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CAPS 390 > L21. Lymphoid System > Flashcards

L21. Lymphoid System Flashcards

1
Q

What is the thymus

A
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2
Q

What are the components in the thymus

A

Connective tissue forms the outer ‘capsule’ which is mesodermally derived.
Reticular epithelial portion (endodermally-derived)
-reticular because the epithelium is not continuous
- forms ‘net-like’ structures throughout the thymus

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3
Q

Describe each lobule in the thymus

A
  • outer basophillic cortex : cortex contains T-cells

- inner medulla (eosinophillic-pink) has HC (Hassall’s Corpuscles

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4
Q

What are Hassall Corpuscles , where are they found

A
  • found in medulla of a thymus lobule
  • HC clusters of reticular epithelial cells in medulla
  • produce cytokines for T-cell development
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5
Q

What is the cytokine for T-cell developmengt

A

thymopoietin

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6
Q

What occurs at the thymic lobule?

A

-T-cell development

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7
Q

L21 pg 7a identify the medulla, epithelial reticular cells , Hassall’s corpuscle , cortex and lymphocytes in the thymic lobule

A

pg 7a L 21

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8
Q

Describe the post-capillary venules at the thymic lobule

A
  • located at the corticomedullary junction
  • no blood-thymus barrier
  • T lymphocutes from marrow enter thymus
  • exit of naive immunocompetent T-cells to secondary lymphoid organs
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9
Q

Describe the epithelial reticular cells in the thymic lobule

A
  1. contribute to the blood-thymus barrier around continuous capillaries in cortex to immunoprotect developing T-cells
  2. work with dendritic cells to present antigens that regulate clonal deletion of pre-T cells at cortico-medullary junction
  3. become conentrically arranged as Hassall’s corpuscles in medula; produce thymopoietin
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10
Q

Name a secondary lymphoid organ

A

lymph nodes

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11
Q

Describe the lymph nodes

A
  • surrounded by a dense irregular CT capsule and trabeculae
  • true reticular CT (collagen 3) stroma
  • have afferent and efferent lymphatics
  • in the path of ‘lymph vascular flow’
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12
Q

What are primary lymphoid organs

A
  1. sites of lymphocyte production
  2. naive, immunocompetent B lymphocyte produced in bone marrow
  3. naive immunocompetent T lymphocytes are produced in bone marrow and thymus
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13
Q

What are secondary lymphoid organ

A

-lymphocite activation occurs (foreign antigens are encountered/presented)

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14
Q

Name secondary lymphoid organ

A
  1. Lymph node
  2. mucosa-associated lymphoid aggregrates (M.A.L.T)
  3. spleen
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15
Q

What is the MALT? Describe it

A
  • Mucosa-Associated Lymphoid Aggregates.
  • sub-epithelial lymphoid aggregates
  • no CT capsule
  • not in lymph vascular flow
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16
Q

Describe the spleen

A
  • dual function; lymphocyte activation and aged RBC destruction
  • surrounded by CT capsule,not in lymph vascular flow
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17
Q

What is the difference between B-lymphocytes and T-lymphocytes

A
  1. B lymphocytes develop in the bone marrow. T lymphocytes develop in the bone marrow and thymus
  2. Lymphocytes proliferate and become lineage restricted to generate many different clones of
    - B lymphoblast that remain in the bone-marrow
    - T lymphoblast that migrate to the thymus
  3. B lymphocyte rearranges Lg genes and inserts proteins into PM ->naive pre-B-cells
    T lymphocyte rearranges T-cell receptor genes into PM where they can recognize a single, specific antigen presented to them by APC
  4. The Ig of the pre-B-cell interacts with self-antigens in the bone-marrow this induces apoptosis. (ensure there is a tolerance to self-antigens). If the TcR of a naive pre-T-cell reacts with self-antigens presented by APC in the thymus this induces apoptosis, this helps ensure there is a tolerance to self-antigen
  5. remaining naive, immunocompetent B-cells leave bone marrow via venous sinusoids. they are ready to be activated by foreign antigens to produce soluble Igs (antibodies).
    immunocompetent T-cells leave thymus and enter post-capillary venules at the corticomedullary junction and are activated by APCs in secondary lymphoid organs
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18
Q

What are dendritic cells?

