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Histology > Lymphoid System > Flashcards

Lymphoid System Flashcards

1
Q

Antigens (Ag)

A

. Molecules recognized by cells of immune system

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2
Q

Cells of immune system

A

. Lymphocytes
. Macrophages
. Dendritic cells
. Granulocytes

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3
Q

Innate immunity

A

. Nonspecific, quickly utilized
. No previous exposure needed
. Macrophages, dendritic, granulocytes involved
. Have physical and chemical barriers of skin and mucous membranes to contribute

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4
Q

Adaptive immunity

A

. Specific response mediate by lymphocytes
. Need previous exposure of antigen
. Only small number lymphocytes will recognize particular antigen
. Slower response
. Generates immunologic memory
. Uses cellular and humoral immune responses

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5
Q

What occurs when lymphocyte recognizes particular antigen?

A

. Activates and divides

. Undergoes clonal expansion where millions of identical effector cells are made

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6
Q

Cellular immune response

A

. Mediated by T lymphocytes

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7
Q

Humoral immune response

A

. Mediated by plasma cell-produced antibodies

. Bind to antigens to mark for destruction

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8
Q

Antigen presenting cells

A

. Antigens processed before recognition
. Found in skin, lymph nodes, spleen, thymus, mucosal epithelia
. Dendritic, langerhans, macrophages, and B cells
. Recognized by T lymphocytes as MHC molecule

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9
Q

Antigen presenting cell mechanism

A

. Initiated when APC ingests antigen (usually protein)
. Ag broken down into small peptide-fragments in cell
. Fragments bind to molecule called histocompatibility complex (MHC)
. Ag-MHC complex is transported to APC surface

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10
Q

MHC in humans also called ____

A

Human leukocyte antigen (HLA)

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11
Q

Population percentage of lymphocytes in circulation in blood or lymph

A

70%

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12
Q

Lymphocyte classification

A

. T cells

. B cells

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13
Q

Lymphocyte general functions

A

. Immunologic surveillance

. Display cell surface receptors that facilitate specific recognition of antigens

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14
Q

T cells

A

. Cell-mediate immunity
. Differentiate in thymus, majority of lymphocytes
. Detect cell-bound Ags presented by MHCs
. T helper cells (Th cells)
. T cytotoxic cells (Tc cells)
. Regulatory T cells

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15
Q

B cells

A

. Humoral immunity
. Differentiate into plasma (antibody-producing)
. Recognize soluble or cell-bound Ags

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16
Q

Antibody

A

. Protein that interacts w/ antigen (Igs do this too)

. Secreted by plasma cells

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17
Q

Reticular cells

A

. In majority of lymphoid tissues/organs

. Produce reticular fibers (collagen III) that for scaffold for lymphoid cells

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18
Q

Epithelioreticular cells

A

. Stellate cells in thymus
. Produce keratins
. Joined by desmosomes

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19
Q

Lymph Nodules

A 
. Densely packed, spherical clusters 
. Embedded in diffuse lymph tissue 
. Not covered by capsule 
. Found in CT 
. Not found in thymus 
. Primary or secondary
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20
Q

Primary nodule

A

. Homogenous

. Formed by small B cells

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21
Q

Secondary nodule

A

. Pale center, darker periphery
. Develop from primary nodules upon Ag stimulation
. Have mantle of just naive B cells

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22
Q

Germinal center of secondary nodule

A

. Dark zone: activated B cells proliferate (centroblasts) and undergo hypermutation where high affinity antibodies enervated
. Light zone: B cells lower profile ration rate and migrate (centrocytes), further differentiate into plasma cells and memory B cells or return to dark zone and become centroblasts again

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23
Q

Primary lymphoid organs

A

. Bone marrow, thymus, fetal liver
. Initial formation of lymphocytes
. Don’t contact Ags

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24
Q

Secondary lymphoid organs

A

. MALT, lymph nodes, spleen
. Cells migrate to here from primary sites
. Lymphocytes activated by encounters w/ Ag to start immune responses
. Ags transported through lymph
. MALT encounters Ags that entered from external environment via M cells

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25
Q

More than 50% lymphoid tissue located in ___

A

Mucosal system of digestive, respiratory, and GU tracts

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26
Q

Lymphocytes in lamina propria

A

. Mostly activated T cells, sometimes B cells and plasma cells

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27
Q

Tonsil lymph tissue

A

. Waldyer’s ring: diffuse and modular tissue in mucosa
. Tonsil epithelium invaginates into underlying lymph to form crypts/pits
. Lymph tissue separated by incomplete CT capsule
. Only have efferent lymph vessels

