17 - The Lymphatic System Flashcards
What is lymph?
Thin fluid that resembles plasma but with lower amounts of protein. Travels within lymphatic vessels.
What is chyle? How is it different from lymph?
Lymph fluid that arises in the GI tract
White, cloudy substance that contains lots of fats and dissolved lipids (+ fat-soluble vitamins)
Where do lymph vessels drain?
Into lymphatic ducts and then into systemic veins
Describe the structure of a lymphatic vessel
- Overlapping endothelial cells, fluid can pass through due to gap junctions opened by pressure (not fenestrations or sinusoids)
- Contain valves for unidirectional flow
- Reticulin fibres anchor the vessels in place (only type of collagen present in lymphatics)
What processes aid the flow of lymph fluid?
- Muscle contraction for deep lymph vessels
- Pressure changes in breathing
- Pulsations of adjacent arteries
- Larger lymph vessels contain smooth muscle in their walls
Where in the body are no lymphatics found?
The central nervous system
What different types of lymph vessel does lymph pass through to get from tissue fluid to vein?
- lymphatic capillary
- lymphatic vessel
- lymph node
- lymphatic trunk
- lymphatic duct
What is a lymphangion?
- Functional unit of lymph vessel flow
- Section of vessel with a valve at either end, when compressed the fluid moves into the next lymphangion and backflow is prevented by closure of the valve
What is the cisterna chyli?
Receives lymph drainage from the GI tract, contains chyle
The upper right quadrant lymphatics of the body drain into …………………………….
The rest of the lymphatics of the body drain into …………………………….
Upper right - Right subclavian/internal jugular veins
Rest of body - Left subclavian/internal jugular veins
How many lymph nodes are there in the body? Which are the most important clinically?
600-700
Neck (cervical), groin (inguinal), armpit (axillae)
What does a lymph node do?
- Filters the lymph as it percolates to the vascular system
- Contain immune cells to coordinate an immune response to pathogens
What vessels enter and leave a lymph node?
- Multiple afferent lymph vessels enter the convex surface
- Single efferent lymph vessel leaves the concave hilium
- Feeding artery and draining vein enter and leave at the hilium
A lymph node has nodules of immune cells. What immune cells are present?
Macrophages, dendritic cells, B cells and T cells
What happens to lymph nodes when they are fighting infection?
The germinal centres fill with increasing numbers of lymphocytes causing the lymph nodes to swell, which can cause pain.
Other than infection, what else may cause enlarged lymph nodes?
- Cancers elsewhere in the body can metastasise to the lymph nodes via afferent lymphatics
- Lymphoma (malignancy of the lymphoid tissue itself) –> Hodgkin’s and non-Hodgkin’s
What is the technical term for enlarged lymph nodes?
Lymphadenopathy
What is the thymus and what does it do?
Lymphatic organ in the superior mediastinum. Similar structure to a lymph node but without an afferent vessel (straight into blood).
Matures bone marrow derived stem cells into T cells (‘thymic cell education’).
Where is the spleen found, what is it’s structure and what does it do?
Inferior to the diaphragm, posterior to the stomach
Similar to a lymph node in structure but has white pulp (immune) and red pulp (haemopoietic)
- Filters blood to remove debris and initiate immune responses
- Immune and haemopoietic functions
What are the immune functions of the spleen?
- Antigen presentation by APCs
- Activation and proliferation of B and T lymphocytes
- Removal of macromolecular antigens from blood by macrophages
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
- Erythrocyte storage
If the spleen is removed (splenectomy), how is its role taken over?
- Liver and bone marrow take over the removal and destruction of ageing red blood cells
- Increases risk of infection by encapsulated bacteria (e.g. meningococcus) and malaria as only the spleen can detect these
What is splenomegaly and what causes it?
An enlarged spleen
- Enlarges in response to local infection, same as lymph nodes
- Also enlarges in response to systemic infection (e.g. malaria or septicaemia) - can enlarge 10x normal size
Where are the tonsils found and what is their function?
- Oropharynx and nasopharynx
- Prevent pathogen ingress through oral and nasal and aural routes
- Crypts increase surface area
What are the three types of tonsil?
- Pharyngeal tonsil (adenoid) - nasal cavity
- Palatine tonsils - either side of oral cavity
- Lingual tonsil - back of the tongue
Where is the vermiform appendix and what is its function?
- Inferior and attached to caecum (ascending colon)
- Prevent pathogen ingress through GI routes
- Prevent pathogen ingress from ilium
- Crypts increase surface area
Where are Payer’s patches found and what do they do?
Inferior and attached to side of the ilium (run along one side of the ilium)
- Prevent pathogen ingress through digestion
What are the primary functions of the lymphatic system?
- Fluid balance - ISF returned to circulation
- Transport of fats and fat-soluble vitamins to venous circulation
- Defence against invading pathogens and disease
- Storage and destruction of aged erythrocytes (spleen)
How can cancer cells travel in the body when they metastasise?
- Through newly produced vasculature (make their own vessels by angiogenesis)
- Through the interstitial space
- Through lymph
What happens to cancer cells when they enter the lymphatic system?
Either:
- Destroyed
- Start making tumour ECM and proliferate
In breast cancer, what are the first lymph nodes to be affected (sentinel lymph nodes)?
Axilla or pectoral nodes
During surgery, by what method does a surgeon know whether a lymph node is affected with malignant cells?
Fluorography
- Blue dye containing fluoro-18-glucose is injected
- Taken up quickly by highly active cancer cells
- Remove anything stained blue in surgery
What conditions cause primary lymphoedema?
- Milroy’s disease (congenital)
- Meige’s disease (early onset)
- Late onset
What are some possible causes of secondary lymphoedema?
- Neoplasia (abnormal growth) in pelvic region or infiltrating a lymph node
- Surgery - accidental infiltration of lymph node
- Radiotherapy - nodal fibrosis
- Autoimmune disease - RA or eczema
- Infections - cellulitis (vessel obstruction) or filariasis (parasitic worm that invades lymph vessels)
