Biology Form 5: Chapter 1

1.4 Lymphatic system

1. Blood that enters the arterial end of a capillary is under high pressure.2. The pressure is sufficient to cause fluid to leak continuously from the blood into the spaces between the cells.3. Interstitial fluid:a) fills the spaces between the cells and constanly bathes the cells.b) important to cells because it is through this fluid that exchange of materials between blood capillaries and cells occurs.c) Nutrients and oxygen diffuse from the blood through the interstitial fluid into body cells.d) Waste products and carbon dioxide from body cells through the interstitial fluid into the blood.e) consists of water, leucocytes, dissolved nutrients, hormones, waste products, gases and small proteins from the blood.4. Blood plasma at the venous end of the capillary is hypertonic compared to the surrounding interstitial fluid. Blood pressure is also much lower at the venous end of the capillary.5. As a result, water, mineral salts and waste products flow back into the capillary.6. 85% of the fluid that leaves the blood at the arterial end of the capillary re-enters at the venous end.7. The fluid must be returned to the circulatory system to maintain normal blood pressure.

8. 15% of the fluid returns to the blood through the lymphatic system.

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Biology Form 5: Chapter 1

The structure of the lymphatic system

1. The lymphatic system collects most of the excess interstitial fluid from the spaces between the cells and returns it to the circulatory system.

2. The lymphatic system is a network of lymph capillaries and larger vessels.

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Biology Form 5: Chapter 1

3. Lymph capillaries:a) blind-ended tubes.b) located in the spaces between the cells.c) channels interstitial fluid which is not absorbed into the bloodstream.4. The lymph capillaries unite to form lymphatic vessels.5. Lymphatic vessels:a) has one way valves that ensure the continuous flow of the lymph away from the tissues and prevent back flow of lymph.6. Lymph nodes:a) located at intervals along the lymphatic vessels.b) produce and store lymphocytes.c) help to defend the body against infection.

6. From the lymphatic vessels, lymph eventually passes intoa) thoracic duct – receives lymph from the left of the head, neck and chest, the left upper limb and the entire body below the ribs.- empties its lymph into left subclavian veinb) right lymphatic duct – receives lymph from the right arm, shoulder area, and the right side of the head and neck.- empties its lymph into right subclavian vein7. Lymph moves toward the subclavian veins with the help of a) one-way valvesb) muscular contractionc) intestinal movementsd) pressure changes that occur during inhalation and exhalation.

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Biology Form 5: Chapter 1

The role of the lymphatic system in transport 1. Maintain the balance of fluid in the body by carrying excess interstitial fluid back to the bloodstream.2. Prevents oedema – excessive accumulation of interstitial fluid in the spaces between the cells caused by a blocked lymphatic vessel.3. Lipids and fat soluble vitamins are transported to the bloodstream via lacteals (lymph capillaries) in the villi.

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