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Anatomy 2 Unit 3 > 10 - Lymphatic System Histology > Flashcards

10 - Lymphatic System Histology Flashcards

1
Q

Major functions of the lymphatic system:

A

Drain Excess Interstitial Fluid
-Return excess interstitial fluid to blood stream to help maintain normal blood volume & prevent edema

Provide an Alternative Transportation Route for Hormones, Nutrients, & Waste Products

Immune Response
-Produce, maintain, and distribute lymphocytes

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2
Q

Components of Lymphatic System:

A 
Lymphatic vessels – connect parts of lymphatic system to blood circulatory system 
Lymphocytes & variety of supporting cells
Diffuse lymphatic tissue
Lymphatic nodules
Lymph nodes
Spleen 
Bone marrow 
Thymus
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3
Q

Lymphatic vessels – connect parts of

A

lymphatic system to blood circulatory system

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4
Q

Lymphatic vessels begin as networks of

A

blind-ended capillaries in microcapillary beds

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5
Q

Lymphatic capillaries form network within

A

loose connective tissues (especially numerous beneath epithelium of skin & mucous membranes)

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6
Q

Lymphatic vessels serve as adjuncts to the

A

blood vessels; unlike blood vessels, which carry blood to and from the body tissues, lymphatic vessels convey fluid only from tissues (to ultimately be returned to blood vascular system)

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7
Q

Smallest lymphatic vessels are called

A

lymphatic capillaries

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8
Q

Lymphatic capillaries: endothelial tubes lacking

A

continuous basal lamina  results in high permeability

Allows for entry of large molecules, antigens, cells, etc.

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9
Q

Lymphatic vessels Collect

A

excess protein-rich extracellular fluid from extracellular spaces
Extracellular fluid referred to as lymph once it enters lymphatic vessel

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10
Q

Vessel wall thickness increases (connective tissue & bundles of smooth muscle) as

A

vessels become larger

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11
Q

There is no

A

central pump in lymphatic system

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12
Q

Lymph moves

A

sluggishly; relies primarily on skeletal muscle compression of vessels

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13
Q

Lymphatic vessels possess

A

valves  prevent backflow of lymph; aid in unidirectional flow

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14
Q

Lymphatic capillaries converge to form

A

lymphatic vessels

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15
Q

Vessels unite to form two main channels:

A

Thoracic duct – largest lymphatic vessel; drains majority of body
Right lymphatic duct – drains right upper limb, right thorax, right neck, & right head

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16
Q

Right lymph valve Valve formed by

A

very small layer of connective tissue covered on both sides with endothelium

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17
Q

Left lymph vessel This layer of connective tissue present on the

A

outside of the endothelium blends with dense connective tissue (DCT) beyond the wall of the vessel

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18
Q

Lymphocytes –

A

definitive cells of lymphatic system; effector cells

3 major types of lymphocytes: B lymphocytes, T lymphocytes, & Natural Killer (NK) cells

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19
Q

Supporting cells –

A

interact with lymphocytes; antigen presentation & regulation of immune responses

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20
Q

B Lymphocytes: First recognized in

A

Bursa of Fabricius of birds (mass of lymphatic tissue associated with cloaca)

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21
Q

B Lymphocytes: Represent

A

20%-30% of circulating lymphocytes

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22
Q

B Lymphocytes: Membrane-bound

A

B-cell receptor (antigen-specific binding site) = Immunoglobulin

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23
Q

B Lymphocytes: Activated B cells (Plasma cells) secrete

A

non-membrane bound form of immunoglobulins = Antibodies

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24
Q

B Lymphocytes: Humoral immunity =

A

secretion of antibodies into the blood upon B cell activation

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25
Q

T Lymphocytes: Mature in the

A

thymus

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26
Q

T Lymphocytes: Represent

A

60%-80% of circulating lymphocytes

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27
Q

T Lymphocytes: Cell-mediated immunity – involves

A

cell-cell interactions and release of cytokines; directed against intracellular pathogens

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28
Q

T Lymphocytes: Subclassified based on

A

presence/absence of cell surface markers: CD4+ and CD8+

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29
Q

Natural Killer (NK) cells : Represent

A

5%-10% of circulating lymphocytes

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30
Q

Natural Killer (NK) cells : Potent killers of

A

certain types of target cells, namely virally infected and malignant cells

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31
Q

Natural Killer (NK) cells : Component of

A

innate immunity

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32
Q

Diffuse lymphatic tissue – accumulations of

A

lymphatic tissue found within alimentary canal, respiratory passages, and genitourinary tract

