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4. Immunology.pdf

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PHGY 209
Erik Cook

Naveen Sooknanan McGill Fall 2011 Immunology: The immune system is an immense system which can be found everywhere in the body. It is through this system that the body is able to fight infection. The immune system must be everywhere, because you can get infected anywhere The primary organs of the immune system are, in the embryonic stage, the yolk can and liver, but then change to the bone marrow and thymus in adulthood The secondary organs are found in adults and comprise the lymph nodes all over the body, the spleen and mucosa associated lymphoid tissue (MALT) which are present, for example, under the bronchial tree or under the gut In some instances, the immune system can malfunction which can cause many different diseases and conditions SCID, or severe combined immune deficiency is essentially a shutdown of the whole immune system forcing the individual to live in a sterile plastic bubble for their whole life AIDS, acquired immunodeficiency syndrome, is a disease which initially affected only the young gay male population in the 1980s. It then spread to be a global pandemic which has affected millions of people o HIV AIDS is caused by a lack of helper T cells, which will be seen later Vaccinations were discovered as a cure for smallpox in 1796 by a Dr. Edward. While smallpox left pox on the face and killed many individuals, Dr. Edward noticed a group of milkmaids who instead has pox marks on their hands, and survived the disease This lead to the discovery of cowpox, which, once you got it, made you immune to smallpox It was in this way that small doses of cowpox were administered to patients in order to immunize themselves from it There are only 2 vials of smallpox disease left The term antigen has many synonyms but its general definition is any cell which the host cannot recognize as self Immunogen is a word preferred by immunologists A hapten is too small to initiate an immune response by itself, so it sits on a carrier molecule to be considered an immunnogen An allergen sits on mast cells within the body and trigger the release of molecules such as histamine o They undergo a specific immune response which wont be seen in this course A tolerogen is an antigen which is allows, or tolerated, in the host o For example, fathers cells are allowed inside the mother during pregnancy A ligand is anything able to bind an antibody, which are released in the immune response The three lines of defense for the immune response are the coverings of the body, the innate response and the adaptive response. By specific chemical messengers called cytokines, these systems are able to interact with each other 1 Naveen Sooknanan McGill Fall 2011 The covering of the body are very nonspecific and allow very few microbes to enter the system The innate response is also nonspecific and also dont have memory, meaning the same reaction takes place every time one microbe enters the body o When we didnt know what this system did, it was called the nonspecific response The adaptive response is acquired, and retains memory of certain microbes making the second response much faster The main cells of the immune systems are leukocytes and other highly phagocytic cells Within the leukocyte category, there are myeloid derivatives and lymphoid derivatives o The myeloid derivatives include neutrophils, basophils, eosinophils and monocytes, which all have phagocytic activities o The lymphoid derivatives are B lymphocytes (B cells), T lymphocytes (T cells) and natural killer (NK) cells Macrophages are large phagocytic cells involved mainly in the innate immune response Dendritic cells are also phagocytic cells which also activate T cells in the adaptive immune response As discussed before, a pluripotent cell is responsible for the production of all blood cells, including leukocytes o This pluripotent cell is part of a totipotent cell (the sperm or egg) which is responsible for all cells in the body The first line of defence of the immune system includes the skin and mucous membranes of the body. Many of these mucous membranes are ciliated and stick so that they are able to trap microbes while the skin acts like more of a shield separating the tissues inside from external microbes These coverings all have unpleasant living conditions for microbes such as pH and the presence of various enzymes located on the epidermis This line of defense is nonspecific, and will act on anything that tries to get through these coverings This system is able to recognize certain molecular properties which are present on the PM of all microbes, such as carbohydrates of lipids In the innate response is also nonspecific and natural (you dont have to learn it) but has no memory functions, which mean the same process is carried out no matter how many times the same microbe penetrates the body coverings There are cellular and humoral (dissolved in plasma) factors involved in the innate immune response Always accompanied with the innate immune response is inflammation o The four main symptoms of inflammation are redness, heat, swelling and pain The innate response can be found early in evolution, such as an lampreys and hagfish The cellular factors involved in the innate response are phagocytic cells and cells with inflammatory mediators o The phagocytic cells include neutrophils, macrophages and interdigitating dendritic cells 2Naveen Sooknanan McGill Fall 2011 o The inflammatory mediating cells are basophils, mast cells and eosinophils and will not be covered o Another cell involved with this response if the natural killer (NK) cell The humoral factors include acute phase reactants such as the C-reactive factor and cytokines such as interferon alpha The first cell to react with bacteria present in the body is the fixed-tissue macrophage. It extends pseudopods around the given bacteria and engulfs is as a vesicle, which is then digested enzymatically. The macrophage has receptors for various constituents which can be found on microbial PMs The engulfing of these bacteria release chemokines and cytokines which are pro-inflammatory Cells which have these signals recognized by macrophages are known as danger signals. Host cells do not contain these factors Neutrophils are the next type of cell which enters the site of infection in order to phagocytose bacteria. Neutrophils are polymorphonucleated cells, meaning they have multiple nucleus fragments which are linked by bridges During infection, vasodilation causes the expansion of spaces between endothelial cells of the blood vessels The macrophage sends out a chemical signal which attracts the neutrophils in nearby blood vessel
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