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histology > unit 7 > Flashcards

unit 7 Flashcards

1
Q

what are the primary lymphoid organs?

A

thymus, bone marrow, GALT

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2
Q

what are the secondary lymphoid organs?

A

lymph nodes and spleen

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3
Q

what happens in the thymus?

A

T cell differentiation

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4
Q

what is a special feature of the thymus?

A

antigen independent proliferation

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5
Q

how does the thymus develop into a lymphoid organ?

A

multipotent lymphoid stem cells enter into the epithelial rudiment and occupy spaces between the epithelial cells

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6
Q

thymus structure

A

thin capsule made of connective tissues
trabeculae extend from capsule into parenchyma and establish thymus lobules

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7
Q

what part of the thymus contains developing T lymphocytes?

A

thymic cortex which is the outer portion of the thymic parenchyma

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8
Q

how will a stain appear when there is a large number of lymphocytes?

A

very basophilic

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9
Q

what do epithelioreticular cells provide?

A

a frame work for developing T lymphocytes

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10
Q

what types of epithelioreticular cells are found in the cortex?

A

I, II, and III

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11
Q

what types of epithelioreticular cells are found in the medulla?

A

IV, V, and VI

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12
Q

what is the major component of the blood-thymus barrier? what is it impermeable to?

A

endothelium
macromolecules

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13
Q

how do type I epithelioreticular cells protect T lymphocytes?

A

contain occluding junctions
surround the capillary wall in the cortex with their basal lamina

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14
Q

where is the perivascular CT contained? what does it do?

A

between the basal lamina of both epithelioreticular cells and endothelial cells
provides protection for developing T lymphocytes

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15
Q

thymic T cell education

A

a process of multipotential lymphoid stem cell maturation and differentiation into immunocompetent T cells

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16
Q

what is positive selection?

A

selection for thymocytes that recognize self MHC molecules expressed on cortical epithelium

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17
Q

what happens if the lymphocyte does not recognize self MHC and self antigen?

A

death of the cell

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18
Q

what happens to cells that pass positive selection?

A

they leave the cortex and enter the medulla and undergo another selection

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19
Q

where does positive selection occur? where does negative selection occur?

A

cortex of thymus
medulla of thymus

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20
Q

expression of what molecules occurs in positive selection?

A

CD2, CD7, CD1, TCRs, CD3, CD4, CD8

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21
Q

what cells present self antigen to developing T cells in positive selection?

A

type II and III epithelioreticular cells

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22
Q

what is negative selection?

A

selection against thymocytes that recognize self antigen in the context of self MHC

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23
Q

what cells are eliminated by negative selection?

A

T cells that demonstrate too high of an affinity for self MHC

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24
Q

cells that survive negative selection become what?

A

either cytotoxic CD8+ or helper CD4+ T lymphocytes

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25
Q

what can help promote the negative selection process?

A

regulatory cytokines secreted by type VI epithelioreticular cells

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26
Q

what are thymic corpuscles derived from?

A

type VI epithelioreticular cells
aka Hassall’s corpuscles

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27
Q

thymic corpuscle characteristics

A

found in thymic medulla
contain closely packed, concentrically arranged type VI cells
exhibit flattened nuclei

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28
Q

what do thymic corpuscles contain? what is their probable function?

A

contain keratohyalin granules, bundles of cytoplasmic intermediate filaments, lipid droplets
thought to produce interleukins that function in T differentiation and education

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29
Q

what results in the formation of different leukocytes and their precursors

A

interactions between bone marrow stromal cells, ECM components, cytokines, and developing hematopoietic cells

30
Q

where are stromal cells that are involved in B cell development located?

A

endosteal surface (surrounds the medulla of bone marrow)

31
Q

B cell development steps

A

stem cell
pro-b cell
pre-b cell
b cell
plasma cell
(at some point, recognize antigen epitope to become a plasma cell)

32
Q

what is the lymph node the main site of?

A

T and B lymphocytes antigen-dependent proliferation and differentiation into effector cells and memory cells

33
Q

what are the parts of the lymph node?

A

capsule, cortex, medulla

34
Q

what is the capsule of the lymph node composed of?

A

dense CT that surrounds the node

35
Q

what is the sub capsular sinus of lymph node? what occurs here?

A

under capsule, adjacent to trabeculae
afferent lymphatic vessels empty here
they communicate with medullary sinuses

36
Q

where do plasma cells not secrete antibodies?

A

in germinal centers

37
Q

what does the parenchyma of a lymph node contain?

A

naive and antigen exposed T and B lymphocytes and accessory cells arranged in a reticular framework

38
Q

what are lymphatic nodules/primary follicles?

