The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include Show
To defend the body against these invaders, the immune system must be able to distinguish between
Antigens are any substances that the immune system can recognize and that can thus stimulate an immune response. If antigens are perceived as dangerous (for example, if they can cause disease), they can stimulate an immune response in the body. Antigens may be contained within or on bacteria, viruses, other microorganisms, parasites, or cancer cells. Antigens may also exist on their own—for example, as food molecules or pollen.
If the immune system malfunctions and mistakes self for nonself, it may attack the body’s own tissues, causing an autoimmune
disorder Autoimmune Disorders An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues. What triggers autoimmune disorders is not known. Symptoms vary depending on... read more
, such as rheumatoid arthritis
Rheumatoid Arthritis (RA) Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more
Disorders of the immune system occur when The immune system has many components: Antigens Innate Immunity are any substance that the immune system can recognize and that can thus stimulate an immune response. Cells are the smallest unit of a living organism, composed of a nucleus and cytoplasm surrounded by a membrane. Chemotaxis is the process of by which a chemical substance attracts cells to a particular site. Helper T cells are white blood cells that help B cells produce antibodies against foreign antigens, help killer T cells become active, and stimulate macrophages, enabling them to ingest infected or abnormal cells more efficiently. Histocompatibility (literally, compatibility of tissue) is determined by human leukocyte antigens (self-identification molecules). Histocompatibility is used to determine whether a transplanted tissue or organ will be accepted by the recipient. Human leukocyte antigens (HLA) are a group of identification molecules located on the surface of all cells in a combination that is almost unique for each person, thereby enabling the body to distinguish self from nonself. This group of identification molecules is also called the major histocompatibility complex. An immune complex is an antibody attached to an antigen. An immune response is the reaction of the immune system to an antigen. Immunoglobulin is another name for antibody. Interleukin is a type of messenger (cytokine) secreted by some white blood cells to affect other white blood cells. Killer (cytotoxic) T cells are T cells that attach to infected cells and cancer cells and kill them. Leukocyte is another name for a white blood cell, such as a monocyte, a neutrophil, an eosinophil, a basophil, or a lymphocyte (a B cell or T cell). The
lymphatic system
Lymphatic System: Helping Defend Against Infection Major histocompatibility complex (MHC) is a synonym for human leukocyte antigens. Mast cells are cells in tissues that release histamine and other substances involved in inflammatory and allergic reactions. A molecule is a group of atoms chemically combined to form a unique substance. Natural killer cells are a type of white blood cell that can recognize and kill abnormal cells, such as certain infected cells and cancer cells, without having to first learn that the cells are abnormal. Phagocytes are a type of cell that ingests and kills or destroys invading microorganisms, other cells, and cell fragments. Phagocytes include neutrophils and macrophages. Phagocytosis is the process of a cell engulfing and ingesting an invading microorganism, another cell, or a cell fragment. A receptor is a molecule on a cell’s surface or inside the cell that can identify specific molecules, which fit precisely in it—as a key fits in its lock. Regulatory (suppressor) T cells are white blood cells that help end an immune response. The body has a series of defenses. Defenses include
The first line of defense against invaders is mechanical or physical barriers:
As long as these barriers remain unbroken, many invaders cannot enter the body. If a barrier is broken—for example, if extensive burns damage the skin—the risk of infection is increased. In addition, the barriers are defended by secretions containing enzymes that can destroy bacteria. Examples are sweat, tears in the eyes, mucus in the respiratory and digestive tracts, and secretions in the vagina. The next line of defense involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and other invaders. This defense has two parts:
These substances are not contained in cells but are dissolved in a body fluid, such as plasma (the liquid part of blood). Some of these molecules, including some cytokines, promote inflammation. Inflammation occurs because these molecules attract immune system cells to the affected tissue. To help get these cells to the tissue, the body sends more blood to the tissue. To carry more blood to the tissue, blood vessels expand and become more porous, allowing more fluids and cells to leave blood vessels and enter the tissue. Inflammation thus tends to cause redness, warmth, and swelling. The purpose of inflammation is to contain the infection so that it does not spread. Then other substances produced by the immune system help the inflammation resolve and damaged tissues heal. Although inflammation may be bothersome, it indicates that the immune system is doing its job. However, excessive or long-term (chronic) inflammation can be harmful. The immune system includes several organs in addition to cells dispersed throughout the body. These organs are classified as primary or secondary lymphoid organs. The primary lymphoid organs are the sites where white blood cells are produced and/or multiply:
