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Microscopic Anatomy Unit 3 > Lymphoid Organs > Flashcards

Lymphoid Organs Flashcards

1
Q

Distribution of lymphoid organs

A
  • bone marrow
  • thymus
  • lymph nodes
  • spleen
  • tonsils
  • Peyer’s patches
  • important components of the immune system
  • immune responses are largely initiated and generated within the lymphoid organs
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2
Q

central components of the immune system

A

-primary lymphoid organs-bone marrow and thymus

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3
Q

peripheral lymphoid organs

A
  • secondary
  • lymph nodes
  • spleen
  • tonsils
  • Peyer’s patches
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4
Q

extralymphoid tissues and organs

A
  • GI
  • Resp
  • Urinary
  • Repro
  • skin
  • blood
  • lymph
  • wandering lymphocytes
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5
Q

lymphocyte recirculation

A
  • blood-lymphoid organs-blood
  • permits continuous immune surveillance and ensures rapid response to antigens
  • connects the three components of the immune system
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6
Q

small/medium lymphocytes

A
  • 30% of leukocytes
  • B cells
  • T cells
  • NK cells
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7
Q

reticular cells

A
  • make reticular fibers
  • form a spongelike meshwork that supports the lymphocytes
  • mesenchymal origin
  • large cells
  • numerous cytoplasmic processes
  • processes wrap around reticular fibers
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8
Q

types of reticular tissue in hematopoietic organs

A
  • lymphoid tissue-free cells are largely lymphocytes

- myeloid tissue-free cells are developing erythrocytes and granular leukocytes (bone marrow)

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9
Q

functions of mesenchymal reticular cells

A
  • synthesis and maintenance of the ECM
  • phagocytosis
  • trophic role in blood cell formation
  • storage place of ferritin
  • antigen processing and presentation-dendritic in both sense of the word
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10
Q

loose lymphoid tissue

A

-reticular cells

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11
Q

dense lymphoid tissue

A

-lymphocytes

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12
Q

nodular lymphoid tissue

A
  • compact
  • spherical
  • lack a CT capsule
  • consist mostly of B cells
  • primary and secondary with germinal center
  • not limited to lymphoid organs
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13
Q

secondary lymphatic nodules

A
  • germinal center with numerous activated B cells
  • antigenic stimulation
  • surrounded by mantle
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14
Q

germinal center

A
  • B cell:
  • proliferation
  • selection
  • apoptosis
  • differentiation
  • storage
  • appear during primary antigenic response and involute in about 4 weeks
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15
Q

lymph nodes

A
  • in line filters of lymph system
  • capsule
  • trabeculae
  • hilum
  • medulla
  • cortex
  • capsule
  • subcapsular sinus (made of loose lymphoid tissue)
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16
Q

components of the cortex

A
  • loose lymphoid tissue:subcapsular and peritrabecular sinuses
  • lymphatic nodules-primary and/or secondary contain mostly B cells
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17
Q

components of the medulla

A
  • dense lymphoid tissue:medullary cords populated largely by B cells and plasma cells
  • loose lymphoid tissue: medullary sinuses (numerous reticular cells)
  • structures of the sinuses facilitates the filtering function of the nodes
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18
Q

flow through a lymph node

A
  • afferent vessels with valves pointing in
  • subcapsular sinus
  • trabecular sinus
  • medullary sinus
  • efferent vessels valves pointing the other way
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19
Q

High endothelial venule

A
  • fat cells
  • lymphocytes leave the efferent vessel and come back through the arteries to HEVs
  • homing addressins on HEVs with corresponding receptors on lymphocytes
  • helps cells perform diapedesis to get out of BV
  • found in tonsils, Peyer’s patches, but not in spleen or thymus
20
Q

key molecules in lymphocyte homing

A
  • selectins
  • integrins
  • carbs (sugars and mucins)
  • immunoglobulin superfamily members (ICAM VCAM)
21
Q

medical relevance of HEVs

A
  • play a role in lymphocyte recirculation-contribute to specificity
  • decrease in number with age (immunologic function decreases with age)
  • implicated in metastasis of lymphoid malignancies
22
Q

deep cortex

A
  • aka paracortex or tertiary cortex
  • located between the cortex and the medulla
  • location of HEVs
  • most lymphocytes are T
23
Q

