BIOLOGY MISC Immune System Complete Study Guide_ Guaranteed Success.

The parts of the immune system are scattered, means its parts are not linked to each other in anatomical succession as that in digestive system, respiratory system or circulatory system, it consists of different parts throughout the body, but they interact and cooperate with each other in a coordinated manner. The Lymphoid organs These organs contain large numbers of lymphocytes where maturation and differentiation of lymphocytes take place, from these organs: 1. Bone marrow It is a tissue inside the flat bones such as the clavicle, the sternum, the skull, the vertebral column, the ribs, the shoulder, the pelvis, and also the heads of the long bones as the bones of the femur, the tibia and the humerus, which are responsible for the production of red blood cells, white blood cells, and blood platelets. 2. Thymus gland: It is located on the trachea above the heart and behind the sternum bone. - Secretes Thymosin hormone that stimulates maturity of lymphoid stem cells to T- cells and their differentiation into different types inside the Thymus gland. 3. The spleen It is a small lymphoid organ, its size is not more than the hand palm, and its dark red and located in the upper left side of the abdominal cavity. - It plays an important role in the body’s immunity: 2 | P a g e • It has a lot of white blood cells called macrophages which pick up all that is strange about the body, whether microbes or foreign bodies or senescent somatic cells as that of senescent red blood cells and disintegrate it to its components to be disposed by the body • It contains other white blood cells called lymphocytes, which release special proteins in the blood known as antibodies which holds the defense of the mission which defend the body against germs and viruses. 4. Tonsils: Tonsils are two lymphoid glands located on both sides of the rear portion of the mouth. - The tonsils pick up any microbe or foreign body that may enter with food or air and prevent its entry into the body, and thus works to protect the body. 5. The lymph nodes - The lymph nodes present along network of the lymphatic vessels that located in all the body parts under the armpits, at the two sides of the neck ,in upper thigh, and near the internal body’s organs. Their size ranging from a pinhead, to the seed of small beans. The node is divided internally into pockets filled with B- lymphocytes, T- lymphocytes, and macrophages and some other types of white blood cells that get rid of germs and the debris cells. • They purify the lymph from any harmful substances or microbes and store white blood cells (lymphocytes) that help in fighting against any disease or infection. • Each lymph node is connected with several lymph vessels that transfer the lymph from the tissue to the nodes for the filtration of the lymph to get rid the suspended foreign pathogen away from the body. The Lymphocytes They form about 20%: 30% of the white blood cells in blood, All Lymphocytes are formed in the red bone marrow, At the beginning they do not have any immune ability, but they pass in the process of maturation and differentiated in the lymphoid organs after that it changes into cells that have the ability of immunization. 3 | P a g e - They revolve in the blood to search for any microbe or foreign body, their defense and immune mechanisms to get rid of the pathogenic microbes to invade the body, reproduce, and spread through it and sabotage its tissue and disruption of its vital physiological functions. There are three types of lymphocytes in the blood which are: 1. B- cells: represents 10-15% of the lymphatic cells, are formed in the bone marrow and complete their growth to become mature. - Their function is the identifying any microbes or foreign materials (such as bacteria or virus), then adhere this foreign material and produces antibodies for his material to destroyed it. 2. T- cells: form about 80% of lymphocytes, and mature in the thymus gland where they differentiate into several types: • Helper T cells (TH): activate other types of T cells and stimulate it to do their responses, as well as stimulate B cells to produce antibodies • Cytotoxic T-cells: (or killer T cell) (Tc): attacking to the foreign cells where. It kills carcinogenic cells, the transplanted organs and body cells infected with the virus. • Suppressor T-cells (Ts): They regulate the degree of immune response required