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HIST Heme-Onc > Lymphoid Tissues > Flashcards

Lymphoid Tissues Flashcards

1
Q

lymphocytes include what main subtypes?

A
  • T-cells
  • B-cells
  • NK cells
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2
Q

innate immunity

  • definition
  • which immune cells are a part of innate immunity?
A
  • immunity that does not require exposure to an antigen
  • includes
    • NK cells
    • phagocytes - neutrophils (granulocytes), monocytes / macrophages
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3
Q

adaptive immunity

  • definition
  • includes what immune cells?
A
  • definition: specific, and develops after exposure to an antigen
  • two types of adaptive immunity
    • humoral:
      • antibodies made by plasma cells (B-lymphocytes)
    • cell-mediated:
      • Tc cells
      • NK cells (also innate)
      • phagocytes - neutrophils, monocytes, macrophages (also innate)
      • the other granulocytes
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4
Q

what are primary lymphatic organs?

A
  • bone marrow
  • thymus
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5
Q

bone marrow is what kind of tissue?

A

reticular connective tissue?

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6
Q

discuss the overall histological structure of bone marrow

A
  • venous sinuses surrounded by hematopoietic cords supported by reticular fibers
    • venous sinuses - come off nutrient arteries
    • hematopoietic cords - made of
      1. immune cells - precursors & mature
      2. adipocytes
      3. stromal cells: fibroblasts + macrophages
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7
Q

what cells make up the hemopoietic cords of bone marrow?

A
  • immune cells - precursors & mature
  • adipocytes
  • stromal cells:
    • fibroblasts
    • macrophages
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8
Q

what cell types comprise the “stromal cells” in hematopoietic cords? what is their role?

A
  • fibroblasts
  • macrophages

role to secrete factors to stimulate hematopoiesis (IL-II)

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9
Q

what forms of B-cells are found in the bone marrow?

A
  • precursor cells
  • mature cells
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10
Q

discuss what stages of B-cell development happen what what tissues

A
  • precursors arise from bone marrow
  • mature to → naïve B-cells in bone marrow
  • differentiated into immuno-competent B-cells in secondary lymphoid organs (nodes, spleen, MASLT) after antigen exposure
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11
Q

thymus

  • anatomy
  • embryological origins
A
  • found in the superior mediastinum (directly posterior to the manubrium)
  • embryological origin
    • endodermal origins - 3rd & 4th pharyngeal pouch
    • bone marrow origins
      • lymphocytes
      • macrophages
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12
Q

what main cells comprise the thymus?

what are their roles?

A
  • T-lymphocytes → mature into naïve T-cells OR
  • epithelio-reticular cells - provide a supporting framework for developing T-cells
  • macrophages → phagocytize T-cells that do not mature into T-cells
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13
Q

summarize the gross structure of the thymus

A

outer CT capsule that is divided into lobules by trabeculae

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14
Q

summarize the histological structure of the thymus

A
  • each lobule is divided into cortex + medulla
    • cortex
      • outer portion
      • densely cellular - densely packed lymphocytes at their l_east mature phase_
    • medulla
      • inner portion
      • less cellular - contains mature T- cells
      • contains Hassall’s corpuscles - concentrically arranged epithelio-reticular cells
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15
Q

what are the roles of macrophages in each of the the primary lymphoid tissues

A
  • bone: secrete factors to induce hematopoiesis
  • thymus: phagocytosis
    • phagocytizes T-cell precursors that do not mature to naïve T-cells
    • phagocytizes antigens attempting to cross from the cortical capillaries into the thymus cortex
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16
Q

discuss the movement of T-cells throughout their maturation

A
  • least mature - in the cortex (outer thymus)
  • most mature - in the medulla (inner thymus)
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17
Q

what are hassali’s corpuscles?

A

spheres made of concentrically arranged epithelioreticular cells that support the T-cells in the medulla of the thymus

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18
Q

what is the blood thymus barrier? what forms the blood thymus barrier?

A

a barrier surrounding cortical capillaries (capillaries in the cortex - outer, densely cellular layer) that prevents antigens from escaping capillaries & contacting immature T-cells. made of

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19
Q

what forms the blood-thymus barrier?

A
  • continuous capillaries - endothelial cells joined by tight junction
  • perivascular CT - CT that surrounds capillaries & is loaded with macrophages that phagocytize antigens trying to escape into cortex
  • epithelioreticular cells - form occluding junctions around capillaries
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20
Q

what is the role of the perivascular CT in the blood-thymus barrier?

