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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
Q

What are the whorls of epithelial cells with a keratin core in the medulla of the thymus called?

A

Hassall’s corpuscles

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26
Q

Describe the epithelial cells of the thymic medulla.

A

Large pale-staining nuclei
Eosinophilic cytoplasm
Prominent basement membranes

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27
Q

What is the function of thymic interdigitating cell?

A

To present self antigens to maturing T-cells

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28
Q

What is another name for epithelioreticular cells?

A

Thymic nurse cells

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29
Q

How do reticular cells in the cortex support clusters of maturing lymphocytes?

A

Cytoplasmic processes linked by desmosomes enclose partially the endothelium of continuous capillaries

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30
Q

What do the blood-thymus barrier do?

A

Create a physical barrier that protects immature lymphocytes from foreign blood-borne antigens

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31
Q

Describe the contents of endothelioreticular cells.

A

Lysosomes
Granules
Abundant tonofilaments (intermediate filaments)

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32
Q

How do macrophages support the effectiveness of the barrier?

A

By engulfing antigens before they can enter the cortex

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33
Q

Why are there only a small number of thymic macrophages in the circulation?

A

Most of them undergo apoptosis during differentiation

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34
Q

True or False: 400-500 lymph nodes are found in the body.

A

False, 500-600

35
Q

Where are lymphoid system cells found?

A

Connective tissue

36
Q

What is the function of the lymphatic vessels and associated lymph nodes?

A
  1. Drainage of lymph
  2. Surveillance of tissues for signs of antigens
  3. Delivery of absorbed fats from the small intestine
37
Q

Describe lymphatic capillaries morphology.

A

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
Q

What does anchoring filaments in lymphatic capillaries prevent?

A

Vessel collapse

39
Q

Where are lymphatic capillaries most abundant?

A

Dermis
Beneath mucous membranes of respiratory, gastrointestinal and genitourinary tracts
C.T. spaces in the liver

40
Q

What is the function of lymph vessels?

A

Absorb interstitial fluid and lymphocytes to add back to the circulation

41
Q

Where do large lymphatic ducts drain to?

A

Subclavian vein at the angle junction (where the jugular vein and subclavian vein join)

42
Q

What embryological tissue do lymph nodes derive from?

A

Mesenchyme

43
Q

List the functions of lymph nodes.

A
  1. Filtration of lymph
  2. Production of lymphocytes
  3. Synthesis of antibodies
  4. Recirculation of lymphocytes
44
Q

What is the basic structure of a lymph node?

A

Capsule
Cortex
Paracortex
Medulla
Subcapsular sinus

45
Q

Describe the capsule of a lymph node.

A

Dense fibrous C.T.
Delicate, radiating partitions into the interior of the node (trabeculae)

46
Q

What is the purpose of lymph node trabeculae?

A

Provide support
Serve as conduits for blood vessels

47
Q

What are the most common cells found in lymph nodes?

A

Lymphocytes
Macrophages
Plasma cells
Reticular cells
Follicular dendritic cells

48
Q

The lymph node cortex consists of lymphoid nodules. What type of lymphocyte occupies this space?

A

B-lymphocytes

49
Q

Name and briefly describe the 2 types of lymph cortical nodules.

A

Primary: spherical tightly-packed aggregates in a reticular fibre mesh
Secondary: germinal centre surrounded by a mantle zone containing resting B cells

50
Q

What is a germinal centre in a lymph cortical nodule?

A

Major sites of B-cell proliferation that contains lymphocytes, lymphoblasts and follicular dendritic cells

51
Q

If B-cells are found in the cortex of the lymph node, where are T-cells found?

A

Paracortex (also called thymus-dependent region)

52
Q

Describe the lymph node medulla.

A

Pale staining
Next to node hilum
Contains medullary cords

53
Q

What are medullary cords?

A

Irregular strands of loosely arranged lymphoid tissue which consist of mainly lymphocytes, macrophages, and plasma cells.

54
Q

True or False: Medullary sinuses are dilated spaces between medullary cords, frequently bridged by reticular cells and fibres.

A

True

55
Q

What are the medullary sinuses continuous with and why?

A

Cortical sinuses
Because they join at the node hilum to deliver lymph to efferent lymph vessels of the node

56
Q

What is the subcapsular/marginal sinus?

A

A narrow channel under the capsule of the lymph node that delivers lymph further into the node

57
Q

What lines the lymph node sinuses?

A

Attenuated, discontinuous layer of endothelial cells

58
Q

What is the function of high endothelial venules?

A

Allow selective diapedesis of T and B lymphocytes from the blood to perivascular areas

59
Q

Where are high endothelial venules found in the lymph node?

A

Paracortex

60
Q

What is a specialisation of high endothelial venules that aid the function?

A

Endothelial cells have cell adhesion molecules that allow highly specific migration of T and B lymphocytes

61
Q

Describe the morphology of high endothelial venules.

A

Cuboidal endothelial cells
Prominent perivascular sheath
Thick basal lamina

62
Q

What is homing?

A

Movement of T and B cells across high endothelial venules into lymph nodes and other sites

63
Q

What lymphoid organ lacks high endothelial venules?

A

Spleen

64
Q

What supports the lymphocyte infiltrations in MALT?

A

A loose framework of reticular fibres

65
Q

What are M cells?

A

Specialised epithelial cells that take up small particles like bacteria so they can be engulfed by submucosal macrophages

66
Q

Where are M cells abundant?

A

Dome epithelium of Peyer’s patches

67
Q

What tissues form Waldeyer’s ring?

A

Palatine tonsils
Lingual Tonsils
Pharyngeal tonsils
Tubal tonsils (adenoids)

68
Q

True or False: The luminal surface of palatine tonsils is covered by stratified cuboidal epithelium.

A

False, stratified squamous epithelium

69
Q

How are the blind-ended tonsillar crypts formed?

A

Deep invaginations of the stratified squamous epithelium of the luminal surface

70
Q

What separates the base of the palatine tonsil from the underlying muscle?

A

A dense collagenous hemicapsule

71
Q

What is contained in the tonsillar parenchyma?

A

Numerous lymphoid follicles with germinal centres

72
Q

What are the functions of the spleen?

A
  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
Q

Describe the basic structure of the spleen?

A

Capsule
White pulp
Red pulp

74
Q

What is a periarteriolar lymphatic sheath?

A

Islands of lymphoid tissue (white pulp) surrounding a central arteriole

75
Q

True or False: T lymphocytes are mainly found in the periarteriolar lymphatic sheaths.

A

True

76
Q

Where are lymphoid nodules, containing B cells, positioned in the white pulp?

A

Peripheral white pulp in relation to arterioles

77
Q

What is the marginal zone of the spleen?

A

A shell of sparsely cellular lymphoid tissue surrounding the white pulp

78
Q

What type of pulp makes up most of the spleen?

A

Red pulp

79
Q

What does the red pulp consist of?

A

Venous sinusoids and cords of Billroth

80
Q

What are cords of Billroth?

A

Reticular tissue rich in lymphocytes

81
Q

What is the lining epithelium of venous sinusoids in the spleen?

A

Longitudinally-oriented endothelial cells with large nuclei that bulge into the sinusoid lumen called stave cells

82
Q

What is unique about the basement membrane of the layer of stave cells?

A

Incomplete so flexible cells can pass through

83
Q

What does the spleen’s marginal zone contain?

A

Lymphocytes, macrophages and blood antigens

Histology 2 (6 decks)

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