Platelets & Hemostasis part 1 Flashcards
Define hemostasis.
What clotting factors are involved?
Stoppage of blood without obstruction of blood flow
–> Blood clotting factors include:
* Prothrombin
* Coagulation factors VII,
IX, X, XI, XII
What do we need for hemostasis to be successful?
We need a balance between coagulation and fibrinolysis. Want to stop blood from escaping vessels via coagulation factors.
As in the diagram shows, Hemostasis requires a balance between coagulation and
fibrinolysis. The multiple steps to reach the goal to stop the blood from scaping the
blood vessel is achieve by coagulation activation (generating thrombin that converts
fibrinogen into fibrin leading to the formation of the clot.
Who participates in this process? First there must be VASCULAR INJURY, then 1-
Vessel wall (vasoconstriction, activation of hemostasis), 2-platelets for the primary
hemostatic plug to form, and activation of coagulation pathway; 3-coagulation factors
are activated (fibrin plug formation, which is the SECONDARY hemostatic),
3
What makes hemostasis balanced?
The goal is to have a balance between enough anticoagulants and coagulants for
good hemostasis> not too much from one side or the other.
Imbalances in hemostasis can lead to?
Define primary hemostasis.
Primary hemostasis comprises: platelets and endothelium
While secondary hemostasis requires: clotting factors (coagulation cascade)
Define secondary hemostasis.
While secondary hemostasis requires: clotting factors (coagulation cascade)
What cells are pictured here?
Platelets
Label the image accordingly
Activated and non-activated platelets on a blood vessel
endothelia cell surface, scanning electron micrograph (SEM)
What can be seen below?
Platelets morphology
* 2-4um
* anucleated
* Blue cytoplasm & reddish cytoplasmic granules
* Alpha and dense granules
Label the image accordingly
What are Alpha granules?
Located within platelets
a) Alpha granules
* Seen in blood smears
* Contain coagulation factors & proteins:
* Fibrinogen,
* Factor V,
* vWF, thrombospondin,
* Platelet-derived-growth factor (PDFG)
What are Dense granules?
located within platelets
Thrombocytes (non-mammalian species)
* Equivalent to platelets in non-mammalian species:
* Round dense nucleus
* Clear cytoplasm (small amounts)
Megakaryocyte and platelet formation, scanning electron
micrograph (SEM).
Newly formed platelet after megakaryocyte differentiation,
scanning electron micrograph (SEM).
Platelets come from megakaryoblast, as these megakaryoblast “mature” to
megakaryocytes they become LARGE
Megakaryocytes are only present in Bone marrow
Where are platelets produced?
- Platelets are produced by megakaryocytes in bone marrow
What are Megakaryocytes?
§ Megakaryocytes are large cells with abundant cytoplasm
§ Present only in bone marrow sinus
§ they replicate the DNA without cell division (endomitosis)
What is an important physical characteristic of Megakaryocytes?
- Megakaryocyte have extensions called ”proplatelets” processes extend into sinus lumen –>
individual platelets - Maturation time: megakaryoblast to platelet release ~4-5 d
Thrombopoiesis is regulated by?
- Thrombopoiesis Regulated by: thrombopoietin (TPO)
- Production & differentiation
- Produced continually by: Liver, also kidney, muscle
- Platelets circulating lifespan 5-9 days
- 30-40% of circulating platelets mass is found in: spleen
Thrombopoietin (TPO) regulates the production and differentiation
TPO is produced by hepatocytes in liver, also comes from kidney and muscle
Platelets last in circulation about a week and interestingly 30-40% of circulating
platelets are found in the spleen
Activated platelets. Colored scanning electron micrograph
(SEM) of activated platelets attached to surgical gauz
What is the function of platelelts?
- Primary hemostasis (vasoconstriction and platelet plug formation)
a. Adhesion
b. Activation
c. Aggregation
d. Granule secretion
All to promote hemostasis - Secondary hemostasis
- Others: clot retraction, inflammation
There are 3 main functions: hemostasis (clot formation) and thrombosis, there are
other functions beyond hemostasis like Clot retraction, FYI: inflammation. We will
cover the secondary hemostasis on part 2 of hemostasis.
How are primary and secondary hemostasis related?
- These 2 processes happen simultaneously and are mechanistically
intertwined - Imbalances due to a defect –>:
- thrombosis (too much clotting)
- bleeding (not enough clotting)
If there is out balance due to a defect in on theses systems, then there will either be:
thrombosis (too much clotting) or bleeding (not enough clotting)
How long does it take for the primary hemostatic plug to form? Explain what happens.
Formation of this primary hemostatic plug takes ~3-5 min
* Platelets adhere to endothelium
* Platelets undergo activation
* Aggregate to form a platelet plug
So lets review this primary hemostasis process and what it involves from the platelet
to reach the goal of hemostasis
Simplified, primary hemostasis is the platelet adhesion and their activation to
produced a platelet plug to stop the bleeding.
How is this activated?