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Microanatomy > Lymphoid System > Flashcards

Lymphoid System Flashcards

1
Q

Where do B cells differentiate?

A

BM

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2
Q

Where do T cell differentiate?

A

Start in BM, continue in thymus

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3
Q

Where does activation occur?

A

Secondary lymphoid organs (LN, spleen, tonsils) and lymphoid tissues in non-lymphoid organs

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4
Q

Is lymphocyte differentiation Ag dept?

A

NO

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5
Q

Blast transformation

A

result of lymphocyte activation, cell enlarges to become immunoblast and divides repeatedly

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6
Q

Thymus is what kind of organ?

A

Lymphoepithelial organ

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7
Q

Development of thymus

A

development begins at about 5wks of gestation, from the endodermal epithelium of 3rd pharyngeal pouch, bi-lobed organ migrates into superior mediastinum of thorax at approx 7wks

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8
Q

Thymic epithelial cells/epithelioreticular cells

A

initially exclusively makes up thymus, connected by desmosomes, first prothymocytes push between these cells and for sheets connected by tight junctions, eventually thymic epithelial cells will become stromal cells of thymus
found in both cortex and medulla, large pale cells with euchromatic nuclei, have tonofibrils composed of cytokeratin tonofilaments
Not phagocytic

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9
Q

Capsule of thymus

A

dense irregular CT with type I collagen and reticular fibers

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10
Q

Septa of thymus

A

sheets of CT that extend inwards from capsule, incompletely subdivide the two lobes into many lobules

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11
Q

Cortex of thymus

A

dark-staining region of each lobule, contains more lymphocytes (dark staining), partially surrounds medulla

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12
Q

Medulla of thymus

A

pale inner region of each lobule, continuous throughout organ, contains more macrophages that lymphocytes

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13
Q

Stroma of thymus

A

formed by thymic epithelial cells, ONLY PRESENT IN THYMUS

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14
Q

Presence of tonofibrils composed of cytokeratin tonofilaments helps to identify what?

A

TECs as epithelial cells vs CT

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15
Q

Cortical TECs

A

Type 1-3

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16
Q

Type I TEC

A

line inner surface of capsule, cover CT septa, surround cortical blood vessels

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17
Q

Type II TEC

A

nurse cells, stellate cells whose long processes are connected by desmosomes, form nests for thymocytes, participate in positive selection

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18
Q

Type III TEC

A

at corticomedullary boundary, connected by tight junctions, also important for + selection

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19
Q

Medullary TECs

A

Type 4-6

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20
Q

Type IV TEC

A

layer just deep to type III, joined by tight junctions

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21
Q

Type V TEC

A

approximately equal to nurse cells, for meshwork throughout medulla, particulate in - selection

22
Q

Type VI TEC

A

arranged in concentric layers to form Hassall’s corpuscles, evidence they may contain thymic stromal lymphopoietin that activates thymic dendritic cells

23
Q

Thymocyte migration path

A
  1. corticomedullary boundary to outermost cortex, just beneath capsule
  2. back to corticomedullary boundary
  3. back to medulla
  4. leave organ as mature naive T cell and migrate to secondary lymphoid organ
24
Q

Tingible body macrophages

A

Macrophages that have phagocytosed apoptotic cells in cortex

25
Q

blood-thymus barrier

A

tight in cortex and leaky in medulla

26
Q

Involution of thymus

A

thymus is fully function and formed at birth, reaches max weight at puberty, then decreases, some functional tissue throughout life

27
Q

DiGeorge syndrome

A

congenitial defect involving malformation of structures derived from 3rd (thymus) and 4th pharyngeal pouches, pt cant product normal T cells

28
Q

Difference between stroma of thymus and LN

A

Epithelial stroma in thymus

CT stroma w/ reticular fibers in LN

29
Q

Do afferent lymphatics have valves?

A

yes, to prevent backflow, so due efferent lymphatics

30
Q

Hilus of LN

A

where efferent lymphatic vessels leave

31
Q

Where are nodules present in LN?

A

Outer cortex contains lymphoid nodules (primary or secondary), paracortex and medulla do not

32
Q

Pathway of lymph flow

A

afferent lymphatics, subcapsular sinus, trabecular, sinuses, medullary sinuses, efferent lymphatic vessel

33
Q

Difference between sinuses and lymphatics?

A

sinuses dont have valves but are very leaky

34
Q

Where are HEVs

A

postcapillary venules found in paracortex of LN

35
Q

T cell and B cell regions of the LN

A

T cell regions are paracortex and internodular cortex

B cell regions are lymphoid nodules

36
Q

Daughter cells of b cell immunoblasts

A

Memory B cells or plasmablasts

37
Q

Plasmablasts function?

A

secrete Ab into medullary sinuses or leave node via efferent lymph and travel to other organs

38
Q

Secondary nodule

A

contains mantle of small memory b cells or inactive B cells pushed aside by germinal center, germinal center contains light-staining activated B cells which move from dark to light zones

39
Q

Names for B cells in dark and light zones

A

dark - centroblasts

light - centrocytes - interact with FDC, mitosis decreases, negative selection

40
Q

FDC form what? and function as?

A

Stroma of primary and secondary nodules, not true APCs, bind immune complexes for long periods of time

41
Q

Causes of lymphadenopathy

A

immune reactions, microbial infection, primary malignancies of LN, replication of metastatic malignant cells

42
Q

Follicular hyperplasia

A

Ab production predominates, but paracortex does not greatly increase in size, ex: rheumatoid arthritis

43
Q

Paracortical hyperplasia

A

cell-mediated response predominates, with relatively few secondary nodules developing, ex: viral infections

44
Q

Dual roles of spleen

A

1) white pulp - filtered antigens from blood and initiates immune response
2) red pulp - destroys old/damaged RBCs

45
Q

Hilus of spleen vs LN

A

Spleen hilium is where blood vessels enter and leave, LN hilium is only where efferent lymphatics leave

46
Q

Splenic capsule

A

dense irregular CT that contains some myofibroblasts, covered by mesothelium

47
Q

Splenic trabeculae

A

composed of CT that extends inward from capsule

48
Q

White pulp

A

is not continuous, organized around central artery, contains PALS (contains mostly T cells - thymus dept region and DCs) and lymphoid nodules (embedded in PALS, B cell regions, contain FDCs, these nodules push central artery to edge of white pulp)

49
Q

Red pulp

A 
splenic sinuses (contain blood) highly permeable sinusoidal capillaries
splenic cords (bilroths cords) sites where old RBCs are destroyed, mixed cell population
50
Q

Marginal zone

A

surrounds white pulp, separating it from red pulp, initiates immune response, B cells present here do not recirculate

51
Q

Open or closed circulation in spleen?

A

In humans - open

52
Q

causes of splenomegaly

A

diseases involving excessive destruction of RBCs, certain lysosomal storage diseases

Microanatomy (10 decks)

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