blood #5, platelets & hemostasis - physiology
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Plateletssmall
granulated
Non-nucleated
round or oval
2 – 4 µ in diameter
150000 – 400000/mm³
life span average 8 days
detached bits from megakaryocyte
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Production of platelets is regulated by thrombopoietin secreted by
fibroblasts
endothelial cells
certain leucocytes
Normally
60 – 75 % of platelets are present in the circulating blood
25 – 40 % of platelets are present in the spleen
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Structure of platelets Granules
Golgi zone
Glycogen
Membrane
Open canalicularsystem
Dense body in
granule
Densebody
DensetubularSystem
Mitochondria
Microtubules
Microfilament
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Structure of platelets I- Plasma membrane
***plasma membrane contains
glycoprotein receptors For
Phospholipids �ُInclude
• collagen
• vessel von-Willebrand factor
• fibrinogen • platelet factor 3
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*** The plasma membrane invaginates into the interior of the platelets to form the open canalicular system
serves as a pathway
uptake of extra cellular calcium
release of intracellular substances
*** There is also a coat of glycoprotein on its surface which helps its adhesion to injured endothelium; but not to normal endothelium
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II – Platelet cytoplasm
1- Contractile proteins
actin myosinthrombosthenine
enable activated platelets to change their shape
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2- A skeleton of microtubules that keeps the disc shape of platelets
3 -Residuals of
Golgi apparatusendoplasmic reticulum
Synthesis of enzymes
Calcium store
4- Mitochondria and enzyme system for synthesis of ATP and ADP
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5 -Lyzosomes containing hydrolytic enzymes.
6 -Glycogen granules for production of energy anaerobically.
7- Enzyme system that synthesize prostaglandins
from phospholipids of the Platelet membrane.
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8 -2 types of granules
A) Dense granules b) Alpha granules
contain non-protein substances
)ATP, ADP, Ca++ and serotonin)
contain the secreted proteins
• clotting factors
• fibrin stabilizing factor XIII
• platelet derived growth factor
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HEMOSTASIS
By Prof\ Sameh ShamaaProf Of medical Oncology and
Internal medicine Mansoura Faculty Of Medicine
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HEMOSTASIS
Def:- stoppage of bleeding from the blood vessels
Mechanisms (I) v.c of blood vessels (II) platelet plug formation (III) Blood coagulation (fibrinogen fibrin)(IV) Clot retraction (V) fibrinolysis to dissolve the clot
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PRIMARY HEMOSTASIS
includes the processes that result in the formation of the platelet plug.
Necessary factors:--The blood vessels : the vessel walls esp. the
subendothelial layer.
-The platelets
-2 plasma glycoproteins :
- fibrinogen
- Willebrand factor ,which also presents inside the platelets
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Mechanisms:
1-v.c of the bl. vessel.
2 -Platelets adhesion to subendothelial layer, ( Willebrand factor is necessary for this stage)
adhesion of platelets- 3- platelets secretion:
their activation and secretion of ADP,adrenaline, noradrenaline –> aggregation & activation of other platelets.
4 -Aggregation of platelets.
5 -Formation of capillary plug.
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Coagulation of Blood
Def :- represent the conversion of fibrinogen (soluble protein) to fibrin (insoluble) meshwork which occludes the point or vessel rupture.
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First Step :Activation of factor X
BY One of 2 systems:
I-urgent system II-delayed system(Extrinsic system.) (Intrinsic system.)
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systems of coagulation I-urgent system. II-delayed systemExtrinsic system. Intrinsic system.12-20'' (seconds) 4-8' (minutes)In vivo only. In vivo & in vitroDue to tissue damage. due to contact with foreign surface
↓ ↓ Tissue factor activation of contact system ↓ ↓
X < ------------------------------------IX a < ---------------- IX↓Xa↓
2- prothrombin thrombin
3-fibrinogen Fibrin
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EXTRINSIC SYSTEM
FACTORS NICESSORY ARE:Factor XTissue factor and Factor VII
Tissue F.
VIIa VII Xa X
Blood vessel
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INTRINSIC SYSTEM
Necessary factors: - XII (Hageman factor)
- Contact system XI Kallikrene kininogene
- F. IX- F. VIII - F. X- Ca. ++- phospholipids of the platelet’s membrane
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Contact System: Foreign surface
|--------------------------------------------------| Kalierne XII kininogene
Fragmentation XIIa
XI XIa
Rest of intrinsic pathway
IX
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Rest of intrinsic pathway IX
Platelets Ca ++
IXa
X VIIIa
VIIIXa
II IIa
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Second Step: of Coagulation
Thrombin Formation: (IIa)
Factors needed:
- prothrombin (II)
- Xa
- V (acceleririe)
- phospholipids
- Ca + +
Platelets
Ca++
V,XaII
IIa
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3rd Step :Fibrin Formation
Fibrin Formation:-------------------------
(Fibrinogen) --------------------(Soluble fibrin)
IIaXIII XIIIa
Ia
Insoluble protein