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33
Q

Accumulations NOT surrounded by a

A

connective tissue capsule

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34
Q

Lymphocytes, plasma cells, fibroblasts & eosinophils found in the

A

lamina propria at these sites

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35
Q

Lymphatic nodules (follicles) –

A

discrete concentrations of lymphocytes contained in meshwork of reticular cells

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36
Q

Localized concentrations of lymphocytes commonly found in

A

walls of alimentary canal, respiratory passages, and genitourinary tract

Sharply defined, but NOT surrounded by connective tissue capsule

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37
Q

Primary nodule – a nodule consisting primarily of

A

small lymphocytes

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38
Q

Secondary nodule – contains

A

light staining germinal center in central region of nodule & an outer mantle zone (corona)

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39
Q

Germinal center – morphologic indication of

A

response to antigen; develops when lymphocyte binds antigen, returns to primary nodule, & proliferates

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40
Q

Germinal center

Light staining

A

(large immature lymphocytes with large amounts of dispersed euchromatin in nuclei)

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41
Q

Follicular dendritic cells (FDCs) also present; found interspersed between

Germinal center

A

B lymphocytes

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42
Q

Mantle zone (corona) –

A

darker outer ring of small lymphocytes that encircle the germinal center

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43
Q

However, aggregations of lymphatic nodules are found in specific locations:

A

Tonsils
Peyer’s patches
Vermiform appendix

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44
Q

Tonsils – form ring of lymphatic tissue at entrance of oropharynx & nasopharynx

A

(“Waldeyer’s ring”)

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45
Q

Lingual tonsils – at the base of the

A

tongue

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46
Q

Pharyngeal tonsils (adenoids) – located in

A

roof of pharynx

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47
Q

Palatine tonsils – between

A

palatoglossal & palatopharyngeal arches
Squamous epithelium of tonsillar surface dips into underlying connective tissue  forms tonsillar crypts (walls of crypts contain numerous lymphatic nodules)

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48
Q

Palatine tonsil: Stratified squamous epithelium forms the

A

surface of the tonsil and dips into the underlying connective tissue, forming tonsillar crypts

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49
Q

Palatine tonsil:

Stratified squamous epithelium (SSE) lines

A

tonsillar crypt. The stratified squamous epithelium is separated by a connective tissue layer (CT) from the lymphatic nodule (LN). In the upper portion of the of the image, the stratified squamous epithelium is just barely recognized because of the heavy infiltration of lymphocytes.

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50
Q

Peyer’s patches – located within the

A

ileum of small intestine; consists of numerous aggregations of lymphatic nodules containing T & B lymphocytes

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51
Q

Vermiform appendix – arises from

A

cecum of large intestine

Lamina propria heavily infiltrated with lymphocytes and contains numerous lymphatic nodules

52
Q

Mucosal membranes are a

A

major site of entry for pathogens

53
Q

Mucosa-Associated Lymphatic Tissue (MALT) –

A

accumulations of lymphocytes (i.e., diffuse lymphatic tissue & lymphatic nodules) associated with different mucosal areas (i.e. wall of alimentary canal, respiratory, urinary, & reproductive tracts)

54
Q

MALT can be given specific names according to region/organ where they appear:

A

GALT (Gut-Associated Lymphatic Tissue) – associated with the alimentary canal
BALT (Bronchus-Associated Lymphatic Tissue) – associated with respiratory system

55
Q

Lymph nodes – small,

A

bean-shaped encapsulated lymphatic organs

Variable in size (1mm to 1–2 cm long)
Interposed along pathway of lymphatic vessels
Filter lymph prior to its return to blood circulation
Dispersed throughout body, but concentrated in certain regions such as the axilla, groin, & mesenteries

56
Q

Afferent Lymphatic Vessels – convey lymph

A

towards the node; enter at convex surface of capsule

57
Q

Efferent Lymphatic Vessels – convey lymph

A

away from the node; leave at hilum

58
Q

Lymph Node Stroma: Capsule –

A

dense connective tissue surrounding node

59
Q

Lymph Node Stroma: Trabeculae –

A

dense connective tissue extending from capsule

60
Q

Lymph Node Stroma:

3Reticular tissue –

A

reticular cells & reticular fibers that form fine supporting meshwork

61
Q

Reticular cells : Synthesize and secrete

A

reticular fibers (type III collagen) & ground substance

62
Q

Reticular cells - Elongated cytoplasmic processes wrap around bundles of

A

reticular fibers; isolates structural components from parenchyma of lymphatic tissues/organs

