2. Tissues of the immune system

Question 1

What is the lymphatic system?

Answer 1

Lymphoid organs (development & growth & release of lymphocytes)
Lymphoid vessels for transport of lymphocytes and fluid

Question 2

What are the functions of the lymphoid organs?

Answer 2

Primary lymphoid organs 
- bone marrow - develop mature B cells 
- fetal liver - haemopoiesis 
Secondary lymphoid organs - site of immune activation 
- spleen

Question 3

What is haemopoiesis?

Answer 3

Megakaryocytes + developing erthyrocytes and granulocytes

Question 4

How are mature B cells generated?

Answer 4

1. B cell precursor rearranges its immunoglobulin genes
2. Immature B cell bound to self cell - surface antigen is removed from the repertoire
3. Mature B cell bound to foreign antigen activated
4. Activated B cells give rise to plasma cells and memory cells

Question 5

How are mature T cells generated?

Answer 5

1. T-cell precursor rearranges its T cell receptor genes in the thymus
2. Immature T cells that recognise self MHC receive signals for survival. Those that interact strongly with self antigen are removed from the repertoire
3. Mature T cells encounter foreign antigens in the peripheral lymphoid organs and are activated
4. Activated T cells proliferate and migrate into the peripheral sites to eliminate infection

Question 6

What are the lymphatics?

Answer 6

Organs of the immune system connected with one another and with organs of the body by a network of lymphatic vessels similar to blood vessels
- immune cells & foreign particles are conveyed through the lymphatics in lymph (clear fluid that bathes the body’s tissues)

Question 7

What are the functions of secondary lymphoid organs?

Answer 7

Site of immune activation:

• spleen
• lymph nodes
• Mucosal - associated lymphoid tissue (MALT)
• • gastrointestinal
• • respiratory tract
• • urogenital tract

Question 8

What is a lymph node?

Answer 8

Small bean shaped structures localised throughout the body along the lymphatic routes
- contain specialised compartments where immune cells congregate, where they encounter antigens

Question 9

What is diffuse lymphatic tissue?

Answer 9

Location
- respiratory canal, alimentary canal, ocular surface and urogenital tract
Loose aggregate of cells and shows no distinct demarkation from surrounding tissue with which it gradually merges

Question 10

What are the lymph node-gut-associated lymphoid tissues (GALT)?

Answer 10

Tonsils 
Adenoids
Peyer's patches 
Appendix 
Colon

Question 11

What are Peyer’s patches

Answer 11

Bulk of tissues in B cells
Organised in a large and highly active domed follicle
- T cells occupy areas between follicles
- antigen enters across a specialised epithelium made up of M cells
- basic divisions maintained

Question 12

Describe the structure of the spleen?

Answer 12

Upper left abdomen

• Consists of red pulp (RP) - site of red blood cell detection
• Secondary lymphoid tissue, white pulp (WP) - lymphocyte responses to blood borne pathogens are made

Question 13

How are lymphocytes recirculated in the body?

Answer 13

Move through the circulation and the lymphatic duct between various organs