Lymphatic System Flashcards
functions of lymphatic system (3)
- fluid balance: 10% fluid released into tissues by capillaries drains back through lymphatic vessels
- filtration: filters out antigens
- immune response: specific (adaptive) defense; produces, matures, maintains lymphocytes
lymph
interstitial fluid that is drained from the tissues
travels in vessels (lymphatics)
lymphatics
lymph vessels that direct the collected lymph into the venous system
primary lymphoid organs and tissue
bone marrow - b cells
thymus gland - t cells
produce and mature lymphocytes
secondary lymphoid organs and tissue
spleen appendix lymph nodes tonsils MALT
-activate lymphocytes - filtration and immune response
clonal proliferation
activated and sensitized to attack specific foreign antigen, give multiple copies of activated tissue
lymph capillaries (terminal lymphatics)
- closed-end structures
- composed of overlapping endothelial cells with incomplete basement membrane
- overlapping allows for larger openings than cardiac, allows large solutes (proteins, viruses, cells) into lymph
- anchoring filaments (microfilament like fibers and elastin fibers that connect to ECM)
collecting lymphatics
- larger lymphatic vessels are like veins in structure but thinner walls
- all have overlapping endothelium and incomplete basement membrane
- larger vessels have thin layer of smooth muscle and an adventitial layer
- MANY valves - at high risk for backflow
2 ways lymphatics exist
superficial vessels in areolar connective tissue
or
deep lymphatics with cardiovascular support to muscle and other organs
how does lymphatic circulation begin
lymph capillaries filtering lymph from interstitial fluid
-trunks drain into one of 2 collecting ducts (right or left (thoracic)
right lymphatic duct
collects from right side of body superior to diaphragm
thoracic (left) lymphatic
collects from left side above diaphragm and entire lower body
more than right lymphatic
how does the lymphatic system return fluid to the venous circulation
through connections to subclavian veins
cisterna chyli
where all lymphatic from lower body is drained into - lower limbs and abdominopelvic drained here
primary lymphatic organ that receives immature T cell lymphocytes from the bone marrow
thymus
thymus structure
- fibrous protective capsule where internal extensions (septa) divide the gland into lobules
- each lobule arranged with an outer cortex layer and an inner medulla
what does the cortex of the thymus contain
thymic epithelial cell (TEC) aggregates that regulate T cell maturation
- TEC act to form thymic blood barrier
process of all immature T cells
enter through cortex, undergo 2 step selection process, if successful then they leave through the medulla to enter circulation
journey through the thymus is…
rough - about 90% do not make it through the thymus at the end of selection
immature T cells enter the thymus cortical layer as
double negative cells - do not possess CD4 or CD8 receptors
mhc II
cd4
t helper cells
mhc I
cd8
cytotoxic t cells
exposure to signaling from thymic hormones results in
double positive cells
have both cd4 AND cd8
as t cells migrate through the cortex they show binding affinity for
either mhc I or mhc II
cells that fail to bind in thymus
are ignored and allowed to die
negative selection
as T cells migrate to the medulla, exposed to antigens and self-markers
- any that bind with high affinity are subject to apoptosis - they cannot tolerate “self”
- intolerant cells are selected against to protect body from autoimune responses
- cells that survive go into circulation
bone marrow
b cells do not do positive selection, do something similar to negative selection
- ensure they will tolerate self
- go through maturity in bone marrow
- once released go to secondary organs
what is spleen composed of
lymphoid tissue but not served by any lymph vessels
splenic artery
enters at hilium, branches, and capillaries release the blood into sinuses
NOT a closed circuit of vessels in spleen
how is the spleen protected
connective tissue capsule
composed of red and white pulp
red pulp
has the sinuses and a reticular fiber network
RBC that survive the distortion of the network return to circulation through splenic vein
-contains high concentration of RBC and macrophages and scattered lymphocytes
what does the spleen act as during hemorrhage
reservoir
spleen holds less than 150cc blood
white pulp
contains lymphoid tissue and has high concentration of B and T lymphocytes
macrophages in sinuses
recycle old RBCs that rupture when passing through reticular network
lymphocytes in red pulp
screen for foreign antigens and recruit additional lymphocytes from the white pulp
where can you find a high concentration of lymph nodes
throat, GI, groin
places where you are more likely to get an infection
lymph node organization
more organized than red or white pulp, it has follicles
subcapsule: for afferent vessel bringing interstitial fluid
connective tissue forming trabeculae - give follicles
outer area: cortex: all follicles have germinal areas - naive b and t cells - produce clones of themselves here
goes into medullary area, comes out efferent vessels
flow through lymph nodes
- afferent vessels direct lymph to node
- lymph enters subcapsular sinus- macrophages start antigen processing
- antigen presented to unsensitized b cells in germinal layer of cortex
- lymph flows to deep cortex and exposed to T cells
- lymph enters medullary sinus which contains medullary cords containing plasma cells
- fluid exits through efferent vessels
nodes are filtering system for immune defense
MALT
- lack a protective fibrous capsule
- exist as aggregates or nodules of lymphoid tissue in areolar connective tissue
-nodules concentrated in regions susceptible to pathogen entry
examples of MALT
tonsils
peyer’s patches
appendix
2 types of immunity
innate and acquired
physical barriers in innate immunity
skin mucous membranes saliva flushing action of tears and urine stomach acid
stop infection before it enters the body
