet binding to endothelial cells, WBCs, and one another
P-selectin (CD 62)
Control platelet shape change, extension of pseudopods and section of granule contents
PLATELET CYTOSKELETON
● Found on the α-granule membranes of the resting platelet but travels via the SCCS to the surface of activated platelets
P-selectin (CD 62)
● Thick, circumferential bundles of these maintains platelet’s discoid shape
○ Helps the platelets to become
biconvex in shape.
● Reside just within, although NOT touching, the plasma membrane
MICROTUBULES
Microtubules, actin microfilaments, and intermediate
filaments
PLATELET CYTOSKELETON
Formed by Tubulins
MICROTUBULES
● Platelets become round when
microtubules disassemble in the cold. Upon warming to 37°C, they recover their original discoid shape
● It also moves inward on activation to enable expression of alpha granule contents.
MICROTUBULES
Proteins that form from the
microtubules
Tubulins
Location of MICROTUBULES
Plasma Membrane
