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SUM: Histology 1 > The immune system & Lymphoid organs > Flashcards

The immune system & Lymphoid organs Flashcards

1
Q

Immune system:

A

Consists of a large, diverse population of leukocytes located within every tissue of the body and lymphoid organs interconnected only by the blood and lymphatic circulation.

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2
Q

Innate immunity:

A

nonspecific involves a wide variety of effector mechanisms

Ex: granulocytes and other leukocytes

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3
Q

When is innate immunity present?

A

Is present from birth and involves leukocytes

(mainly granulocytes),

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4
Q

What proteins are part of the

Innate Immunity?

A

Proteins such as defensins, complement, lysozyme, and interferons (signaling proteins released by host cell in response to the presence of pathogens-Eg. Viruses, bacteria, parasites or tumor cells.

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5
Q

Adaptive immunity:

A

Adaptive immunity aims at specific microbial invaders, is mediated by lymphocytes and antigen-presenting cells (APCs)

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6
Q

Adaptive immunity: Produce?

A

produces memory cells that permit a similar, very rapid response if that specific microbe appears again.

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7
Q

Adaptive immunity: Distributed

A

lymphocytes and APCs for adaptive immunity are distributed throughout the body in the blood, lymph, and epithelial and connective tissues.

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8
Q

How do Immune cells communicate?

A

communicate with one another and regulate one another’s activities via polypeptide hormones called cytokines

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9
Q

Define Antibodies:

A

Antibodies are immunoglobulins produced by plasma cells after a progenitor B cell is activated by a specific antigen and rearranges its immunoglobulin genes so the antibody matches the antigen.

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10
Q

Define Antigens:

A

Are the regions of macromolecules, usually proteins, that are recognized by lymphocytes to elicit a specific immune response
against them.

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11
Q

Where is Lymphocyte found?

A

Initially in primary lymphoid organs (the thymus and bone marrow)

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12
Q

Lymphocyte activation and proliferation

Occur:

A

Secondary lymphoid organs (the lymph nodes,
And spleen, diffuse lymphoid tissue found in the mucosa of the digestive system, including the tonsils, Peyer patches & appendix

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13
Q

Innate immunity

A

Is present from birth and involves: leukocytes

(mainly granulocytes

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14
Q

What type of Proteins are present in Innate Immunity

A

Proteins such as defensins, complement, lysozyme, and interferons

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15
Q

How does Adaptive immunity develop?

A

slowly and is based on antigen presentation to lymphocytes

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16
Q

Immune cells communicate & regulate

Each another’s activities via?

A

polypeptide hormones called cytokines .

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17
Q

Antigens are the regions of what?

A

Macromolecules

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18
Q

What are Macromolecules?

A

Proteins, that are recognized by lymphocytes to elicit a specific immune response

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19
Q

What are lymphocytes?

A

Type of white blood cell that is part of the immune system.

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20
Q

What is a function of Lymphocyte?

A

To eliminate the antigen, by releasing antibodies (B cell), cytotoxic granules (cytotoxic T cells) or by signaling to other cells of the immune system (helper T cell).

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21
Q

What are Antibodies?

A

Immunoglobulins produced by plasma cells after a progenitor B cell is activated by a specific antigen and rearranges its immunoglobulin genes so the antibody matches the antigen.

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22
Q

What are immunoglobulin’s:

A

Large Y shaped protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens (bacteria & viruses)

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23
Q

What is MHC?

A

Major Histocompatibility complex

A set of cell surface proteins essential for the acquired immune system to recognize foreign molecules.

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24
Q

Surfaces of all nucleated cells bear what?

A

They bear fragments of their constituent proteins on major histocompatibility complex (MHC) class I molecules.

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25
Q

What type of cells derive from monocytes?

A

Only Antigen-Presenting cells (APCs) also present fragments of endocytosed foreign (usually from microorganisms) proteins on surface MHC class II molecules.

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26
Q

Where do Lymphocytes originate?

A

Primary lymphoid organs: bone marrow for B lymphocytes and the thymus for T lymphocytes.

