blood #5, platelets & hemostasis - physiology
DESCRIPTION
TRANSCRIPT
Plateletssmall
granulated
Non-nucleated
round or oval
2 – 4 µ in diameter
150000 – 400000/mm³
life span average 8 days
detached bits from megakaryocyte
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
Structure of platelets Granules
Golgi zone
Glycogen
Membrane
Open canalicularsystem
Dense body in
granule
Densebody
DensetubularSystem
Mitochondria
Microtubules
Microfilament
Structure of platelets I- Plasma membrane
***plasma membrane contains
glycoprotein receptors For
Phospholipids �ُInclude
• collagen
• vessel von-Willebrand factor
• fibrinogen • platelet factor 3
*** 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
II – Platelet cytoplasm
1- Contractile proteins
actin myosinthrombosthenine
enable activated platelets to change their shape
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
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.
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
HEMOSTASIS
By Prof\ Sameh ShamaaProf Of medical Oncology and
Internal medicine Mansoura Faculty Of Medicine
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
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
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.
Coagulation of Blood
Def :- represent the conversion of fibrinogen (soluble protein) to fibrin (insoluble) meshwork which occludes the point or vessel rupture.
First Step :Activation of factor X
BY One of 2 systems:
I-urgent system II-delayed system(Extrinsic system.) (Intrinsic system.)
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
EXTRINSIC SYSTEM
FACTORS NICESSORY ARE:Factor XTissue factor and Factor VII
Tissue F.
VIIa VII Xa X
Blood vessel
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
Contact System: Foreign surface
|--------------------------------------------------| Kalierne XII kininogene
Fragmentation XIIa
XI XIa
Rest of intrinsic pathway
IX
Rest of intrinsic pathway IX
Platelets Ca ++
IXa
X VIIIa
VIIIXa
II IIa
Second Step: of Coagulation
Thrombin Formation: (IIa)
Factors needed:
- prothrombin (II)
- Xa
- V (acceleririe)
- phospholipids
- Ca + +
Platelets
Ca++
V,XaII
IIa
3rd Step :Fibrin Formation
Fibrin Formation:-------------------------
(Fibrinogen) --------------------(Soluble fibrin)
IIaXIII XIIIa
Ia
Insoluble protein