Woodbury - Histology Of Lymphoid Tissue

Question 1

Bone marrow is made up of a ___ portion where blood cells are born and a ___ portion where blood cells can get into circulation

Answer 1

Stromal portion (cord) is where blood cells are born and the vascular sinuses is where blood can get into circulation.

Question 2

Where is the thymus found??

Answer 2

Mediastinum

Question 3

What are the two major parts of the thymus?

Answer 3

Cortex and medulla

• the cortex is the outer part and is lighter staining
• the medulla is lighter staining and is in the middle

Question 4

Epithelial Reticular Cells

Answer 4

Endodermally derived

• they underlie the thymocytes in the thymus.
• They are sometimes even called nurse cells because they form intimate associations with some thymocytes.

Question 5

What is the macrophages role in Thymocyte development?

Answer 5

• produce positive factors

- remove thymocytes that fail the central tolerance program

Question 6

T cell maturation - which CDs do they start with? End with? Etc

Answer 6

Start: CD4-/CD8- (in the subcapsular space)
In the middle: CD4+ and CD8+ (in the cortex)
End: CD4 or CD8 (in the medulla)

Question 7

We said that thymoctes start in the bone marrow and then develop in the thymus. How do they get into the thymus?

Answer 7

High Endothelial Venules

• can’t really see them but They are right next to the medulla.
• then they migrate to the subcapsule
• then they proliferate
• then they descend again towards the medulla
• then they exit via the vasculature and lymphatics.

Question 8

Blood-thymus barrier

Answer 8

Composed of 5 layers in the thymic cortex

• endothelial layer
• endothelial BM
• subendothelial space
• ERC BM
• ERC

Question 9

Hassal’s Corpuscles

Answer 9

Concentric circles of ERC’s

- you know you are in the medulla of the thymus if you see Hassals corpuscles.

Question 10

Transport of lymphatics

Answer 10

Fluid is leaked out while going from arteriole to Venule. It is picked up by a lymphatic and is carried to lymph nodes via afferents lymphatic vessels, which have valves to prevent backflow. Then it leaves the lymph node by way of the hilus to enter the efferent lymphatic. Ultimately it makes its way to the right lymphatic duct or the thoracic duct.

Question 11

Physical characteristics of the lymph node

Answer 11

Capsule sends a trabeculae into the lymph node.
Afferents lymphatics pierce the capsule to deliver the lymph
There is a cortex and medulla with a whole loaf of lymphocytes. The cortex and medulla are less discernible than the thymus though.
There is also a efferent lymphatic as well as blood vessels leaving the hilus.
There is a subscapular sinus under the capsule.

Question 12

Reticular fibers

Answer 12

NOT THE ERC THAT WE SAW IN THE THYMUS

• the structure of the lymph node is maintained by these guys
• they are made by reticular cells
• you can see them best in the subcapsular sinus
• lymphocytes travel on these guys like a highway

Question 13

Where to the B cells hang out in the lymph node?? T cells?

Answer 13

B cells - follicles in the cortex

T cells - paracortex

Question 14

DiGeorge Syndeome

Answer 14

We see several abnormalities at birth. It can causes severe birth defects in the heart. You can also have thymus abnormalities which cause the child to be immunodeficient
- the B cells will still be present but the T cells. Will be gone.

Question 15

Will lymph nodes have cords and sinuses like the thymus?

Answer 15

Yes

Question 16

Germinal center

Answer 16

Follicles containing B cells that are actively proliferating. They have a lighter staining in the middle.
- also called secondary follicle

Question 17

Primary Follicle

Answer 17

Follicles containing quiescent B cells, they will not be clear in the middle.

Question 18

What type of B cells will be in the middle of a lymph node?

Answer 18

Cells that came from germinal centers

Question 19

Palatine tonsil under histological section

Answer 19

Stratified squamous epithelium with crypts. There is no lymphatics because antigens come from the oral cavity and don’t need to be brought to them.
- also have follicles.

Question 20

Starry night appearance of tonsils

Answer 20

Macrophages engulfing lymphocytes that Aren’t up to the standard of the tonsil.
- remember, it is a secondary lymphoid organ.

Question 21

Where will B cells go from the tonsil?

Answer 21

To the sublingual salivary gland.

Question 22

M cells

Answer 22

In the GI tract - Responsible for lumen sampling and delivery of antigen to the waiting immune system

Question 23

What is the job Of white pulp? red pulp?

Answer 23

White - immune surveillance

Red - removal of expired RBCs

Question 24

Important histological characteristics of the spleen

Answer 24

Has a Capsule but NO SUBCAPSULAR SPACE
No cortex or medulla
Has reticular fibers
No afferents lymphatics 
White pulp is blue and red pulp is red
Has a lot of trabeculae, visible connective tissue

Question 25

Blood flow within the spleen

Answer 25

Trabecular artery –> centra artery –> red pulp

• the central artery is surrounded by T cells called PALS. Close in proximity is also the B cells. This collection is the white pulp.

Question 26

Open and closed circulation of the spleen

Answer 26

Closed - some blood just goes into the spleen and then travels out.
Open - the other 90% Of the blood comes into the spleen via open circulation and are dumped in a cord. It then has to squeeze back into the sinuses. However, macrophages lurk there and will eat them if they can’t squeeze in quick enough. Older cells aren’t as good at squeezing back in.

Question 27

Primary, secondary, and tertiary lymphoid tissues

Answer 27

Primary - where lymphocytes are born and mature
- bone marrow and thymus

Secondary - where lymphocytes interact with APCs
- Peyer’s patches, spleen, lymph nodes

Tertiary - transient aggregations that occur anywhere and then disappear.