The Lymphoid System Flashcards
1
Q
what are the primary lymphoid organs
A
bone marrow and thymus
2
Q
what are the primary lymphoid organs the major site of
A
lymphopoiesis
-here, lymphocytes differentiate from lymphod stem cells, proliferate, and mature into funtional cells
3
Q
where do T cells undergo most of their development
where do B cells
A
T=thymuc
B=bone marrow
4
Q
where do lymphocytes acquire their repertoire of specific antigen receptors in order to cope w/ antigenic challenges
A
primary lymphoid organs
-bone marrow and thymus
5
Q
do developing t and b cells respond to foreign antigens in the primary lympoid organs
A
no
6
Q
what is hematopoiesis
A
the process by which all red and white blood cells are produced
7
Q
where does hematopoiesis occur in adults
A
the bone marrow of the sternum, vertebrae, iliac bones, and ribs
8
Q
hematopoiesis occurs in the yolk sac of the fetus and is then taken over by the _____, followed by the ____
A
spleen and liver
bone marrow
9
Q
what is red marrow
A
marrow in which hematopoiesis occurs
10
Q
what are stromal cells (reticular cells)
A
supoprting meshwork of fibroblasts and they secrete reticular fibers which red and white cells develop
aka hematopoietc cords
11
Q
red and white cells exit the bone marrow to enter the circulation via…
A
a dense netowrk of vascular sinuses
12
Q
what are all bone marrow cells dervied from
A
a common self-renewing stem cell whicih develops into a pluripotent stem cell
13
Q
what do pluripotent stem cells differneitate into
A
either a myeloid of lymphoid precursor cell
14
Q
what do the myeloid progenitors develop into
A
gives rise to all blood cells except B, T, and NK cells
15
Q
what do the lymphoid progenitors develop into
A
B, T, and natrual killer cells
16
Q
what are colony stimulated factors
A
factors that promote growth of lineage of WBCs
17
Q
what act on stem cells to stimulate blood cell formation?
what are they produced by?
A
cytokines such as colony stimulated factors
and a host of cytokines referred to as interleukins
-produced by stromal cells, monocytes, and helper lymphocytes
18
Q
what is IL3 important in
A
hematopoiesis
19
Q
what is neupogen
A
granulocyte CSF
used with patients with low neutrophil cell numbers
can be used for aids and cancer patients
20
Q
what are reticulocytes
A
erythrocyte stage right before full maturity
21
Q
where is the thymus located
A
in the mediastinum in the center of the chest above the great vesssels of the heart and consists of 2 lobes which are further divded into locules by fibrous septae
22
Q
where does the majority of T cell maturation occur
A
outer cortex of the thymus
23
Q
what does the cortex contain, what cells
A
densely-packed T cells
macrophages
APCs called dentritic cells
24
Q
what speciliazed cells form the structural framework of the thymus
A
reticular ep cells aka cortical thymic ep cells (cTEC)
25
the cortical thymic ep cells DO NOT secrete reticular fibers, how can they support developing T cells?
only with their cell membrane
26
what are hassall's corpuscles and wehre are they located
tightly packed whorls of ep cells located in the medulla
| significance is unknown
27
how do the hassall's corpuscles change after pubert
decrsease in number but increase in size after puberty
28
how can the hassall's corpuscles serve as a valuable radiological marker
calcify later in life, show where the thymus is
29
lymphocytes destined to develop into T cells begin their maturation int he bone marrow and leave while they are....
- they then go to the....