A

loaded with macrophages to phagocytize any antigens that attempt to leave cortex capillaries into cortex

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21
Q

discuss the phases of T-cell education. in which location does each stage occur?

A

in the cortex

  • double negative stage (outer cortex)- no TCR, CD3, CD4 or CD8
  • double positive stage (inner cortex)
    • cells have TCR, CD3, CD4, CD8
    • positive selection occurs during this stage: T-cells presented with MCH-I & MHC-II
      • cells that bind → move to medulla
      • cells that bind neither → eliminated

medulla:

  • single positive stage
    • cells have either CD4 or CD8
      • if they bound stronger to MHC-II: have CD4
      • if they bound stronger to MHC-I: have CD8
    • negative selection occurs during this phase: any T-cells that bind self-MHC are eliminated (prevents autoimmunity)
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22
Q

positive selection of T-cell education

  • occurs where?
  • to what cells?
  • has what purpose?
A
  • inner cortex of thymus
  • occurs to cells in double positive phase (TCR, CD3, CD4, CD8
  • purpose: T-cells presented with both MCH-I & MHC-II to ensure viability
    • cells that bind → advance to medulla
    • cells that bind neither → eliminated
23
Q

negative selection of T-cell education

  • occurs where?
  • to what cells?
  • has what purpose?
A
  • medulla of thymus
  • occurs to cells in single positive phase (are either CD4+ or CD8+)
  • purpose: to prevent autoimmunity - any T-cells that bind self-MHC are eliminated
24
Q

secondary lymphoid tissue

  • has what purpose?
  • includes what forms/locations?
A
  • lymphocytes are introduced to antigen to become → immunocompetent
  • includes
    • MALT
      • diffuse lymphoid tissue
      • lymphoid follicles
      • aggregated lymphoid follicles
    • tonsils
    • spleen
25
Q

what is MALT?

in what forms is MALT found?

A
  • mucosa associated lymphoid tissue: secondary lymphoid tissue that is typically found in the gut, respiratory tract, and GU tract
    • forms
      • diffuse lymphoid tissue
      • lymphoid follicles
      • aggregated lymphoid follicles
26
Q

diffuse lymphoid tissue

  • location
  • structure
  • made of what cell types?
A

MALT (secondary lymphoid tissue)

  • found in gut, respiratory tract, GU tract
  • structure - loosely arranged cells + no capsule
  • cell types
    • B-lymphocytes
    • T-lymphocytes
27
Q

lymphoid follicles

  • location
  • structure
  • made of what cell types?
A

MALT (secondary lymphoid tissue)

  • location: gut, respiratory tract, GU tract, + lymph nodes, tonsils, spleen
  • structures: well defined spherical structures + no capsule
  • cell types
    • mostly B-lymphocytes (B-cells > T-cells)
    • follicular dendritic cells
28
Q

discuss the classifications of lymphoid follicles. what makes the classifications different?

A

MALT (secondary lymphoid tissues)

  • primary follicles: contain only non-activated B-cells
  • secondary follicles: non-activated B-cells + activated B-cells
    • germinal center: contains
      • large, activated lymphocytes (B-cells) that are undergoing mitosis
        • dendritic cells
    • mantle
      • small, lymphocytes (B-cells)
29
Q

what are germinal centers? discuss their structure.

A

MALT (secondary lymphoid tissue)

  • the inner portion of secondary lymphoid follicles. contains
    • large, activated lymphocytes (B-cells) that are undergoing mitosis
    • dendritic cells
30
Q

aggregated lymphoid follicles

  • are located where?
  • structure?
A
  • in the ileum + appendix
    • lamina propria of vermiform appendix is heavily infiltrated with aggregated lymphoid follicles
31
Q

what kind of secondary lymphoid tissue does the vermiform appendix contain?

A

aggregated lymphoid follicles - contained within the lamina propria

32
Q

tonsils

  • made of what lymphoid tissue
  • location?
A
  • made of lymphoid follicles (MALT, secondary lymphoid tissue)
  • locations based on type
    • palatine tonsils: post part of soft palate
    • pharyngeal tonsils: post part of nasopharynx
    • smaller tonsils -lingual (tongue), tubal (auditory tube)
33
Q

palatine tonsils

  • made of what type of lymphoid tissue?
  • location
  • describe their structure
A
  • made primarily of lymphoid follicles (B-lymphocytes) + scattered throughout
    • location: post part of soft palate
    • structure:
      • covered w/ non-keratinized stratified epithelium, that
        • forms multiple tonsillar crypts: “dips” infiltrated with T-cells
      • rich in lymphoid follicles (containing B-cells)
      • T-cell spaces:
        • in between follicles
        • rich
          • T-cells
          • high endothelial venules: lymphocytes enter blood stream
34
Q

pharyngeal tonsil

  • made of what type of lymphoid tissue?
  • location
  • describe their structure
A
  • made primarily of lymphoid follicles (MALT, secondary lymphoid tissue)
  • located - post part of nasopharynx
  • lined with ciliated pseudostratified columnar
35
Q

small tonsils

  • made of what type of lymphoid tissue?
  • location?
A
  • made primarily of lymphoid follicles
  • location
    • lingual - tongue
    • tubal - auditory tube
36
Q

palatine tonsils are covered with what type of epithelium? what are its epithelium?

