L7: Immune Tissues

Question 1

Haematopoiesis occurs in the bone marrow in adults. It differs in foetal development. Where does it occur?

Answer 1

• Yolk sac from week 4
• Liver shortly before birth.
• Spleen until cartilaginous bone has become vascularised.

Question 2

Haematopoiesis in children vs. adults?

Answer 2

Children = bone marrow. Adults = bone marrow of larger bones only, mainly the pelvis, sternum, vertebrae and cranial bones.

Question 3

Explain the term extramedullary haematopoiesis.

Answer 3

This is emergency haematopoiesis (e.g. due to chronic inflammatory conditions), and it can occur in the spleen, liver and lymph nodes.

Question 4

What percentage of immature T cells that migrate to the thymus will mature?

Answer 4

2%

Question 5

Describe the structure of the thymus.

Answer 5

Two lobes - left lobe and right lobe. Other structures inside the lobe include the capsule, the cortex, the medulla and the trabeculae/septa.

Question 6

What is thymic involution?

Answer 6

The shrinking of the thymus and a decrease in the production of naive T cells, in association with ageing.

Question 7

What does MALT stand for? Is it a secondary or primary lymphoid organ?

Answer 7

Mucosal Associated Lymphoid Tissue. It is a secondary lymphoid organ.

Question 8

Where are MALTs found and what is there function?

Answer 8

They are found along the mucosal linings in the human body. They initiate immune responses to specific antigens found along these surfaces.

Question 9

Two sub categories of MALT?

Answer 9

GALT = Gut Associated Lymphoid Tissue - Peyer's patches are a component; found in the ileum. 
NALT = Nasal Associated Lymphoid Tissue (NALT).

Question 10

The spleen is the largest lymphoid organ. Explain the functions of red pulp and white pulp.

Answer 10

Red pulp = filters the blood, removing old RBCs.

White pulp = specific lymphoid microenvironments.

Question 11

What are lymphatic vessels constructed with?

Answer 11

Overlapping endothelial cells that respond to fluid pressure - liquid can only flow in one direction, so vessels drain tissues.

Question 12

What does lymph consist of?

Answer 12

It is plasma containing proteins and solutes that filter out of venules and capillaries due to hydrostatic pressure.

Question 13

There are two types of lymphatic vessels. Name them.

Answer 13

Superficial and deep.

Question 14

Superficial?

Answer 14

Superficial lymphatic vessels follow superficial veins. They start in tissues just below the skin. They flow into the lymph nodes in the axillary armpit, inguinal/groin and cervical/neck areas.

Question 15

Deep?

Answer 15

Follow main vessels. Para-aortic lymph nodes are found at either side of the aorta; pre-aortic lymph nodes are found anterior to the aorta.

Question 16

Name the key structures found in a lymph node.

Answer 16

Follicles, Gernimal Centres, paracortical areas and medullary cords.

Question 17

Follicles contain…

Answer 17

B cells.

Question 18

Germinal centres are areas of…

Answer 18

B cell proliferation (occurs in response to Ag stimulation).

Question 19

Paracortical areas contain…

Answer 19

T cells.

Question 20

Medulla contains…

Answer 20

Lymphatic sinuses, plasma cells, B cells and macrophages.

Question 21

How do naive lymphocytes enter and leave the lymph nodes?

Answer 21

Enter via the blood stream and leave via efferent lymphatics.

Question 22

How do APCs enter and leave the lymph nodes?

Answer 22

Enter via the afferent lymphatics and leave via the efferent lymphatics.

Question 23

How do naive lymphocytes and APCs move towards the lymph nodes?

Answer 23

Chemotaxis. This will be covered in more detail in the summer term lectures.

Question 24

Peyer’s patches?

Answer 24

They are found in the ileum in the GALT and they monitor bacterial populations in the intestine. They contain a large number of antibody producing plasma cells.