Thymus & Lymph Nodes

Question 1

What does lymph consist of? What do the lymphatic vessels do with these contents?

Answer 1

Extracellular fluid and debris - they drain them to regional lymph node for immune surveillance

Question 2

Describe the structure of the thymus.

Answer 2

Composed of a medulla (inner, lighter region) and a cortex (outer, denser region) that are located in mediastinum and are divided into irregular rectangular lobes by septae of connective tissue

Question 3

Which part of thymus is rich in T lymphocytes?

Answer 3

Cortex

Question 4

Which part of thymus is rich in epithelial reticular cells/epitheliocytes?

Answer 4

Medulla

Question 5

What type of intermediate fiber is found in epithelial reticular cells?

Answer 5

Keratin

Question 6

How do epithelial reticular cells communicate with each other?

Answer 6

Desmosomes

Question 7

Are epithelial reticular cells stromal?

Answer 7

No - they do not have extracellular reticular fibers

Question 8

What are two functions of epithelial reticular cells?

Answer 8

Form lattice network that engulfs the developing T cells, aids in formation of thymic blood barrier

Question 9

What are Hassall’s Corpuscles?

Answer 9

Flattened, concentrically arranged epithelial reticular cells that are degenerating.

Question 10

What are the 5 layers of the blood-thymus barrier?

Answer 10

Endothelial cell of blood vessel, basal lamina of endothelial cell (thick), layer of connective tissue (fibroblasts and ECM), basal lamina of epithelial reticular cell, epithelial reticular cell itself

Question 11

What part of the thymus is rich in T cells?

Answer 11

Cortex

Question 12

Where do T lymphocytes migrate to the cortex from?

Answer 12

Bone marrow

Question 13

What part of the thymus do T lymphocytes enter first?

Answer 13

Subcapsular cortex

Question 14

In what part of the thymus does positive selection process for MHC marker take place?

Answer 14

Cortex

Question 15

If cells do not positively select for MHC, what happens to them?

Answer 15

Apoptosis or get eaten by macrophages

Question 16

If T lymphocytes recognize MHC and pass first selection process, where do they migrate next?

Answer 16

Medulla

Question 17

What selection process happens in the medulla? Which cells present the antigen in question?

Answer 17

Negative selection for recognition of self antigens - dendritic cells present the self Ags

Question 18

What happens to mature T cells (the 2% who pass both selection processes)?

Answer 18

They re-enter vascular circulation through leaky blood/thymus barrier in medulla.

Question 19

What makes up secondary lymphoid tissue?

Answer 19

Spleen and lymph nodes, and tonsils (diffuse lymphoid tissue)

Question 20

Describe the general structure of lymph nodes and general function.

Answer 20

Kidney bean-shaped, encapsulated filters that filter regional lymph fluid to neck, axilla, groin, para-aortic regions.

Question 21

What are two main regions of lymph node?

Answer 21

Cortex (outer region) and medulla (inner region)

Question 22

What types of structural cell exists in lymph node? What type of fiber?

Answer 22

Reticular cells (fibroblasts) and reticular fibers (collagen Type III)

Question 23

Where do afferent lymphatics enter the lymph node?

Answer 23

Subcapsular sinus in outer convex surface of cortex

Question 24

Where does the single efferent lymphatic vessel exit the LN?

Answer 24

Hilus on inner concave surface of cortex

Question 25

What does lymph percolate through in the lymph node?

Answer 25

Septae of connective tissue that is composed of reticular cells (fibroblast-like) and reticular fibers

Question 26

Where do lymphocytes enter the lymph node?

Answer 26

They are circulating in blood and enter through high endothelial venules (HEVs) located in paracortex region

Question 27

What types of immune cells exist in lymph nodes?

Answer 27

B cells, T cells, plasma cells, macrophages

Question 28

Where in lymph node are B cells found? How are they grouped?

Answer 28

Cortex - they are grouped into primary and secondary nodules

Question 29

What is a germinal center?

Answer 29

Clear area that is site of B cell activation and proliferation on secondary B cell nodules

Question 30

Where do B cells go as they mature? And what do they become?

Answer 30

Become plasma cells that move more into deep cortex (paracortex) and medulla region

Question 31

What immune cells are found in medulla?

Answer 31

Plasma cells and macrophages

Question 32

Where do T cells in lymph nodes reside?

Answer 32

Internodal space

Question 33

Explain how T lymphocytes are activated for clonal selection.

Answer 33

Antigen on MHC II of APC binds to CD4 of helper T cell and its TCR. Helper T cell releases IL-2, to stimulate helper T cells. Activated helper T cells then proliferate and differentiate to form clones of both activated and memory helper T cells.

Question 34

Explain two ways in which cytotoxic T cells are activated.

Answer 34

1) CD8 on cytotoxic T cell binds with MHC class I molecule of various cells - the TCR interacts w/ Ag on MHC I molecule.
2) IL-2 released from activated helper T cells stimulates cytotoxic T lymphocyte.

Question 35

Explain two ways B cells are activated.

Answer 35

1) Free Ag binds to BCR. B cell engulfs BCR and presents Ag to activated helper T cell using MCH II.
2) IL-4 released from activated helper T cells stimulates B cells so they proliferate and differentiate to form clone of plasma cells that will release Abs and memory B cells.