Chapter 14: The Immune System & Lymphoid Organs

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1

What system in the body provides defense against infectious agents?

immune system

2

What are the two partially overlapping divisions of the immune system?

  1. innate immunity
  2. adaptive immunity
3

What are the primary lymphoid organs?

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  1. thymus
  2. bone marrow
4

What are the secondary lymphoid organs?

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  1. lymph nodes
  2. spleen
  3. mucosa-associated lymphoid tissue
5

Which division of the immune system involves immediate, nonspecific actions?

innate immunity

6

Which type of leukocytes are especially important in the innate immune response?

granulocytes

7

What receptors on leukocytes allow the recognition and binding of surface components of invaders?

toll-like receptors (TLRs)

8

Which type of leukocytes destroy unhealthy host cells, including infected or tumorigenic cells?

natural killer (NK) cells

9

What are five antimicrobial chemicals produced by the innate immune system?

  1. hydrochloric acid lowers pH to kill microbes
  2. defensins disrupt bacterial cell walls
  3. lysozyme hydrolyzes bacterial cell walls
  4. complement proteins enhance phagocytosis
  5. interferons signal NK cells to kill infected cells
10

Which division of the immune system acquired gradually, more specific, and slower to respond?

adaptive immunity

11

Which type of leukocytes are especially important in the adaptive immune response?

lymphocytes

12

Which cells function to present molecules from invaders to lymphocytes in the adaptive immune response?

antigen-presenting cells (APCs)

13

What cells, produced in the adaptive immune response, allow more rapid responses to future invaders?

memory lymphocytes

14

What substances are used by cells of the immune system to communicate with each other?

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cytokines

15

What process, mediated by cytokines, enables directed cell movements toward sites of inflammation?

chemotaxis

16

What are cytokines that produce chemotaxis called?

chemokines

17

What group of cytokines stimulate or suppress lymphocyte activities in adaptive immunity?

interleukins

18

What is a molecule that is recognized by cells of the adaptive immune system called?

antigen

19

What is the specific molecular domain of the antigen that immune cells react to called?

epitope

20

What are the two types of immune responses to antigens?

  1. cellular
  2. humoral
21

What is primarily responsible for mediating the cellular immune response?

lymphocytes

22

What is primarily responsible for mediating the humoral immune response?

antibodies

23

What family of glycoproteins do antibodies belong to?

immunoglobulins (Ig)

24

What type of cells, derived from clonally proliferating B lymphocytes, function to secrete antibodies?

plasma cells

25

What is the basic structure of an immunoglobulin?

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There are two identical light chains and two identical heavy chains bound by disulfide bonds.

26

What is the isolated carboxyl-terminal portion of the heavy-chain molecule of an immunoglobulin called?

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constant region (Fc)

27

What are the amino-terminal ends of the light and heavy chains of an immunoglobulin called?

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variable portions (Fab)

28

What do the variable portions of one heavy and one light chain of an immunoglobulin comprise?

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antigen-binding site

29

What are the five main classes of immunoglobulins in humans?

  1. IgG (75%-85%)
  2. IgA (10-15%)
  3. IgM (5-10%)
  4. IgE (0.002%)
  5. IgD (0.001%)
30

Which immunoglobulin is the most abundant in the blood and has the longest half life?

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IgG

31

What is a unique property of IgG?

It crosses the placental barrier into the fetal circulation to confers passive immunity to the newborn.

32

Which immunoglobulin is present in exocrine secretions as a dimeric form?

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IgA

33

What polypeptide functions to join monomers of immunoglobulins to form polymers?

J chain

34

What protein is released with IgA to confer resistance to proteolysis in exocrine secretion?

secretory component

35

Which immunoglobulin usually exists in a pentameric form united by a J chain?

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IgM

36

What is unique about the function of IgM?

It is the first antibody produced in an initial response to an antigen and the most effective antibody class in activating the complement system.

37

Which immunoglobulin usually exists as a monomer bound to mast cells and basophils?

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IgE

38

What type of reaction is mediated by binding of cell-bound IgE with the antigens?

allergic reaction

39

Which immunoglobulin is the least abundant and least understood class of antibody?

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IgD

40

What three actions are accomplished by binding of an antigen-binding site of an antibody to an antigen?

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  1. neutralization
  2. agglutination
  3. precipitation
41

What three actions are mediated by the Fc portion of an antibody bound to an antigen?

  1. complement activation
  2. opsonization
  3. NK cells activation
42

What specialized integral membrane protein complexes function in antigen presentation?

major histocompatibility complex (MHC)

43

What are the two key types of major histocompatibility complexes?

  1. MHC class I
  2. MCH class II
44

Which MCH class is found on all nucleated cells presenting “self-antigens”?

MHC class I

45

Which MCH class is found only in cells of the mononuclear phagocyte system, presenting peptides from potentially pathogenic cells?