functions of lymph nodes

A
  • filtration of lymph
  • production and selection of B lymphocytes
  • immune response to lymph born antigens
24
Q

fetal thymus

A
  • dual embryological origin- epithelial lining of 3rd and 4th brachial pouches and surrounding mesenchyme
  • develops early
  • maximum size within first year of life
  • capsule
  • trabeculae
  • lobular
  • cortex-dense lymphoid tissue
  • medulla-loose lymphoid tissue
25
Q

adult thymus

A
  • atrophy begins by the age of 2

- much of the parenchyma is replaces by CT

26
Q

principal cell types within the thymus

A
  • thymocytes-predominate in cortex-proliferate, selection, apoptosis, some travel to other organs
  • epithelial reticular cells-derived from endoderm of 3rd and 4th brachial pouches
  • desmosomes and tonofilaments (mesenchymal reticular cells have no desmosome)
27
Q

epithelial reticular cell

A
  • not normally phagocytic
  • do not make reticular fibers
  • not antigen presenting cells
28
Q

functions of epithelial reticular cells

A
  • secretion-provide supporting framework (cytoreticulum)-thymosins, thymopoietin
  • form Hassall’s corpuscles
  • contribute to blood thymus barrier
29
Q

thymosins

A
  • family of polypeptides that promote T cell differentiation

- may also produce a factor that has a trophic role in the lymphoid system

30
Q

Hassall’s corpuscles

A
  • in medulla of thymus
  • concentric epithelial reticular cells
  • frequently keritanize of calcify
  • decrease in number but increase in size with age
  • may remove apoptotic thymocytes??
  • may play a role in generation of regulatory T cells?????
31
Q

blood thymus barrier

A
  • epithelial reticular cells help form a barrier to the movement of macromolecules from the blood into the thymic cortex
  • provides and immunologically privileged site for the differentiating thymocytes
32
Q

principal cell types in the thymus

A
  • thymocytes
  • epithelial reticular cells
  • mesenchymal reticular cells-black in thymus because they are phagocytes
33
Q

cortex of thymus

A
  • mostly thymocytes
  • production
  • selection
  • apoptosis
34
Q

medulla of thymus

A
  • mostly epithelial reticular cells
  • selected thymocytes begin maturation into T cells
  • presence of Hassall’s corpuscles
35
Q

functions of the thymus

A
  • development of a diverse population of T cells that can respond to foreign antigens (thymosin)
  • trophic role in the development of other lymphoid organs (thymopoietin)
36
Q

spleen

A
  • largest single accumulation of lymphoid tissue
  • filtration of blood
  • immunodefense
  • white pulp (20%), capsule, red pulp (80%)
  • trabeculum
37
Q

red pulp

A
  • splenic cord
  • splenic sinus (discontinuous sinusoid)
  • has central arteries
38
Q

PALS

A

-periarterial lymphatic sheath

39
Q

white pulp

A

-PALS and lymphatic nodules

40
Q

marginal zone

A
  • between white and red pulp
  • most arterial blood runs through MZ
  • contains macrophages, T and B cells, dendritic cells
  • site of initiation of immune resonses
  • blood then enters the red pulp
41
Q

blood flow through the spleen

A
  • splenic artery
  • trabecular arteries
  • central arteries
  • penicillar arteries
  • capillaries
  • sinuses
  • red pulp veins
  • trabecular veins
  • splenic vein
42
Q

closed circulation

A

-blood flows directly from caps to sinuses

43
Q

open circulation

A
  • blood flows from caps into cords before it enters sinuses

- most blood flows this way

44
Q

endothelium of splenic sinuses

A
  • elongated cells
  • spaces between them
  • gaps in the BM
  • highly porous
45
Q

functions of the spleen

A
  • production of lymphocytes
  • immune response to blood borne antigens
  • destruction of old erythrocytes (by macrophages)
  • storage of blood (esp in cells and platelets)
  • a reservoir of monocytes that can be rapidly released to regulate inflammation
46
Q

palatine tonsil

A
  • aggregates of lymphoid tissue lying beneath the epithelium in the upper pharynx
  • pharyngeal, palatine, lingual
  • epithelium, lymphoid tissue, crypt, capsule nodules
47
Q

functions of tonsils

A
  • detection and response to pathogens in the oral cavity

- production of lymphocytes

Microscopic Anatomy Unit 3 (3 decks)

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