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Histopathology > Lymphatic Tissues > Flashcards

Lymphatic Tissues Flashcards

Week 7

1
Q

Diffuse Lymphoid

A
  • Strategically located tissue beneath the surface of most organs
  • Most prominent in the gut and respiratory system
    F: Site of initial immune response
  • travel to region lymph nodes - proliferation and differentiation
  • most specialized beneath the intestine: lamina appropria
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2
Q

Diffuse lymphoid tissue (lamina Popria)

A
  • Beneath mucous membrane of the following tracts:
    • alimentary, respiratory, genitourinary
  • Loose connective tisue
    • fibroblasts, scattered smooth muscle
  • Lymphocytes, eosinophils, plasma cells
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3
Q

Lymph Nodules; Mucosa-associated lymphoid tissue (MALT)

A

GALT: gut
BALT: bronchus (respiratory)
- Germinal center: located in the central region of the nodule
- lymphocytes + dendritic cells – becomes enlarged during immune response
- Mantle zone: small lymphocytes – not proliferating

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4
Q

GALT lymph nodules

A
  • Germinal center paler
    • immature cells, euchromatic nuclei, mitotic figures present
  • Mantle Zone
    • heterochromatic nuclei
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5
Q

Tonsils

A

Lymph nodules
- Whole pharynx is lined by stratified squamous

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6
Q

Palantine tonsils; Tonsillar crypts

A
  • Aggregation of lymph nodules found in specific locations
  • Tonsils: covered by a stratified squamous epi on top of a basement membrane
  • Multiple nodules
  • Drain through efferent lymphatic vessels to the circulation
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7
Q

Peyer’s patch – ileum (end of SI that connects to LI) of small intestine

A
  • Aggregation of lymph nodules found in the distal end of the small intestine
  • multiple nodules with T and B lymphocytes
  • shaped like a C, distinguishable from appendix
    • appendix goes all the way around
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8
Q

Appendicitis

A
  • Occurs when the appendix becomes blocked and bacteria infect the wall and lumen of the appendix
  • Inflammatory cells infiltrate - primarily neutrophils
  • marginalization - leaving blood stream (neutrophils line up around veins and arteries)
  • Edema: fluid build up between smooth muscle cells
  • enlarged appendix
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9
Q

Lymphatic and Blood Systems

A

Run near each other because of dynamic interplay

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10
Q

Lymph Nodes

A
  • Immature dendritic cells reside in peripheral tissues
  • Dendritic cells migrate via lymphatic vessels to regional lymph nodes
  • Mature dendritic cells activate naive T cells in lymphoid organs such as lymph nodes
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11
Q

Lymph vessels

A
  • Pick up and return excess filtered fluid
    • Defense against disease
      • Lymph nodes have phagocytes which destroy bacteria-filtered from interstitial fluid
  • Transport of absorbed fat
  • Return on filtered protein
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12
Q

Lymphatic vessels and lymph nodes

A

Lymphocytes circulate the body
- enter from the tissue through afferent lymphatic
- enter from blood through high endothelial venules
- Leave through efferent vessel

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13
Q

Lymphatic histology

A
  • simple squamous with basement membrane
  • vales prevent backflow
  • smooth muscle for propulsion
  • peristalsis
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14
Q

Lymph Node Structure

A
  • Capsule: DCT
  • Trabeculae: extends into node (DCT framework)
  • Reticular tissue: skeleton of the organ
  • reticular cells and fibers containing many cell types
  • hilium: opening
  • capsule: outside
  • medulla: inside
  • cortex:
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15
Q

Reticular cell

A
  • Fibroblast-like cell: secrete collagen and reticular fibers
  • secrete factors that attract T+B lymphocytes and dendritic cells
    • chemokines
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16
Q

Dendritic cells and macrophages

A
  • Antigen presenting cells
  • Phagocytose foreign antigens and display on either MHC I/II to T cells
  • Dendritic cell: large SA and higher expression of MHC II
17
Q

Parenchyma of the lymph node

A

Cortex:
- superficial: contains lymph nodules
- germinal centers: proliferating B cells
- Deep: free of nodules and contains mostly T cells
- AKA thymus dependent cortex
Medulla: contains T+B cells and macrophages
- draings into medullary sinus -> efferent lymphatic