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28
Q

Types of tonsil

A

Palatine
Lingual
Pharyngeal

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29
Q

Palatine tonsils

A

. Btw palatopharyngeal and palatoglossal arches at post. Aspect of oral cavity
. Paired
. Covered by SSNK

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30
Q

Lingual tonsil

A

. On base of tongue
. Paired
. Converted by SSNK

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31
Q

Pharyngeal (adenoids) tonsil

A

. In post. Wall of nasopharynx
. Unpaired
. Psuedostratified ciliated epithelium w/ goblets (respiratory type)
. Can hypertrophy and obstruct nasal openings

32
Q

Lymph nodes

A

. Kidney bean shaped along lymph vessels
. Has hilum
. Blood vessels enter and leave at hilum, lymph vessels leave at hilum
. Surround by dense CT capsule
. Capsule sends trabeculae into node where stroma of reticular cells and fibers attach
. Macrophages and dendritic cells in reticular fiber network
. Afferent and efferent lymph vessels

33
Q

Lymph node parenchyma

A

. Diffuse and modular lymph tissue divided into cortex/medulla

34
Q

Lymph node cortex

A

. Area beneath capsule
. Outer cortex: diffuse T cells and modular B cells (B-lymphocyte area)
. Inner cortex/paracortex: diffuse only, thymus-dependent area, has T cells

35
Q

Lymph node medulla

A

. Pale staining
. Diffuse tissue forms medullary cords (strands)
. Cords contain plasma cells, lymphocytes, and macrophages
. Cords separated by medullary sinuses

36
Q

Subcapsular (marginal sinus)

A

. Btw capsule and lymph tissue of outer cortex

37
Q

Trabeculae sinuses

A

. Cortical/intermediate

. Btw trabeculae and lymph tissue in cortex

38
Q

Medullary sinuses

A

. Btw medullary cords

39
Q

Afferent lymphatics

A

. Bring lymph to node for filtering
. Come from other organs or other nodes
. Numerous vessels pierce capsule of node at periphery to drain subcapsular sinus

40
Q

Efferent lymphatics

A

. Fewer
. Formed by coalescence of medullary sinuses
. Exit at hilum and carry lymph away
. Efferent lymphatic plus node can become afferent lymphatic of next node

41
Q

T/F lymph flow multidirectional

A

F, unidirectional, towards hilum

42
Q

Pattern of lymph flow

A

. Afferent lymphatics -> subcapsular sinus -> cortical sinus -> medullary sinus -> efferent lymphatic

43
Q

Circulation of lymphocytes through nodes

A

. Some enter lymph, most enter from blood stream in deep cortex area
. Cross walls of cuboidalish endothelium of high endothelial post-capillary venules (HEV) by diapedesis
. T cells stay in deep cortex
. B cells migrate to nodules of superficial cortex

44
Q

HEV cells

A

. high endothelial cells of lymph nodes
. Have surface receptors for lymphocytes
. Gate for circulating lymphocytes

45
Q

Lymphadenopathy

A

. Lymph node enlargement

. Common consequence of infection

46
Q

Lymphoma

A

. Primary tumor of lymphoid tissue

47
Q

Spleen functions

A

. Filters blood and detects blood-borne antigens
. Removal and destruction of damaged RBCs and platelets
. Retrieval of iron from Hb

48
Q

Spleen characteristics

A

. Largest lymphoid organ
. Splenic a. Enters hilum and splenic v. Exits spleen at hilum
. Has no direct connections w/ lymph vessels
. Lymphocytes enter spleen via blood vessels
. Surrounded by dense CT capsule that extends into it via trabeculae
. Trabeculae partially divide parenchyma
. Rich reticular network
. White pulp and red pulp

49
Q

White pulp of spleen

A

. Lymphoid tissue
. Cuff of lymphocytes around central arterioles running through spleen
. Accumulations called periarteriolar lymphatic sheaths (PALS)
Lymphoid nodules at intervals along PALS that have mostly B cells
. Marginal zone of nodule surrounds follicle and is rich in macrophages
. Blood borne Ags filtered from blood in marginal zone

50
Q

Arterial circulation in spleen

A

. Splenic a. Branches into trabecular aa. That follow trabeculae
. Become central arterioles after they leave trabeculae and are surrounded by PALS
. Some branches of central arterioles end as marginal sinuses that supply marginal zone
. Central arterioles lose PALS and terminate as small penicillar aa/ entering red pulp

