Lymphatic System Flashcards
What does the lymphatic system consist of?
1) Fluid - lymph
2) Vessels - lymphatic
3) Cells - lymphocytes (B, T NK), Supporting cells e.g. Follicular dendritic cells and macrophages
4) Tissues
5) Organs
What propels lymph along along lymphatic vessels?
Skeletal muscle movement, pressure changes in the thorax during breathing and the pulsation of adjacent arteries
Increased physical activity
What direction is lymphatic flow?
Superficial to deep
What do lymphatic lie adjacent to?
Arteries and veins
What do lymphatic pass through?
Muscles - muscle contraction within deep compartments is critical to lymph circulation
What do larger lymphatics (e.g. In a dome and thorax) contain in their walls?
Smooth muscle - contraction of this smooth muscle is an important contributor to lymph flow
Are there lymphatics in the CNS
No
What does the lymphatic system consist of?
Tissues
- Diffuse, mucosal associated lymphatic tissue (MALT) including gut-associated (GALT) and bronchus-associated (BALT)
- Lymphatic nodules
Organs
- Lymph nodes
- Thymus
- Spleen
Is there bacteria in the small bowel?
Shouldn’t be
Is there bacteria in the colon?
Always normally have bacteria in the colon
Not in small bowel
These need to stay in colon
Illea-caecal valve and lymph nodes prevent bactera from getting into the digestive system
What is the function of lymph nodes?
Serve as filters as lymph percolates on its way to the vascular system
How many lymph nodes in the human body?
700
Describe the lymphatics flow to and away from the lymph nodes
Each node has afferent lymphatic vessels that enter via the convex surface and efferent lymphatics that leave via the hilum
Describe the blood supply to the lymph nodes
Each lymph node has a feeding artery and draining vein that enter and leave via the hilum
Good blood supply
What are follicular dendritic cells?
Located in the germinal centres
Antigen antibody complexes adhere to their dendritic processes and the cell can retain antigen for months Follicular dendritic cells cause proliferation of B cells, in particular
memory B cells
What are professional APCs?
Unlike B cells, T cells fail to recognize antigens in the absence of antigen presentation
Most cells are capable of presenting antigens and activating the
adaptive response. Some cells, however, are specially equipped
to acquire and present antigen, and prime naive T cells. B cells
and macrophages play a major role in the innate response, also
acting as professional antigen-presenting cells (APC). These
professional APCs are equipped with special immunostimulatory
receptors that allow for enhanced activation of T cells
What is inflammation
The initial reaction of the body to an antigen is an inflammatory response. Mediated mainly by neutrophils and/or macrophages.
Degradation of the antigen may lead to presentation of a portion of the antigen to elicit a specific immune response
What is the specific immune response?
The specific immune response is usually a mixture of humoral and cell-mediated.
Briefly describe humoral immunity
Humoral immunity is B lymphocyte mediated and involves antibody production by B lymphocytes that transform into plasma cells that synthetise and secrete a specific antibody
Describe cell-mediated immunity
Cell-mediated immunity is T cell mediated. T cells need antigen presenting cells (macrophages, B lymphocytes) to recognise antigen.
Cell-mediated immunity is important in defence against:
– viral, fungal and mycobacterial infections
– tumour cells
– transplant rejection
What are 2 functions of lymph nodes?
Serve as filters as lymph percolates on its way to the vascular system, traps antigen, processes antigen and presents processed antigen to T cells
Is a repository of macrophages, B cells and T cells that work together to produce an inflammatory (macrophages, neutrophils) response followed by an immune response (B cells, T cells)
Where do lymphocytes enter and leave lymph nodes?
The majority of lymphocytes enter lymph nodes via the feeding artery (a few in lymph) and the majority leave in the efferent lymphatics
When do lymph nodes enlarge?
As lymph nodes fight infection the germinal centres fill with increasing numbers of lymphocytes causing the lymph nodes to swell can this can also cause some pain
Cancers can metastasise to lymph nodes vie the afferent lymphatics
Lymphoma often presents with lymphadenopathy
What is the spleen?
Largest lymphatic organ, very rich blood supply
What are the immune functions of the spleen?
Immune functions
– Antigen presentation by APCs
– Activation and proliferation of B and T lymphocytes, production of antibodies
– Removal of macromolecular antigen from blood (macrophages do this)
What are the haemopoietic functions of the spleen?
Removal and destruction of old, damaged and abnormal erythrocytes and platelets
Retrieval of iron from erythrocyte haemoglobin
Why do surgeons often remove the spleen and what consequences does this have?
Surgeons often remove the spleen (e.g trauma)
– The liver and bone marrow can take over the removal and destruction of ageing red cells
– Splenectomy increases the risk of infection by encapsulated bacteria
(e.g the meningococcus) and malaria
– Splenectomy increases the risk of DVT and pulmonary embolism
threefold (partly due to increased platelet count?)
When may the spleen enlarge?
In the same way that lymph nodes enlarge in response to infection (usually localised), the spleen may enlarge in response to systemic infection (glandular fever, malaria, septicemia)
What is the function of the thymus?
Its role is the maturation of bone marrow derived stem cells into immunocompetent T cells. This is called thymic cell education
Where is the thymus located
It is located in the superior mediastinum, is fully formed and functional at birth, it involutes after puberty and by the late teens is mostly fat
