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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
What type of cells derive from monocytes?
Only Antigen-Presenting cells (APCs) also present fragments of endocytosed foreign (usually from microorganisms) proteins on surface MHC class II molecules.
26
Where do Lymphocytes originate?
Primary lymphoid organs: bone marrow for B lymphocytes and the thymus for T lymphocytes.
27
B cells produce antibodies for?
Humoral immunity
28
What is Humoral Immunity?
Aspect of immunity that is mediated by macromolecules found in the extracellular fluids such as secreted antibodies, body fluids
29
T cells function in?
In cell-mediated immunity
30
What does T cells develop receptors | (TCRs) contain?
Usually containing ` and A chains.
31
What are ‘ and A chains responsible for?
They bind antigen along with another surface protein designated by a CD (“cluster of differentiation”) numbering system .
32
What are the important classes of T cells?
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.
33
What is IgM
Immunoglobulin M- largest antibody --first to appear in the response to initial exposure to an antigen.
34
What are B-cell receptors (BCRs)?
IgM or IgD antibodies on the cell surface that bind specific antigens whenever they contact them.
35
Where are B and T cells often activated | & proliferate and begin to function
In the secondary lymphoid organs: the lymph nodes, all mucosa-associated lymphoid tissue (MALT), and the spleen .
36
In these organs, lymphocytes are distributed within a meshwork of what?
Reticulin
37
What is Reticulin produced by?
Produced by fibroblastic reticular cells , and most APCs are dendritic cells with many processes.
38
What occurs in the secondary | Lymphoid tissues?
``` BCRs bind antigen not presented in MHC class II molecules of another cell, the follicular dendritic cell (FDC) . ```
39
How is FDC B cell activated?
With Cytokines form helper T cell
40
What happens to FDC-activated B Cell?
It proliferates clonally to produce Temporarily a large lymphoid nodule (or follicle), which develops a pale germinal center
41
From lymphoid nodules cells | produced & disperse as what?
Plasma cells, various T cells, B, T memory cells that respond and proliferate quickly if their specific antigen reappears
42
What are T lymphoblast’s?
look up
43
What are Thymocytes?
Hematopoietic progenitor cells present in Thymus.
44
What is primary function of Thymocytes?
Is the generation of T Lymphocytes (T Cells)
45
What is Thymopoiesis?
Process in the Thymus by which thymocytes differentiate into mature T lymphocytes.
46
What is a Thymus gland?
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
Where do T lymphoblasts, or | thymocytes, attach to?
The thymus to a cytoreticulum | composed of interconnected epithelioreticular cells .
48
What do Thymic epithelioreticular cells secrete?
Many cytokinesis,
49
What are Thymic epithelioreticular | cells responsible for ?
Compartmentalizing of the thymus into a cortex and a medulla, and in the cortex surround blood vessels in the blood-thymus barrier.
50
What happens to/if Developing T cells | have nonfunctional TCRs
Once detected they are removed in the thymic cortex by a process of positive selection
51
Cells with functional TCRs move into?
The thymic medulla.
52
Define Thymic medulla:
look up
53
What happens once Cells w/ | functional TCR move to thymic medulla?
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
What does this two-stage thymic | selection lead to?
To central immune tolerance, | producing functional T cells that do not bind to proteins of the host.
55
At what point does the Peripheral immune tolerance occur through out the body?
When specific immune reactions are suppressed by regulatory T cells
56
Where do Regulatory T cells originate?
Largely in the Thymic medulla
57
How are T cell formed in the thymus?
Formed in the thymus upon interacting with dendritic cells presenting self-antigens in a process
58
What is this T cell formation & | interaction promoted by?
Promoted by kines from epithelioreticular cell aggregates called Hassall corpuscles
59
Where are Hassall corpuscles | Found?
Found only in the thymic medulla.
60
What are Hassall corpuscles
Distinguished concentric arrangements of flattened epithelioid cells that are acidophilic future of the medulla
61
Where is MALT found?
MALT is found in the mucosa of most tracts
62
Provide examples of tracts where | MALT is found:
Concentrated in the palatine, lingual and pharyngeal tonsils , Peyer patches , and the appendix .
63
What is Lymph node?
