The Immune System Lesson 1: The Immune Systems 28 The Immune System Lesson 1: The Immune Systems

Lesson Objectives Upon completion of this lesson, students should be able to … Define and spell the terms to learn for this chapter. Identify and discuss the anatomy of the immune system. Discuss the functions of the immune system. Explain the immune system and its response.

Composition of the Immune System Tissues Organs Physiological processes that identify abnormal cells Foreign substances Foreign tissues, such as transplants

Structures Central to the Immune System Central lymphoid tissue Comprised of the bone marrow Peripheral lymphoid tissue Consisting of the lymph nodes, spleen, and mucosa-associated lymphoid tissue

Critical Thinking Questions What is so critical about the immune system to one’s overall health? If one has a compromised immune system would that shorten the person’s life?

The Immune System Operates throughout the body Structures are part of the lymphatic system, which is a subsystem of the circulatory system Primary function of the lymphatic system is to defend the body against invasion by pathogens such as viruses, bacteria, and fungi Immunosuppressants, medications, and stress can suppress the immune system

The Lymphatic System

Bone Marrow Comprises the central lymphoid tissue Contains stem cells that create all the cells that make up the tissues and structures of the immune system Produces red blood cells, white blood cells, and platelets, along with B cells and natural killer cells

Location and Purpose of the Thymus Gland Comprises the central lymphoid tissue Located posterior to the sternum, in the anterior mediastinum Manufactures infection-fighting T cells and helps distinguish normal T cells from those that attack the body’s own tissues Enlarges during childhood but shrinks again after maturity, continuing to function throughout life

Compartments of the Thymus Gland Outer cortex and an internal medulla Immature lymphoid cells enter the cortex, reproduce and mature, then move to the medulla where they reenter the circulation

Peripheral Lymphatic System Consists of the lymph nodes, spleen, and other lymphoid tissue Lymphatic capillaries, lymphatic vessels, and lymphatic ducts are part of the peripheral lymphatic system

Lymph Nodes Take many different sizes and shapes Most are bean-shaped and about 1 inch long Covered with a thick fibrous capsule Node is subdivided into different compartments by inward-pointing trabeculae

Two Parts of Lymph Nodes Cortex Populated mainly with lymphocytes Medulla Primarily made up of macrophages attached to reticular fibers

B Lymphocytes The germinal centers are the primary locations where B lymphocytes reproduce quite prolifically Cells responsible for production of circulating antibodies Each unique type of B cell produces only one type of antibody When an antigen enters the body, these B lymphocytes rapidly undergo mitosis and divide This produces a large quantity of an antibody to seek out and help destroy the antigen

The spleen is not an essential organ for life. Located in the upper left quadrant of the abdomen Consists of lymphatic tissue that is highly infiltrated with blood vessels Spleen’s blood vessels are lined with macrophages, which swallow and digest debris in the blood such as worn-out red blood cells and platelets Factoid: The spleen is not an essential organ for life. 15

Tonsils are often removed when infected. Located in the depressions of the mucous membranes of the throat and the pharynx The function of the tonsils is to filter bacteria and aid in the formation of white blood cells Factoid: Tonsils are often removed when infected. 16

The Immune System The body’s defense against infectious organisms and other pathogenic invaders Through the immune response, the cells, tissues, and organs work together to attack organisms and substances that invade body systems and cause disease Leukocytes, or white blood cells (WBCs), combine to seek out and destroy harmful organisms

Phagocytes and Lymphocytes A type of WBC that attacks the invading organism A number of different cells are considered to be phagocytes, but the most common are neutrophils, which primarily fight off bacteria

Phagocytes and Lymphocytes A type of WBC that allows the body to remember and recognize previous invading organisms Originate in the bone marrow and either stays there and matures into B cells or move to the thymus gland, where they mature into T cells

B and T Lymphocytes B lymphocytes and T lymphocytes have separate responsibilities within the immune system B lymphocytes Seek out invading organisms and send defenses to attach onto them T cells Destroy the organisms that the B lymphocytes have identified

Antigen Foreign substance that invades the body When an antigen is detected, several types of cells work together to recognize and respond to it These cells trigger the B lymphocytes to produce antibodies This process is known as humoral immunity

Antibodies Specialized proteins that lock onto specific antigens Immunoglobulins are glycoproteins that function as antibodies The terms antibody and immunoglobulin are often used interchangeably Antibodies are found in blood, tissue fluids, and many secretions

Antibodies Structurally antibodies are globulins, which means they are synthesized and secreted by plasma cells derived from the B cells of the immune system

B Cells of the Immune System Activated upon binding to their specific antigen and differentiating into plasma cells In some cases the interaction of the B cell with a T cell is necessary Once antibodies have been produced, they remain in the body

B Cells of the Immune System If the same antigen is presented to the immune system again, the antibodies are already there to neutralize it Although antibodies can recognize an antigen and lock onto it, they are not capable of destroying it alone. That is the job of the T cells.

T Cells Part of the system that destroys antigens which have been tagged by antibodies or cells that have been infected or somehow changed Assist other cells, such as phagocytes Antibodies can neutralize toxins produced by different organisms Antibodies can activate a group of proteins called complement that are also part of the immune system Complement assists in destroying bacteria, viruses, or infected cells

Immunity The body’s ability to defend itself against pathogens Forms of immunity Innate Active Passive 27

Innate Immunity Everyone is born with innate, or natural, immunity Renders many of the viruses and bacteria that affect other species incapable of harming human beings Provided in part by the external barriers of the body Including the skin and mucous membranes that line the nose, throat, and gastrointestinal tract

Innate Immunity If this outer defensive wall is broken, such as by a cut in the skin, special immune cells on the skin attack any invading microorganisms

Active Immunity The introduction of immunity by infection or with a vaccine Is permanent, meaning that the individual has lifelong protection against the disease

Types of Active Immunity Acquired active immunity Occurs when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response Artificially acquired active immunity Active immunity is induced by a vaccine, a substance that contains the antigen and stimulates a primary response against the antigen without causing symptoms of the disease

Passive Immunity “Borrowed” from another source and lasts for only a short time An inherited immunity to certain diseases

Questions? 33