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