A
  • derived from monocytes/macrophages in CT
  • are APC
  • bridge between innate and adaptive immune response
  • digest non-self proteins and carbohydrates
  • present them as very specific antigens on their surface to lymphocytes
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19
Q

What is diapedesis

A

extravasation ( leakage of fluid). how WBC move from vessels into CT

20
Q

Describe the process of diapedesis

A

capture ( through tethering)-> rolling ->slow rolling-> firm adhesion ( by integrins) ->transmigration

  1. tethering of WBC and rolling –selectins
  2. strong adhesion and migration across endothelium– integrins
21
Q

How is WBC recruitment mediated

A
  1. cytokines : paracrine factors released by macrophages and neutrophiles, NK cells
  2. Dendritic/ Monocytic cells (APC)antigen presenting cells. present antigens from pathogens to lymphocytes that exit the blood by diapedesis
22
Q

What are the cytokines released by macrophages and neutrophils

A

interleukins

23
Q

What are the cytokines produced by Natural killer cells

A

interferons

24
Q

What are complement proteins

A
  • plasma proteins made in the liver
  • released into CT due to blood vessel injury
  • binds to lipids/ carbs on pathogens
  • binds to receptors on macrophages /neutrophils
25
Q

What are Toll like receptors

A
  • on surface of macrophages and neutrophils

- recognize various pathogen molecules non-specifically (LPS, glycoproteins, dsRNA)

26
Q

What are some non-specific pathogen molecules

A
  • LPS
  • glycoproteins
  • dsRNA
27
Q

Who initiates innate immunity

A
  • phagocytic activity of macrophages and neutrophils

- Natural Killer Cells facilitate cell-mediated killing of target cells

28
Q

Describe the Natural killer cells

A
  • recognize and bind to target cells ( virus-infected cells ) with low specificity
  • transfer pore-forming ‘perforins’ to bound target cell membranes; kills target cell
  • releases interferon gamma, a cytokine that stimulates macrophages
29
Q

What are the 2 types of immunity

A
  1. innate immunity

2. adaptive immunity

30
Q

Describe innate immunity

A
  • natural immune system ; rapid response
  • non-specifically eliminates pathogens
  • initiated by macrophages and neutrophils, facilitated by granulocytes
31
Q

Describe adaptive immunity

A
  • ‘acquired’ immune system; slower response
  • responds to highly specific molecular epitopes = antigens
  • mediated by B and T lymphocytes; develop in primary and secondary lymphoid organs
32
Q

Describe the lymph interstital fluid

A
  1. plasma like
  2. foreign antigens
  3. lymphocytes
  4. antigen-presenting cells
33
Q

Describe the lymph vascular system

A
  1. moves interstitial fluid (lymph) from connective tissues back to the venous system
  2. empties into subclavian veins in the root of the neck
  3. begins at lymphatic capillaries
  4. blind-ended, one way flow
  5. NO TIGHT JUNCTIONS ( intercellular clefts between endothelial cells facilitate movement in/out no tight junctions
34
Q

Describe the tissue organization of the lymph vessels ( TI,TM,TA)

A
  1. TI fold to form one way valves in the direction of flow back to the venous system
  2. thin walled for all 3 organization: TI, TM, TA
  3. neuro vascular bundle in dense irregular connective tissue
35
Q

Describe lymph flow in a lymph node

A

lymph moves through sinuses ( spaces from outer cortex to inner medulla)

36
Q

What occurs at the paracortex of the lymph nodes

A

activation of T cells to form CD-8 Cytotoxic T cells and Helper (CD-4) T cells (help activate B cells)

37
Q

What happens at the cortex/nodule in a lymph node

A

The activation of B cells to either plasma cells ( secrete antibodies or memory cells ( rapid secondary response)

38
Q

What are CD-8 T cells

A

Cytotoxic T cells

39
Q

What are CD-4 T cells ?

A

Helper T cells

40
Q

How do T and B cells enter and exit the thymus?

A

post capillary venules in the paracortex

41
Q

Identify the cortex/nodules, subcapsular sinus, paracortex,medulla, medullary sinus, lymph (in out) and post capillary venules on PAGE 9 of LECTURE 21

A

page 9 lecture 21

42
Q

Name examples of Mucosa Associated Lymhoid Tissues

A

tonsils, pharynx

43
Q

Describe the MALT

A
  • prominent in mucosal connective tissue ( ie. sub-epithelial lamina propria )
  • sites of B-cell and T-cell activation.
  • no capsule or afferent lymphatics ( not in the path of lymph-vascular flow)
44
Q

What are the functions of the spleen?

A
  • RBC destruction
  • secondary lymphoid organs
  • it has a marginal zone ( macrophages /dendritic cells)
  • dendritic cells present antigens to T-cell
  • macrophages destroy slow moving /old RBC in red pulp
45
Q

What are the sites of white pulp in the spleen?

A

Site of B and T cell activation ( basphillic- lymphocytes)

46
Q

What are the sites of red pulp in the spleen?

A

RBC, site of RBC destruction ( eosinophillic)

CAPS 390 (35 decks)

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