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Histology -- Zach H. > Lecture #25: Immune and Lymphatic System 2 > Flashcards

Lecture #25: Immune and Lymphatic System 2 Flashcards

1
Q

Since the thymus does not have afferent lymphatics, how do lymphocytes get from the bone-marrow to the thymus for differentiation?

A

Since the thymus does not have afferent lymphatic vessels the lymphocytes cannot enter the thymus from the lymph system and can only enter the thymus via blood vessels. The lymphocytes going to the thymus in the blood are released form bone marrow and go to the thymus to differentiate into T-cells.

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2
Q

Are efferent lymphatics present in the capsule of the thymus?

A

YES

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3
Q

What do the trabeculae of the thymus divide it into?

A

incomplete lobules

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4
Q

What is found in the capsule of the thymus?

A

Blood Vessels
Efferent lymphatics
Extends trabeculae (septa) into the parenchyma.

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5
Q

Is the medulla or cortex of each lobule in the thymus stain a dark color?

A

The lobule of the thymus is composed of an outer, darker staining cortex and an inner, lighter staining medulla.

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6
Q

True or False:

Afferent lymphatics are present in the capsule of the thymus?

A

False - afferent lymphatics are NOT present in the thymus.

**Thus, lymph does not circulate through the thymus.

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7
Q

What different cell types are found in the dark staining cortex of the thymus?

A

> Epithelial reticular cells
- secrete thymosin

> T-cells in various stages of differentiation

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8
Q

What do epithelial reticular cells of the cortex secrete?

A

Thymosin

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9
Q

What is the importance of blood vessels in the cortex being surrounded by a continuous epithelial barrier?

A

It allows the thymus to maintain lymphopoiesis while segregated from antigens.

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10
Q

Are the capillary beds in the light staining medulla sheathed by epithelial cells?

A

NO

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11
Q

What are Hassall’s corpuscles and what do they produce?

A

Hassall’s corpuscles are highly keratinized medullary epithelial cells that produce cytokine thymic stromal lymphopoietin, which stimulates thymic dendritic cells needed for the maturation of single positive T-cells.

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12
Q

What does cytokine thymic stromal lymphopoietin function to do?

A

Stimulates thymic dendritic cells needed for the maturation of single positive T-cells.

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13
Q

What are whorls of highly keratinized medullary epithelial cells found in the medulla of the thymus lobule?

A

Hassall’s corpuscles

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14
Q

When is the thymus the most developed?

A

at puberty

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15
Q

In what age does the thymus involute?

A

During Adolescence

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16
Q

True or False:

The thymus has lymph follicles (nodules), afferent lymph vessels, and lymph sinuses.

A

FALSE -

NO lymph follicles (nodules)
NO afferent lymph vessels
NO lymph sinuses

**Thus, the thymus is solely devoted to the differentiation of T-cells

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17
Q

What is a double negative T-cell?

A

> Lacks cell surface molecules typical of mature T-cells
Enter cortex from blood vessels
Proliferate in subcapsular area

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18
Q

Where does the double negative T-cell proliferate at?

A

Proliferate in subcapsular area.

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19
Q

Where do double negative T-cells enter the thymus from blood vessels?

A

Enter cortex of thymus from blood vessels.

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20
Q

True or False:

Double negative T-cells lack cell surface molecules typical of mature T-cells.

A

True

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21
Q

What is a double positive T-cell?

A

Expresses both CD4 and CD8 co-receptors and TCR receptors.

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22
Q

True or False:

Double positive T-cells are confronted with epithelial cells with cell surface MHC classes I and II for clonal selection.

A

TRUE

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23
Q

What does single positive T-cells express on their surface?

A

Express TCR receptors and either CD4 and CD8 co-receptors.

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24
Q

Where is clonal deletion completed in the thymus?

A

Clonal deletion is completed in the medulla.

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25
Q

What kind of T-cell is typically found in the inner cortex of the thymus?

A

Single Positive T-Cells

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26
Q

What kind of T-cells are typically found in the outer cortex of the thymus?

A

Double Positive T-Cells

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27
Q

What type of T-cells are typically found in the subcapsular area?