18
Q

Follicular Dendritic cells

A
  • Interact with B cells in the germinal center
  • not antigen-presenting cells
  • bind to antibody-antigen complexes using specialized receptors
19
Q

Deep Cortex

A
  • Mostly T cells and contains high endothelial venules (HEVs)
    • HEV: site of entrance of 90% of circulating lymphocytes
      • 10% enter through afferent lymphatics
  • lined by simple cuboidal to columnar epithelium
  • macrophages extend processes into the lumen
    • antigen sampling
  • lymphocytes exit via diapedysis
20
Q

Medulla and Hilum

A
  • Contains medullary sinuses, draining lymph
  • converge onto the efferent lymphatics at the hilum
  • vessels lined by simple squamous epi with valves are present
21
Q

Arthracosis of the lymph node

A
  • Carbon build-up in lymph nodes of the pulmonary region
  • No major affect on nodes but the lungs are severely damages
22
Q

Thymus

A
  • located anterior to the heart
  • fully formed and functional at birth and persists until puberty
  • degenerates and filled with CT in adults
  • site of T-cell education
  • Looks similar to lymph nodes at low mag
  • all T-cells
  • Capsule: DCT
  • Trabeculae: sep the thymus into lobules
  • Cortex: basophilic because of tightly packed heterochromatic T cells
  • Medulla: lightly stained because of larger T cells with euchromatic nuclei
23
Q

Thymus vs Lymph nodes

A

Distinguishing features:
- epithelioreticular cells (6 types): 1-3 found in cortex and 4-6 found in medulla
- thymic corpuscles: type 6 epithelioreticular cells

24
Q

Thymus epithelioreticular cell of the cortex

A

Type 1: form boundary between cortex and capsule - anchored to one another through a series of adhesion molecules
Type 2: form the extracellular meshwork of the cortex
- stellate in shape - express MHC I/II - T cell education
Type 3: Form the boundary between cortex and medulla
- form a sheet: also express MHC I/II
Type 4: together with type III they form the barrier between cortex and medulla
Type 5: Form Form meshwork of the medulla
Type 6: make up the thymic corpuscles - T cell education

25
Q

Thymic (Hassall’s Corpuscle)

A
  • Function is to produce various cytokines and chemokines to support T cell proliferation, differentiation, migration, and survival
  • Keratinized; reflects their developmental origin
  • Also contain lipid droplets and intermediate filaments
  • Secrete interleukins which may contribute to T cell maturation
26
Q

Spleen: Two major functions

A

1) Lymphoid organ
- lymph nodules with germinal centers
- White pulp
- T and B cell activation/proliferation
- phagocytosis of antigens in the body
2) Removal and recycling of erythrocytes
- phagocytosis and destruction of worn RBCs
- retrieval of iron from hemoglobin
- fetus: hematopoetic

27
Q

Spleen structural components

A
  • Capsule with trabeculae - DCT
  • Myofibroblasts: contractile cells - in other mammals (not so much humans), the spleen stores blood - contraction dispels it
  • Hilum: splenic artery, vein, nerves, and lymphatics enter/exit
  • Splenic pulp: white vs red
28
Q

Splenic white pulp

A
  • Lymphatic tissue
  • Basophilic: tightly packed heterochromatic lymphocytes
  • splenic artery -> central artery -> arterioles pass through the nodules (B cells) and PALS
  • PALS: periarterial lymphatic sheath (mostly T cells)
  • Splenic sinuses: open capillaries
  • Splenic cord: reticular cells (loose), reticular fibers, lots of erythrocytes, macrophages, and lymphocytes
29
Q

Splenic sinus

A
  • splenic artery -> central artery -> penicillar arterioles which become sinusoidal capillaries surrounded by macrophages
  • blood is picked up by the splenic sinuses
30
Q

Splenic infarction

A

Blood supply blocked by spleen
- two most common causes of splenic infarction are thromboembolic disease and infiltrative hematologic diseases. In patients under 40 yo, the most common cause is hematologic disease
- blood-borne malignancy (leukemia, lymphoma)
- thromboembolic disorders (atrial fib, endocarditis)

Histopathology (13 decks)

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