1.Host defense mechanisms of any human body naturally consist of two basic types of immunity – innate and acquired, which are also often called non-specific and specific, respectively.The difference between these forms of immunity is the following: while innate immunity is considered to be the immediate defense, when cells and molecules that are always present in healthy individuals block the entry of infectious microbes and try to eliminate them quickly from a living organism, acquired immunity in this case needs some time to adapt to the presence of infectious microbes in an organism and only in a while starts to react to any foreign substances. Immunity can also be subdivided into active and passive. Active one is an immunity that was induced in an individual by infection or vaccination, passive one is an immunity that was conferred on an individual by transfer of antibodies or lymphocytes from an actively immunized individual. (Abul K. Abbas, Andrew H. Lichtman, 2004)
2. Different materials, such as leukocytes –lymphocytes and monocytes in particular, glucose, proteins, neutral fats, and other mineral substancesmay be found in the fluid called the lymph.Lymph enters the lymphatic vessels due to the flaps of cell cytoplasm. Thenmuscles contractions that occur near the lymphaticspropel the fluid into larger vessels that lead to the heart. The flaps formed by cells called the valves always point in one direction, so they do not allow lymph to flow backwards.Lymph nodes – small bean-shaped organs that form along lymph vessels – function to survey lymph for pathogens and filter them out; they contain masses of cells called lymphocytesthat vigorously react to foreign materials– antigens.(Young, 2008)
3.It is known that lymphocytes are the only cells with specific receptors for antigens, therefore they are considered the key mediators of adaptive immunity. Two main types of lymphocytes can be distinguished: B – lymphocytes and T -lymphocytes. The antibodies produced by B – lymphocytes are designed to specifically recognize extracellular microbial antigens, whereas T- lymphocytes recognize antigens produced by intracellular microbes. Another important difference between B and T lymphocytes is that most T cells recognize only microbial protein antigens, whereas antigens are able to recognize many different types of microbial molecules, including proteins, carbohydrates, and lipids. (Abul K. Abbas, Andrew H. Lichtman, 2004)Speaking about exposures, it should be noted that the immune system of an individual responses in more effective way to repeated exposures of the same antigen.So the first exposure is more important if to compare it with the second or subsequent as due to it the antigen is memorized and afterwards can be easily overcome.
4.Under certain circumstances the immune system can fail to protect the body. This leads to particular dysfunctions that can be subdivided into 3 categories:
- immunodeficiencies (any congenital or acquired condition that causes immune cells, phagocytes, or complement to behave abnormally);
- autoimmune diseases ( occur whenthe immune system loses its ability to distinguish friend (self) from foe (foreign antigens).When this happens, the artillery of the immune system, like friendly fire, turns against itself. The body produces antibodies (autoantibodies) and sensitized T-cells that destroy its own tissues. This process usually leads to autoimmune disease).
- hypersensitivities ( simply speaking allergies. An allergen is an antigen that causes an allergic reaction. Allergic reactions can last for half an hour or even for months).(Elaine N. Marieb, Katja Hoehn, 2006)
5.Fevers can affect an organism both in a positive and negative way. First of all, it is necessary to define the term itself. So, a fever is a systemic response of the body to infectious microbes that penetrate into the organism and shows up through abnormally high body temperature. High fevers are considered to be bad mechanisms as they are really dangerous for a variety of reasons and among themenzymes denaturation. Mild or moderate fever is so to say quite a good mechanism for a body, as it is a kind ofan adaptive response, which increases the metabolic rate of tissue cells, thus speeding up repair processes. Moreover,during a fever the liver and spleen sequester such nutrients as iron and zinc, making them less available. This slows down the process of bacteria spreading and increasing asin order to multiply bacteria require large amounts of iron and zinc.(Elaine N. Marieb, Katja Hoehn, 2006)
Abul K. Abbas, Andrew H. Lichtman. (2004). Basic Immunology. Functions and Disorders of the Immune System. Philadelphia: Saunders.
Elaine N. Marieb, Katja Hoehn. (2006). Human Anatomy & Physiology. New York : Benjamin Cummings.
Young, J. K. (2008). Human Anatomy: The Beauty of Form and Function. Recorded Books.