Lymphoid System Flashcards
3 components of secondary lymphoid organs?
lymph nodes: filters lymph and returns it to blood via ducts
spleen: filters blood
MALT (mucosal associated lymphoid tissue): counteracts infection
in the stroma of lymphoid tissues and organs, ____ tissue makes up the capsule and trabecula (septum/septa)
dense connective tissue (type I collagen)
fill in the blanks regarding lymph flow:
1. blood plasma exits capillaries as ETC tissue fluid, and excess fluid drains to ____ lymph capillaries
2. lymph flows through vessels, which have _____ for unidirectional flow
3. lymph goes through lymph nodes, enters via ____ lymph nodes/ exits via ____ lymph nodes
4. lymph goes through _______
5. lymph enters blood
- blood plasma exits capillaries as ETC tissue fluid, and excess fluid drains to BLIND ENDED lymph capillaries
- lymph flows through vessels, which have VALVES for unidirectional flow
- lymph goes through lymph nodes, enters via AFFERENT lymph nodes/ exits via EFFERENT lymph nodes (*Efferent = Exit)
- lymph goes through LYMPHATIC DUCTS
- lymph enters blood
where does lymph enter blood (2)
- thoracic duct: returns lymph from right side of body below the diaphragm and ENTIRE LEFT side of body (at left venous angle)
- right lymphatic duct: returns lymph from RIGHT side of body above diaphragm (at right venous angle)
left vs right venous angle
thoracic duct returns lymph from entire left side of body at left venous angle: junction between left subclavian vein and left internal jugular vein
right lymphatic duct returns lymph from right side of body above diaphragm at right venous angle: junction between right subclavian vein and right internal jugular vein
a patient presents with edema throughout the left side of their body. You suspect a problem with their lymph drainage. What duct may be at fault?
thoracic duct; returns lymph from right side of body below diaphragm and entire left side of body at the left venous angle (junction between L subclavian and L internal jugular veins)
*right lymphatic duct only drains right side above diaphragm via right venous angle
lymphangitis
inflammation of lymphatic channels that occurs as a result of infection at a site distal to the channel, may spread within hours
the most common initial path for carcinoma cells (epithelial cancers) after detaching from primary site is _____
enter lymphatic vessels and become trapped in lymph nodes as secondary (metastatic) cancer site
lymphedema is caused by
interrupted lymph drainage
*removal of axillary lymph nodes during mastectomy is common cause of upper limb lymphedema
what is found in the parenchyma of bone marrow?
cords: hematopoietic cells
sinuses: mature cells go to circulation
3 places where you find MALT (mucosal associated lymphoid tissue)
- GALT (gut associated lymphoid tissue): tonsils, Peyer’s patches (ilium), appendix
- BALT (breathing associated): respiratory tract
- urinary/reproductive tracts
*MALT can be temporary or permanent (tonsils), early line of defense (mostly lymphocytes)
what is found in the nodules/follicles of MALT?
located in loose CT, not fully encapsulated
MOSTLY B CELLS (T cells nearby)
can be primary (resting) and secondary (activated)
where are germinal centers found in MALT nodules/follicles
secondary (active) nodules/follicles (stain lighter than primary/inactive) with dark mantle zone/corona with inactive B cells
antigen-activated B cells, follicular DC (FDC) rescue antigen-specific B cells from apoptosis
germinal centres remain for weeks after antigen exposure, disappear when infection is cleared
in lymph nodes, active follicles are _____ follicles, NONactive follicles are ____ follicles
primary - NONactive
secondary - ACTIVE
what will you find in the cortex, paracortex, and medulla of lymph node parenchyma?
cortex:
- sinuses: afferent lymph vessels, subcapsular/marginal sinus, trabecular/paratrabecular sinus
- nodules/follicles: primary and secondary follicles, B CELLS (proliferation with activation), DC, macrophage, plasma cells
paracortex: HEVs (high endothelial venules - lymphocytes exit blood and enter lymph node), T cells
medulla:
- sinuses: macrophages, reticular cells, efferent lymph vessels
- cords: macrophages, DC, lymphocytes, plasma cells
where in lymph node parenchyma can you find afferent lymph vessels? (be specific)
sinuses of cortex have AFFERENT lymph vessels
[sinuses of medulla have efferent lymph vessels, efferent = exit]
where (specifically) in lymph node parenchyma can lymphocytes exit blood and enter lymph node?