When needed to defend the body, the white blood cells are mobilized, mainly from the bone marrow. They then move into the bloodstream and travel to wherever they are needed. Lymphatic System: Helping Defend Against Infection
The secondary lymphoid organs include the
These organs trap microorganisms and other foreign substances and provide a place for mature cells of the immune system to collect, interact with each other and with the foreign substances, and generate a specific immune response. Lymph nodes are one of the first places that cancer cells can spread. Thus, doctors often evaluate lymph nodes to determine whether a cancer has spread. Cancer cells in a lymph node can cause the node to swell. Lymph nodes can also swell after an infection because acquired immune responses to infections are generated in lymph nodes. Sometimes lymph nodes swell because bacteria that are carried to a lymph node are not killed and cause an infection in the lymph node (lymphadenitis). A successful immune response to invaders requires
To be able to destroy invaders, the immune system must first recognize them. That is, the immune system must be able to distinguish what is nonself (foreign) from what is self. The immune system can make this distinction because all cells have identification molecules (antigens) on their surface. Microorganisms are recognized because the identification molecules on their surface are foreign. In people, the most important self-identification molecules are called
HLA molecules are called antigens because if transplanted, as in a kidney or skin graft, they can provoke an immune response in another person (normally, they do not provoke an immune response in the person who has them). Each person has an almost unique combination of HLAs. Each person’s immune system normally recognizes this unique combination as self. A cell with molecules on its surface that are not identical to those on the body’s own cells is identified as being foreign. The immune system then attacks that cell. Such a cell may be a cell from transplanted tissue or one of the body’s cells that has been infected by an invading microorganism or altered by cancer. (HLA molecules are what doctors try to match when a person needs an organ transplant.) Some white blood cells—B cells (B lymphocytes)—can recognize invaders directly. But others—T cells (T lymphocytes)—need help from cells called antigen-presenting cells:
How T Cells Recognize AntigensT cells are part of the immune surveillance system. They travel through the bloodstream and lymphatic system. When they reach the lymph nodes or another secondary lymphoid organ, they look for foreign substances (antigens) in the body. However, before they can fully recognize and respond to a foreign antigen, the antigen must be processed and presented to the T cell by another white blood cell, called an antigen-presenting cell. Antigen-presenting cells consist of dendritic cells (which are the most effective), macrophages, and B cells. White blood cells are activated when they recognize invaders. For example, when the antigen-presenting cell presents antigen fragments bound to HLA to a T cell, the T cell attaches to the fragments and is activated. B cells can be activated directly by invaders. Once activated, white blood cells ingest or kill the invader or do both. Usually, more than one type of white blood cell is needed to kill an invader. Immune cells, such as macrophages and activated T cells, release substances that attract other immune cells to the trouble spot, thus mobilizing defenses. The invader itself may release substances that attract immune cells. Resolution involves confining the invader and eliminating it from the body. After the invader is eliminated, most white blood cells self-destruct and are ingested. Those that are spared are called memory cells. The body retains memory cells, which are part of acquired immunity, to remember specific invaders and respond more vigorously to them at the next encounter. What is the body's first line of defense against invading microorganisms?Skin, tears and mucus are part of the first line of defence in fighting infection. They help to protect us against invading pathogens. You have beneficial bacteria growing on your skin, in your bowel and other places in the body (such as the mouth and the gut) that stop other harmful bacteria from taking over.
Which of the following is not one of the body's first lines of defense against invading microorganisms?The option (a) Skin is the first line of defense against harmful pathogens like microbes. Immune cells within the skin fight invading organisms. The option (b) Tears also acts as the first line of defense in the body, protecting the eyes from bacterial pathogens.
What is the body's first line of defense quizlet?The first line of the defense is the surface barrier. Skin as a chemical and physical defense.
Why is skin the first line of defense?Skin is a barrier that serves as one of the body's first lines of defense against harmful microbes. Specialized immune cells within skin tissue help to fight invading organisms. Yet the skin hosts diverse communities of beneficial bacteria, collectively known as the skin microbiota.
|