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Higher Biology Cellular Defence Mechanisms In Animals By the end of this lesson: You should be able to: Know what phagocytosis is Know what lysosomes are and the job they do Know how lymphocytes defend our body 2 Introduction Both plants and animals need to defend themselves against being: Eaten by animals Infected by pathogens 3 Cellular Defence in Animals The internal environment of an animal provides the ideal conditions for pathogens to thrive I.e. plenty of food A constant warm temperature 4 Lines of defence Animals have 3 lines of defence against attack by pathogens: 1. First line Non-specific 2. Second line Non-specific 5 Lines of defence 3. Third line Specific- acts at the same time as the second line of defence. The immune system directly targets the invader. 6 First Line Defence Consists of: Skin Mucous membranes- lining the digestive, respiratory and genitourinary tracts Remember- mucus & cilia in the trachea? Sebaceous & sweat glands give the skin a pH of 3-5, too acidic for most microbes to reproduce. Tears, saliva and mucous secretions continually wash away microbes from the surface. These secretions also contain anti-microbial proteins (e.g. lysozyme) which can digest the cell walls of many bacteria. 7 First Line Defence cont. The highly acidic environment in the stomach destroy most microbes ingested in food or drinks. 8 Second Line Defence Has 3 components: Phagocytic white blood cells Antimicrobial proteins Inflammatory response. Phagocytosis Process whereby solid particles are taken up by a cell. Carried out by specialised white blood cells called phagocytes. 9 Phagocytosis Stages in phagocytosis 1. 2. 3. 4. Phagocyte detects chemicals released by a foreign intruder (e.g. bacteria) Phagocyte moves up the concentration gradient towards the intruder The phagocyte adheres to the foreign cell and engulfs it in a vacuole by an infolding of the cell membrane. Lysosomes (organelles which are rich in digestive enzymes & found in the phagocytes cytoplasm) fuse with the vacuole & release their contents into it. 10 Phagocytosis 5. The bacterium is digested by the enzymes, and the breakdown products are absorbed by the phagocyte. During infection, hundreds of phagocytes are needed. Pus is dead bacteria and phagocytes! link to phagocytosis 11 Third line defence White blood cells called lymphocytes are responsible for this. These cells recognise particles that do not belong to the individual as foreign and try to eliminate them Foreign particles can include transplanted tissues. Viruses, bacteria, fungi and parasitic worms all carry complex molecules on their surface. 12 Third line defence These molecules are called antigens and are recognised by lymphocytes as foreign. In response lymphocytes produce special proteins called antibodies. This is a specific response as each antibody has binding sites which are specific to one type of antigen. 13 Third line defence Immune response- Cells alive site 14 Primary Immune Response The immune system has the capacity to respond to millions of different antigenic molecules. The first time a lymphocyte is activated to produce antibodies to a particular antigen is called the primary immune response. This is short lived and often unable to prevent the person from becoming ill. 15 Secondary Immune Response If the person survives (!) and comes into contact with this antigen again then the secondary immune response is activated This time the disease is usually prevented because: Antibody production is much quicker A higher concentration of antibodies is produced Graph from Scholar 16 Secondary Immune Response The secondary response is possible because some of the lymphocytes from the primary response, specific to that antigen, remain in the blood as memory cells. This is why people say that if you catch chickenpox as a child you are unlikely to catch it as an adult. 17 Organ and Tissue Transplantation Many types of tissues and organs can be transplanted E.g. corneas Kidneys Hearts In addition to the risks associated with surgery there is also the risk of rejection 18 Organ and Tissue Transplantation Try to answer the following questions based on organ and tissue transplants 1. Why do you think is there a growing demand for tissue and organ transplants? 2. Why are organs and tissues often rejected following transplantation? 3. Why would it not be a good idea to transplant tissue into a patient from a donor whose tissue had been rejected in the past by that patient? 19 Organ and Tissue Transplantation 4. 5. 6. 7. Why are the most suitable organ donors often closely related to the patient? Who, if they existed, would be the ideal choice for a donated organ for you? Usually transplant patients have to take immunosupressor drugs for the rest of their lives. Explain the reason for this. Why can taking immunosupressor drugs lead to difficulties? 20 Practice Questions Torrance TYK page 73 Q1-3a AYK pages 76-77 Q1, 3a and 4. 21