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27
Q

B cells produce antibodies for?

A

Humoral immunity

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28
Q

What is Humoral Immunity?

A

Aspect of immunity that is mediated by macromolecules found in the extracellular fluids such as secreted antibodies, body fluids

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29
Q

T cells function in?

A

In cell-mediated immunity

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30
Q

What does T cells develop receptors

(TCRs) contain?

A

Usually containing ` and A chains.

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31
Q

What are ‘ and A chains responsible for?

A

They bind antigen along with another surface protein designated
by a CD (“cluster of differentiation”) numbering system .

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32
Q

What are the important classes of T cells?

A

CD4 + T helper cells ; CD8 +
cytotoxic T cells ; CD4 + CD25 + regulatory T cells and f􀀀c T cells ,
which have those TCR chains and are mainly in epithelia.

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33
Q

What is IgM

A

Immunoglobulin M- largest antibody –first to appear in the response to initial exposure to an antigen.

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34
Q

What are B-cell receptors (BCRs)?

A

IgM or IgD antibodies on the cell surface that bind specific antigens whenever they contact them.

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35
Q

Where are B and T cells often activated

& proliferate and begin to function

A

In the secondary lymphoid organs: the lymph nodes, all mucosa-associated lymphoid tissue (MALT), and the spleen .

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36
Q

In these organs, lymphocytes are
distributed within a meshwork of
what?

A

Reticulin

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37
Q

What is Reticulin produced by?

A

Produced by fibroblastic reticular cells , and most APCs are dendritic cells with many processes.

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38
Q

What occurs in the secondary

Lymphoid tissues?

A 
BCRs bind antigen not presented
in MHC class II molecules of another cell, the follicular dendritic cell (FDC) .
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39
Q

How is FDC B cell activated?

A

With Cytokines form helper T cell

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40
Q

What happens to FDC-activated B Cell?

A

It proliferates clonally to produce Temporarily a large lymphoid nodule (or follicle), which develops a pale germinal center

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41
Q

From lymphoid nodules cells

produced & disperse as what?

A

Plasma cells, various T cells, B, T memory cells that respond and proliferate quickly if their specific antigen reappears

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42
Q

What are T lymphoblast’s?

A

look up

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43
Q

What are Thymocytes?

A

Hematopoietic progenitor cells present in Thymus.

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44
Q

What is primary function of Thymocytes?

A

Is the generation of T Lymphocytes (T Cells)

45
Q

What is Thymopoiesis?

A

Process in the Thymus by which thymocytes differentiate into mature T lymphocytes.

46
Q

What is a Thymus gland?

A

Contains glandular tissue and produces several hormones, associated with the immune system then with Endocrine System. +
Serves a vital role in training & development of T lymphocytes or T cells(very important White Blood C.)

47
Q

Where do T lymphoblasts, or

thymocytes, attach to?

A

The thymus to a cytoreticulum

composed of interconnected epithelioreticular cells .

48
Q

What do Thymic epithelioreticular cells secrete?

A

Many cytokinesis,

49
Q

What are Thymic epithelioreticular

cells responsible for ?

A

Compartmentalizing of the thymus into a cortex and a medulla, and in the cortex surround blood vessels in the blood-thymus barrier.

50
Q

What happens to/if Developing T cells

have nonfunctional TCRs

A

Once detected they are removed in the thymic cortex by a process of positive selection

51
Q

Cells with functional TCRs move into?

A

The thymic medulla.

52
Q

Define Thymic medulla:

A

look up

53
Q

What happens once Cells w/

functional TCR move to thymic medulla?

A

Once in thymic medulla T cells whose TCRs bind strongly to “ selfproteins
, “ including proteins of many nonthymus cell types made by epithelioreticular cells expressing the Airegene , are induced to
undergo apoptosis there in a process of negative selection .

54
Q

What does this two-stage thymic

selection lead to?

A

To central immune tolerance,

producing functional T cells that do not bind to proteins of the host.

55
Q

At what point does the Peripheral
immune tolerance occur through
out the body?