A

spherical shaped aggregates of lymphocytes in the lymph node cortex

39
Q

what occurs in a germinal center?

A

B cell proliferation and differentiation in response to an antigen

40
Q

what is contained in the medulla of lymph nodes?

A

medullary cords and sinuses

41
Q

what does the deep cortex of lymph nodes contain?

A

high endothelial venues consisting of cuboidal endothelial cells
T cells

42
Q

what is contained with primary nodules of lymph nodes?

A

naive B cells

43
Q

what do medullary cords contain

A

lymphocytes, macrophages, dendritic cells, plasma cells

44
Q

what are cells of the reticular meshwork

A

reticular cells, dendritic cells, macrophages, follicular dendritic cells

45
Q

what do reticular cells do?

A

secrete type III collagen
cytoplasmic processes wrap around bundles of reticular fibers
provide supports
express surface molecules and produce substance that attract T and B cells and dendritic cells

46
Q

what do dendritic cells do?

A

express high levels of MHC and co-stimulatory molecules
involved in antigen presentation

47
Q

what do macrophages do?

A

phagocytosis
antigen-presenting cells, express MHC I and II and costimulatory molecules

48
Q

what do follicular dendritic cells do?

A

have thin, hair like branching cytoplasmic processes that interdigitate between B lymphocytes in the germinal centers

49
Q

what do high endothelial venules contain?

A

receptors for antigen primed lymphocytes

50
Q

what do high endothelial venules do?

A

signal lymphocytes to leave circulation and migrate into lymph nodes

51
Q

how do lymphocytes enter the lymph node

A

through afferent lymphatic vessels

52
Q

how do lymphocytes exit the lymph node

A

through efferent lymphatic vessels

53
Q

how do lymphocytes from the blood enter the deep cortex?

A

high endothelial venules

54
Q

what is lymphadenopathy?

A

abnormal enlargement of lymph nodes that undergo hypertrophy

55
Q

what are some general features of the spleen?

A

derived from mesenchyme in the dorsal mesogastrium
temporarily an organ for hematopoiesis embryonically
it is a major repository for mononuclear phagocytic cells
filters the blood

56
Q

structural features of the spleen

A

surrounded by a CT capsule
capsule trabeculae project into the substance of the spleen
consists of red and white pulp

57
Q

what are periarteriolar lymphatic sheaths? what kind of cells are typically found here?

A

a portion of white pulp that surround the splenic artery
T lymphocytes are predominantly contained here

58
Q

what is the red pulp?

A

consists of splenic sinuses surrounded by splenic cords
contains large number of RBCs that it filters

59
Q

open splenic circulation

A

splenic artery –> trabecular arteries –> central arteries –> penicillar arterioles –> reticular meshwork of splenic cords surrounding splenic sinus

60
Q

what are the immune functions of the spleen?

A

antigen presentation
initiation of immune response
activation and proliferation of B and T cells
production of antibodies
removal of macromolecular antigens from the blood

61
Q

what is splenomegaly?

A

enlargement of the spleen, commonly caused by portal hypertensions

62
Q

histologic features of splenomegaly

A

thick and fibrotic capsule
red pulp shows venous sinusoids and increased macrophage numbers
white pulp is atrophic

63
Q

which tonsils form a ring of lymphoid tissue in the entrance of the oropharynx?

A

pharyngeal tonsil, palatine tonsils, lingual tonsil

64
Q

what are tonsils crypts?

A

epithelium forming the surface on the tonsils dips into underlying CT

65
Q

what happens in tonsilar crypts?

A

many lymphatic nodules are evident in the walls of the crypt
IgA antibodies are secreted from plasma cells that differentiate here

66
Q

where are Peyer’s patches found? what do they consist of?

A

the ileum
numerous aggregations of lymphatic nodules containing T and B cells

67
Q

where do Peyer’s patches originate?

A

in the lamina propria, extend into the submucosa of the ileum
they have specialized epithelium containing M cells that are involved in antigen presentation

68
Q

what is unique about the lamina propria in the appendix?

A

heavily infiltrated with lymphocytes, contains numerous lymphocytic nodules

69
Q

what are mucosal associated lymphoid tissues?

A

lymphoid tissue associated with the mucous membrane, not enclosed by a capsule

70
Q

what do type I interfeurons have?

A

critical anti-viral and immunostimulatory effects
they are produced within a few hours after viral infection

71
Q

what cells can produce type I interferon?

A

almost any cells

72
Q

what are plasmacytoid dendritic cells?

A

specialized interferon-producing cells

histology (15 decks)

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