LYMPHATIC SYSTEM Flashcards
what is the lymphatic system?
related in both structure & function to CV system.
Forms basis of Immune System
what are the 3 components of the lymphatic system?
Extensive network of capillaries & collecting vessels
Lymph Nodes
Lymphoid organs
what is the function of the extensive network of capillaries & collecting vessels?
receive fluid from loose connective tissues throughout body and transport to CV system
what is the function of the lymph nodes?
filter fluid in collecting vessels
what do the lymphoid organs consist of?
include lymphatic nodules, tonsils, spleen & thymus
what is interstitial fluid?
fluid that accumulates in intercellular spaces
how is interstitial fluid formed?
Slightly more fluid leaves capillaries (with plasma proteins) than enters them
what happens if the fluid is left unchecked?
there would be a build-up of plasma proteins which would lead to oedema
where do plasma proteins enter?
cannot re-enter capillaries but can enter lymphatic vessels
what is the interstitial fluid in lymphatics called?
lymph
what is the one-way system of lymph?
flows to the heart, which begins in tiny, blind-ended lymph capillaries.
what are the types of lymphatic vessel types?
capillary
collecting vessel
trunk
duct
what happens at the arterial end of the capillary beds?
Hydrostatic & osmotic pressures force fluids, with plasma proteins, into interstitial space.
what happens at the venous end of the capillary bed?
Most fluid is reabsorbed
but some remains and needs to be returned to the blood
where are lymph capillaries not found?
occur alongside blood capillaries except: bone, bone marrow, teeth, and entire CNS
what are lymph capillaries?
Like blood capillaries but very permeable.
what are the 2 structural modifications of lymph capillaries?
Endothelial cells loosely overlap, open easily, create mini-valves.
Endothelial cells anchored to surrounding structures by fine filaments that separate with interstitial fluid vol.
what is the function of endothelial cells in lymph capillaries?
Expose gaps in capillary wall but close if fluid pressure is > inside capillary, preventing leakage.
how do lymph capillaries help prevent inflammation?
take up large particles eg. debris, pathogens, cells. Use this route to travel around body but only to “detour” lymph nodes filter fluid & I/S examines
what are lacteals?
Highly specialized lymph capillaries in villi of intestinal mucosa.
what is the lymph like in the intestinal mucosa?
Lymph here is milky white rather than clear as it contains digested intestinal fats and is called chyle.
what is the structure of the collecting vessels?
3 tunics like veins
thinner walls
more valves
more anastomosing
how do larger lymphatic vessels receive blood supply?
from vasa vasorum
how do collecting vessels in the skin travel?
with superficial veins
how do deep lymphatics travel?
with deep arteries
what do lymphatic trunks do?
Drain large areas of body; named after areas drained
what does the right lymphatic duct do?
drains lymph from right upper arm, right side of head and thorax.
what is the thoracic duct?
Much larger than right lymphatic duct, arises from cisterna chyli (enlarged sac), drains rest of body.
where does each duct empty its lymph?
into the venous circulation at the junction of the internal jugular vein and subclavian vein.
what is lymph transport like?
is pump-less thus have low pressure and slow moving
what are the same mechanisms as veins that lymph has?
milking action of muscles
breathing-induced pressure changes in thorax
use of valves
rhythmic contractions of smooth muscle in the trunks and ducts
what is an important component of typhoid tissue?
loose CT (reticular CT) in all L. organs except the thymus.
where are macrophages and lymphocytes found?
Macrophages live on the fibers
lymphocytes reside temporarily in spaces
what are the 2 ways lymphoid tissue is “packaged” in different ways?
diffuse
follicles/nodules
how is lymphoid tissue diffuse?
found in most body organs esp. in mucous memb & in lymphoid organs.
what are follicles/nodules?
solid, tightly packed, spherical bodies with centres (germinal centres)
what does the centre of the follicles/nodules contain?
B cells
where are follicles/nodules found?
within organs eg. lymph nodes but also singly in intestine (Peyer’s Patches).
how is lymph filtered on the way to the bloodstream?
through lymph nodes
where are lymph nodes found?
cluster along the lymphatic vessels of the body
what is the function of lymph nodes?
Provide protective function via phagocytes activate Immune System
where do lymph nodes cluster?
where lymphatic vessels converge to form trunks
eg. groin (inguinal), Arm pit (axillary), neck (cervical)
what do lymph nodes contain?
fibrous capsule from which CT strands emerge (aka Trabeculae) and divide node into compartments
what do lymph nodes provide?