HEV (high endothelial venules) in paracortex
you will find mainly T cells in paracortex
where can reticular cells be found in lymph node parenchyma?
in the medullary sinuses, along with macrophages and efferent lymph vessels
HEVs and location
high endothelial vessels, where lymphocytes can exit blood and enter lymph nodes
found in paracortex of lymph node parenchyma
where can you find subcapsular/marginal sinuses and trabecular/paratrabecular sinuses?
in the sinuses of the cortex of lymph nodes, along with afferent lymph vessels
lymph node follicles are found in the _____
lymph node cords are found in the ______
follicles/nodules are in cortex
cords are in medulla
in DiGeorge syndrome, the thymus is not well developed. What effect does this have on lymph node parenchyma?
T cells mature in the thymus
if the thymus is not well-developed, T cells can’t develop well
if T cells can’t develop well, they can’t populate the paracortex of lymph nodes
therefore the paracortex of lymph nodes is also not well developed
in viral infections, an extreme immune response is sometimes induced that causes hyperplasia of the _____ of lymph nodes
paracortex - contains HEVs (for lymphocyte entry from blood) and population of T cells
the connective tissue capsule of lymph nodes continues/protrudes internally as ____
trabeculum - makes sort of dividers between pie slices
blood vessels and the efferent [exit] lymphatic vessel are found at the ____ of lymph nodes
hilum (stalk)
describe the journey of lymphocytes through lymph nodes
travel via sinuses (discontinuous, porous endothelium with reticular connective tissue)
- afferent lymph vessel (afferent = arrive)
- subcapsular (beneath the capsule) sinus
- trabecular sinus (remember that trabeculum are continuation of capsule)
- medullary sinus (within medulla, which = middle)
- efferent (exiting) lymph vessels
the outer dense connective tissue (note that it is fragile, though) capsule of the spleen continues internally as ____
trabecula
which of these are TRUE regarding the spleen?
a. contains reticular fibers
b. is divided by cortex and medulla
c. contains a hilum through which blood vessels enter and exit
d. is encapsulated by dense CT that continues internally as trabeculum
spleen:
a. contains reticular fibers
c. contains hilum
d. capsule of dense CT continues internally as trabecula/trabeculum (same thing)
*parechyma is organized into pulps
lymph nodes:
- CT capsule continues inwards as trabeculum
- cortex, paracortex, medulla
- also contains reticular fibers and hilum
how is splenic parenchyma organized?
pulps:
- white pulp (WBC): PALS (periarteriolar lymphoid sheath), nodules
- red pulp (RBC): sinusoids/sinuses and cords (of Bilroth)
what can be found in the white pulp of the spleen (specifically)?
PALS (periarteriolar lymphoid sheath): surrounds center arteriole, T cells
nodules: resting or activated follicles, B cells, DC, macrophage, plasma cells
*remember that white pulp is WBC, so its function is immune response to blood-borne antigens
what will you find (specifically) in red pulp of spleen parenchyma?
sinusoids/sinuses: capillaries with endothelial cell slits, contain macrophages
cords of Bilroth: RBCs, DC, granulocytes, lymphocytes, plasma cells, macrophages with hemosiderin (brown pigment because they have taken up old RBC)
*remember that the role of red pulp in spleen is to remove old RBCs
where will you find cords of Bilroth
red pulp of the spleen
contains RBCs, DC, granulocytes, lymphocytes, plasma cells, and macrophages with hemosiderin (because they have take up old RBCs)
[also in red pulp are sinusoids/sinuses]
where in the spleen will you find:
a. T cells
b. hemosiderin-laden macrophages
T cells make up PALS of white pulp (periarteriolar lymphoid sheath, because it surrounds central arteriole)
hemosiderin-laden macrophages are in CORDS OF BILROTH of red pulp (have brown pigment because they cells have taken up old RBC and are degrading them)
where are immune responses initiated in the spleen?
the marginal zone, between the red and white pulp
is splenic circulation in humans open or closed?
in humans splenic circulation is open - not all blood goes directly from arterioles into sinuses, most goes right onto cords of spleen
macrophages in cords sample blood and filter it
surviving blood passes through into sinus, then leaves via splenic veins
A 7yo pt with Hx of sickle cell disease is admitted with LUQ abdominal pain and tachycardia. Hemoglobin levels are low, spleen is easily palpated below L costal margin.
