12. The Lymphatic System Flashcards
What is lymph?
Fluid in the lymphatic vessels and lymph nodes that resembles plasma but has lower amounts of protein.
What are the major roles of the myphatic system?
- Return fluid to heart
- Helps large molecules enter the blood
- hormones
- lipids - Immune surveillance
What is the organisation of the lymphatic system?
- Lymph - fluid
- Lymphatic vessels - collects excess interstitial fluid to return to circulation
- Lymphoid tissues and organs
- Cells contained within the tissues and organs
What is chyle?
> Lymph that arises in the GI tract
White, cloudy substance
Contains fats and dissolved lipids – Chylomicrons and fat soluble vitamins
Approximately, how much lymph is produced and recycled each day?
3-4 litres
What are lymphatic vessels?
Lymphatic vessels are microvessels that form an interconnected system of simple endothelial tubes within tissues.
What do lymphatic vessels transport?
They do not carry blood but instead transport fluid, serum proteins, lipids, and even foreign substances from the interstitial spaces back to the circulation. Approximately 20 litres of fluid seeps out from the arteries and 17 litres are reabsorbed, so the remaining 3 litres is returned to the circulation by lymphatic vessels
What are the different lymphatic vessels, in ascending order?
Capillaries > Trunks > Ducts > Veins
What does blind ended mean?
Blind ended - the lymphatic system typically begins as blind-ended tubes, or lymphatic bulbs, which drain into the meshwork of interconnected lymphatic vessels
Describe a feature o lymphatic capillaries
Lymphatic capillaries are found throughout the interstitial space and are extremely permeable because the walls are made of endothelial cells.
The endothelial cells loosely overlap, forming one way minivalves.
How are lymphatic capillaries anchored to the interstitial fluid?
Lymphatic capillaries are anchored to the interstitial fluid by reticular fibres
How are the minivalves opened and closed?
- When oncotic pressure in the interstitial space is greater than the pressure in the lymphatic capillary, the endothelial minivalves open up, allowing fluid to enter.
- When the pressure in the interstitial space is less than the lymphatic capillary, the endothelial minivalves are pushed shut, which keeps the lymph inside.
How is lymph flow created?
• there are no pumps pushing lymph through the lymphatic vessels
• Lymphatic vessels tend to lie adjacent to cardiovascular vessels (capillaries, arteries and veins)
• The flow of blood through cardiovascular vessels compresses lymphatic vessels and acts as the pump pushing the lymph through
• Lymphangion compression by local veins and arteries propels the lymph
• In the limbs, the deep lymphatics pass through muscles where skeletal muscle contraction aids lymph movement
• Larger lymphatic vessels (ducts and trunks), contain smooth muscle cells in their walls
e.g. in the abdomen or thorax - Contraction of smooth muscle is an important contributor to lymph flow at these sites
Which direction is lymph flow?
• Like veins, lymphatic vessels are arranged into superficial and deep (deep to the deep fascia)
- Flow is superficial to deep
Where are lymphatic systems not present?
In the central nervous system
Compare lymphatic capillary to vein
- Both Low pressure system
- Both have little smooth muscle
- Valves present in both
- (BUT) no cells (normally) in lymphatic capillary
Describe Lymphatic trunks and ducts
- Equivalent to larger veins
- Larger fbrocartilaginous valves
- Skeletal muscle and organ movement for ‘flow’
What is cisterna chyli?
large container of chyle from GI tract
Where does the upper right quadrant of the lymphatic ducts drain into?
Upper right quadrant drains into right subclavian vein/internal jugular vein
Where does the rest of the lymphatic ducts in te body drain into?
The rest of the body into the left subclavian vein/internal jugular vein
What does lymph pass through?
Lymph nodes
Approximately how many lymph noes are there in the body?
Approximately 600 - 700 in the body
Where are the most clinically important lymph nodes present?
- Neck (cervical)
- Groin (inguinal)
- Armpit (axillae)
What is the function of lymph nodes?
Filters lymph as it percolates on its way to the vascular system. traps antigen, processes
antigen and macrophage presents processed antigen to T cells
What are lymph nodes shaped like?
Kidney
How many afferent lymphatic vessels do search node have and where do they enter from?
