Book contents
- Frontmatter
- Contents
- 1 What is disease?
- 2 Understanding the immune system
- 3 The control of bleeding
- 4 Heart disease
- 5 Physiological effects of exercise
- 6 Food and health
- 7 Diseases of the gaseous exchange system
- 8 Kidney failure
- 9 Fertility and contraception
- 10 The brain: memory, ageing and the effects of drugs
- 11 Medical genetics
- 12 Biotechnology and medicine
- Index
3 - The control of bleeding
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- 1 What is disease?
- 2 Understanding the immune system
- 3 The control of bleeding
- 4 Heart disease
- 5 Physiological effects of exercise
- 6 Food and health
- 7 Diseases of the gaseous exchange system
- 8 Kidney failure
- 9 Fertility and contraception
- 10 The brain: memory, ageing and the effects of drugs
- 11 Medical genetics
- 12 Biotechnology and medicine
- Index
Summary
A cut is the signal that begins a series of events which eventually stops the bleeding:
constriction of the ends of the damaged blood vessels reduces the loss of blood;
clotting – blood leaking from damaged blood vessels solidifies and forms a clot which plugs the wound, sealing it against infection from pathogens.
Blood clotting
The release of certain substances into the blood plasma begins the process of clotting. Serotonin (5-hydroxytryptamine) causes constriction of the damaged blood vessels. Other substances react with blood factors in the plasma, beginning a cascade of at least 15 chemical reactions that ends with the soluble plasma protein fibrinogen changing into insoluble fibrin. Figure 3.1 shows the process of clot formation. Production of the lipoprotein thromboplastin is a key stage in the process. It requires various substances including factor VIII in the plasma. Thromboplastin originates from:
damaged tissues outside the blood vessels (the extrinsic mechanism);
platelets in the blood (the intrinsic mechanism).
Whether thromboplastin is extrinsic or intrinsic in origin, different blood clotting factors including calcium ions (Ca2+– factor IV) are required for it to convert the inactive blood protein prothrombin from the liver into its active form thrombin. Thrombin acts on fibrinogen (also produced in the liver), converting it to insoluble fibrin. The fibrin forms a mesh of fibres across the wound and traps red cells and platelets, forming a plug-like clot.
- Type
- Chapter
- Information
- Medical Physiology , pp. 35 - 38Publisher: Cambridge University PressPrint publication year: 1997