A

Double Negative T-Cells

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28
Q

Fill in the Blank:

All T-cells keep the ________receptor and either the CD4 or CD8 co-receptors.

A

TCR

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29
Q

Thymic epithelial cells from the cortex and medulla derive from a common ectodermal cell precursor. What 2 keratins are expressed by this common ectodermal cell precursor?

A

Keratin 5 and Keratin 18

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30
Q

What transcription factor differentiates ectodermel cell precursor in to either corical thymic epitheliam cells or medullary thymic epithelial cells?

A

Foxn1 Transcription Factor

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31
Q

What keratin does cortical thymic epithelial cells express?

A

Keratin 18

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32
Q

What keratin does medullary thymic epithelial cells express?

A

Keratin 5

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33
Q

What transcription factor, besides Foxn1, is needed for differentiation into medullary thymic epithelial cells? Also, is this transcription factor needed for cortical thymic epithelial cells?

A

AIRE (AutoImmune REgulator)

NO, not needed for cortical thymic epithelial cell differentiation

34
Q

What does thymic cortical epithelial cells participate in?

A

Participate in the clonal selection of immunocompetent T-cells.

35
Q

What does thymic medullary epithelial cells participate in?

A

Participate in the clonal deletion of autoreactived T-cells.

36
Q

What happens if there is defective expression of transcription factor AIRE?

A

APECED syndrome

(autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy.

37
Q

What 2 things does the thymic epithelial cells play an important function in?

A

Clonal selection and clonal deletion of differentiating T-cells.

38
Q

What is the transcription factor Foxn1 critical for?

A

Foxn1 is essential for the differentiationg of thymic epithelial cells.

39
Q

What does the transcription factor AIRE promote?

A

AIRE promotes the expression of a portfolio of tissue-specific cell proteins by thymic medullary epithelial cells, which normally do not express these proteins.

**these proteins permit the identification and disposal of autoreactive T-cells.

40
Q

What is the trabeculae of the thymus?

A

The trabeculae is an extension of the capsule down the corticomedullary region. It forms the boundary of each lobule.

41
Q

What does the blood-thymic barrier consist of?

A 
endothelium 
endothelial basal lamina 
perivascular space 
basal lamina of reticular cells 
reticular cells 
thymic parenchymal cells
42
Q

Where is the blood-thymus barrier located?

A

Thymic Cortex

43
Q

What does the blood-thymus barrier prevent?

A

Prevents antigens in the blood from reaching developing T-cells in thymic cortex.

44
Q

Why is the blood-thymus barrier leaky during fetal life?

A

leaky during fetal life to allow for development of immunologic tolerance to self-antigen.

45
Q

What is the spleen divided into?

A

Red pulp and White pulp

46
Q

Where do blood vessels enter and leave the spleen?

A

Hilus

47
Q

True or False:

The spleen has lymph sinuses and afferent lymph vessels.

A

False - the spleen has NO lymph sinuses and afferent lymph vessels.

48
Q

What does the mesothelium-lined connective tissue capsule of the spleen contain?

A

Contains some smooth muscle fibers and sends trabeculae into parenchyma.

49
Q

What is the spleen covered by?

A

peritoneum, except at hilus.

50
Q

What are the blood filtering functions of the spleen?

A 
> only lymphatic organ specialized to filter blood 
> stores and removes worn-out RBCs 
> recycles iron 
> converts hemoglobin to bilirubin 
> blood formation in the fetus
51
Q

What is the immunologic functions of the spleen?

A

> screens foreign material in the blood
produces lymphocytes and plasma cells
removal leads to overwhelming bacterial infections in infants, children, and young adults.

52
Q

What does the removal of the spleen lead to?

A

Removal leads to overwhelming bacterial infections in infants, children, and young adults.

53
Q

True or False:

Lymphocytes and plasma cells are produced in the spleen.

A

TRUE

54
Q

Does the blood filtering functions of the spleen recycle iron, convert hemoglobin to bilirubin, store and remove worn-out RBCs, and form blood in the fetus?

