Lymphoid System II

Question 1

What two secondary lymphoid organs are encapsulated?

Answer 1

Spleen, lymph nodes!

Question 2

What are the two methods of lymph resorption in the nodes?

Answer 2

1. Inter-endothelial flow

2. Vesicle transcytosis

Question 3

Describe lymph flow in small lymphatics.

Answer 3

Passive; relies on adjacent muscular contraction. Valves prevent backflow.

Question 4

Do large lymphatic vessel walls have smooth muscle?

Answer 4

Yeah

Question 5

Where are reticular fibers found in lymph nodes? What is the function?

Answer 5

In the sinuses, to slow the flow of lymph, structural support, and trap pathogens.

Question 6

Where does lymph drain from the nodes?

Answer 6

Efferent lymphatic out of the hilum.

Question 7

What is typical of the endothelium that lines the sinuses of lymph nodes?

Answer 7

It is discontinuous, to allow antigens and other material to enter the node.

Question 8

What type of lymphoid tissue is predominant in the outer cortex of the lymph nodes?

Answer 8

Nodular tissue.

Question 9

What type of lymphoid tissue is predominant in the inner cortex (paracortex)?

Answer 9

Diffuse; devoid of nodules - rich T cell zone.

Question 10

What are high endothelial venules? Where are they found and what do they do?

Answer 10

In the paracortex of lymph nodes, they allow circulating lymphocytes in the bloodstream to enter the node.

In the thymus, HEVs allow T cells to exit.

They are FOUND IN ALL SECONDARY LYMPHOID ORGANS EXCEPT THE SPLEEN

Question 11

What molecule on the HEVs signals to lymphocytes that they should enter the node?

Answer 11

Selectins. These can increase in numbers on endothelial cells in the HEV during viral infection

Question 12

Where are lymph node medullary cords located and what do they contain?

Answer 12

Located between the medullary sinuses in the lymph nodes, they are a loose CT containing reticular fibers, plasma cells, lymphocytes, fibroblasts, neutrophils, and macrophages.

Question 13

What are Reed-Sternberg Cells?

Answer 13

Diagnostic of Hodgkin’s lymphoma/leukemia. Can be found in lymph nodes. They are bilobed or multinucleated and have an “owl’s eye appearance”

Question 14

What cell type lies above the CT capsule of the spleen?

Answer 14

Stratified squamous mesothelium

Question 15

What are trabecular beams of the spleen?

Answer 15

CT capsule extensions that penetrate the organ. They contain blood vessels - trabecular arteries or veins.

Question 16

Compare and contrast trabecular arteries and veins.

Answer 16

• Arteries have smooth muscle in the tunica media, and the adventitia is composed of the CT of the beams.
• Veins have NO tunica media and only have an adventitia composed of CT of the trabecular beams.

Question 17

What is the name of white pulp organization? What do they surround?

Answer 17

Periarterial lymphoid sheath (PALS). They surround the central arteries (hence PERI-arterial)

Question 18

What do the central arteries of the spleen do?

Answer 18

They extend arteries to the periphery of the white pulp and terminate in the marginal sinuses. They dump blood into the marginal zone.

Question 19

Where are sheathed arteries found in the spleen?

Answer 19

Downstream of the penicillar arteries, they release RBCs in to the red pulp for “sifting out” by the CT and macrophages.

Question 20

Are reticular fibers found in both cords and sinuses in the lymph nodes?

Answer 20

Yeah.