Leaving Certificate Agricultural Science

1. Leaving Certificate Agricultural Science The Lymphatic System

2. Introduction • The lymphatic system consists of : • Lymphatic Vessels that carry lymph (clear watery liquid formed from tissue fluid) • Lymph tissue called lymph nodes. • Lymph nodes are often called glands. • The spleen, tonsils (lymph nodes in the throat) and thymus are also considered part of the Lymphatic System.

4. Functions of the Lymphatic System • The functions of the Lymphatic System are • Drainage – returns extra cellular (leaked) fluid to the blood • Transport – lipid (fats and oils) are absorbed from the small intestine and carried to the skin or other organs for storage. • Defence – filters blood. Germs that enter the blood or tissue fluid will pass through the lymph and lymph nodes, where WBC’s attack and destroy them. Swollen glands are actively fighting infection.

5. Formation of Lymph • When blood is pumped by the heart under high pressure, some plasma leaks out of the capillaries and into the space around the cells. • This extra-cellular fluid is collected by vessels called lymphatics. • The lymph moves along through the lymphatics by the action of our muscles. • Valves prevent the backflow of lymph in these vessels. • The direction of flow is controlled by valves in the lymph nodes (found in the groin, armpits etc). • These lymph nodes are also areas of lymphocyte action and can swell when the body is infected with a pathogen. • All lymph joins the blood stream in the Vena Cava just before entering the heart.

6. Immunity • Immunity is the ability of an organism to resist infection. • Pathogens are micro-organisms that can cause a disease. • Your have two types of defence system: General and Specific. • There are a number of types of immunity. • Natural, Acquired, Artificial and Passive.

8. Natural Immunity • Skin provides a physical barrier • Mucus in our lungs trap germs • Cilia in our lungs remove the mucus • Acid in our stomach kill bacteria • Enzymes in our tears protect the eye • Platelets seal damaged blood vessels • White Blood Cells eat germs.

9. Acquired Immunity • Acquired immunity arises when an organism makes it own antibodies. • Antibodies are Y shaped proteins, which attach onto antigens (pathogens). • Each antibody is specific to one type of antigen. • Should an infection occur, lymphocytes rush to the area of infection and start producing antibodies. • It usually takes a couple of days for the right antibody to be produced that will match the invading antigen.

10. Acquired Immunity - 2 • Once a match is found, that lymphocyte is triggered to multiply. • This marks the cell for destruction by other white blood cells. • Some of these lymphocytes remain in the blood and act as memory cells. • Should the same antigen invade again, the body can react to the infection much more quickly. At this point, one is said to be immune from the disease.

11. Artificial Immunity (Vaccination) • Some germs have the power to kill a human well before the correct antibody can be found. • For this reason, doctors have developed vaccination. • Vaccination involves injected “dead germs” which causes a particular disease into the bloodstream. • They cannot grow or cause major problems, but the body still detects them and produces antibodies against them. • Should the “real germ” invade, the body had the antibody ready to defend against it.

12. Passive Immunity • Passive immunity involves the body using antibodies which were not produced in the body. • Examples include an unborn child receiving antibodies from the mother’s placenta and during breast feeding.