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Histology 2 > Lymphoid System > Flashcards

Lymphoid System Flashcards

1
Q

List 5 examples of innate immunity.

A
  1. Barriers e.g. skin
  2. Chemical defence e.g. stomach acid
  3. Phagocytic cells
  4. Complement activated system
  5. Extracellular killers e.g. natural killer lymphocytes
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2
Q

What is a complement activated system?

A

A cascade of plasma proteins that forms an enzyme system that defend against bacteria

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3
Q

True or False: Adaptive immune system is faster to react than the innate system.

A

False, it’s slower

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4
Q

What is immune tolerance?

A

The ability of lymphocytes not reacting to self antigens

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5
Q

What are the primary lymphoid organs?

A

Bone marrow
Thymus

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6
Q

What are the secondary lymphoid organs?

A

Spleen
Lymph nodes
MALT tissues

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7
Q

What does MALT stand for?

A

Mucosal Associated Lymphoid Tissue

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8
Q

What tissues are included in MALT?

A

Tonsils
Adenoids
Peyer’s patches
Lymphoid aggregates in the intestines

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9
Q

What embryonic tissue is all lymphoid tissue derived from, except for the thymus?

A

Mesoderm

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10
Q

What is the function of natural killer lymphocytes?

A

Kill virus-infected cells and some tumour cells

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11
Q

What is the function of B-lymphocytes?

A

Produce antibodies

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12
Q

What is the function of the 4 types of T-lymphocyte?

A

Helper: Secreting interleukins that start a cascade response
Cytotoxic: Kill infected cells and cancer cells
Suppressor: Suppress immune response to self antigens and stop an immune response
Memory: Provide a rapid response to the same antigen in the event of reinfection

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13
Q

What does CD stand for?

A

Cluster designation

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14
Q

Where do the 3 types of lymphocytes develop?

A

Natural killer and B lymphocytes develop in the bone marrow, while T lymphocytes differentiate and mature in the thymus

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15
Q

Describe the thymus.

A

2 lobes subdivided by septa
Highly cellular outer cortex
Less cellular inner medulla

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16
Q

Why are the septa of the thymus unusual?

A

Composed of connective tissue and epithelioreticular cell

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17
Q

Which segment of the thymus stains more intensely with H&E?

A

Cortex (basophilic)

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18
Q

What processes does thymus involution include?

A

Fatty infiltration
Lymphocyte depletion

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19
Q

True or False: The thymus continues to provide mature T-cells to the circulation.

A

True

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20
Q

What secretes thymic hormones?

A

Cords of epithelial cells in the thymus

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21
Q

What is the epithelial lining type of postcapillary venules at the corticomedullary junction in the thymus?

A

Specialised cuboidal endothelium that allows the passage of lyphocytes

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22
Q

What is the term for immature and maturing T-cells?

A

Thymocytes

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23
Q

What happens to T-cells as they move from the cortex to the medulla?

A

They mature and surface markers are acquired to specialise their role

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24
Q

What is clonal deletion (negative selection) in the thymus medulla?

