Lymphatic System Flashcards
(41 cards)
Function of lymphatic system
The body’s cleansing anddrainage system as well as being a transport route for immune cells and fat.
consists of lymphatic vesselsoperating as a one-waydrainage system(containinglymph) and the lymphoid organs (the roleof which is mainly in hostdefence).
Anatomy of lymphatic system
One way drainage system
Tissue fluid absorbed by initial lymphatics- blind ending lymphatic capillaries to become lymph
Lymph flows in small streams and to bigger channels to lymph nodes
Where is lymph collected and where does it exit the lymphatic system?
Largest lymph vessels collect it from both peripheral (superficial) and central tissues
Lymph draining channels converge on thoracic duct + lymph exits system here to enter great veins of neck
What are lymphoid organs?
Lymphoid organs/tissuesare organized structures within the lymphatic system that support immune responses through lymphocyte production or activationand are important for host defence
What are the primary lymphoid orgas=ns?
Thymus and Bone Marrow
They generate lymphocytes from immature progenitor cells. (responsible for production and maturation of lymphocytes)
What are the secondary lymphoid organs?
Lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT)
where lymphocytes are activated
What are the tertiary lymphoid organs?
acquired loose lymph node-like immune cell clusters in tissues
Develop in response to inflammation
What is the difference in function between the reticuloendothelial system (RES) and the lymphoid organs?
The RES is responsible for phagocytosis and the removal of organic and inorganic material from blood and tissues
The lymphoid organs are responsible for immunity and specifically the production and activation of lymphocytes in order to generate immune responses to microbes
What are the 2 types of lymphatic vessel?
- Initial lymphatic- absorbs fluid and material
2. Collecting lymphatic
Passage of lymph down upper limb
Initial lymphatics generates lymph -> travels downstream through arm to lymph glands in axilla
What type of vessel are collecting lymphatics?
Contractile - have smooth muscle
Also have valves
Lymphatic capillaries vs collecting vessels
Initial lymphatics:
blind ended
no SM
incontinuous basement membrane
Collecting vessels:
SM coverage
luminal valves
basement membrane
What do lymphatic vessels form from?
Cardinal vein (MAIN)
and mesenchymal stem cells
Development of lymphatics
Lymphatic endothelial cells (LECs)
differentiate from venous endothelial cells on the cardinal vein
Expansion and maturation
of LECs proceed via growth factors and specific lymphatic genes
To form lymph sacs
Further expansion and differentiation
produces mature initial
and collecting lymphatics
How do lymphatic vessels work?
Initial lymphatics are passive structures dependent on alternating changes in surrounding tissue hydrostatic and oncotic pressures to drive fluid (and proteins and cells) into and along the vessels
process:
nitial- delicate vessels dependant on pressure changes for lymph formation and transport, pressure wave compresses initial lymphatic w lymph -> empties it and send fluid downstream to collecting vessel
once emptied it can open due to recoil generated by anchoring filaments outside of endothelial cells
recoil generates pressure difference between inside and outside lymphatic = neg pressure inside encouraging fluid to move from tissue into initial lymphatic through gaps between endothelial cells (primary valves)
fluid flows through lymphatic -> equilibirum -> flat valves close and nothing happens until another pressure wave comes along and cycle repeats
How do collecting lymphatics work?
Collecting lymphatics receive lymph
from initial lymphatics and actively
pump lymph towards the lymph node.
Internal valves ensure flow is in one direction
Each section of collecting lymphatic
between two valves, known as a lymphangion, contracts like an individual heart
collecting lymphatics have valves- section between valves that contracts independently- lymph enters section (lymphangion) distends vessel aka muscle relaxes and section fills
then filling point reached -> valve closes and muscle contracts, valve to next section opens and so lymph passes along towards lymph node
this is why lymph can be pumped up a leg against gravity
Process of lymph drainage- when is muscle involved?
Raised interstitial fluid pressure drives tissue fluid into initial lymphatics during relaxation of skeletal muscle.
Next wave of muscle contraction compresses full initial lymphatic and drives lymph drainage downstream towards collecting lymphatics.
Smooth muscle contractions of collecting lymphatics pump lymph towards lymph nodes
Lymph drainage without pumping collecting lymphatics depends on passive effect of skeletal muscle contractions and compression
Main role of lymphatic system
Controls tissue and plasma volume homeostasis
Controls immune cell trafficking and adaptive immunity
Facilitates fat transport
Tissue fluid is drained predominantly by the…
lymphatic NOT venous reabsoprtion
In the steady state all vascular filtrate/interstitial fluid drains via the lymphatic with only periods of transient reabsorption directly back into the blood circulation.
The clinical significance of this new physiology is that all chronic oedema represents lymphatic failure. If one accepts that the composition of lymph in pre-nodal lymphatics is not significantly different from interstitial fluid one could argue that chronic peripheral oedema is no different from lymphoedema (peripheral swelling with accumulation of lymph in the tissues due to inadequate lymph drainage).
Microvascular filtration is governed by what?
Starling principle of fluid exchange
In capillary fluid exchange what acts as a regulator?
The subglycocalyx acts as a regulator or stabiliser for filtration so
the default position is no reabsorption
Revised Starling principle includes interstitial forces as well as hydrostatic and osmotic pressures
Subglycocalyx- plasma proteins held and control osmotic pressure outside of blood and so gradient is controlled by it, acts as a regulator
Process of pitting oedema
Tissue (interstitial) fluid is drained predominantly by the lymphatic and not by venous reabsorption
Blood capillary plasma filtrate becomes interstitial fluid and then lymph. The capillary filtration fluid is the lymph load
Oedema develops when lymph load exceeds lymph drainage
Lymph drainage is the rate limiting step for all oedema and so any chronic oedema is, in principle, a lymph drainage problem
Venous hypertension increases lymph load (fluid filtration from blood capillaries)
Venous oedema occurs when lymph load exceeds lymph drainage for a period of time
Lymphoedema occurs when the dominant fault is with the lymph drainage
Process of pitting oedema
Tissue (interstitial) fluid is drained predominantly by the lymphatic and not by venous reabsorption
Blood capillary plasma filtrate becomes interstitial fluid and then lymph. The capillary filtration fluid is the lymph load
Oedema develops when lymph load exceeds lymph drainage
Lymph drainage is the rate limiting step for all oedema and so any chronic oedema is, in principle, a lymph drainage problem
Venous hypertension increases lymph load (fluid filtration from blood capillaries)
Venous oedema occurs when lymph load exceeds lymph drainage for a period of time
Lymphoedema occurs when the dominant fault is with the lymph drainage
Lymphatics in immune system
Antigen arrives at lymph node and presents to dendritic cells in lymph which then presents to B and T cells –> generates immune response
From lymph node mature B lymphocytes leave bone marrow and T lymphocytes to infection
A tender lymph gland indicates immune response to infection
