Exposure leads to immunological memory Found in nearly all forms of life Found only in jawed vertebrates Both innate and adaptive immunity depend on the ability of the immune system to distinguish between self and non-self molecules. In immunology, self molecules are those components of an organism's body that can be distinguished from foreign substances by the immune system. One class of non-self molecules are called antigens short for antibody generators and are defined as substances that bind to specific immune receptors and elicit an immune response. Innate immune system Microorganisms or toxins that successfully enter an organism encounter the cells and mechanisms of the innate immune system.
Nonspecific, innate immunity Most microorganisms encountered in daily life are repelled before they cause detectable signs and symptoms of disease. These potential pathogens, which include virusesbacteriafungiprotozoansand wormsare quite diverseand therefore a nonspecific defense system that diverts all types of this varied microscopic horde equally is quite useful to an organism.
The innate immune system provides this kind of nonspecific protection through a number of defense mechanisms, which include physical barriers such as the skinchemical barriers such as antimicrobial proteins that harm or destroy invaders, and cells that attack foreign cells and body cells harbouring infectious agents.
The details of how these mechanisms operate to protect the body are described in the following sections. Clonal selection of a B cellActivated by the binding of an antigen to a specific matching receptor on its surface, a B cell proliferates into a clone.
Some clonal cells differentiate into plasma cells, which are short-lived cells that secrete antibody against the antigen. Others form memory cells, which are longer-lived and which, by proliferating rapidly, help to mount an effective defense upon a second exposure to the antigen.
External barriers to infection The skin and the mucous membrane linings of the respiratory, gastrointestinal, and genitourinary tracts provide the first line of defense against invasion by microbes or parasites.
Skin Human skin has a tough outer layer of cells that produce keratin. This layer of cells, which is constantly renewed from below, serves as a mechanical barrier to infection.
In addition, glands in the skin secrete oily substances that include fatty acidssuch as oleic acidthat can kill some bacteria; skin glands also secrete lysozymean enzyme also present in tears and saliva that can break down the outer wall of certain bacteria. Victims of severe burns often fall prey to infections from normally harmless bacteria, illustrating the importance of intact, healthy skin to a healthy immune system.
Mucous membranes Like the outer layer of the skin but much softer, the mucous membrane linings of the respiratory, gastrointestinal, and genitourinary tracts provide a mechanical barrier of cells that are constantly being renewed.
The lining of the respiratory tract has cells that secrete mucus phlegmwhich traps small particles. Other cells in the wall of the respiratory tract have small hairlike projections called ciliawhich steadily beat in a sweeping movement that propels the mucus and any trapped particles up and out of the throat and nose.
Also present in the mucus are protective antibodieswhich are products of specific immunity. Cells in the lining of the gastrointestinal tract secrete mucus that, in addition to aiding the passage of food, can trap potentially harmful particles or prevent them from attaching to cells that make up the lining of the gut.
Protective antibodies are secreted by cells underlying the gastrointestinal lining. Furthermore, the stomach lining secretes hydrochloric acid that is strong enough to kill many microbes. There they encounter a variety of chemical substances that may prevent their growth.
These substances include chemicals whose protective effects are incidental to their primary function in the body, chemicals whose principal function is to harm or destroy invaders, and chemicals produced by naturally occurring bacteria.
Chemicals with incidental protective effects Some of the chemicals involved in normal body processes are not directly involved in defending the body against disease.Description.
The immune system is a network of cells, tissues, and organs that work together to defend the body against infection by bacteria, parasites, fungi and viruses. (d)contain unique molecules not normally found in bacterial cells (e)Lack many enzymes and must therefore be provided with many of the molecules they need for growth Bacteria that customarily grow in the bottom layers of deep-water bodies are usually.
The immune system attacks these disease causing organisms through a sequence of steps referred to as the immune response.
The immune system is composed of a number of cells, tissues and organs that work in association and attacks the disease causing microorganisms and protect the human body. The chapter also gives description of the specialized set of lymphocytes (T and B) that has been called adaptive immunity.
The T and B cells give rise to a unique set of immune cells for each individual of a species. These make an individually specific repertoire for molecular recognition by which the immune system can detect microbes. The complement system consists of a group of proteins that are involved in a series of reactions 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. cancer cells, and dead or damaged cells from the tissues to the. Dendritic cells serve as a link between the bodily tissues and the innate and adaptive immune systems, as they present antigens to T cells, one of the key cell types of the adaptive immune system.