Physiology of Blood
Platelets
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Small granulated non-nucleated bodies
2-4 micron in diameter
Life span….. 8 days
Count…300,000/mm3
Hemostasis
It is a prevention of blood loss after injury
Mechanism
1. Constriction of the blood vessel .
local myogenic contraction, nervous reflex & local
factors ( serotonin, ADP ,thromboxane A2)
2. Formation of platelet plug
3. Conversion of platelet plug to a definitive clot by
fibrin threads ( blood clot)
4. Dissolution of the clot by plasmin after tissue repair
2- Platelet plug formation
Platelet reactions
1- Platelet adhesion ( to subendothelial collagenneeds von-Willebrand factor)
2- Platelet activation ( swell& change the shape)
3- Platelet release reaction ( Ca2+ ,coagualtion
factors, serotonin, thromboxane A2........
4- Platelet aggregation ( platelet plug)
5- Platelet procoagulant activity ( activation of coagulation
factors)
6- Platelet fusion ( fusion of aggregated platelets)
3- Formation of blood clot
(Mechanism of blood coagulation)
Intrinsic pathway
subendothelial collagen
Extrinsic pathway
tissue injury
FXII
Tissue thromboplastin FIII
FVII
FXI
FIX
FVIII, Ca,Pl
Pl,Ca2+
active FX
FX
Pl, FV, Ca2+
Prothrombin
thrombin
Fibrinogen
Fibrin
Coagulation factors
• Plasma proteins synthesized by the liver
• Most are known by capital Roman numerals
• Inactive serine protease enzymes which when
activated lead to activation of other factors in
a cascade effect
4- Dissolution of the clot by plasmin after tissue
repair
Plasmin ( fibrinolysin)
• Plasmin is formed from inactive plasminogen by the
action of tissue plasminogen activator TPA &
thrombin
• Plasmin lyses fibrin & fibrinogen into fibrinogen
degradation products
Anticlotting mechanisms
General limiting reactions…smooth endothelium, rapid
blood flow, heparin, liver
Specific limiting reaction
• Prostacyclin # thromboxane A2
• Antithrombin III …… inhibits F IX, X, XI, XII
• Protein C & protein S ….inhibit F V & VIII
• Fibrinolytic system ( plasmin)……lyses of fibrin
Anticoagulants ( heparin , dicumarol )
In vitro anticoagulants……precipitation of Ca 2+
,silicon coated tubes & heparin
In vivo anticoagulants …….. Heparin & dicumarol
Anticoagulant
origin
heparin
dicumarol
Mast cells & basophiles
Plant
Mode of action Facilitates ant thrombin III
Inhibit vitamin K
Site of action
In vivo & in vitro
Only in vivo
Onset
rapid
slow
Duration
short
long
Administration
Iv, im
Orally
antidote
Protamin sulphat
Vitamin K
Abnormalities of hemostasis
Thrombocytopenic purpura
Decreased platelet count
Subcutaneous hemorrhage
Plonged bleeding time
Vitamin k deficiency
vit K is important for formation of factors II,VII, ,IX, X in the liver
It is a fat soluble vitamin & is formed by intestinal flora
Its absorption is decreased in obstruction of bile duct
Hemophilia
Congenital sex-linked disease transmitted by females to males
Characterized by sever bleeding after trauma
It is due to absence of factor VIII or IX or XI
White blood cells
4000-11000
Granulocytes
Neutrophils----50-70%
ingest & kill bacteria
Agranulocytes
Lymphocytes 20-40%
immunity
Esinophils 1-4 %
parasites & allergy
Monocytes 2-8%
tissue macrophage
Basophils 0.5%
histamine & heparin
Immunity
Specific
Non specific
•Doesn't’ depend on antigen type
•Mechanical & chemical barriers
•Cells
phagocytes & macrophages
natural killer cells
•Complement
•interferon
Humoral
Antibody- mediated
Bacteria
B-lymphocytes
(antibodies)
Antigen specific
lymphocytes
Cellular
Cell-mediated
Virus
Antigen presenting cells
T-lymphocytes