51
Q

Class I MHC

A

. Expressed by all nucleated cells

. HLA-A, B, C

52
Q

Class II MHC

A

. Expressed by APC

. HLA-DR, DQ, DP

53
Q

T helper cells

A

. CD4+
. Helps via contacts with APCs and other lymphocytes
. Help II: helps B lymphocytes to be plasma cells
. Helper I: activates macrophages

54
Q

Tc cells

A

. CD8+
. Cytotoxic functions
. Recognition and lysis of virally infected cells

55
Q

T regulatory cells

A

. CD4+, FoxP3

. Limit immune response, produce inhibitory cytokines

56
Q

Classes of Ig

A 
. IgA: secretory on mucosal surfaces
. IgE: basophil cell importance 
. IgG: most prevalent in blood plasma 
. IgM 
. IgD
57
Q

NK cells

A

Kills virally infected cells and tumor cells

Assists Tc cells

58
Q

Frequency for lymphocyte to recognize specific Ag

A

1 in 10,000 to 100,000 chance

. Even less for both B and T cells to recognize

59
Q

T/F there are reticulocytes I all lymphoid tissue

A

F, there aren’t in thymus

60
Q

Follicular dendritic cells

A

. In lymphoid nodules

. Mesenchymal origin, NOT bone-marrow derived

61
Q

Ig class-switch recombination (CSR)

A

. Centrocytes become plasma cells

3

62
Q

T/F neutrophils are rare in healthy MALT

A

T

63
Q

Red pulp of spleen

A

. Splenic sinusoids and cords (cords of Billroth)
. Cords supported by reticular cells/fibers, contain B and T cells, macrophages, plasma cells, dendritic cells, granulocytes, and rbcs
. Lined by stave cells

64
Q

Macrophage role in red pulp

A

. Phagocytosis old rbcs and begin breakdown of Hb and Fe recycling

65
Q

Stave cells

A

. Loosely connected, elongated endothelial cells
. Oriented parallel to blood flow
. Spaces btw cells allow blood to leave or enter sinus

66
Q

Closed circulation through red pulp

A

. Capillaries branching from pencillar arterioles connect directly w/ sinusoids
. Blood alway in blood vessel

67
Q

Open circulation in red pulp

A

. Capillaries from 0.5 penicillar arterioles are open-ended
. Blood enters splenic cords
. Cells return to circulation by squeezing spaces between stave cells of sinusoid
. Platelets, leukocytes, and young rbcs are flexible to do it
. Old rbcs are blood from reentry and phagocytosed

68
Q

Thymus embryological origin

A

. Lymphoid cells from hematopoietic mesenchyme
. Stroma made of epithelioreticular cells from endodermal epithelium of 3rd laryngeal pouch (no reticular fiberS)
. CT capsule and trabeculae from mesoderm

69
Q

Thymus structure

A

. In mediastinum
. 2 lobes divided into incomplete lobules
. CT capsule w/ trabeculae that have blood vessels, nerves, and efferent lymphatics
. CT in capsule has reticular fibers and fibroblasts
. Cortex w/ thymocytes(dark)
. Medulla less cellular (light)

70
Q

Epithelioreticular cells

A

. Provide framework for T cell development
. 6 cel types
. Form Hassall’s corpuscles (characteristic of thymus)
.

71
Q

Thymic education steps

A

. T cell precursors from bone marrow enter corticomedullary junction of thymus and migrate to outer cortex (thymocytes)
. Thymocytes interact w/ APCs and selected (positive selection) to mature further and enter medulla (10% survive, rest undergo apoptosis)
. Thymocytes that would mount immune response against itself is eliminated (neg. selection) in deeper cortex
. Cells that made it leave thymus and populate secondary lymphoid organs as naive T cells

72
Q

What mediate positive selection in thymus?

A

. epithelioreticular cells that display both MHC I and II

.

73
Q

What mediates negative selection in thymic education?

A

. Bone marrow-derived dendritic cells ad macrophages are main APCs

74
Q

Percentage of thymocytes that survive education process?

A

2%

75
Q

Thymus Medulla contents

A

. Paler
. Contains fewer cells
. Cells larger, have lighter nuclei and more cytoplasm

76
Q

Blood-thymus barrier

A

. Thymocytes mature into T cells in absence of Ags
. Barrier prevents contact btw thymocytes and Ags
. Created by endothelium (continuous w/ tight junctions), macrophages in perivascualr tissue, and epithelioreticular cells w/ tight junctions surrounding capillary wall in cortex

Histology (22 decks)

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