63
Q

Reticular cells : play

A

supporting role

64
Q

Reticular cells

Express

A

surface molecules & produce substances that attract T cells, B cells, and dendritic cells

65
Q

Dendritic Cells: Bone marrow-derived

A

antigen presenting cells

66
Q

Dendritic Cells: Monitor environment for

A

antigens; process & present antigen to T cells

67
Q

Dendritic Cells: In lymph node, usually localized to

A

T cell-abundant areas

68
Q

Macrophages

Act as both

A

phagocytes & antigen presenting cells

69
Q

Follicular dendritic cells (FDCs) : Have multiple,

A

thin, hairlike branching cytoplasmic processes that interdigitate between B cells in germinal centers

70
Q

Follicular dendritic cells (FDCs) : Antigen-antibody complexes adhere to

A

FDC cytoplasmic processes via Fc receptors

71
Q

Follicular dendritic cells (FDCs) : Not technically

A

antigen presenting cells
(act similarly to macrophages, but lack
MHC II molecules)

72
Q

Parenchyma of lymph node divided

A

into a cortex and medulla
Cortex – forms outer portion of lymph node (except at hilum)
Medulla – inner portion of lymph node

73
Q

Cortex - Superficial (nodular) cortex –

A

outer part of cortex; just deep to capsule
Primary nodules – consist chiefly of small lymphocytes
Secondary nodules – contain germinal centers

74
Q

Deep cortex (paracortex) – between

A

superficial cortex and medulla
No nodules
Contains the majority of T cells within lymph node

75
Q

Medulla – consists of

A

cords of lymphatic tissue (medullary cords) separated by lymphatic sinuses (medullary sinuses)

76
Q

medulla - Network of

A

reticular cells and fibers traverses medullary cords and sinuses; serve as framework for the parenchyma

77
Q

medulla Medullary cords contain:

A

lymphocytes (mostly B cells), macrophages, dendritic cells, plasma cells

78
Q

Medullary sinuses converge near

A

hilum & drain into efferent lymphatic vessels

79
Q

Thymus structure:

A

Capsule
Trabeculae
Cortex
Medulla

80
Q

Thymus structure 2 -

A 
Capsule 
Trabeculae
Thymic Lobules
Cortex
Medulla
81
Q

Flow of lymphocytes from

blood through lymph node:

A

High Endothelial Venules (HEVs)

Deep Cortex

Superficial Cortex

Medulla

Efferent Lymph Vessel

82
Q

Flow of lymphocytes from

lymph through lymph node:

A

Afferent Lymph Vessel

Subcapsular (Cortical) Sinus

Trabecular Sinus

Medullary Sinus

Efferent Lymph Vessel

83
Q

Flow of lymphocytes from

lymph through lymph node:

A

Afferent Lymph Vessel

Subcapsular (Cortical) Sinus

Trabecular Sinus

Medullary Sinus

Efferent Lymph Vessel

84
Q

Splenic Sinuses:

A

Wall has lattice-like structure

85
Q

Splenic sinuses: 3Prominent intercellular spaces between endothelial cells

A

Allow blood cells easy access into/out of sinuses

Macrophage processes extend between endothelial cells into lumen of sinuses to monitor blood for antigens

86
Q

Thymus – bilobed organ located in the

A

superior mediastinum, anterior to heart and great vessels

Fully formed & functional at birth
Persists as large organ until puberty, at which point:

87
Q

Thymus at puberty: T cell differentiation & proliferation

A

reduced; most lymphatic tissue replaced with adipose tissue

88
Q

Thymus at puberty: However, thymus can be

A

restimulated under conditions that demand rapid T cell proliferation

89
Q

Capsule – thin

A

connective tissue capsule

Connective tissue contains: collagen fibers, fibroblasts, variable numbers of plasma cells, granulocytes, lymphocytes, mast cells, adipocytes, & macrophages

90
Q

Trabeculae – extend from

A

capsule into parenchyma of thymus
Establish domains called thymic lobules  cortical caps over portions of highly convoluted but continuous medullary tissue

91
Q

*Note: In some planes of section, the “lobular” arrangement of the cortical cap and medullary tissue resembles a

A

lymphatic nodule with a germinal center (often confusing)

92
Q

Cortex – outer portion of

A

thymic parenchyma

93
Q

Thymus cortex: Markedly

A

basophilic (closely packed developing T lymphocytes with intensely staining nuclei)

94
Q

Thymus cortex: Developing lymphocytes (thymocytes) occupy

A

spaces within extensive meshwork of epithelioreticular cells

95
Q

Thymus cortex: Macrophages also

A

present; phagocytose apoptotic T cells (those that do not fulfill thymic education requirements)

