Changes

==Vascular Responses==

==Vascular Responses==

There are several possible vascular responses, of which one or more may be recruited in normal haemostasis.

There are several possible vascular responses, of which one or more may be recruited in normal haemostasis.

The plasma and tissue (intrinsic and extrinsic) components combine to produce thrombin which releases ADP from platelets in order to recruit more platelets to the plug.

The plasma and tissue (intrinsic and extrinsic) components combine to produce thrombin which releases ADP from platelets in order to recruit more platelets to the plug.

==Platelet factors==

==Platelet Responses==

Platelet responses are critical in maintaining haemostasis. When platelets are activated, the haemostatic plug is formed. Regulation by thrombosthenin gives clot organisation and fibrin formation; the clot continues to organise and contract over the 3-5 days following formation.   

Platelet responses are critical in maintaining haemostasis. When platelets are activated, the haemostatic plug is formed. Regulation by thrombosthenin gives clot organisation and fibrin formation; the clot continues to organise and contract over the 3-5 days following formation.   

A series of events activates platelets to allow them to form the haemostatic plug:

A series of events activates platelets to allow them to form the haemostatic plug:

===Adhesion===

===Adhesion===

The first stage in platelet activation is an increase in the adhesiveness of platelets which may be initiated by several scenarios:

The first stage in platelet activation is an increase in the adhesiveness of platelets which may be initiated by several scenarios:

[[Granulation Tissue|Granulation tissue]] is formed within 3 days, and permanent repair, either functional or non-functional, occurs in around 1 week.

[[Granulation Tissue|Granulation tissue]] is formed within 3 days, and permanent repair, either functional or non-functional, occurs in around 1 week.

==Factors Affecting Coagulation==

==Regulation of Coagulation==

The blood coagulation process is beneficial, as it is designed to minimise blood loss, however, if the mechanism is prematurely or inadvertently triggered or fibrin deposition becomes excessive, the blood vessels may become obstructed. There is an inhibition system to guard against the  cascade being inappropriately triggered, and a mechanism to remove clots once their purpose has been achieved - ([[Haemostasis -  Pathology#Fibrinolysis|fibrinolysis]]). Normally there is a dynamic equilibrium between clotting and fibrinolysis so that the vascular system is guarded from the two principal hazards - [[Haemorrhage - Pathology|haemorrhage]] and excessive clotting.

The blood coagulation process is beneficial, as it is designed to minimise blood loss, however, if the mechanism is prematurely or inadvertently triggered or fibrin deposition becomes excessive, the blood vessels may become obstructed. There is an inhibition system to guard against the  cascade being inappropriately triggered, and a mechanism to remove clots once their purpose has been achieved - ([[Haemostasis -  Pathology#Fibrinolysis|fibrinolysis]]). Normally there is a dynamic equilibrium between clotting and fibrinolysis so that the vascular system is guarded from the two principal hazards - [[Haemorrhage - Pathology|haemorrhage]] and excessive clotting.

==Natural Inhibitors==

===Natural Inhibitors===

A number of factors act on the clot within a few minutes, limiting excessive clot formation:

A number of factors act on the clot within a few minutes, limiting excessive clot formation:

*Antithrombins reduce the level of free thrombin and absorb thrombin from fibrin strands.  The most important antithrombin is antithrombin III.

*Antithrombins reduce the level of free thrombin and absorb thrombin from fibrin strands.  The most important antithrombin is antithrombin III.

*Free thrombin negative feedback - high levels of free thrombin destroys activated Factor VIII.

*Free thrombin negative feedback - high levels of free thrombin destroys activated Factor VIII.

====Enhancement of Coagulation====

===Increased Coagulation - haemorrhagic shock syndrome==

Coagulants enhance the clotting process - the most commonly encountered coagulants are toxins such as snake venoms. Some venoms have a thrombin-like activity whereas other venoms have a plasma thromboplastin-like effect.

Coagulants enhance the clotting process - the most commonly encountered coagulants are toxins such as snake venoms. Some venoms have a thrombin-like activity whereas other venoms have a plasma thromboplastin-like effect. Some snakes (Russell's viper, Malayan Pit viper) induce defibrination.  

===Fibrinolysis===

===Fibrinolysis===

==Other systems involved in haemostasis:==

==Other systems involved in haemostasis:==

 

Activation  of the blood coagulation cascade often activates, or is accompanied by the activation of other systems. This  appears to be largely the result of activating Factor XII (the Hageman  factor) - i.e. the initiation of  plasma thromboplastin.

<p>Activation  of the blood coagulation cascade often activates, or is accompanied by the activation of other systems. This  appears to be largely the result of activating Factor XII (the Hageman  factor) - i.e. the initiation of  plasma thromboplastin.</p>

===Kinin system===

===Kinin system===

Usually this system is associated with inflammatory reactions.   

Usually this system is associated with inflammatory reactions.   

*Inactive kininogen (a 2-globulin fraction of plasma) is activated by plasmin and kallikreins.

*Inactive kininogen (a 2-globulin fraction of plasma) is activated by plasmin and kallikreins which increases vascular permeability and leucocyte migration and may give rise to the pain sensation.

*Increases vascular permeability

*Increases leucocyte migration

*May give the pain sensation

===The Complement System===

===The Complement System===

* Antigen-antibody complexes

* Antigen-antibody complexes

* Thrombin

* Thrombin

[[Category:Haemostasis|A]]

[[Category:Haemostasis|A]]