A

When specific immune reactions are suppressed by regulatory T cells

56
Q

Where do Regulatory T cells originate?

A

Largely in the Thymic medulla

57
Q

How are T cell formed in the thymus?

A

Formed in the thymus upon interacting with dendritic cells presenting self-antigens in a process

58
Q

What is this T cell formation &

interaction promoted by?

A

Promoted by kines from epithelioreticular cell aggregates called Hassall corpuscles

59
Q

Where are Hassall corpuscles

Found?

A

Found only in the thymic medulla.

60
Q

What are Hassall corpuscles

A

Distinguished concentric arrangements of flattened epithelioid cells that are acidophilic future of the medulla

61
Q

Where is MALT found?

A

MALT is found in the mucosa of most tracts

62
Q

Provide examples of tracts where

MALT is found:

A

Concentrated in the palatine, lingual and pharyngeal tonsils , Peyer patches , and the appendix .

63
Q

What is Lymph node?

A

Lymph nodes are small encapsulated structures positioned along lymphatic vessels to filter lymph and facilitate antibody production.

64
Q

What ensures one-way flow of lymph?

A

Valves in the lymphatic vessels ensure the one-way flow of lymph

65
Q

Unlike MALT, lymph nodes are
completely encapsulated and occur
where?

A

Along the lymphatic vessels; each has several afferent lymphatics
and one efferent lymphatic.

66
Q

What surrounds the Lymph node?

A

Dense connective Tissue

67
Q

What is the role of a Lymph node?

A

Lymph node filters lymph and provides a site for B-cell activation and differentiation to antibody-secreting plasma cells.

68
Q

What are the most abundant cells

of lymph nodes

A

Lymphocytes

69
Q

What are other types of lymphocytes:

A

Plasma cells, dendritic cells, macrophages, and other APCs

70
Q

What are present within lymphoid nodules

A

FDCs

71
Q

What are FDC’s:

A 
follicular dendritic cells (FDCs), 
have long filamentous processes
 -are mesenchymal in origin and their function does not involve MHC class II molecules.
72
Q

Where are lypmphocytes cells arranged?

A

In a stroma of reticulin fibers

and reticular cells to form three major regions

73
Q

What are the three major reagions?

A

Outer cortex receiving lymph from
the afferent lymphatics,
inner paracortex smaller area, where most lymphocytes enter via high endothelial venules (HEVs),
central / inner medulla with sinuses converging at the efferent lymphatic.

74
Q

What are the regions of Cortex?

A

Subcapsular & Cortical sinuses

75
Q

What is subcapsular sinus?

A

Immediately inside the capsule,

receives lymph from the afferent lymphatics

76
Q

Cortical sinuses are also known as?

A

Trabecular sinuses

77
Q

What are the Cortical sinuses lined by?

A

Very thin discontinuous endothelium penetrated by the reticulin fibers & processes of dendritic cells.

78
Q

What cells pass through the Cortical sinuses?

A

Lymph containing antigens, lymphocytes, and APCs passes through
these sinuses and percolates easily into the surrounding lymphoid tissue.

79
Q

Lymphoid nodules are formed by?

A

fill most cortical areas are formed largely by helper T lymphocytes and proliferating B lymphoblasts

80
Q

What is the region between the cortex

and medulla?

A

The Paracortex

81
Q

How is Paracortex distinguished from

the outer cotex?

A

It does not have precise boundaries.. distinguished from the outer cortex by its lack of B-cell lymphoid nodules

82
Q

Paracortex contains what type of tissue?

A

Contains lymphoid tissue rich T cells

83
Q

What is high endothelial venules (HEVs)?

A

Specialized postcapillary venules in the paracortex

84
Q

What is the role of HEV?

A

Represent an important entry point for most (90%) lymphocytes into lymph nodes.

85
Q

What are HEV’s lined with?

A

Unusual endothelial lining of cuboidal
cells, whose apical surface glycoproteins and integrins facilitate
rapid diapedesis of lymphocytes out of the blood into the paracortex of the lymph node

86
Q

HEVs also occur?

