DD Thymus and peripheral lymphoid organs

Question 1

Why do blood vessels bypass the cortex via trabeculae?

Where do they enter?

Answer 1

Enter the medulla

ensures that differentiating T-lymphocytes (in cortex and medulla) do not get exposed to antigens in the blood until they are fully differentiated

Question 2

What is the hallmark of the thymus? What is it?

Answer 2

Hassalls corpuscles

-circular light bodies in the medulla

Question 3

2 arteries that enter the thymus?

Answer 3

Internal thoracid

inferior thyroid

Question 4

Are there afferent and efferent supply of lymph to the thymus?

Answer 4

No afferent, just efferent

Question 5

Describe the blood and lymphatic drainage of the thymus

Answer 5

Arteries in,

Venous and efferent lymphatic drainage out.

Question 6

What creates the difference between the medulla and cortex of the thymus?

Answer 6

difference in lymphocyte population and staining of their nuclei

medulla:

• lighter
• has hassals corpuscles (circular bodies)
• less lymphocytes

cortex:

• darker
• characterized by its heavylymphocyteconcentration, is the site of much lymphocytic proliferation.

Question 7

Describe lymphatic drainage entering the lymph node

Answer 7

Lymph enters lymph node via afferent lymphatic vessels along outer capsule > drains to subcapsulary sinus > reaches cortex + medulla via trabecular sinus > exit via efferent lymphatic vessel

Question 8

Which vessels leave the lymph node? Thymus?

Answer 8

lymph node?

• efferent vessel
• artery
• vein

Thymus?

• efferent vessel
• vein

Question 9

What is found in the germinal center and marginal zone of lymph nodes? explain the differences

Answer 9

GC: aggregation of lymphocyte in outer cortex of the lymph node

• rapidly dividing lymphocytes - stain lighter
• activated by B cells

MZ: lymphocytes
-stain darker

Question 10

Do unchallenged lymph nodes contain germinal centers?

Answer 10

No

• challenged nodes/secondary follicles have clearly visible germinal center with a marginal zone surrounding it
• unchallenged /primary follicles have no germinal center

Question 11

Whats special about high endothelial venules in paracortical region?

Answer 11

HEV are lined by thicker than usual endothelial cells > lymphocytes recognize and pass btwn

• allows circulating T and B lymphocytes to enter lymphatic fluid from blood
• HEVs are found in all secondary lymphoid organs (with the exception of spleen)

Question 12

Which organ contains an abundance of plasma cells? Why is this important?

Answer 12

Spleen - many circulated Antibodies are produced here

Question 13

Red pulp

Answer 13

RBC rich
more fiber rich for support

75% of spleen, where blood flows through loosely arranged sinuses
- stains lighter than white pulp since white pulp is lymphocyte rich

Question 14

White pulp

Answer 14

Lymphocyte rich
less fiber rich

○ Darker than red pulp (because it is lymphocyte rich)

Question 15

What do PALS that surround incoming arteriole in the spleen consist mainly of?

How are they different from nodules?

Answer 15

T-cells

nodules: contain mostly B-cells

Question 16

Do red blood cells or white blood cells move between the endothelium of the spleen?

Answer 16

Both

RBC: enter red pulp space
WBC: entter through spleen

Question 17

Are macrophages in the spleen easily stained? How?

Answer 17

Yes:
macrophages of spleen ingest ink particles and readily visualized
- fewer in white pulp region

Question 18

When do lymph nodes become activated in the secondary follicles?

Answer 18

A lymph node becomes activated when B-cells migrate to germinal centers in response to recognition of an antigen. (Get swelling of the lymph nodes)

• remember MZ trap antigen from circulation and present it to lymphocyte