18 Lymphatic System Flashcards
How does the lymphatic system work in relation to the venous 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 (natural killer)
- Supporting cells: follicular dendritic cells and macrophages
Identify the organs of the lymphatic system
- Lymph nodes
- Thymus
- Spleen
- Appendix
- Tonsils
- Payer’s patches
- (small masses of lymphatic tissue found throughout the ileum region of the small intestine)*
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 (lymph flows superficial–>deep)
- Large vessels (ducts and trunks) eg in abdomen contain smooth muscle
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 (contain APCs)
- 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?
600-700
Describe the structure of a lymph node (general terms).
Shaped like kidney, mainly= CT fibre
- 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
- Follicles=nodules containing immune dendritic cells
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
(B cells don’t require APCs to recognise antigens)
What is the structure, function and location of follicular dendritic cells (found in lymphoid tissue)?
- 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 humoral response (in terms of immunity).
- 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
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
What are the functions of the spleen?
(The spleen is the largest lymphatic organ and has a very rich blood supply.)
- IMMUNE:
- Antigen presentation
- Activation and proliferation of B and T lymphocytes= Production of antibodies
- HAEMOPOIETIC
- Removal + destruction of old, damaged erythrocytes/platelets
- RBC storage
- Iron retrieval from haemoglobin
Discuss the implications of a splenectomy (2)
- Splenectomy increases the risk of infection by encapsulated bacteria e.g. the meningococcus and 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
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 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
Outline how fluid flows from the capillaries back to the veins via the lymphatics.
Which of the structures shown below is a lymphatic vessel and which is a small vein?
Describe the structure of a lymphatic capillary.
- Low pressure system w./ valves
Name some main areas where there are lymph nodes. (3) (clinically important)
- Neck (cervical)
- Groin (inguinal)
- Armpit (axillae)
Fill in the missing labels:
Where are follicular dendritic cells found and what is their function?
- In germinal centres
- Cause proliferation of B cells- as antigen antibody complexes adhere to them- can retain antigen for a month
Where is the spleen located and what is it’s structure (in general terms)?
Location: Inferior to diaphragm, posterior to stomach
Structure: Similar to lymph node BUT White pulp and Red pulp
Why is a ruptured spleen usually removed?
Risk of death by exsanguination (loss of blood)
Where can the tonsils be found?
Oropharynx and nasopharynx
What is the structure and function of the tonsils?
Nodules- reside inferior to surface invaginations
Prevent pathogen ingress:
- Surface epithelia- numerous microfold cells
Outline the location, structure and function of the Appendix (Veniform).
- LOCATION Inferior&attched to ascending colon
- STRUCTURE Nodules reside inferior to surface invaginations- many microfold cells
- FUNCTION prevent pathogen ingress
Outline the Location, Structure and Function of Payer’s patches?
LOCATION: inferior and attched to ileum
STRUCTURE: nodules= on inferior surface of domes
FUNCTION: Prevent pathogen ingress through digestion
What are the functions of the lymphatic system?(4)
- Fluid balance-return interstitial fluid to circulation
- Transport- fats and fat-soulble vitamins- from digestive system to venous circulation
- Defence against invading pathogens-nodes filter out organisms/cancer cells
- Storage and destruction- aged erythrocytes (spleen
What is a ‘sentinel lymph node’?
First lymph node to which cancer cells are most likely to spread from a primary tumor eg breast cancer
Outline the relationship between sentinel lymph nodes and the prevention of a secondary tumour.
How is lymphodema treated? (4)
- Compression hosiery
- Specialised massage
- Skincare
- Exercises
What are the primary causes of lymphodema? (3)
What are the secondary causes of lymphodema? (4)
- Surgery- node involvement
- Radiotherapy- nodal fibrosis
- Autoimmune- rheumatoid arthritis
- Infections- cellulitis (vessel obstruction)
