Physiology - Lecture 2

Front 1

Describe how lymphocytes enter and exit a lymph node via lymphatic vessels OR via the blood.

Back 1

Lymphatic vessels:
Through afferent lymphatic vessels

Blood:
Through HEVs ("High endothelial venules")
These lymphocytes enter by diapedesis into the deep cortex

Activated T cells, as well as naive, mature T cells that recirculate, exit the lymph nodes through efferent lymphatic vessels.

When B cells are activated and differentiate into plasma cells or memory B cells, some of these cells will migrate to the medulla of the lymph node while others will leave through the efferent lymphatic vessel.

Front 2

Describe the histology of HEVs, where they are found and their significance to lymphocyte circulation in the lymph node

Back 2

HEV stands for high endothelial venules. These are specialized venues in the deep cortex (aka paracortex) that have thicker endothelium. They are composed of simple cuboidal or columnar cells and regulate the egress of mature-naive B & T lymphocytes.

Luminal membrane receptors (adhesion molecules) on the HEV signal mature-naive B & T lymphocytes to leave the blood circulation and enter the lymph node tissue during diapedesis.

They also contain a large amount of water channels, that allow the movement of the ISF back into circulation.

Front 3

Describe how antigens enter and exit (or not) a lymph node

Back 3

***

General lymph flow through a lymph node:

afferent lymphatic vessels, subcapsular sinuses, trabecular sinuses, medullary sinuses, efferent lymphatic vessels

Front 4

Indicate the regions of a lymph node where B cells migrate to and are concentrated as well as the regions where T cells migrate to and are concentrated.

Back 4

B cells:
B cells enter the superficial cortex through HEVs or afferent lymphatic vessels. Mature but naive B cells gather to form primary follicles. When the cells are presented with an antigen, they form a secondary follicle that consists of a "germinal center" and a "mangel zone." The cells eventually migrate through the deep cortex (and potentially the medulla) and into the efferent blood vessels.

T cells:
Enter the deep cortex (aka "T Cell Zone") through the HEVs. There, they form loose aggregates in response to high concentrations of specific chemokines in the deep cortex. If presented with antigens from myeloid derived dendritic cells, they p proliferate and differentiate into memory T cells, and then exit via efferent lymph vessels.

Front 5

Describe the general role of myeloid-derived dendritic cells, follicular dendritic cells, and macrophages in the lymph node

Back 5

Myeloid derived dendritic cells: migrate to the deep cortex and present antigens to T cells.

Follicular dendritic cells: capture and "display" antigens to activated B cells. They reside specifically in lymphatic follicles

Macrophages: located within the sub capsular region, cortex and paracortex

Front 6

Describe the stromal architecture for a lymph node cortex and medulla and how this contributes to its overall function

Back 6

Reticular protein fibers (type III collagen) form the scaffolding in lymph nodes. It is produced by reticular cells and allows for maximum cell to cell interactions.

Front 7

Compare and contrast primary and secondary lymphatic follicles while considering the significance of observing secondary lymphatic follicles

Back 7

The primary follicle contains mature but naive B cells. When B cells in the primary follicle are activated by an antigen (presented by follicular dendritic cells, for example), a secondary follicle develops and the activated B cells migrate to a specific region within the follicle called a germinal center. The staining here is lighter compared to the mantel zone, which surrounds the germinal center and contains mature naive B cells.

Front 8

Describe the cells within and the appearance of a germinal center vs. a mantle zone

Back 8

Activated B lymphocytes are found within a germinal center, which is more lightly stained compared to the mantel zone. Activated B cells can become plasma cells or memory B cells.

The mature naive cells contained in the mantel zone stain darker and originally constituted the primary follicle from which the secondary follicle evolved.

Front 9

*** Indicate the embryological origin of the spleen and describe the role of the spleen in the development of lymphocytes in utero and post-natally

Back 9

The spleen is derived from mesodermal mesenchyme. It develops during the 5th week of the embryological period.

In utero the spleen is a hematopoietic organ, and while this function ceases after birth, it can resume hematopoiesis if the need is extreme post-natally. The spleen also utilizes macrophages that phagocytize aged or damage blood cels.

Front 10

*** Indicate when the yolk sac, spleen, liver, and bone marrow contribute the most to hemopoiesis and lymphopoiesis

Back 10

***

Front 11

*** Describe the functions of the spleen and indicate how the function of the spleen is analogous (i.e. not identical) to the function of the lymph nodes

Back 11

***

Front 12

*** Describe the stromal architecture for the spleen and how this contributes to its overall function

Back 12

***

Front 13

*** Compare and contrast the function and locations of white pulp and red pulp of the spleen

Back 13

***

Front 14

*** What is the difference between the splenic sinuses and splenic cords? Describe what is meant by the open circulation of blood flow in the human spleen

Back 14

***

Front 15

***Indicate the regions where B cells migrate to and where T cells migrate to when they enter the spleen

Back 15

***

Front 16

***Indicate and describe the cells within a marginal zone, a mantle zone, and a germinal center

Back 16

***

Front 17

*** Describe the route a T cell would take from entering the spleen, getting activated, to exciting the spleen

Back 17

***