Bleeding & clotting disorders

BLEEDING AND CLOTTING DISORDERS

a biological process that stops bleeding.

Hemostasis

it can be divided into four general phases:
the vascular phase
the platelet phase
the coagulation cascade phase: consisting of intrinsic, extrinsic, and common pathways
and the fibrinolytic phase.

The first three phases are the principal mechanisms that stop the loss of blood after vascular injury.
Fibrinolysis is the major means of disposing of fibrin after its hemostatic function has been fulfilled.

After tissue injury, there is an immediate reflex vasoconstriction that may alone be hemostatic in small vessels. Reactants such as sertonin histamine, prostaglandins, and other materials are vasoactive and produce vasoconstriction of the microvascular bed in the area of the injury.



Vascular phase

The first step in healing a wound is the activation of platelets. When platelets touch the damaged wall of a blood vessel, they become "sticky". They bind to the injured cells in a wound as well as to each other.
During this activation process, the platelets become more rounded in shape and develop spikes.
Platelet phase

Activated platelets form a platelet plug, that covers and fills a wound. The plug temporarily stops bleeding and is a very helpful emergency response to a wound.

But it is weak and may be removed by flowing blood unless it's strengthened by a blood clot.

It is often classified into three pathways;

the extrinsic pathway,
the intrinsic pathway,
and the common pathway.

The coagulation cascade phase

extrinsic pathway

is triggered by a chemical called tissue factor that is released by damaged cells. This pathway is "extrinsic" because it's initiated by a factor outside the blood vessels.


intrinsic pathway

is triggered by blood coming into contact with collagen fibers in the broken wall of a blood vessel. It's "intrinsic" because it's initiated by a factor inside the blood vessel.

Both pathways eventually produce a prothrombin activator.

The prothrombin activator triggers the common pathway

common pathway

in which prothrombin becomes thrombin followed by the conversion of fibrinogen to fibrin.

The liver must be able to use Vitamin K to produce Factors II, VII, IX, and X.

When a blood clot has served its function and the tissue underneath it has been repaired, the clot needs to be removed. In addition, it's important that any clots inside a blood vessel don't become large enough to block the vessel. Fortunately, the body is able to deal with these problems.

Fibrinolysis phase

Fibrinolysis
is the process in which fibrin is destroyed by an enzyme called plasmin.
Plasmin cuts the fibrin threads up into smaller pieces, which can then be further broken up by other enzymes and removed from the body in the urine.

BLEEDING AND CLOTTING DISORDERS

Clinical manifestations of bleeding disorders can involve various systems, depending on the extent and type of disease.

Individuals with mild disease may present with no clinical signs

Clinical Manifestations

individuals may present with petechiae, ecchymosis, hematoma, or jaundice.

hemarthroses of major joints may affect severe hemophiliacs and result in disability or death

The two clinical tests used to evaluate primary hemostasis are

the platelet count
and bleeding time (BT

Clinical Laboratory Tests

. Normal platelet counts are 150,000 to 450,000/mm3
. Surgical or traumatic hemorrhage is more likely with platelet counts below 50,000/mm3.
the platelet count

. Disorders of platelet quantity may result in

hepatosplenomegaly
spontaneous gingival bleeding
and risk of hemorrhagic stroke

Bleeding time is the interval between the moment when bleeding starts and the moment when bleeding stops.

Normal bleeding time is into 2-9 minutes.

Bleeding time

Clotting time

is the interval between the moment when bleeding starts and the moment when the fibrin thread is first seen.
Normal value is 8-15 minutes.

Bleeding time and clotting time are not the same.

Bleeding time depends on the integrity of platelets and vessel walls, whereas clotting time depends on the availability of coagulation factors.


In coagulation disorders like haemophilia, clotting time is prolonged but bleeding time remains normal.

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