Sistema Inmunitario PDF

# Sistema Inmunitario ## Introducción The immune system defends the body against the invasion of harmful microorganisms and toxins. The organs and tissues of the immune system are known as lymphoid because they are all involved in the development, growth, and dissemination of lymphocytes, a type...

# Sistema Inmunitario ## Introducción The immune system defends the body against the invasion of harmful microorganisms and toxins. The organs and tissues of the immune system are known as lymphoid because they are all involved in the development, growth, and dissemination of lymphocytes, a type of white blood cell. The immune system has three main components: - Lymphoid tissue and organs - Lymphoid tissue and organs - Lymphoid tissue and organs Despite the fact that the immune system and blood are two different entities, they are important. Their cells share a common origin in bone marrow. ## Lymphoid Tissue and Organs ### Central - Bone marrow and thymus play a role in the development of B lymphocytes, the two main types of lymphocytes. **Bone Marrow** - Contains stem cells that develop into any type of cell. These cells are pluripotent, which means they can take many forms. - Immune system and blood cells develop from stem cells in a process called hematopoiesis. **Thymus** - After differentiation from stem cells, some cells that will make up the immune system become lymphocytes, while others become phagocytes (cells that ingest microorganisms). - Those that become lymphocytes are further differentiated into B lymphocytes (which mature in bone marrow) or T lymphocytes (which travel to the thymus to mature). **B & T Lymphocytes** - B and T lymphocytes are distributed throughout all lymphoid organs, especially in the lymph nodes and spleen. - B and T lymphocytes have special receptors that respond to specific forms of antigen molecules. - In B lymphocytes, the receptor is an antibody that targets pathogens or directs other cells, such as phagocytes, to the attack. - In fetuses and infants, the thymus is a lymphoid tissue organized into two lobes located at the base of the heart, in the mediastinum. - The thymus helps in the development of T lymphocytes for several months after birth. - Thereafter, it has no role in the body's immunity. ### Peripheral - The peripheral structures of the immune system include lymph nodes, lymphatic vessels, and the spleen. **Lymph Nodes** - Lymph nodes are small, oval structures located along the network of lymphatic ducts. - Lymph nodes are most abundant in the head, neck, armpits, abdomen, pelvis, and groin. - They help eliminate and destroy antigens (substances capable of triggering immune reactions) that circulate in the blood and lymph. **Spleen** - Located in the upper left quadrant of the abdomen, below the diaphragm. - It is a reddish-purple, oval structure that is about the size of a fist. - It is the largest lymphoid organ. **Functions of the Spleen** - **Phagocytes** inside the spleen engulf and break down worn-out red blood cells, releasing hemoglobin for degradation into its components. - These phagocytes also retain and destroy damaged or abnormal red blood cells, as well as cells with abnormal hemoglobin. - The spleen filters and removes bacteria and other foreign substances from the bloodstream, and splenic phagocytes quickly eliminate these substances. - Splenic phagocytes interact with lymphocytes to trigger an immune response. - The spleen stores blood and 20 to 30% of platelets. - If the spleen is removed from the body due to some disease or trauma, the liver and bone marrow take over its function. ## Accessory Lymphoid Tissue & Organs - Tonsils, adenoids, appendix, and Peyer's patches eliminate external waste in a way similar to lymph nodes. - They are located where microorganisms are most likely to enter, such as in the nasopharynx (tonsils and adenoids) and abdomen (appendix and Peyer's patches). ## Function of the Immune System - Immunity is the body's ability to resist the invasion of microorganisms and toxins, preventing tissue and organ damage. - The immune system is designed to recognize, respond to, and eliminate antigens, such as bacteria, fungi, viruses, and parasites. - It maintains the body's internal environment by eliminating dead or damaged cells and searching for antigens constantly. To carry out these functions efficiently, the immune system uses three strategies: - Surface Phenomena - Host Defenses - Specific Immune Responses