IB Biology Topic C3.2.3: Sealing of Cuts in Skin by Blood Clotting Notes

Blood Clotting Seals a Wound to Block Blood Loss and Infection

Why Clotting Matters

1. Prevents blood loss: without clotting, even a small cut could cause dangerous bleeding.
2. Protects against infection: the clot acts as a barrier that keeps pathogens out until the skin heals.

Platelets Trigger Clotting the Moment a Vessel Is Damaged

The First Steps at the Wound

1. Platelet activation: platelets, small cell fragments, rush to the injury site.
2. Temporary plug: they stick together to form a plug that slows the bleeding.
3. Release of clotting factors: platelets release chemicals that start a cascade of reactions to build a stable clot.

The Clotting Cascade Turns Fibrinogen Into a Fibrin Mesh

1. Thrombin activation: clotting factors convert the inactive enzyme prothrombin into active thrombin.
2. Fibrin formation: thrombin converts soluble fibrinogen into insoluble fibrin.
3. Mesh creation: fibrin strands form a mesh that traps red blood cells and platelets into a stable clot.

Fibrin Polymerises Into a Net That Holds the Clot Together

1. Conversion to fibrin: thrombin snips fibrinogen so the fibrin units can link together.
2. Formation of a mesh: the fibrin units join into long strands that cover the wound.
3. Trapping of cells: the mesh traps red blood cells and platelets, forming a stable clot.

The Clot Dries Into a Scab While New Skin Grows Beneath

1. Clot hardening: the soft clot dries in the air and hardens into a scab.
2. Tissue repair: new skin cells grow underneath the scab.
3. Scab shedding: once healing is done, the scab falls off to reveal healthy skin.

Understanding Clotting Guides Real Medical Treatments

1. Bleeding disorders: understanding clotting helps treat conditions like haemophilia and deep vein thrombosis.
2. Surgery: surgeons use clotting agents to control bleeding during operations.