L7: Immune Tissues Flashcards
Haematopoiesis occurs in the bone marrow in adults. It differs in foetal development. Where does it occur?
- Yolk sac from week 4
- Liver shortly before birth.
- Spleen until cartilaginous bone has become vascularised.
Haematopoiesis in children vs. adults?
Children = bone marrow. Adults = bone marrow of larger bones only, mainly the pelvis, sternum, vertebrae and cranial bones.
Explain the term extramedullary haematopoiesis.
This is emergency haematopoiesis (e.g. due to chronic inflammatory conditions), and it can occur in the spleen, liver and lymph nodes.
What percentage of immature T cells that migrate to the thymus will mature?
2%
Describe the structure of the thymus.
Two lobes - left lobe and right lobe. Other structures inside the lobe include the capsule, the cortex, the medulla and the trabeculae/septa.
What is thymic involution?
The shrinking of the thymus and a decrease in the production of naive T cells, in association with ageing.
What does MALT stand for? Is it a secondary or primary lymphoid organ?
Mucosal Associated Lymphoid Tissue. It is a secondary lymphoid organ.
Where are MALTs found and what is there function?
They are found along the mucosal linings in the human body. They initiate immune responses to specific antigens found along these surfaces.
Two sub categories of MALT?
GALT = Gut Associated Lymphoid Tissue - Peyer's patches are a component; found in the ileum. NALT = Nasal Associated Lymphoid Tissue (NALT).
The spleen is the largest lymphoid organ. Explain the functions of red pulp and white pulp.
Red pulp = filters the blood, removing old RBCs.
White pulp = specific lymphoid microenvironments.
What are lymphatic vessels constructed with?
Overlapping endothelial cells that respond to fluid pressure - liquid can only flow in one direction, so vessels drain tissues.
What does lymph consist of?
It is plasma containing proteins and solutes that filter out of venules and capillaries due to hydrostatic pressure.
There are two types of lymphatic vessels. Name them.
Superficial and deep.
Superficial?
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.
Deep?
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.
Name the key structures found in a lymph node.
Follicles, Gernimal Centres, paracortical areas and medullary cords.
Follicles contain…
B cells.
Germinal centres are areas of…
B cell proliferation (occurs in response to Ag stimulation).
Paracortical areas contain…
T cells.
Medulla contains…
Lymphatic sinuses, plasma cells, B cells and macrophages.
How do naive lymphocytes enter and leave the lymph nodes?
Enter via the blood stream and leave via efferent lymphatics.
How do APCs enter and leave the lymph nodes?
Enter via the afferent lymphatics and leave via the efferent lymphatics.
How do naive lymphocytes and APCs move towards the lymph nodes?
Chemotaxis. This will be covered in more detail in the summer term lectures.
Peyer’s patches?
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.
