immunity

• external defence system: epithelial cells that cover the airways, hydrochloric acid in the stomach, platelets that aid in the clotting of blood
• internal defence system: white blood cells (phagocytes and lymphocytes)
• macrophage function: engulf pathogens using receptor sites on their surface membrane
• white blood cell types: phagocytes - macrophages, neutrophils, eosinophils; lymphocytes - B-cells and T-cells
• neutrophil function: phagocytosis and release enzymes to destroy bacteria
• an antigen is a molecule which the body recognizes as foreign
• antibodies are glycoprotein molecules produced to act against specific antigens
• cell surface antigens are molecules on the surface of our cells that are not found on the surface of the cells of other organisms. these antigens do not stimulate antibodies in our bodies but stimulate antibodies when they enter the bodies of other people.
• immune response is the response of lymphocytes to the presence of a foreign antigen
• phagocytes are produced in the bone marrow and remove dead cells as well as invasive microorganisms
• neutrophils: produced in large numbers during an infection, short-lives, can leave the blood by squeezing through capillaries
• monocytes: cells which are yet to fully develop
• macrophages: larger than neutrophils, mostly found in lungs, liver and lymph nodes. made in the bone marrow but travel in the blood as monocytes.
• monocytes develop into macrophages once they leave the blood and settle in the organs.
• macrophages are long-living cells and help initiate immune responses by cutting up pathogens to display antigens that can be easily recognized by the lymphocytes
• chemotaxis: chemical movement, when pathogens invade the body, some of the cells respond by secreting chemicals like histamine. These with the chemicals released by the pathogens attract the neutrophils on patrol to the site of the infection,
• phagocytosis: 1. chemotaxis 2. phagocytosis 3. neutrophils die and collect at the site of the infection as pus
• why is it important that pathogens are covered in antibodies?

  because these antibodies allow the receptor proteins on the surface of the neutrophils to attach to the pathogens
• what happens once the neutrophil engulfs the pathogen?

  traps it in a phagocytic vacuole. Digestive enzymes are then secreted into the vacuole where they destroy the pathogen.
• lymphocytes: smaller than phagocytes, have a large nucleus
• b-lymphocytes: stay in the bone marrow until they mature and then spread throughout the body, mainly in the lymph nodes and spleen
• t-lymphocytes: leave the bone marrow to the thymus where they mature
• once b-lymphocytes mature, they can become plasma cells which produce many antibodies very quickly.
• Plasma cells secrete antibodies into the blood, lymph and linings of the lung or gut. The plasma cells die quickly but the antibodies live longer
• Some B cells are memory cells which are able to remember an antigen that has been introduced to the body before and can often destroy repetitive infections before symptoms develop
• T-Lymphocytes: have receptors on their surface that are specific to one antigen and similar to antibodies (T cell receptors)
• when T-cells meet the antigen that they are specific to, they divide by mitosis to increase the number of cells
• 2 types of t cells: helper t-cells, killer t-cells
• cytokines: chemical that stimulate B cells and send out a signal to B cells that are specific to that antigen
• helper t-cells?

  1. release hormones (cytokines) that stimulate the appropriate B-cells to divide and secrete antibodies?
  2. some helper T-cells secrete hormones that stimulate macrophages to carry out phagocytosis more aggresively
• killer t cells?

  1. search the body for cells that have been invaded by pathogens
  2. recognize foreign antigens, attach themselves to the surface of the infected cells, and secrete harmful substances to kill the invaded cells
  3. helper t cells can stimulate the rapid division of killer t cells.
• during bacterial infections or inflammation: number of neutrophils increases
• during viral infections and tuberculosis: number of lymphocytes increases
• HIV specifically attacks helper T-cells and destroys them. Monitoring the number of helper T-cells can help provide information on the progression of the disease and success of treatment
• all white blood cells develop from stem cells
• myeloid stem cells produce neutrophils, monocytes and platelets
• lymphoid stem cells produce lymphocytes
• antibodies are globular glycoproteins with a quaternary structure which form a group of plasma proteins called immunoglobins.
• the basic antibody molecule consists of 4 polypeptide chains (two heavy and two light)
• the polypeptide chains in antibodies are held together by disulfide bonds and each molecule has 2 identical antigen-binding sites