Question

Draw all 4 pathways to describe how they fire when Johnny gets a bruise on his abdomen while playing a sport.

Answer 1

A Bruise or Contusion is characterized by localized internal bleeding that extravasates into the interstitial tissue due to injury to capillaries. Skin is usually intact and hence there are low chances of infection after a bruise. Color changes of bruise are helpful in determining the age and time required for healing and resolution. Bruise formation and resolution can be summarized under the following heads:

1. Vasoconstriction

2. Primary Hemostasis: Formation of platelet plug

3. Secondary hemostasis: Coagulation cascade

4. Removal of clot or Fibrinolysis

1. Vasoconstriction occurs immediately after injury to the vessel. Endothelium of the damaged capillary releases a hormone endothelin which causes causes vasoconstriction of blood vessel (vasoconstriction) to minimize further bleeding.

2. Damage to capillary endothelium also causes release of von Willebrand factor that triggers primary hemostasis by platelet plug formation. It consists of Platelet adhesion and activation, Platelet release reaction causing further vasoconstriction due to release of serotonin and Thromboxane A₂, Platelet aggregation by ADP, and Pro-coagulant activity.

3. Secondary hemostasis is taken care by coagulation pathways. This involves both intrinsic and extrinsic coagulation pathways. Both pathways ultimately lead to Factor X which activates prothrombin into thrombin which in turn converts fibrinogen into fibrin. Fibrin helps in the formation of a stable clot by reinforcing platelet plug. Once a clot is formed, it plugs the ruptured area of the vessel and thus stops blood loss.

4. Red blood cells escape capillaries and enter extracellular space where the hemoglobin content is broken down by macrophages. This reaction causes color change of bruise. A bruise may appear red-blue (hemoglobin), green (biliverdin), yellow (bilirubin) or golden-brown (hemosiderin).