Provides stroma of support for ever changing resident lymphoid cells
what are the 2 distinct regions of lymph nodes?
outer cortex & inner medulla
what does the cortex contain?
densely-packed follicles, many with germinal centers
what wraps around the follicles?
Dendritic cells, to separate from transit T-cell rich interspaces
what do T cells do?
circulate between blood, lymph and LNs for immune surveillance
what does the medulla contain?
cords inward extensions of the cortex which contain lymphocytes and plasma cells
what are lymph sinuses?
spanned by reticular fibres with resident M phi, enter the nodes, and phagocytose foreign material. Some leakage of antigens into surrounding reticular tissue that activate L.
what is the only lymphoid tissue that filters lymph?
lymph node
where does lymph enter?
many afferent lymphatic vessels on convex side
where does lymph move through?
Moves through large bag-like sub-capsular sinus into smaller sinuses that pass through cortex to medulla.
where does lymph leave?
via fewer efferent lymphatic vessels at hilus, an indented region on other side
what does lymph leaving cause?
Causes lymph stagnation & increased access by M phi and lymphocytes
where does lymph pass before its fully cleaned?
passes several nodes
what is the spleen?
Largest L. organ; soft, blood-rich organ, fist size
where is the spleen located?
on left abdomen under diaphragm
how is the spleen supplied?
by large splenic artery & splenic vein that enter hilus on concave side
what are the functions of the spleen?
L proliferation & immune surveillance/response
Cleans blood -remove old RBC/platelets, bacteria, virus, foreign matter, debris, toxins etc.
Storage of RBC constituents and release of others to liver
Stores platelets
Site of RBC production in fetus
what is the structure of the spleen?
Like LN; Thin capsule with Trabeculae, contains L & M phi
what are the 2 distinct area of the spleen?
Areas of L on reticular fibres: white pulp and form “cuffs” around central arteries.
Areas of red cells, venous sinus, splenic cords, and red pulp. Dispose of effete RBC and pathogens
what is the thymus?
Bilobular organ located in lower neck, prominent in early life
what is the function of the thymus?
Secretes thymosin, thymopentin to make T L immunocompetent.
when is the thymus prominent?
in newborns, increases in size and is most active in childhood, begins to atrophy in adolescence. Is replaced by fibrous and fatty tissue in old age.
what is the structure of the thymus?
Compare to cauliflower head: with flowerets the thymic lobules each with outer cortex and inner medulla
what does the dark-staining cortex do?
Rapidly dividing, densely packed L, few M phi
what does the light-staining medulla do?
fewer L, contains bizarre-shaped structures
what are Hassal’s or thyme corpuscles?
responsible for the conversion of self-reactive T-lymphocytes into suppressive T-lymphocytes
what 2 ways does the thymus differ from other lymphoid organs?
Functions only in T cell maturation
Stroma (framework)
why does the thymus only function in T cell maturation?
does not fight antigens directly - blood-thymus barrier - prevents premature activation of immature L
how does the stroma differ in thymus?
consists of star-shaped epithelial cells, not reticular cells, which aid L by secreting stimulating hormones
what are the tonsils?
Simplest lymphoid organs - ring of tissue around entrance to throat (pharynx). Part encapsulated as swellings in mucosa
what is the function of the tonsils?
Gather/remove pathogens entering in inhaled air/food
what are the 4 tonsils?
palatine
lingual
pharyngeal (adenoids)
tubal
where is the palatine?
largest tonsils and are located on either side of posterior end of oral cavity. Most often infected.
where is the lingual?
Located at base of tongue
where is the pharyngeal?
in posterior wall of nasopharynx
where is the tubal?
surround opening of auditory tubes into pharynx
what does the tonsils contain?
Contain nodules with germinal centers surrounded by diffusely scattered L.
what does the exterior surface of the tonsil do?
Covered by squamous epithelium that invaginates deep into tonsil to form blind-ended crypts that trap bacteria & particles.
where is bacteria killed?
in lymphoid tissue. Produces ‘memory’ immune cells.
what are peyer’s patches?
Large isolated clusters of nodules similar to tonsil, located in wall of ileum
what is the appendix?
clusters of nodules
what is the function of the Peyer’s Patches & appendix?
destroy bacteria (many in gut) generate memory L for long-term immunity. MALT -for respiratory and digestive tract protection.