MHC class II

46

What are tissue grafts in which the donor and the host are the same individual classified as?

autografts

47

What are tissue grafts which involve two related or unrelated individuals classified as?

allografts (homografts)

48

What are tissue grafts taken from an animal individuals classified as?

xenografts

49

Which immunosuppressive drugs have allowed for more widespread use of allografts?

cyclosporins

50

What specialized cell plays an important role in the immune response as APCs?

dendritic cells

51

What are the primary lymphoid organs?

  1. bone marrow
  2. thymus
52

Where do cells destined to become B lymphocytes develop?

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bone marrow

53

Where do cells destined to become T lymphocytes develop?

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thymus

54

What are the secondary lymphoid organs?

  1. lymph nodes
  2. spleen
  3. mucosa-associated lymphoid tissue
55

What type of collagen comprises the reticulin fiber network supporting all secondary lymphoid tissue?

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type III collagen

56

What fibroblastic cells produce the reticulin fiber network supporting all secondary lymphoid tissue?

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reticular cells

57

What surface proteins allow lymphocytes to be distinguished as B cells and subcategories of T cells?

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CD markers (“cluster of differentiation”)

58

Which lymphocytes are long lived and constitute nearly 75% of circulating lymphocytes?

T lymphocytes

59

What surface protein complexes enable T lymphocytes to recognize antigenic epitopes?

T-cell receptors (TCRs)

60

What is the basic structure of a TCR?

Most consist of two glycoproteins called the α chain and β chain, each with variable regions.

61

What term is used to describe the property of T cells only being able to recognize antigenic peptides when presented as part of MHC molecules?

MHC restricted

62

What are four important subpopulations of T cells?

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  1. helper T cells (Th cells)
  2. cytotoxic T lymphocytes (CTLs)
  3. regulatory T cells (Tregs)
  4. γδ T lymphocytes
63

Which CD characterizes helper T cells cells?

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CD4

64

Which MCH class does TCR require CD4 as a coreceptor to recognize?

MHC class II

65

Which CD characterizes CTLs?

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CD8

66

Which MCH class does TCR require CD4 as a coreceptor to recognize?

MHC class I

67

What type of immunity is mediated by the actions of cytotoxic T lymphocytes?

cell-mediated immunity

68

What cells, formed after activation of cytotoxic T cells, allow for more rapid immune responses in the future?

memory cytotoxic T cells

69

Which CDs characterize regulatory T cells cells?

CD4 and CD25

70

What term is used to describe the inhibitory effect of T regulatory cell on specific immune responses?

peripheral tolerance

71

Which cells are targeted by the retrovirus that causes acquired immunodeficiency syndrome (AIDS)?

helper T cells

72

What surface protein complexes enable B lymphocytes to recognize antigenic epitopes?

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B-cell receptors (BCRs)

73

What cells do B lymphocytes interact with in secondary lymphoid tissues?

follicular dendritic cells (FDCs)

74

What is formed by the aggregation of B cells attaching to FDCs in secondary lymphoid tissues?

primary lymphoid nodule

75

What develops from the primary lymphoid nodule with the help of adjacent T cells?

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secondary lymphoid nodule

76

What are the lightly stained centers of secondary lymphoid nodules filled with large lymphoblasts called?

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germinal centers

77

What is the darkly stained periphery of secondary lymphoid nodules filled nonproliferating B cells called?

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mantle

78

What antibody-producing cells are formed by differentiation of B lymphocytes?

plasma cells

79

What type of immunity is mediated by the actions of B lymphocytes?

humoral immunity

80

What cells, derived from newly formed B cells, allow for more rapid immune responses in the future?

memory B cells

81

What is the the primary or central lymphoid organ in which T cells are produced?

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thymus

82

What term is used to describe the function of the thymus in preventing autoimmunity?

central tolerance

83

What term is used to describe the decrease in mass of the thymus during puberty?

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involution

84

What disease is caused by failed development of the third (and fourth) pharyngeal pouches, producing thymic hypoplasia and resultant immunodeficiency?

DiGeorge syndrome

85

What two zones make up each incompletely separated lobule of the thymus?

  1. cortex
  2. medulla
86

What unique cells with both epithelial and reticular features are found in the thymic cortex and medulla?

  1. T lymphoblasts (or thymocytes)
  2. thymic epithelial cells (TECs)
87

What are the three populations of TECs in the cortex of the thymus?

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  1. TECs forming a blood-thymus barrier
  2. TECs forming the cytoreticulum
  3. TECs forming a corticomedullary barrier
88

What are the aggregates of concentrically arranged TECs in the thymic medulla called?

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Hassall corpuscles

89

What are two stages do thymocytes undergo in the thymus to become mature T cells?

  1. positive selection
  2. negative selection
90

Where is the site of positive selection in the thymus?

cortex

91

What does T cell survival depend on in the positive selection process?

The ability of the T cell to recognize and bind antigens on the MHC molecules properly.

92

Where is the site of negative selection in the thymus?

medulla

93

What does T cell survival depend on in the negative selection process?

The ability of the T cell to not bind to self-antigens on the MHC molecules.

94

What gene expressed by medullary thymic epithelial cells allows maturing T cells to be exposed to a variety of tissue-specific antigens during negative selection?

Aire gene (autoimmune regulator)

95

What percentage of developing T lymphocytes pass both positive and negative selection?

