S6) Lymphatic System Flashcards
How does the lymphatic system work in relation to the venous system?
The lymphatic system collects 3 litres per day of interstitial fluid and returns it to the venous system
State the names of the fluid and vessels of the lymphatic system
- Fluid – lymph
- Vessels – lymphatics
Identify the cells of the lymphatic system
- Lymphocytes: B cells, T cells and NK cells
- Supporting cells: follicular dendritic cells and macrophages
Identify the tissues of the lymphatic system
Mucosal associated lymphatic tissue (MALT):
- Gut-associated lymphatic tissue (GALT)
- Bronchus-associated lymphatic tissue (BALT)
Identify the organs of the lymphatic system
- Lymph nodes
- Thymus
- Spleen
Identify the lymphatic nodules of the lymphatic system
- Tonsils
- Peyer’s patches
- Vermiform appendix
What 3 factors help to propel lymph along?
- Skeletal muscle movement
- Pressure changes in the thorax during breathing
- Pulsations of adjacent arteries
Describe the arrangement of lymphatic vessels in the body
- Lymphatics tend to lie adjacent to arteries and veins
- Lymphatics are arranged into superficial and deep (deep to the deep fascia)
In which region of the body are there no lymphatics?
The Central Nervous System
What are the functions of lymph nodes?
- Serve as filters for lymph: traps antigen, processes antigen and presents processed antigen to T cells
- Contains macrophages, B cells and T cells which work to produce an inflammatory response (macrophages) then an immune response (B & T cells)
Approximately how many lymph nodes are there in the human body?
700
Describe the structure of each lymph node
- Afferent lymphatics that enter via the convex surface
- Efferent lymphatics that leave via the hilum
- Feeding artery that leaves via the hilum
- Draining vein that leaves via the hilum
How do lymphocytes enter lymph nodes?
- Enter via the feeding artery
- Leave via the efferent lymphatics
Account for possible causes of lymphadenopathy
- Infection as germinal centres in lymph nodes fill with lymphocytes
- Lymphoma as cancer metastasises to afferent lymphatics
Lymph nodes contain professional antigen presenting cells (APCs).
What is the role of such cells?
APCs are specially equipped with immunostimulatory receptors to acquire and present antigens which allows for enhanced activation of T cells
What is the structure, function and location of follicular dendritic cells?
- Structure: contain antigen-antibody complexes adhere to its dendritic processes
- Function: cause proliferation of B cells, in particular, memory B cells
- Location: found in germinal centres
Outline the inflammatory response
- Initial reaction of the body to an antigen
- Mediated 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
Outline the humoral response
- Humoral immunity is B lymphocyte mediated
- It involves B lymphocytes which transform into plasma cells that synthesise and secrete a specific antibody
What is cell-mediated immunity?
Cell-mediated immunity is when T cells need antigen presenting cells (macrophages, B lymphocytes) to recognise antigens
What is the importance of cell-mediated immunity?
Important in defence against:
- Viral, fungal and mycobacterial infections
- Tumour cells
- Transplant rejection
Outline the structure, function and location of the thymus gland
- Structure: fully formed and functional at birth, involutes after puberty and ends up being mostly fat
- Function: maturation of bone marrow derived stem cells into immunocompetent T cells (thymic cell education)
- Location: found in superior mediastinum
The spleen is the largest lymphatic organ and has a very rich blood supply.
Outline its immune functions
- Antigen presentation
- Activation and proliferation of B and T lymphocytes
- Production of antibodies
- Removal of macromolecular antigen from blood
The spleen is the largest lymphatic organ and has a very rich blood supply.
Outline its haemopoietic functions
- Removal and destruction of old, damaged and abnormal erythrocytes and platelets
- Retrieval of iron from erythrocyte haemoglobin
Discuss the implications of a splenectomy
- Splenectomy increases the risk of infection by encapsulated bacteria e.g. the meningococcus, malaria
- Splenectomy increases the risk of DVT and pulmonary embolism
Which organs/structures perform the spleen’s functions after a splenectomy?
Liver and bone marrow take over the removal & destruction of old RBCs
Distinguish between the lymph node and spleen response to infection
- Lymph nodes enlarge in response to local infection
- Spleen enlarges in response to systemic infection e.g. glandular fever, malaria, septicaemia
What is phagocytosis?
Phagocytosis is a specific form of endocytosis by which cells internalise solid matter, including microbial pathogens
Identify the professional phagocytes of the immune system
- Macrophages
- Neutrophils
- Immature dendritic cells
Outline the 5 steps in the process of phagocytosis
⇒ Binding of opsonins and/or PAMPs to cell surface receptors on the phagocyte
⇒ Receptor clustering which triggers phagocytosis
⇒ Cell membrane then extends around the target, forming a phagosome
⇒ Phagosome fuses with lysosomes & acidifies to form a phagolysosome
⇒ Contents are degraded by hydrolytic enzymes
What is opsonisation?
Opsonisation is the molecular mechanism whereby molecules, microbes, or apoptotic cells are chemically modified to have stronger interactions with cell surface receptors on phagocytes and NK cells
What effect does opsonisation have?
- With the antigen coated in opsonins, binding to immune cells is greatly enhanced
- Opsonisation also mediates phagocytosis via signal cascades from cell surface receptors
What is complement?
Complement consists of a group of serum proteins that activates inflammation, destroys cells and participates in opsonisation
Complement proteins respond in a sequential manner called the complement cascade.
Describe the Classical pathway in the complement cascade
Classical pathway – C1 is activated when it binds to an antigen-antibody complex
Complement proteins respond in a sequential manner called the complement cascade.
Describe the Alternative pathway in the complement cascade
Alternative pathway – C3b is activated when it reacts with antigens such as bacterial cell wall
What are the results of both of the different complement cascades ?
What is oedema?
Oedema is an accumulation of an excessive amount of watery fluid in cells, tissues or serous cavities
What is lymphoedema?
Lymphoedema is swelling (especially in subcutaneous tissues) due to obstruction of lymphatic vessels or lymph nodes and the accumulation of large amounts of lymph in the affected region
Describe the appearance of lymphoedema
Lymphoedema is non-pitting oedema due to the build-up of lymph and protein in the interstitial space
How does oedema change with position?
- If someone is standing up, oedema often appears first at the ankles (gravity)
- If someone is lying down/sitting in bed, the oedema is expected to appear in the sacral region
