overview : reconnaissance, recognition and response- An animal must defend itself against unwelcome intruders—the many potentially dangerous viruses, bacteria, and other pathogens it encounters in the air, in food, and in water.
- It must also deal with abnormal body cells, which, in some cases, may develop into cancer.
what are Two major kinds of defense that have evolved to counter threats.?-the first kind of defense is innate immunity.
- Innate defenses are largely nonspecific, responding to a broad range of microbes.
- Innate immunity consists of external barriers formed by the skin and mucous membranes, plus a set of internal cellular and chemical defenses that defend against microbes that breach the external barriers.
- The internal defenses include macrophages and other phagocytic cells that ingest and destroy pathogens.
the second kind of defense is acquired immunity
- Acquired immunity develops only after exposure to microbes, abnormal body cells, or other foreign substances.
- Acquired defenses are highly specific and can distinguish one inducing agent from another.
- This recognition is achieved by white blood cells called lymphocytes, which produce two general types of immune responses.
- In the humoral response, cells derived from B-lymphocytes secrete defensive proteins called antibodies that bind to microbes and target them for elimination.
- In the cell-mediated response, cytotoxic lymphocytes directly destroy infected body cells, cancer cells, or foreign tissue.
43.1 innate immunity provides broad defenses against infection
- Microbes present in food or water, or those in swallowed mucus, must contend with the highly acidic environment of the stomach.
- The acid destroys many microbes before they can enter the intestinal tract.
- One exception, the virus hepatitis A, can survive gastric acidity and gain access to the body via the digestive tract.
- phagocytic cells and antimicrobial proteins
- Microbes are destroyed within lysosomes in two ways.
- Lysosomes contain nitric oxide and other toxic forms of oxygen, which act as potent antimicrobial agents.
- Lysozymes and other enzymes degrade mitochondrial components.
- Four types of white blood cells are phagocytic.
- The phagocytic cells called neutrophils constitute about 60–70% of all white blood cells (leukocytes).
- Another set of proteins that provide innate defenses are the interferons, which defend against viral infection.
- Enhanced blood flow and vessel permeability have several effects.
- First, they aid in delivering clotting elements to the injured area.
- Clotting marks the beginning of the repair process and helps block the spread of microbes elsewhere.
- Second, increased blood flow and vessel permeability increase the migration of phagocytic cells from the blood into the injured tissues.
- Phagocyte migration usually begins within an hour after injury.
- 43.2 in acquired immunity, lymphocytes provide specific defenses against infection
- Lymphocytes provide the specificity and diversity of the immune system.
- The vertebrate body is populated by two main types of lymphocytes: B lymphocytes (B cells) and T lymphocytes (T cells).
- Both types of lymphocytes circulate throughout the blood and lymph and are concentrated in the spleen, lymph nodes, and other lymphatic tissue.
- B and T cells recognize antigens by means of antigen-specific receptors embedded in their plasma membranes.
- A single B or T cell bears about 100,000 identical antigen receptors.
- 43.3 humoral and cell mediated immunity defend against different types of threats!
- The immune system can mount two types of responses to antigens: a humoral response and a cell-mediated response.
- Humoral immunity involves B cell activation and clonal selection and results in the production of antibodies that circulate in the blood plasma and lymph.
- Circulating antibodies defend mainly against free bacteria, toxins, and viruses in the body fluids.
- In cell-mediated immunity, activation and clonal selection of cytotoxic T lymphocytes allows these cells to directly destroy certain target cells, including “nonself” cancer and transplant cells.
- 43.4 The immune system’s ability to distinguish self from nonself limits tissue transplantation
- to attacking pathogens, the immune system will also attack cells from other individuals.
- One source of potential problems with blood transfusions is an immune reaction from individuals with incompatible blood types.
- B antigens are found on type B red blood cells.
- Both A and B antigens are found on type AB red blood cells.
- Neither antigen is found on type O red blood cells.
- 43.5 exaggerated , self - directed or diminished immune responses can cause diseases
- Allergies are exaggerated responses to certain environmental antigens, called allergens.
- Sometimes the immune system loses tolerance for self and turns against certain molecules of the body, causing one of many autoimmune diseases.
- AIDS is another acquired immune deficiency.
- Healthy immune system function appears to depend on both the endocrine system and the nervous system
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