Platelet Structure And Function Flashcards
Where are megakaryocytes found?
Only in bone marrow and not in peripheral blood
Largest cell in the bone marrow
Megakaryocytes
Megakaryocyte mission is to proliferate and release fragments of _____________ Into circulation. 
Cytoplasm (Platelets) 
 Megakaryocytopoiesis Is controlled by growth factors such as….
Interleukins and thrombopoietin (TPO, a renal hormone)
From the kidneys (Also from liver and spleen) Is a major growth factor for megakaryocytic progenitor cells to mature and release Platelets
Thrombopietin (TPO) 
What is the old name for platelets?
Thrombocytes
What is the normal platelet range? 
150 to 450,000 µL
Where are megakaryoblasts or MK-I found? 
In bone marrow only
megakaryoblasts or MK-I nucleus undergoes __________. 
Endomitosis
megakaryoblasts (MK-I) nucleus…
Overlapping nuclear lobes (Can only see one)
megakaryoblasts (MK-I) cytoplasm…
Contain scanty, blue cytoplasm, and no granules yet*
megakaryoblasts (MK-I) N:C ratio is _______
High
megakaryoblasts (MK-I) size?
14 to 18 micrometers
can megakaryoblasts (MK-I) be classified by visual morphology? 
No! Cannot be classified by visual morphology alone! 
How to Promegakaryocytes (MK-2) composite to megakaryoblasts (MK-I) in size?
Larger (14 to 30 µm) 
- an exception to the rule that older cells get smaller
Promegakaryocytes (MK-2) nucleus…
Becomes lobulated or indented
Promegakaryocytes (MK-2) N:C ratio?
Moderate 
Promegakaryocytes (MK-2) cytoplasm?
Begins to develop dense, alpha and lysosomal granules (Red-pink)
Promegakaryocytes (MK-2):
demarcating membrane system (DMS) develops; Importance?
Forms eventual “perforations” where platelets break off
The largest cell in the bone marrow? What’s the size? 
Basophilic/granular megakaryocyte (MK-3)
16 to 56 µm
Basophilic/granular megakaryocyte (MK-3) N:C ratio?
Moderate
Basophilic/granular megakaryocyte (MK-3) nucleus…
Intensely lobulated
Basophilic/granular megakaryocyte (MK-3) cytoplasm…
Has distinct granulation (Eosinophilic and granular)
what do Basophilic/granular megakaryocyte (MK-3) have on their surface?
Various platelet specific receptors expressed
At what stage is shedding of platelets?
Mature megakaryocyte
Mature megakaryocyte nucleus….
Multi lobed nucleus
Mature megakaryocyte N:C ratio?
Low
Mature megakaryocyte cytoplasm…
-basophilia of cytoplasm has disappeared
-pink granules in the cytoplasm are now clustered into small aggregates called platelet fields
Pink granules in the cytoplasm of mature megakaryocytes that cluster into small aggregates are called….
Platelet fields
Mature Megakaryocytes buds/sheds between ____________ cytoplasmic Fragments which become the platelets
2000 to 4000
Maturation time from blast stage to platelet formation is typically _____ days. 
5
Normal marrow contains approximately __________ Megakaryocytes
15 million
Normal circulation life of a platelet is ______ days 
8 to 10
Platelets are removed or destroyed by ______________ In the liver and spleen, or by active use. 
Macrophages
Circulating platelets are distributed between the spleen and blood. What proportion is always in the spleen? 
1/3
Under normal conditions, the platelet count or mass is consistent even with active use. What does this indicate?
A feedback system adjust production to consumption
_______ stimulates production of platelets
TPO
___________ activates platelets.
Thrombin
A single megakaryocyte may shed _________ Platelets
2000 to 4000
___________ is the primary serine protease of coagulation. 
Thrombin