Lymph nodes are small encapsulated structures positioned along lymphatic vessels to filter lymph and facilitate antibody production.
64
What ensures one-way flow of lymph?
Valves in the lymphatic vessels ensure the one-way flow of lymph
65
Unlike MALT, lymph nodes are completely encapsulated and occur where?
Along the lymphatic vessels; each has several afferent lymphatics and one efferent lymphatic.
66
What surrounds the Lymph node?
Dense connective Tissue
67
What is the role of a Lymph node?
Lymph node filters lymph and provides a site for B-cell activation and differentiation to antibody-secreting plasma cells.
68
What are the most abundant cells | of lymph nodes
Lymphocytes
69
What are other types of lymphocytes:
Plasma cells, dendritic cells, macrophages, and other APCs
70
What are present within lymphoid nodules
FDCs
71
What are FDC’s:
``` follicular dendritic cells (FDCs), have long filamentous processes -are mesenchymal in origin and their function does not involve MHC class II molecules. ```
72
Where are lypmphocytes cells arranged?
In a stroma of reticulin fibers | and reticular cells to form three major regions
73
What are the three major reagions?
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
What are the regions of Cortex?
Subcapsular & Cortical sinuses
75
What is subcapsular sinus?
Immediately inside the capsule, | receives lymph from the afferent lymphatics
76
Cortical sinuses are also known as?
Trabecular sinuses
77
What are the Cortical sinuses lined by?
Very thin discontinuous endothelium penetrated by the reticulin fibers & processes of dendritic cells.
78
What cells pass through the Cortical sinuses?
Lymph containing antigens, lymphocytes, and APCs passes through these sinuses and percolates easily into the surrounding lymphoid tissue.
79
Lymphoid nodules are formed by?
fill most cortical areas are formed largely by helper T lymphocytes and proliferating B lymphoblasts
80
What is the region between the cortex | and medulla?
The Paracortex
81
How is Paracortex distinguished from | the outer cotex?
It does not have precise boundaries.. distinguished from the outer cortex by its lack of B-cell lymphoid nodules
82
Paracortex contains what type of tissue?
Contains lymphoid tissue rich T cells
83
What is high endothelial venules (HEVs)?
Specialized postcapillary venules in the paracortex
84
What is the role of HEV?
Represent an important entry point for most (90%) lymphocytes into lymph nodes.
85
What are HEV’s lined with?
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
HEVs also occur?
In the large accumulations of MALT
87
What are the two components of Medulla?
Medullary cords & Medullary sinuses
88
What are Medullary cords?
Medullary cords are branched cordlike | Masses of lymphoid tissue extending from the paracortex contain T and B lymphocytes and many plasma cells.
89
Define Medullary sinuses:
Are dilated spaces lined by discontinuous endothelium that separate the medullary cords.
90
Describe the Medullary sinuses:
The lumens of medullary sinuses include a meshwork of processes from reticular cells, which represent a final lymph filter.
91
What happens if the lymph node | has an infected region
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
Describe what happens as Lymphatics | Enter the cortex:
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
Where do Lymphocytes enter?
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
What does Medulla consist of ?
Medulla has medullary cords
95
Medullary cords consist of?
Reticular fibers with many plasma cells, macrophages, and other leukocytes;
96
What is found between the | Medullary cords?
Between the cords are lymph-filled medullary sinuses that converge at the efferent lymphatic.
97
Define Spleen?
Spleen is a large lymphoid organ without a cortex/medulla structure;
98
What components make up Spleen?
Two intermingled but functionally differen regions: white pulp and red pulp .
99
What are four characteristics of Spleen?
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
Where is Spleen located?
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
What is Spleen surrounded by?
The organ is surrounded by a capsule of dense connective tissue from which emerge trabeculae to penetrate the parenchyma or splenic pulp.
102
Where are Trabeculae found?
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
Name some Characteristics of White pulp?
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
Characteristics of Red Pulp?
Filters blood, removes defective erythrocytes, and recycles hemoglobin iron
105
Red Pulp consist of what?
consists of splenic cords with macrophages and blood cells of all kinds and splenic sinusoids .
106
What are splenic sinusoids lined with?
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
Describe the Red pulp circulation:
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
Describe Blood filtration in Open | Circulation
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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