A
  • covered w/ non-keratinized stratified epithelium, that
    • forms multiple tonsillar crypts: “dips” infiltrated with T-cells
37
Q

what are the locations of the T-cells in the palatine tonsils?

A
  • in the crypts of the NKSS epithelium
  • in the T-cell spaces in between follicles (B-cells)
38
Q

where are high endothelial venules found in the tonsils?

what is the purpose?

A
  • in the T-cell space (space in between the lymphoid follicles) of the palatine tonsils
  • role is to allow T-cells to move into blood
39
Q

spleen

  • general role
  • general structure
A
  • filters blood and exposes lymphocytes to blood born antigens (type of MALT, secondary lymphoid tissue)
  • general structure
    • capsule: rich in myofibroblasts + forms trabeculae between parenchyma
      • parenchyma
        • white pulp: PALS (T-cells) + lymphoid follicles (B-cells)
        • red pulps: RBCS + splenic cords + splenic sinuses
40
Q

what is are the roles & features of the splenic capsule?

A
  • contains myofibroblasts: allows the organ to contract & eject blood
  • projects into parenchyma with trabeculae
    • trabeculae contains splenic artery branches
41
Q

describe the structure of the white pulp

A

= spleen parenchyma

  • contains large number of WBCs
    • periarterial lymphatic sheath
      • most T-cells
      • surrounds central artery
    • lymphoid follicles
      • mostly B-cells
      • attach to the PALS
42
Q

describe the structure of the red pulp

A
  • contains RBCS + splenic sinuses + splenic cords
    • splenic cords: made of
      • dense meshwork of reticular fibers
      • macrophages that phagocytize damage red blood cells
    • splenic sinuses:
      • have rod shaped endothelial cells
      • receive blood that has been filtered through the cords
43
Q

splenic cords - location / structure / role

A
  • red pulp parenchyma)
  • made of
    • dense meshwork of reticular fibers
    • macrophages
      • damage red blood cells
  • role: to filter blood
44
Q

splenic sinuses - location / structure / role

A
  • red pulp (parenchyma)
  • have rod shaped endothelial cells
  • role; receive blood that has been filtered from the cords
45
Q

discuss the arteries of the spleen

  • what are the name of the branches & where in the spleen are they found?
A
  • splenic artery: moves through capsule, and becomes
  • trabecular arteries: travel through trabeculae (formed by capsule), then become
  • central artery: in the PALS of white pulp (surrounded by T-cells), then exits to become
  • penicillar arteries: in the red pulps, becomes
  • sheathed capillaries: surrounded by a sheath of macrophages, which empty blood into
  • open circulation
    • splenic cords → splenic sinuses
46
Q

what splenic arteries are NOT surrounded by lymphocytes?

A

trabecular arteries (in the trabeculae from the capsule) preceding the central artery

47
Q

which splenic arteries are found it the white pulp?

A

the central artery (surrounded by PALS aka T-cells)

48
Q

which splenic arteries are found in the red pulp?

A

penicillar arteries

49
Q

which splenic arteries are surrounded by a sheath of macrophages?

where are they found?

what did they branch off of?

what do they become?

A
  • sheath capillaries
    • found in red pulp
    • came off penciller arteries
    • dump blood into “open circulation”
      • splenic cords (also rich in macrophages) → splenic sinuses
50
Q

after reaching the splenic sinuses, how does blood travel?

A

collected into pulps veins (parenchyma) → trabecular veins (capsule trabeculae) → splenic vein

51
Q

list the general functions of the spleen

A
  • immune functions
  • blood maintainence / hematopoiesis
52
Q

what are the immune functions of the spleen?

A
  • antigen presentation to B-cells and T-cell
  • production of antibodies
  • removal of encapsulated bacteria by macrophages
53
Q

what are the blood maintenance / hematopoietic functions of the spleen

A
  • removal of damaged / abnormal RBCs & platelets

HIST Heme-Onc (2 decks)

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