A

In the large accumulations of MALT

87
Q

What are the two components of Medulla?

A

Medullary cords & Medullary sinuses

88
Q

What are Medullary cords?

A

Medullary cords are branched cordlike

Masses of lymphoid tissue extending from the paracortex contain T and B lymphocytes and many plasma cells.

89
Q

Define Medullary sinuses:

A

Are dilated spaces lined by discontinuous endothelium that separate the medullary cords.

90
Q

Describe the Medullary sinuses:

A

The lumens of medullary sinuses include a meshwork of processes from reticular cells, which represent a final lymph filter.

91
Q

What happens if the lymph node

has an infected region

A

The Medullary sinuses contain many macrophages and sometimes neutrophils if the lymph node is draining an infected region. They
are continuous with the cortical sinuses and converge at the hilum as the efferent lymphatic vessel

92
Q

Describe what happens as Lymphatics

Enter the cortex:

A

Lymphatics enter at the cortex of a node, where B cells encounter
antigens, proliferate in lymphoid nodules, and then move into the
deeper regions of the lymph node.

93
Q

Where do Lymphocytes enter?

A

Most lymphocytes enter at the paracortex of the lymph node via
high endothelial venules (HEVs) located there only; most lymphocytes
in this region are T helper cells .

94
Q

What does Medulla consist of ?

A

Medulla has medullary cords

95
Q

Medullary cords consist of?

A

Reticular fibers with many plasma cells, macrophages, and other leukocytes;

96
Q

What is found between the

Medullary cords?

A

Between the cords are lymph-filled medullary sinuses that converge at the efferent lymphatic.

97
Q

Define Spleen?

A

Spleen is a large lymphoid organ without a cortex/medulla structure;

98
Q

What components make up Spleen?

A

Two intermingled but functionally differen regions: white pulp and red pulp .

99
Q

What are four characteristics of Spleen?

A
  1. contains the largest single accumulation of lymphoid
    tissue in the body
  2. is the only lymphoid organ involved in filtration of blood in defense against blood-borne antigens.
  3. It is also the main site of old erythrocyte destruction.
  4. Is a production site of antibodies
    and activated lymphocytes, which here are delivered directly into the blood.
100
Q

Where is Spleen located?

A

Located high in the left upper quadrant of the abdomen and typically about 12 Å~ 7 Å~ 3 cm in size, the spleen’s volume varies with its content of blood and tends to decrease very slowly after puberty.

101
Q

What is Spleen surrounded by?

A

The organ is surrounded by a capsule of dense connective tissue from which emerge trabeculae to penetrate the parenchyma or splenic pulp.

102
Q

Where are Trabeculae found?

A

Large trabeculae originate at the hilum, on the medial surface of the
spleen, and carry branches of the splenic artery, vein, lymphatics,
and nerves into the splenic pulp.

103
Q

Name some Characteristics of White pulp?

A

White pulp , only 20% of the spleen, is secondary lymphoid tissue
associated with small central arterioles that are also enclosed by
periarteriolar lymphoid sheaths (PALS) T cells.

104
Q

Characteristics of Red Pulp?

A

Filters blood, removes defective erythrocytes, and recycles hemoglobin iron

105
Q

Red Pulp consist of what?

A

consists of splenic cords with macrophages and blood cells of all kinds and splenic sinusoids .

106
Q

What are splenic sinusoids lined with?

A

Lined by unusual endothelial cells called stave cells that are elongated and aligned parallel to the blood flow, with open slits between the cells.

107
Q

Describe the Red pulp circulation:

A

Blood flow in red pulp is either a closed circulation, moving from
capillaries into the venous sinusoids, or an open circulation , with capillaries opening directly into the splenic cord

108
Q

Describe Blood filtration in Open

Circulation

A

Blood filtration in the open circulation involves interaction with splenic cord macrophages that remove old, swollen RBCs unable to slip between stave cells to reenter the venous blood flow.

SUM: Histology 1 (5 decks)

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