Each node has multiple afferent lymphatic vessels
- that enter via the convex surface
How many efferent lymphatic vessels do search node have and where do they leave from?
A single efferent lymphatic vessel
- that leaves via the concave hilum
What two vessels does each lymph node have that also leave and enter via the hilum?
Each lymph node has a feeding artery and draining vein that also
enter and leave via the hilum
What do the multiple follicles in lymph nodes contain?
Multiple ‘follicles’ - nodules that contain immune cells
(macrophages, dendritic, B and T cells
What are the main connective fibres in lymph nodes?
Reticulin
Where are follicular dendritic cells found?
In the germinal centres in the cortex of of lymph nodes
What is the function of follicular dendritic cells?
If bacteria found in the interstitial space, the dendritic cells in the lympathic vessels will pick up the bacteria and bring it to the nearest lymph node and give it up to the macrophages. Macrophages engulf the bacteria and digest it and produce proteins which are passed onto dendritic cells within the T cell zone. It presents it to the T cells which either migrate into the B cell area or out into the circulation. When in the B cell area, the T cell activate the B cells into plasma cells which produce antibodies against the protein.
What is the difference between b and t lymphocytes?
B lymphocytes recognise antigens
T lymphocytes do not
- they need to be presented to the antigen
How do the majority of lymphocytes enter and leave the 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
What do most dendritic cells enter the lymph nodes with?
Most dendritic cells enter with pathogens within lymph
What causes Enlarged lymph nodes (lymphadenopathy)
?
• As lymph nodes fight infection, the germinal centres fill with increasing numbers of lymphocytes causing the
lymph nodes to swell - Can cause considerable pain
• Cancers can metastasise to lymph nodes via the afferent
lymphatics to also cause swelling
• Lymphoma (malignancy of the lymphoid tissue itself)
often presents with lymphadenopathy
• Lymphadenopathy can occur in all the nodal regions or
affect lymphatic organs
What are the two types of lymphoma and what is the difference between them?
Hodgkin’s and non-Hodgkin’s lymphoma.
Hodgkin’s can be cured, non-hodgkin’s cannot be cured
What a re the 5 lymphatic organs and where are they found?
- Thymus – in the mediastinum
- Spleen – left side of abdomen (posterior to stomach)
- Tonsils – in the oropharynx and nasopharynx
- Appendix – lower right quadrant of abdomen
- Payer ’s patches – under the mucosal membrane of small intestine
Where is the thymus found?
superior mediastinum
When is the thymus functional?
- is fully formed and functional at birth
* involutes after puberty by late teens, is mostly fat
What is the structure of the thymus?
Similar to lymph node (but no hilum) - no affenert vessel
What is the function of the thymus?
maturation of bone marrow derived stem cells into immunocompetent T cells.
This is called ‘thymic cell education’
Wha are the capsule and septa of the thymus mainly made of?
Capsule and septa made mainly of reticulin/reticular fibres in ECM
What is changes in the thymus associated with?
Changes in the thymus associated with myasthenia gravis
Describe the location of the spleen
- Inferior to diaphragm
- Posterior to stomach
is fully formed and functional at birth
What is special about the spleen?
Largest lymphatic organ, very rich blood supply!
What is the structure of the spleen?
Similar to lymph node
but separated into white pulp and red pulp
What are the functions of the spleen?
• The spleen filters blood in the same way that lymph nodes
filter lymph
• It has functions in both the immune and haemopoietic
systems
What are the immune functions of the spleen?
- 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
- Erythrocyte storage
Where in the spleen do the immune function=toon occur?
White pulp
Where in the spleen do the haemopoietic functions occur?
Red pulp
What is Splenectomy and what are the consequences?.
Splenectomy is a surgical procedure to remove your spleen.
- The liver and bone marrow can take over the removal and destruction of ageing red blood cells
- Splenectomy increases the risk of infection by encapsulated bacteria (e.g. meningococcus) and malaria
What is splenomegaly and what is the caused by?
abnormal enlargement of the spleen.
Enlarges in response to localised infection (just like lymph nodes) Enlarges in response to systemic infection (glandular fever, malaria, septicaemia)
