Flashcards in Lymphatic System Deck (17):
What is the role of the lymphatic system?
- Maintains homeostasis - blood pressure. Takes up 3L (out of 20L/day) of blood plasma forced out of arterial end of capillary beds into the tissues, and returns it to CVS.
- Identification and defence against pathogens.
What are the 3 components of the lymphatic system?
- Lymphoid tissues
- Lymphatic vessels
What is lymph?
- Consists of blood plasma forced out of capillaries (leakage helps exchange of nutrients and gases between blood and tissues) and that is not reabsorbed.
What is the difference between primary and secondary lymphoid tissues?
- Primary: tissues in which lymphocytes are generated and differentiate into mature naive lymphocytes - bone marrow for B cells, thymus for T cells (thymic cell education).
- Secondary: tissues in which immune responses are initiated - e.g. Lymph nodes, spleen, MALT
Describe the role of lymph nodes and give examples of such nodes.
- Serve as filters as lymph percolates on its way to the vascular system. Trap, process and present antigens to T cells.
- Approx. 700 in body, e.g. Pharyngeal, palatine and lingual tonsils, appendix and Peyer's patches.
Describe the structure of lymph nodes.
- Each node has afferent vessels that enter via the convex surface and efferent vessels that leave via the hilum to transport lymph.
- Each node has a feeding artery and draining vein that enter and leave via the hilum.
- Lymph is exposed to professional APCs (macrophages and B cells - produce an inflammatory followed by an immune response) of the blood in germinal centres.
- GCs also contain follicular dendritic cells - cause B cell proliferation, esp. memory B cells. Antigen-antibody complexes adhere to their dendritic processes and these antigen can be retained for months.
Describe the functions of the spleen as a lymphoid tissue.
- Is the largest lymphatic organ, very rich blood supply.
- Collects antigen from bloodstream - filters blood in the same way that lymph nodes filter lymph.
- Immune functions:
- Antigen presentation by APCs - activation and proliferation of B and T cells, antibody production
- Removal of macromolecular antigen from blood (by macrophages)
- Haemopoietic functions:
- Removal and destruction of old, damaged and abnormal RBCs and platelets
- Retrieval of iron from RBS haemoglobin
What is the function of mucosa-associated lymphoid tissues (MALT)?
- Collect antigen from respiratory (BALT - bronchus-associated lymphatic tissue), gastrointestinal (GALT - gut-associated lymphatic tissue) and urogenital tracts.
What is the role of lymphatic vessels?
Connect lymph nodes to the tissues and bloodstream.
- Afferent lymphatics drain fluid from the tissues into the nodes.
- Efferent lymphatics carry lymph out of secondary lymphoid tissues and ultimately into the thoracic duct or cervical duct, into the subclavian vein or internal jugular vein, to the heart and into the bloodstream.
Where are lymphatic capillaries found?
- All over the body, with the exception of bones, BM and the CNS.
What is the structure of lymphatic capillaries and how does relate to its regulation of pressure?
- Made of loosely overlapping endothelial cells, forming flap-like valves.
- One-way opening function ensures that lymph fluid will not leak back into the interstitial space no matter how high the pressure is within the lymphatic capillary. If pressure in IS > pressure within lymphatics, valves open and take in fluid to relieve the pressure.
How is lymph propelled along lymphatic vessels despite being a low pressure system?
- Smooth muscle in the vessel walls help a little to move fluid.
- But skeletal muscle movement, pressure changes in the thorax during breathing and the pulsations of adjacent arteries also help propel lymph along.
What is lymphadenopathy?
Enlarged lymph nodes. Can be caused by:
- infection: as lymph nodes fight infection, the GCs fill with increasing numbers of lymphocytes - nodes swell (can cause pain).
- lymphoma. Cancers can metastasise to lymph nodes via the afferent lymphatics (e.g. Lung cancer spreads to cervical nodes).
Why is trauma to the spleen dangerous?
The spleen has a very rich blood supply but is relatively fragile. Rupture can easily lead to death through exsanguination.
What are the consequences of splenectomy?
- Liver and BM can take over the removal and destruction of ageing RBCs.
- Increases risk of infection by encapsulated bacteria (e.g. Meningococcus) and malaria.
- Increases the risk of DVT and pulmonary embolism threefold (partly due to increased platelet count?).
Why might a spleen be enlarged?
- In response to systemic infection, e.g. Glandular fever, malaria, septicaemia.