The Lymphatic System and immunity Flashcards
What does the lymphatic system consist of?
Fluid-lymph-mainly water
Vessels-lymphatics
Cells-lymphocytes (B cells, T cells and Natural Killer cells)
Supporting cells, follicular dendritic cells and macrophages
Tissues
Organs
Where are lymphatic vessels found and how do they work?
What happens when they fail?
Lie adjacent to arteries and veins
Arranged into superficial and deep, flow is superficial to deep
In the limbs the deep lymphatics pass through muscles- contraction is critical to lymph circulation
Larger lymphatics eg abdomen or thorax- contraction of smooth muscle is an important contributor to lymph flow at these sites
No lymphatics in central nervous system
Failure of lymphatics leads to oedema
Which tissues does the lymphatic system consist of ?
Diffuse- mucosal associated lymphatic tissue
(Includes gut associated lymphatic tissue GALT and bronchus associated lymphatic tissue BALT)
Lymphatic nodules- tonsils, peyers patches and vermiform appendix
Which organs are associated with the lymphatic system?
Lymph nodes
Thymus
Spleen
What are lymph nodes?
Filters for lymph
Each one has afforestation lymphatic vessels that enter via the convex surface and efferent lymphatics that leave via the hilum and a feeding artery and a draining vein that enter and leave via the hilum
What is a follicular dendritic cell?
Located in the germinal centres of lymph nodes
Antigen antibody complexes adhere to dendritic processes and the cell can retain the antigen for months
This causes proliferation of B cells- especially memory B cells
What makes an APC a professional APC?
B cells and macrophages are equipped with special immunostimulatory receptors that allow for enhanced activation of T cells
Which cells mediate the inflammatory response?
Neutrophils and macrophages
How do B lymphocytes develop into plasma cells and what are these?
B lymphocytes transform into plasma cells when stimulated by T cells. Plasma cells synthesise and secrete a specific antibody for the antigens that stimulated the T cell
What is cell mediated immunity protecting against?
Viral, fungal and mycobacterium infections
Tumour cells
Transplant rejection
What is the medical name for enlarged lymph nodes?
Lymphadenopathy
What are the immune functions of the spleen?
Antigen presentation by APC’s
Activation and proliferation of B and T lymphocytes, production of antibodies
Removal of macro molecular antigen from blood by macrophages
What are the haemopoeitic functions of the spleen?
Removal and destruction of old, damaged and abnormal erythrocytes and platelets
Retrieval of iron from erythrocytes haemoglobin
What is the clinical importance of the spleen?
Very rich blood supply and relatively fragile- a ruptured spleen can easily cause death from internal bleeding.
If surgeons have to remove the spleen the liver and bone marrow take over its haemopoeitic role, however patients have slightly weakened immunity
The spleen may enlarge in response to systemic infection
Where is and what is the thymus gland?
Located in the superior mediastinum
It is involved in the maturation of bone marrow derived stem cells into immunocompetent T cells (thymic cell education)
Explain the process of phagocytosis
It occurs in five steps namely uptake, endosome formation, phagolysosome formation, lysis, diffusion of digested material and exocytosis. In order to uptake microorganism, pseudopodia developed arrount the microbe and takes up the microbe to form endosome.
Endosome again combines with lysosomal fraction to form phagoendosome. When the pH of the phagoendosome changed to acidic, lysosomal enzyme activated and they lyse microbes. After lysis, digested materials are passed through diffusion into cellular compoenent. Undigested materials during phagocytosis, will be excreted out. Some of these may be presented on surface for activation of T lymphocytes.
What is oxygen dependent killing?
Activated phagocytes produce a number of reactive oxygen intermediates (ROIs) and reactive nitrogen intermediates that have potent antimicrobial activity. During phagocytosis, a metabolic process known as the respiratory burst occurs in activated macrophages. This process results in the activation of a membrane-bound oxidase that catalyzes the reduction of oxygen to superoxide anion, reactive oxygen intermediate that is extremely toxic to ingested microorganisms. The superoxide anion also generates other powerful oxidizing agents, including hydroxyl radicals and hydrogen peroxide. As the lysosome fuses with the phagosome, the activity of myeloperoxidase produces hypochlorite from hydrogen peroxide and chloride ions. Hypochlorite, the active agent of household bleach, is toxic to ingested microbes.
What is opsonisation?
The addition of molecules to the outside of pathogens which stimulates phagocytes to ingest them
What is complement?
A group of serum proteins that activates inflammation, destroys cells and participates in opsonisation
Can be activated by a number of different molecules
Respond in a sequential manner called the complement cascade
Can be activated by the classical pathway or the alternative pathway
What is the classical pathway?
C1 is activated when it binds to an antigen antibody complex
What is the alternative pathway?
It is activated when C3b reacts with antigens
What is the similarities between the classical pathway and the alternative pathway?
Both pathways follow the same sequence after c3 resulting in inflammation, opsonisation ad membrane attack complexes
What is oedema and lymph oedema?
Oedema is an accumulation of an excessive amount of watery fluid in cells due to an increase in venule pressure (can be caused by congestive heart failure due to backup of blood in vena cava) or a drop in oncotic pressure. Lymphoedema is caused by an obstruction of lymphatic vessels and does not pit.