96
Q

Epithelioreticular cells: Provide framework for

A

developing T cells (therefore serve role played by reticular cells & reticular fibers found in other lymphatic organs. HOWEVER, reticular cells and their fibers are NOT present in thymic parenchyma)

97
Q

Epithelioreticular cells: Exhibit certain features characteristic of

A

epithelium (i.e., intercellular junctions & intermediate filaments)

98
Q

Epithelioreticular cells

Serve as the supporting

A

stroma; thymocytes occupy spaces within extensive meshwork of epithelioreticular cells

99
Q

Epithelioreticular cells

6 types recognized on the basis of function

A

3 Types in Cortex:
Type I
Type II
Type III

3 Types in Medulla:
Type IV
Type V
Type VI

100
Q

Medulla –

A

inner portion of thymic parenchyma

101
Q

Medulla thymus: Contains large number of

A

epithelioreticular cells & loosely packed T cells

102
Q

medulla thymus; Stains less intensely than

A

cortex  large lymphocytes with pale-staining nuclei & more cytoplasm than small lymphocytes

103
Q

medulla thymus: type VI epithelioreticular cells form the most

A

characteristic feature of the medulla:

Thymic (Hassall’s) corpuscles

104
Q

Thymic (Hassall’s) corpuscles : Isolated masses of

A

closely-packed, concentrically arranged type VI epithelioreticular cells with flattened nuclei

105
Q

Thymic (Hassall’s) corpuscles : Possess

A

keratohyalin granules  make corpuscles very eosinophilic

106
Q

Thymic (Hassall’s) corpuscles: Center of corpuscle contains

A

fully keratinized cells

107
Q

Thymic (Hassall’s) corpuscles

Distinguishing feature of

A

thymic tissue!

108
Q

Thymic (hassall’s) corpuscles: Function not fully

A

understood

[Believed to produce interleukins (IL-4 & IL-7) involved in thymic differentiation & T cell education]

109
Q

Spleen – largest lymphatic organ; located in

A

upper left quadrant of abdominal cavity

110
Q

Spleen Has

A

rich blood supply  filters blood (analogous to lymph node filtering lymph)
Abundant lymphocytes, macrophages, and dendritic cells
Specialized vascular spaces/channels
Meshwork of reticular cells and reticular fibers

111
Q

Spleen Enclosed in

A

dense connective tissue capsule from which trabeculae extend into the parenchyma

112
Q

Spleen Hilum – located on

A

medial surface of spleen; site for passage of splenic artery and vein, nerves, and lymphatic vessels

113
Q

Spleen contains:

red pulp

A

Red Pulp - primary role of red pulp is blood filtration (i.e., removal of particulate materials, removal of antigens, and removal of worn-out or defective RBCs, WBCs, and platelets)

114
Q

Red pulp Consists of

A

splenic sinuses separated by splenic cords (cords of Billroth)

115
Q

Splenic sinuses –

A

blood-filled sinuses; few contact points between adjacent endothelial cells  prominent intercellular spaces; allow blood cells to pass readily into/out of sinuses

116
Q

Splenic cords (cords of Billroth) –

A

loose meshwork of reticular cells and reticular fibers; contain large numbers of erythrocytes, macrophages, lymphocytes, dendritic cells, plasma cells, and granulocytes

117
Q

Red pulp has red appearance in fresh state, as well as in histologic sections because it contains

A

large numbers of red blood cells.

118
Q

Splenic macrophages phagocytose

A

damaged red blood cells; iron from these cells used for formation of new red blood cells.

119
Q

Spleen contains:

white pulp

A

White Pulp – consists of lymphatic tissue, mostly lymphocytes

120
Q

White pulp: Appear basophilic in

A

H&E sections (dense heterochromatin of lymphocyte nuclei)

121
Q

White pulp: Branches of splenic artery course through

A

through capsule and trabeculae and enter white pulp

122
Q

White pulp: Central artery  branch of

A

splenic artery initially in central position within white pulp

123
Q

White pulp: Periarterial lymphatic sheath (PALS)  aggregates of

A

lymphocytes around central artery

124
Q

White pulp: In cross-section, PALS appear

A

circular; develop lymphatic/splenic nodule (with germinal centers) in some locations

125
Q

White pulp: Lymphatic nodules displace

A

central artery to an eccentric position

126
Q

capsulated structures are

A

organs

Anatomy 2 Unit 3 (14 decks)

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