Topic+10+Defense+Against+Infectious+Disease

Platelets are small cell fragments that circulate in the blood plasma. The clotting process begins when damaged tissue or platelets release clotting factors. Clotting factors set off a series of reactions through which the product of each reaction is the catalyst of the next. This helps to ensure that clotting only happens when necessary, and that it occurs quickly. In the last reactions of the clotting process, prothrombin is activated, producing thrombin. Thrombin causes the soluble plasma protein fibrinogen to become fibrous fibrin. This is done through the removal of sections of peptide with many negative charges, allowing the resulting polypeptide to bind to others, forming fibrin. Fibrin then forms a mesh of fibres across wounds, where blood cells get caught, forming a semi solid clot. Upon exposure to the air, the clot dries to form a scab to protect the wound until it is healed.
 * 10.1.1 Describe the process of clotting**
 * //Limit this to the release of clotting factors from platelets and damaged cells resulting in the formation of thrombin. Thrombin catalyzes the conversion of soluble fibrinogen into the fibrous protein fibrin which captures red blood cells.//** L

10.12
 * Outline the principle of challenge and response, clonal selection and memory cells as the basis of immunity**

//Challenge and response//
 * A clone of B cells can produce large amounts of antibody quickly and thus give immunity to the disease with which the antigen is associated.
 * Immunity to the disease is only developed if the immune system is challenged by the disease.
 * This is the principle of challenge and response.

//Clonal selection//
 * A few B-cells that make each type of antibody are produced
 * If these cells encounter an antigen to which their antibody binds, they multiply to form a clone of many cells.
 * The specific interaction of macrophage selecting the particular B cells with required surface receptors is is //clonal selection//
 * Polyclonal selection occurs when several types of antibody can bind to the same antigen. Here, more than one clone of cells is formed.

//Memory cells//
 * Memory cells are B-cells and T-cells that are formed when these cells are activated.
 * After the activated cells and the antibodies produced to fight the disease have disappeared the memory cells persist and allow a rapid response if the disease is encountered again.
 * Memory cells give long-term immunity to a disease
 * Memory T-cells remain in the lymphoid tissue

__10.1.3 Define active immunity, passive immunity, natural immunity and artificial immunity.__


 * Active Immunity:** Immunity produced by the body in response to stimulation by a disease-causing organism. Person will acquire active immunity when their body's defense mechanisms have been stimulated by the invasion of the foreign micro-organism and as a result the person is unlikely to be infected for a second time. (Ex. Measles) Active immunity takes some time to develop.


 * Passive Immunity:** Immunity aquired by the transfer of antibodies from another organism in which active immunity has been stimulated. This kind of immunity gives protection from immunity immediately. An example of aquired passive immunity is when a baby receives antibodies from its mother via the placenta.


 * Artificial Immunity:** Immunity given due to innoculation with a vaccine. Aquired (active or passive) immunity produced by deliberate exposure to an antigen, as in vaccination. Places the pathogen in the body to ignite the defense mechanism.


 * Natural Immunity:** Immunity to a diseases or an infection that occurs as a part of an individual's natural biologic make-up. Can be either active or passive.

__10.1.4 Explain antibody production__

B-cells can be found in the lymph nodes. They will form a clone and then differentiate into plasma cells, producing one kind of antibody. MHC proteins are membrane proteins found on macrophages. T-cell receptors do not respons to antigens unless the antigens are associated with MHC proteins. The macrophages will present the antigen to the T-helper cell. T-helper cells secrete a substance which activates nearby B-cells. B-cells will divide, form a clone and differentiate into plasma cells producing specific antibodies. Cytotoxic T-cells are involved in the cell mediated response. Cytotoxic T-cells kill pathogens and viruses which invade cells. A cell which contains a virus or pathogen will be detected and destroyed. B-cell can form memory cells. This means that the second response to exposure of the antigen is much faster and stronger than the first response.

__10.1.5 State that cytotoxic T-cells destroy cancer cells and body cells infected with viruses.__

Viruses don't only invade the organism, but also moves into the cells of the organism. This way, the T-helper cells cannot find the viruses, even if the organism has antibodies against this virus, the antibodies cannot go into body cells to destroy it. Therefore another method is used. A cell infected by a virus will place a special 'marker' on the outside of its cell membrane. Any cell carrying this marker will be destroyed by a specific kind of T-cell: the cytotoxic T cell. These cells also destroy cancer cells.

__10.1.6 Describe the production of monoclonal antibodies; one use of them in diagnosis and one use in treatment.__

When an antigen enters the human body it selects the appropriate B cell clone, from many in the body, to bind with; this is called clonal selection. Since microorganisms are usually complex they tend to have more that one antigen and need more then one type of antibody to bind to its different antigens. As a result, the several different types of B cells produce a mixture of antibodies to bind to their respective antigens this is called polyclonal selection.

However, sometimes scientists need, for research purposes, a pure preparation of of antibodies with a single specificity. These types of antibodies are know as **Monoclonal antibodies**. Monoclonal antibodies are produce from single B cell clones. Inject a mamal with an antigen, this will stimulate B cells, or antibody- producing cells, production against the antigen that was injected. Remove theses B cells from the mammal and culture them. Then remove B cell tumour cells, culture them, and then fuse them with the cultured B cells from the mammal. The fusion of the B cells with the tumour cells will produce hybridoma cells which will grow and produce identical antibodies to ones from the B cell taken from the mammal.

This could possibly be used for treating cancer. For example, if they are used against tumour antigens and they are coupled to cytotoxic drugs they could result in cells which target and destroy tumour cells but leave healthy cells alone.

Monoclonal antibodies can also be used for diagnosing pregnancy. For example, once monoclonal antibodies against HCG, a hormone secreted during pregnancy, are obtained they are put on a testing stick. Then add urine, from a female, to the testing stick. If the woman is pregnant, then HCG in the urine, which is present in pregnant women, will attach to the antibodies because the monoclonal antibodies against HCG will only attach the HCG antigen. The test has been disigned to show a color representing a positive test.

__10.1.8 Discuss the benefits and dangers of vaccination against bacterial and viral infection, including the MMR vaccine (combined measles/mumps/rubella) and two other examples.__

Benefits of vaccination against bacterial and viral infections:
 * Help prevent epidemics
 * Interrupts transmission, so that the few people who are suseptible to the diseases don't come in contact with the pathogen
 * Saves many lives
 * Small pox has even been eradicated as a result of vaccination

Dangers of vaccination against bacterial and viral infections:
 * Not always safe and people can develop the disease as a result
 * If vaccinated with a live vaccine, pathogens can be passed through faeces and infect others
 * Some might not respond to a vaccine and are not immune eventhough they think they are

In the case like the common cold, the virus mutates regularly and makes previously formed antibodies useless. In the case of malnutrition, antibodies are not always formed.

The MMR vaccine (combined measles/ mumps/ rubella) protects against two diseases: measles and mumps. Rubella can be just as dangerous because when pregnant women are infected, it can often lead to serious conditions in their babies (deafness, blindness...etc).