16 - Lymphatic System Flashcards
What is the lymph system made up of?
- Lymph
- Lymph vessels (lymphatics)
- Organs
- Lymphocytes
- Follicular dendritic cells and macrophages
What is lymph?
Similar to plasma. Excess fluid collected from the interstitial space.
What are the primary and secondary organs of the lymphatic system, and what are the functions of primary and secondary?
Primary:
- Thymus + Bone marrow
- Generate lymphocytes from immature progenitor cells that arise from stem cells in the bone marrow
Secondary:
- Spleen + Lymph Nodes
- Site of lymphocyte activation and provide environment for antigens to interact with lymphocytes
What is tertiary lymphoid tissue?
Formed during autoimmune diseases, e.g rheumatoid arthiritis. Assume a role when challenged with antigens tha result in inflammation.
Ectopic lymphoid follicles
What is the function of the thymus and what happens to it over a life span?
- Located in superior mediastinum
- Thymic cell education (matures T-cells) and induction of central tolerance
- Increases in size from birth due to post-natal antigen stimulation, atrophy by teenage years, by adult thymic stroma is mostly replaced by adipose tissue
What is the structure of the thymus?
Lobules joined by septa and encapsulated by a capsule.
Capsule and Septa made mainly by reticulun fibres in ECM
ONLY HAS EFFERENT LYMPH VESSELS
What is the structure of the spleen and where is it located?
Left side of abdomen, posterior to stomach, inferior to diaphragm.
ONLY HAS EFFERENT LYMPH VESSELS
What is the function of the spleen?
FILTER BLOOD LIKE LYMPH NODE FILTERS LYMPH
Haemopoietic:
- Remove of old, abnormal, damaged blood cells
- Store erythrocytes
- Retrieve Fe from Hb
- Produce blood cells up to 5 months foetus
Immune:
- Removing big antigens from blood using macrophages
- Antigen presenttion
- Activation and proliferation of lymphocytes
- Produce immune cells
What is a germinal centre?
Sites within secondary lymphatic organs where B-cells proliferate and undergo monoclonal selection
Contain memory cells and IgA produced here
What is splenomegaly?
Where the spleen enlarges in response to localised/systemic infection due to proliferation B-cells.
Can lead to rupturing and exsanguiation
What would you do with a ruptured spleen and why would you try to avoid it?
Splenectomy
- Needed in case it ruptures and causes internal bleeding
- Removal leads to increased risk of infection by encapsulated bacteria and malaria
- Liver can take over haemolysis
What is the structure of a lymph node?
- Several afferent vessels, lymph follicles in cortex, medulla, hilum, single efferent vessel.
- Arteries and veins enter node via hilum
- Reticulin CT
How many lymph nodes are there and where are they mainly located?
- 600-700
- Cervical, Inguinal, Axillae
- Clusters anywhere that lymph is collected from regions likely to sustain pathogen contamination
What are sentinel lymph nodes?
Lymph nodes closest to major organs, that interact with foreign antigens or tumour cells.
First lymph node to interact with metastasising cancer.
What is the function of a lymph node?
Acts as a filter as the lymph goes back to the vascular system. Traps antigens and mediates immune response using macrophages, T-cells and B-cells
What is an enlarged lymph node called and why is it enlarged?
- Lymphadenopathy
- Proliferation of T and B-cells in germinal centres because of infection
- Can also be due to metastatic tumours in nodes
- Can be due to lymphoma
- Painful
What is local and generalised lymphadenopathy?
Local: Few nodes locally are enlarged due to infection
Generalised: Nodes in different areas enlarged. Can be due to cancer or infection
What is MALT?
Mucosae-associated LT
- Beneath epithelia in submucosa are lymphoid follicles
- Nodule contains lymphocytes, plasma cells, macrophages
- Tonsils, Peyers Patches (ileum), Appendix
What do follicular dendritic cells do? APC
- Take pathogen into lymph node to macrophage zone
- Activate T-cells which can then activate B-cells
What are the main differences between T and B cells?
- B cells recognise antigens, T cells do not
- T cells attack invades in cell, B-cells attack outside evaders