2%

96

What is lymphoid organ is dispersed diffusely in mucosa throughout the body?

mucosa-associated lymphoid tissue (MALT)

97

Where are the three areas in which the MALT is most concentrated?

  1. tonsils
  2. Peyer patches
  3. appendix
98

What are the large masses of lymphoid tissue in the mucosa of the posterior oral cavity and nasopharynx?

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tonsils

99

What are the three groups of tonsils called?

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  1. palatine
  2. lingual
  3. pharyngeal
100

Which tonsils are located on the soft palate, covered by stratified squamous epithelium, and are characterized by tonsillar crypts and a partial capsule?

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palatine tonsils

101

Which tonsils are located on the base of the tongue, covered by stratified squamous epithelium, and have tonsillar crypts but no distinct capsule?

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lingual tonsils

102

Which unparied tonsil is situated in the posterior wall of the nasopharynx covered by pseudostratified ciliated columnar epithelium, and has a capsule but no crypts?

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pharyngeal tonsil

103

What condition is caused by chronic inflammation of the pharyngeal lymphoid tissue?

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adenoids

104

What are the large aggregates of lymphoid nodules in the mucosa and submucosa of the ileum called?

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Peyer patches

105

What unique epithelial cells covers Peyer patches, specialized for uptake of microorganisms?

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M (microfold) cells

106

What short, small projection from the cecum contains a significant collection of MALT, as well as the normal bacterial flora of the large intestine?

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appendix

107

What are the bean-shaped, encapsulated structure distributed along the lymphatic vessels?

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lymph nodes

108

What are the lymphatic vessels entering the convex surface of the lymph node called?

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afferent lymphatics

109

What are the lymphatic vessels exiting the concave depression of the lymph node called?

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efferent lymphatic

110

What is the concave depression of the lymph node where the efferent lymphatic leaves and the artery, vein, and nerve penetrate the organ?

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hilum

111

What feature of lymph vessels ensures unidirectional lymph flow throughout the lymphatic system?

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valves

112

What are the three regions of a lymph node?

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  1. cortex
  2. paracortex
  3. medulla
113

What two components make up the cortex of a lymph node?

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  1. subcapsular sinus
  2. lymphoid nodules
114

What are the spaces branching internally among the lymphoid nodules from the subcapsular sinus?

cortical sinuses

115

What is lacking from the paracortex of a lymph node which allows it to be distinguished from the cortex?

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nodules

116

What specialized postcapillary venules in the paracortex provide an important entry point for lymphocytes into lymph nodes?

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high endothelial venules (HEVs)

117

What are the two major components of the medulla of a lymph node?

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  1. medullary cords
  2. medullary sinuses
118

What are the branched masses of lymphoid tissue extending from the paracortex into the medulla of a lymph node?

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medullary cords

119

What are the dilated spaces lined by discontinuous endothelium that separate the medullary cords of a lymph node?

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medullary sinuses

120

What is the first lymph node which metastatic cancer cells are most likely to spread called?

sentinel lymph node

121

What is neoplastic proliferation of lymphocytes called?

lymphoma

122

What disease is characterized by obliteration of the normal architecture of lymph nodes and conversion into enlarged structures filled with lymphocytes?

lymphadenopathy

123

What is the largest single accumulation of lymphoid tissue in the body?

spleen

124

What is unique about the function of the spleen among the lymphoid organs?

It is the only lymphoid organ involved in filtration of blood.

125

What is the parenchyma of the spleen called?

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splenic pulp

126

What are the two components of splenic pulp?

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  1. white pulp (20%)
  2. red pulp (80%)
127

What two elements compose the white pulp of the spleen?

  1. lymphoid nodules
  2. periarteriolar lymphoid sheaths (PALS)
128

What two elements compose the red pulp of the spleen?

  1. sinusoids
  2. splenic cords
129

What are the first arteries branching from the hilum to enter the spleen called?

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trabecular arteries

130

What are the arterioles branching from the trabecular arteries to enter the parenchyma of the spleen called?

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central arterioles

131

What are the T cells surrounding the central arterioles in the white pulp of the spleen called?

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periarteriolar lymphoid sheaths (PALS)

132

What are the short straight arterioles that branch from the central arterioles in the red pulp?

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penicillar arterioles

133

What are the elongated endothelial cells lining the splenic sinusoids of the red pulp?

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stave cells

134

What are the two routes of blood flow through the splenic red pulp?

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  1. closed circulation
  2. open circulation
135

In which route of blood flow through the splenic red pulp is the blood is always enclosed by endothelium?

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closed circulation

136

In which route of blood flow through the splenic red pulp is the blood dumped into the stroma of the splenic cords?

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open circulation

137

What happens to stiff or effete, swollen RBCs that enter open circulation through the splenic red pulp?

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They are blocked from passing between the stave cells and undergo selective removal by macrophages.

138

What do the small red pulp veins that converge as, which in turn form the splenic vein?

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trabecular veins

139

What is enlargement of the spleen called?

splenomegaly

140

What is removal of the spleen called?

splenectomy