The Body s Defenses CHAPTER 24

Transcription

1 CHAPTER 24 The Body s Defenses PowerPoint Lectures for Essential Biology, Third Edition Neil Campbell, Jane Reece, and Eric Simon Essential Biology with Physiology, Second Edition Neil Campbell, Jane Reece, and Eric Simon Lectures by Chris C. Romero

2 Biology and Society: The Next Pandemic? A vaccine is a harmless derivative or variant of a disease-causing microbe. In many industrialized nations, Vaccination programs have eliminated previously feared viral disease.

3 A permanent vaccination for the influenza virus has yet to be developed. This virus has been responsible for some of the deadliest pandemics of the twentieth century.

4 Some medical researchers fear that a pandemic may start from a newly discovered strain of influenza virus called the avian flu.

5 Nonspecific Defenses Three lines of defense protect us from invaders of varying types.

6 Figure 24.2

7 The human body s first line of defense is a set of physical barriers and chemical agents that prevent foreign invaders from getting inside.

8 External Barriers The body has several physical barriers: An outer layer of intact skin Hair in the nostrils Mucous membranes

9 Cilia

10 Figure 24.3

11 In addition, the body also employs nonspecific chemical defenses: Sweat, saliva, and tears contain antimicrobial chemicals. Glands produce oils and acids.

12 Internal Defenses When an invader penetrates the body s external barriers, a set of nonspecific internal defenses that depend mostly on white blood cells acts as a second line of defense.

13 Figure 24.4

14 Other nonspecific internal defenses include proteins that either attack microbes directly or impede their reproduction.

15 Figure 24.5

16 The Inflammatory Response The inflammatory response Is a coordinated set of nonspecific defenses in response to damaged cells.

17 Figure 24.6

18 Damaged cells release histamine and prostaglandins that increase blood flow to the damaged area.

19 The Lymphatic System The lymphatic system

20 Figure 24.7

21 The lymphatic system has two main functions: Return tissue fluid to the circulatory system Fight infection

22 The organs of the lymphatic system are lymph nodes, packed with white blood cells that fight infection.

23 Specific Defenses: The Immune System The immune system Consists of a large collection of cells that work together to present a specific response to infection.

24 Antigens Are foreign substances that elicit an immune response. Antibodies Are proteins found in blood plasma that attach to one particular kind of antigen and help counter its effects.

25 In addition to being specific, the immune system can remember antigens and react more promptly to second exposures to infection.

26 Immunity Is resistance to specific invaders. Is usually acquired by natural infection.

27 Vaccinations Trigger active immunity, stimulating the body to defend itself.

28 Passive immunity Is acquired by receiving premade antibodies.

29 Recognizing the Invaders Lymphocytes Lymphocytes Are white blood cells found most often in the lymphatic system. Produce the immune response. Originate from stem cells in the bone marrow.

30 There are two kinds of lymphocytes: B cells, which develop in the bone marrow T cells, which become specialized in the thymus

31 Figure 24.9

32 In the humoral immune response, B cells secrete antibodies as a form of defense. In the cell-mediated immune response, T cells circulate in the blood and lymph, attacking infected body cells.

33 When T or B cells develop, the cell synthesizes molecules of a specific protein and builds them into its plasma membrane.

34 Antibodies Antibodies produced by B-cells Are proteins that serve as molecular weapons of defense. Contain four polypeptide chains arranged in a Y shape. Antibodies

35 Figure 24.10

36 An antibody molecule has two related functions in humoral immunity: Recognize and bind to a certain antigen By binding to it, help to counter its effect

37 Responding to the Invaders The immune system stops infections by destroying antigen-bearing invaders.

38 B Cells and Clonal Selection Clonal selection Is a process by which the immune system can defend against almost an infinite variety of antigens.

39 Clonal selection in B cells Role of B Cells

40 Figure 24.11

41 Monoclonal antibodies Are the antibodies produced by a single clone.

42 Immunological Memory The primary immune response takes several days to produce effector cells via clonal selection. Clonal selection also produces memory cells, which can last decades in the lymph nodes.

43 The secondary immune response Is produced when the same antigen is encountered again. Is initiated much faster due to the presence of memory cells.

44 T Cells T cells Respond to pathogens that have already entered body cells.

45 Helper T cells Bind to other white blood cells that have previously encountered an antigen. Helper T Cells

46 Figure 24.12

47 A helper T cell is activated by the binding of a T cell receptor to a self-nonself complex.

48 Figure 24.13

49 Cytotoxic T cells Are the only T cells that actually kill other cells. Cytotoxic T Cells T Cell Receptors

50 Figure 24.14

51 Immune Disorders If the interplay of immune cells malfunctions, problems in the immune response can result.

52 Allergies Allergies Are abnormal sensitivities to antigens in the environment. Allergens Are antigens that cause allergies.

53 The symptoms of an allergy result from a two-stage reaction sequence.

54 Figure 24.15

55 Anaphylactic shock Is an especially dangerous type of allergic reaction. Can be counteracted with injections of epinephrine.

56 Figure 24.16

57 Autoimmune Diseases The body s immune system Normally reacts only against foreign (nonself) substances. Generally rejects transplanted organs, whose cells lack the recipient s unique fingerprint of self proteins.

58 In autoimmune diseases The immune system turns against the body s own molecules.

59 Figure 24.17

60 Immunodeficiency Diseases In immunodeficiency diseases, Immune components are lacking, and infections recur.

61 Immunodeficiencies May arise through inborn conditions or from disease.

62 AIDS AIDS is a worldwide epidemic that kills millions of people each year. HIV, the AIDS virus, Attacks helper T cells, crippling both humoral and cell-mediated immunity.

63 Practicing safer sex can prevent the spread of HIV and save many lives.

64 Figure 24.18

65 Evolution Connection: HIV Evolution HIV has one of the fastest rates of mutation of any pathogen ever studied. HIV Reproductive Cycle

66 Figure 24.19

67 Drug-resistant HIV strains are now being documented in newly infected patients, Exhibiting how this virus readily adapts through natural selection.