A

The destruction of any T-cells that react when presented with self antigens

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25
What are the whorls of epithelial cells with a keratin core in the medulla of the thymus called?
Hassall's corpuscles
26
Describe the epithelial cells of the thymic medulla.
Large pale-staining nuclei Eosinophilic cytoplasm Prominent basement membranes
27
What is the function of thymic interdigitating cell?
To present self antigens to maturing T-cells
28
What is another name for epithelioreticular cells?
Thymic nurse cells
29
How do reticular cells in the cortex support clusters of maturing lymphocytes?
Cytoplasmic processes linked by desmosomes enclose partially the endothelium of continuous capillaries
30
What do the blood-thymus barrier do?
Create a physical barrier that protects immature lymphocytes from foreign blood-borne antigens
31
Describe the contents of endothelioreticular cells.
Lysosomes Granules Abundant tonofilaments (intermediate filaments)
32
How do macrophages support the effectiveness of the barrier?
By engulfing antigens before they can enter the cortex
33
Why are there only a small number of thymic macrophages in the circulation?
Most of them undergo apoptosis during differentiation
34
True or False: 400-500 lymph nodes are found in the body.
False, 500-600
35
Where are lymphoid system cells found?
Connective tissue
36
What is the function of the lymphatic vessels and associated lymph nodes?
1. Drainage of lymph 2. Surveillance of tissues for signs of antigens 3. Delivery of absorbed fats from the small intestine
37
Describe lymphatic capillaries morphology.
Blind-ended channels in C.T. spaces Thin walled capillaries that anastomose and become larger Anchoring filaments connect endothelial cells to adjacent collagen fibres
38
What does anchoring filaments in lymphatic capillaries prevent?
Vessel collapse
39
Where are lymphatic capillaries most abundant?
Dermis Beneath mucous membranes of respiratory, gastrointestinal and genitourinary tracts C.T. spaces in the liver
40
What is the function of lymph vessels?
Absorb interstitial fluid and lymphocytes to add back to the circulation
41
Where do large lymphatic ducts drain to?
Subclavian vein at the angle junction (where the jugular vein and subclavian vein join)
42
What embryological tissue do lymph nodes derive from?
Mesenchyme
43
List the functions of lymph nodes.
1. Filtration of lymph 2. Production of lymphocytes 3. Synthesis of antibodies 4. Recirculation of lymphocytes
44
What is the basic structure of a lymph node?
Capsule Cortex Paracortex Medulla Subcapsular sinus
45
Describe the capsule of a lymph node.
Dense fibrous C.T. Delicate, radiating partitions into the interior of the node (trabeculae)
46
What is the purpose of lymph node trabeculae?
Provide support Serve as conduits for blood vessels
47
What are the most common cells found in lymph nodes?
Lymphocytes Macrophages Plasma cells Reticular cells Follicular dendritic cells
48
The lymph node cortex consists of lymphoid nodules. What type of lymphocyte occupies this space?
B-lymphocytes
49
Name and briefly describe the 2 types of lymph cortical nodules.
Primary: spherical tightly-packed aggregates in a reticular fibre mesh Secondary: germinal centre surrounded by a mantle zone containing resting B cells
50
What is a germinal centre in a lymph cortical nodule?
Major sites of B-cell proliferation that contains lymphocytes, lymphoblasts and follicular dendritic cells
51
If B-cells are found in the cortex of the lymph node, where are T-cells found?
Paracortex (also called thymus-dependent region)
52
Describe the lymph node medulla.
Pale staining Next to node hilum Contains medullary cords
53
What are medullary cords?
Irregular strands of loosely arranged lymphoid tissue which consist of mainly lymphocytes, macrophages, and plasma cells.
54
True or False: Medullary sinuses are dilated spaces between medullary cords, frequently bridged by reticular cells and fibres.
True
55
What are the medullary sinuses continuous with and why?
Cortical sinuses Because they join at the node hilum to deliver lymph to efferent lymph vessels of the node
56
What is the subcapsular/marginal sinus?
A narrow channel under the capsule of the lymph node that delivers lymph further into the node
57
What lines the lymph node sinuses?
Attenuated, discontinuous layer of endothelial cells
58
What is the function of high endothelial venules?
Allow selective diapedesis of T and B lymphocytes from the blood to perivascular areas
59
Where are high endothelial venules found in the lymph node?
Paracortex
60
What is a specialisation of high endothelial venules that aid the function?
Endothelial cells have cell adhesion molecules that allow highly specific migration of T and B lymphocytes
61
Describe the morphology of high endothelial venules.
Cuboidal endothelial cells Prominent perivascular sheath Thick basal lamina
62
What is homing?
Movement of T and B cells across high endothelial venules into lymph nodes and other sites
63
What lymphoid organ lacks high endothelial venules?
Spleen
64
What supports the lymphocyte infiltrations in MALT?
A loose framework of reticular fibres
65
What are M cells?
Specialised epithelial cells that take up small particles like bacteria so they can be engulfed by submucosal macrophages
66
Where are M cells abundant?
Dome epithelium of Peyer's patches
67
What tissues form Waldeyer's ring?
Palatine tonsils Lingual Tonsils Pharyngeal tonsils Tubal tonsils (adenoids)
68
True or False: The luminal surface of palatine tonsils is covered by stratified cuboidal epithelium.
False, stratified squamous epithelium
69
How are the blind-ended tonsillar crypts formed?
Deep invaginations of the stratified squamous epithelium of the luminal surface
70
What separates the base of the palatine tonsil from the underlying muscle?
A dense collagenous hemicapsule
71
What is contained in the tonsillar parenchyma?
Numerous lymphoid follicles with germinal centres
72
What are the functions of the spleen?
1. Produce immune response against blood-borne antigens 2. Removal of particulate matter and old blood cells 3. Blood cell production during foetal life
73
Describe the basic structure of the spleen?
Capsule White pulp Red pulp
74
What is a periarteriolar lymphatic sheath?
Islands of lymphoid tissue (white pulp) surrounding a central arteriole
75
True or False: T lymphocytes are mainly found in the periarteriolar lymphatic sheaths.
True
76
Where are lymphoid nodules, containing B cells, positioned in the white pulp?
Peripheral white pulp in relation to arterioles
77
What is the marginal zone of the spleen?
A shell of sparsely cellular lymphoid tissue surrounding the white pulp
78
What type of pulp makes up most of the spleen?
Red pulp
79
What does the red pulp consist of?
Venous sinusoids and cords of Billroth
80
What are cords of Billroth?
Reticular tissue rich in lymphocytes
81
What is the lining epithelium of venous sinusoids in the spleen?
Longitudinally-oriented endothelial cells with large nuclei that bulge into the sinusoid lumen called stave cells
82
What is unique about the basement membrane of the layer of stave cells?
Incomplete so flexible cells can pass through
83
What does the spleen's marginal zone contain?
Lymphocytes, macrophages and blood antigens

Histology 2 (6 decks)

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