1.4.2 The Formation of the Interstitial Fluid and Lymph

The Formation of the Interstitial Fluid and Lymph
1. The blood from the arteries flows at a high pressure into the blood capillaries.
2. The high hydrostatic pressure in the capillaries forces the blood plasma to 
    leak out through the capillary walls into the space between the body cells.
3. The fluids that fill up the spaces between the cells is called tissue fluid or 
    interstitial fluid.
4. The interstitial fluid is made up of water, digested food, gases, hormones, 
    waste products, and small proteins from the blood.
5. The larger molecules like erythrocytes, platelets and plasma proteins 
    cannot pass through the capillary walls. Leucocytescan squeeze into the fine 
    pores between the capillary walls and pass through it.

6. The exchange of substances between the blood capillaries and the body cells 
    occurs in the interstitial fluid.
    (a)  Nutrients and oxygen diffuse from the blood through the interstitial fluid 
         into the body cells.
    (b)  Carbon dioxide and other waste products diffuse from the body cells 
          through the interstitial fluid into the blood.
7. There are two ways the interstitial fluid is returned to the circulatory system:
    (a)  About 90% of the interstitial fluid diffuses back into the blood 
         capillaries because the pressure in the capillary end of the venule is 
         lower than the arteriole end.
    (b)  The remaining 10%of the fluid diffuses into the lymph capillaries of the 
          lymphatic system. The fluid in the lymphatic vessels is known is 
          lymphEventually, the lymph will return to the circulatory system when 
          it flows into the subclavian veins in the shoulder.

1.4 The Lymphatic System

  1. The lymphatic system is part of the circulatory system, comprising a network of conduits called lymphatic vessels that carry a clear fluid called lymph directionally towards the heart.
  2. The lymphatic system consist of
    1. lymophatic vessels
    2. lymphatic capillaries
    3. lymph nodes
    4. spleen
    5. thymus

1.3.2 Consequences of Blood Clotting Related Problem


  1. Haemophilia is a group of hereditary genetic disorders that impair the body's ability to control blood clotting or coagulation.
  2. As a result, minor injuries and internal bleeding can results in death owing to excessive loss of blood.


  1. Thrombosis is the formation of a blood clot (thrombus) inside a blood vessel, obstructing the flow of blood through the circulatory system.
  2. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss.
  3. However, when a blood vessel is not injured, blood clots may form in the body under certain conditions such as a defective blood vessel causes the blood clotting factors to be released into the blood.
  4. When a blood clot can cause obstruction to the blood flow.
  5. If clotting occurs in the coronary artery, it is called coronary thrombosis. Coronary thrombosis can cause a heart attack.
  6. If it occurs in the artery in the brain, it will cause a stroke.
  7. Thrombosis may also cause atherosclerosis, which is the deposition of fat and cholesterol on the walls of arteries.

1.3.1 Mechanism of Blood Clotting

The figure below shows the mechanism of blood clotting.

  1. When a blood vessel is damaged, platelets will gather around the wound and coagulate.
  2. At the same time, an enzyme called thrombokinase will be released.
  3. Thrombokinase will convert the inactive prothrombin to the active thrombin.
  4. The thrombin will then catalyses the soluble fibrinogen to the insoluble fibrin.
  5. Fibrin will form a fibrous network to trap the blood cells and form the blood clot.

1.3 Blood Clotting


  1. Hemostasis is a process which causes bleeding to stop and keep blood within a damaged blood vessel. It is the first stage of wound healing.
  2. Blood clotting is an important part of hemostasis, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel.

Significant of Blood Clotting