Platelet structure and formation Flashcards
Platelets derived from
Megakaryocytes
Function of platelets
Hemostasis
Shape of inactivated platelets
biconvex
size of platelets
2-3 micrometers in diameter
Hormone that regulates megakaryocyte and platelet formation
Thrombopoietin
Thrombopoietin is produced by
liver and kidney
How many platelets does one megakaryocyte produce
1000-3000
How many platelets are produced in an adult in a day
10 raised to the power 11
Percentage of platelets stored in the spleen at any point in time
30-40%
Why does splenic contraction occur
To release sequestered platelets through induction by sympathetic system
Why do sickle cell patient have higher platelet count
By the time they reach their teens, they undergo autosplenectomy hence platelets are released into the circulation
Average lifespan of circulating platelet
8-10 days
How are platelets destroyed
By phagocytosis by the reticular activating system
How many lobes does megakaryocyte have
multiple lobed
When is a megarkaryocyte said to be active
When it has tiny dots or platelets present on it
How many zones are platelets seperated into
4.
Peripheral zone
Sol gel zone
Membranous zone
organelle zone
POMS
What do you find in the peripheral zone
It has glycoproteins required to platelet adhesion, aggregation, activation
Sol gel zone contains
Microfilaments and microtubules which maintain discoid shape of platelet.
Under what conditions do platelets turn round
Under cold conditions when microfilaments dissasemble.
Under warm conditions they go back to their original shape
Membranous zone contains
Membranes derived from the smooth endoplasmic reticulum of megakaryocytic cells.
These membranes form a tube to the surface of the platelet membrane and synthesize and release thromboxane A2
Organelle zone contains
2 types of platelet granules.
- Alpha granules which contain clotting factors like factor V,VIII, Fibrinogen
- Delta granules or dense bodies ; Contain ADP, calcium. serotonin which are platelet activating mediators
Normal platelet count
150-450 times 10 raised to the power 9 L
Thrombocytopenia
Low platelet count
< 150 TIMES TEN RAISED TO THE POWER 9 L
Causes of thrombocytopenia( Not producing enough)
Bone marrow faluire Hereditary Marrow infiltration Chemotherapy Radiation therapy
Causes of Increased destruction of platelets
Immune thrombocytopenic purpura ( autoantibodies against platelets) DIC Von willebrands disease type 2b Heparin induced Mechanical destruction Neonatal alloinduced thrombocytopenia
Other causes of thrombocytopenia
hypersplenism drugs gestational-Increased plasma volume will affect platelets infections Hemophagocytosis
Thrombocytosis
Increased platelet count
Types of thrombocytosis
Primary
Secondary- due to a disease
Causes of primary thrombocytosis
Polycythemia vera myelofibrosis myelodysplastic syndromes chronic myeloid leukemia essential thrombocytosis
Secondary thrombocytosis
infection inflammatory disorders Acute/ chronic blood loss tissue damage from trauma/surgery medicines splenectomy malignancy rebound from chemotherapy
Spurious platelet counts
A situation where full blood count will give a false low or high platelet count
Causes of false thrombocytosis
Anything that causes red cell fragmentation so machine counts it as smaller sized platelets
burns
microangiopathic hemolytic anemia
Microorganisms
Fragments of white cells in patients with leukemia
Causes of false thrombocytopenia
Platelet aggregation by EDTA, myeloma etc.
Larger than normal platelets
Platelet satellitism where they surround WBCs and are counted as one