A

YES

55
Q

What is the white pulp the site of?

A

Site of clonal expansion of antigen-stimulated lymphocytes.

56
Q

Is the white pulp always associated with arteries?

A

Yes - elongated, branched strands always associated with arteries.

57
Q

True or False:

The white pulp is zones of diffuse lymphoid tissue and germinal centers.

A

True

58
Q

True or False:

B-cell area contains secondary follicles in which central arterioles is off center.

A

True

59
Q

Where are T-cells found in the white pulp?

A

T-cells are found in the areas surrounding the central artery near the center of the white pulp.

60
Q

What forms the periarterial lymphatic sheath (PALS)?

A

T-cells are found in the areas surrounding the central artery near the center of the white pulp, which forms the periarterial lymphatic sheath (PALS).

61
Q

What is associated with fixed macrophages and supports splenic pulp?

A

Reticular fibers are associated with fixed macrophages and support splenic pulp.

62
Q

What does the marginal zone of the spleen form?

A

Forms sinusoidal interface between red pulp and white pulp.

63
Q

Does the marginal zone has an abundance of antigen-presenting cells?

A

YES

64
Q

Where in the spleen do lymphocytes first encounter antigens?

A

Marginal Zone -> lymphocytes first encounter antigens here.

65
Q

Where in the spleen does activated T-helper cells activate B-cells?

A

Marginal Zone

66
Q

True or False:

Activated T-helper cells activate B-cells in the white pulp of the spleen.

A

False -> activated T-helper cells activate B-cells in the marginal zone of the spleen.

67
Q

What percentage of the spleen is made up of red pulp?

A

80%

68
Q

What is the function of the red pulp in the spleen?

A

Red pulp functions to filter blood.

69
Q

Does the red pulp surround the white pulp?

A

Yes

70
Q

What forms the red pulp parenchyma?

A

Billroth cords form red pulp parenchyma

71
Q

Billroth cords form red pulp parenchyma. What is its function and what cell types are found here ?

A

> contain various blood cells, plasma cells, and antigen presenting cells

> terminal capillaries open directly into substance of cords (open circulation)

> macrophages destroy worn-out or defective red blood cells

72
Q

What are venous sinusoids found in the red pulp of the spleen and what does it store?

A

> endothelial-lined sinusoids with a discontinuous basement membrane

> storage sites for healthy red blood cells (closed system)

73
Q

Between billroth cords and venous sinusoids, which one is a closed system and which is an open system?

A

Venous sinusoids -> closed system

Billroth cords -> open system (open circulation)

74
Q

True or False:

After capillaries form, supplying white pulp, central arteries lose their white pulp investment and enter the red pulp to form a penicillus.

A

TRUE

75
Q

What is a penicillus formed by arteries in the spleen?

A

A penicillus is composed of pulp arteriole, sheathed arteriole, and terminal capillary.

** after capillaries form, supplying white pulp, central arteries lose their white pulp investment and enter red pulp to form a penicillus.

76
Q

What do the terminal capillaries in the spleen drain into?

A

Drains into:

 - intercellular spaces (open system)
 - venous sinuses lined with reticuloendothelial cells (closed system
77
Q

True or False:

Venous sinuses are not lined with reticuloendothelial cells.

A

False - venous sinuses are lined with reticuloendothelial cells.

78
Q

What veins merge together to form the splenic vein, which exits through the hilus?

A

Pulp veins unite with trabecular veins, forming the splenic vein, which exits at the hilus.

79
Q

What is the path of blood through the spleen? Starting at the splenic artery and ending at the splenic vein.

A 
Splenic Artery entery hilus
Trabecular Arteries branch off
Central Arteries 
Capillaries Form 
Penicillus
Terminal Capillary
Venous Sinuses or Intercellular Spaces 
Venous Sinuses drain into pulp veins
Pulp Vein unites with trabecular veins
Splenic vein forms from pulp vein and trabecular vein.
80
Q

Look over the diagram of blood flow through the spleen that Dr. Anderson illustrated.

A

Keep working hard everyone!!

Histology -- Zach H. (21 decks)

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