You recognize that the patient is experiencing splenic sequestration crisis. Explain
sickle RBCs pool in the spleen and cause painful splenomegaly
Remember that in the spleen of humans, there is open circulation so most blood goes over cords and is sampled by macrophages before returning to sinus and leaving via veins. The slits in the endothelium are small, so sickle cells could get stuck here
where is the thymus located anatomically
found in thorax, in the anterior mediastinum, posterior to the sternum
what happens to the thymus with age (how is tissue changed?)
in children, thymus is mostly T cells
with age, thymus becomes fatty
ectopic thymus
thymus forms in head/neck region and migrates,
but sometimes some of it is left behind, resulting in ectopic thymus
how can you tell if you’re looking at a histology image of a child’s thymus?
not a lot of adipose (an adult’s would have more fatty tissue)
describe structure of thymus
- 2 lobes (R/L)
- cortex and medulla
- outer capsule, continues inwards as trabeculum
*however, trabeculum only partially divides lobes into lobules
*NO nodules in cortex - distinguishes thymus from lymph node (don’t want B cells here - you do not want an immune reaction against developing T cells)
how can you histologically differentiate between thymus and lymph nodes? what is the significance of this difference?
thymus does NOT have nodules in cortex - you do NOT want a B cell immune reaction against developing T cells (remember that T cells become immunocompetent in the thymus)
lymph nodes have nodules in their cortex
are there more T cells in the cortex or medulla of the thymus
cortex > medulla
where can epithelial reticular cells be found in the thymus?
describe them
cortex AND medulla
- stellate/star shaped
- connected via desmosomes
- provide support, secretions, barrier from blood
*** in the medulla, reticular cells form Hassall’s corpuscles (accumulate with age)
where does T cell selection occur in the thymus
CORTEX
Hassall’s corpuscles
formed by epithelial reticular cells in the MEDULLA of the THYMUS (look like whorls)
accumulate with age
aka thymic corpuscles
why is it important that there is a blood-thymus barrier?
what to protect developing T cells from immune reaction
contains:
- continuous capillary endothelium held together with tight junctions
- basement membrane
- perivascular CT
- basement membrane with desmosomes
what genetic mutation causes DiGeorge syndrome, and how does it manifest?
22q11 deletion —> DiGeorge syndrome (velocardiofacial)
remember Catch 22
Cleft palate
Abnormal face
Thymic aplasia
Cardiac defects
Hypocalcemia
22 gene segment deletion
thymic aplasia epithelial reticular cells don’t form properly in thymus —> immunodeficiency because T cells are not forming —> NO T CELLS in thymus-dependent zones (such as paracortex of lymph node, PALS of white pulp of spleen - wherever you’re supposed to see T cells)
do primary lymphoid organs contain nodules?
NO
do not want an immune response triggered in bone marrow and thymus, where B/T cells are developing
*secondary lymphoid organs, whose job it is to produce immune response, contain nodules
how is parenchyma of tonsils organized
crypts
partial capsule of loose CT
which lymphoid organs are encapsulated by reticular CT?
bone marrow (primary)
lymph nodes and spleen (secondary)
[all others have loose CT]
where do immunocompetent T cells exit the thymus?
corticomedullary junction
open circulation in the spleen occurs where blood cells pass from ____ into ____
capillaries into cords
then squeeze through endothelial slits to reach sinuses for exit
what are the T-dependent zones of the lymphoid system?
- paracortex of lymph nodes
- PALS of splenic white pulp