- what are they called
still very immature, then go go to the thymus cortex and complete their differentation
known as thymocytes
30
what do the most undifferentiated T cells do when they enter the thymus
proliferate, mature, and begin migrating toward the medulla, where they eventually enter the ciruclation
-they DO NOT express T cell receptors, CD4 or CD8 molec
31
what is the purpose of cTEC (cortical thymic ep cells)
1. to secrete thymic homromes such as thymopoeitin, thymosin, and interleukin 7 which are though tot promote T cell matruation
2. to bind to, and positively select for T cells with the ability to recognize and bind to self MHC molecules
32
what are the thymic hormones
thymopoietin
thymosin
interleukin 7
33
what happens to T cells that are unable to bind to MHC molecules
elminated by apoptosis
34
what happens to the cellular DNA, nucleus and cytoplasm during apoptosis
what happens to the cell for macrophages to phagocytose these
cellular DNA is fragmented
nucleus and cytoplasm condense
dying cell often framents into membrane bound apoptic bodies that are rapidly phagocytosed and digested by macrophages
35
what is positive selection
if a T cell matures which cannot recognize self MHC, it will be ineffective in responding to an antigenic stimulus and will be apoptosed
36
where does negative selection take place
cortico-medullary junction
37
what are dendritic cells, why are they important
specilaized APCs derived from the bone marrow
| play a role in binding to and eliminating cells that bind to self MHC with an inappropriately high affinity
38
what is negative selection
binding affinity to MHC alone, nothing with what antigen is
| -cells with an inappropriately high affinity that bind to self MHC are eliminated through apoptosis
39
why is negative selection necessary
the T cells that bind too strong to MHC can develop into autoreactive cells which are cells tat can recognize elf antigens as foreign and attack them
40
how much % of all T cells in the thymic cortex are elminiated by positive and negative selection
50%
41
which structure in the thymus has the structural specilializations that prevent antigen entry
thymic cortex, NOT medulla
42
what is the blood/thymus barrier
the thymic cortex with ep cells slapped on that prevents antigen entry
43
why must antigens need to be kept out of the thymus and bone marrow while T cells are maturing
bc any antigen which does not enter may interfere w/ T cell development and the T cells will NOT be able to recognzie that antigen and ignore them to be left in the thymus
44
what are the speciliaztoins which constitute the blood/thymus barrier
1. tight junctions btwn endothelial cells and a thick endo cell basement membrane
2. a thin layer of ep cells which completely encloses the thymic cortex and vascular basement membranes
45
the absense of afferent lymphatic vessles does what to the antigens
contributes to the lack of antigens in the thymic cortex
46
what happens to the thymus with again
undergoes partial involution (gets smaller)
| but it continues to produce T cells throughout the life of the indiv
47
what are the 2ndary lympoid organs
lymph nodes
spleen
mucosal and cutaneous immune systems
48
which organs do the immune cells come into contact w/ antigens
2ndary lymphoid organs
49
what form can lymphatic tissues be found as
dispersed cells
| aggregates of cells situated beneath epithelia
50
what are some examples of mucosal and cutaneous immune systems
what do these tissues contain
```
tonsils in the oral cavity
peyer's patches in GI tract (GALT)
immune cells in upper resp tract and bronchi (BALT)
conjunctiva (CALT)
skin (SALT)
```
contain T and B cells, macrophages and APCs
51
what ist the langerhans cell
an important APC in the skin
52
what is an example the body's response to antigenic stimulation (lymphatic tissue developing anywhere in bod)
uveitis : infl disease where lymphocytes and other immune cells wreak havoc on uvea and retina
colitis: occurs in distal ileum
53
whta happens to the antigen if it escapes elimination in the subepithelia areas
it will be taken up by draining lymphatic vessels which are supplied with antigenic filters (lymph nodes)
54
what are lymph nodes
wehre are they located
what are they surrounded by
small nodular aggregares of lymphoid tissue
situated along lymphatic channels
surrounded by a fibrous capsule that is pierced by numerous afferent lymphatic vessels
55
what do afferent lymphatic vessels do
| what do efferent lymphatics exit at
bring lymph fluid and cells into the node which course through the node as nodular sinuses and eventually join efferent lymphatics which exit the node at the hilus
56
why are subcapsular sinuses leaky
to allow both cells and fluid to freely exchange btwn the sinus lumen and the parenchyma of the node
-to create back pressure
57
what is the primary cell type in diffuse lymphatic tissue
| what about nodular
diffuse=T cell
| nodular=B cell
58
what do radial trabeulae together with reticular fibers do
support the various cellular compartments w/in the lymph node
59
wehre is the B cell and T cell area in lymph nodes
| what does the central medulla contain
B cell area is the outer cortex
T cell area is the inner or para cortex
central medulla contains the differentiation products of lymphocyte activation such as plasma cells
60
where are APCs especially prevalent in in the cortex
present throughout but especially prevalent in the outer cortex
-the cells are referred to as interdigitating or dendritic cells
61
where is the bulk of lymphoid tissue found
outer and inner cortices
62
what are medullary cords
some lymphoid tissue that extend into the medulla where they are found along strands of connective tissue fibers
63
what are medullary cords separated by
large sinuses and contain most of the plasma cells in the lymph node
64
macrophages are present in lymph nodes and are especialy present in...
the medulla
65
what cells are present in primary or secondary follicles
B cells in the outer cortex
66
what are primary follicles
dense, round, or ovoid aggregations of resting B cells
| unstimulated
67
what cells do secondary nodules contain
activated B cells
68
what is the germinal center
| what cells does it contain
pale staining central region which contains activated, enlarged, proliferating B cells as well as B cells that are differentiaing into plasma cells
69
what surrounds the germinal center
| what does it contain, how does it stain
the mantle zone
| smaller, resting B ceslls that looks and stains like primary nodules
70
where are APCs primary located
diffuse tissue, but also in nodular
71
which tissue type of B cells in
| what about T cells
B=nodular/flolucullar tissue
| T=diffuse tissue
72
where will antigens that stimulate an antibody response enter? what will they bind to? what will they induce?
- enter the primary follicles
- bind to B cell cantigen receptors
- induce secondary follicle formation and plasma cells production
73
where will antigens that stimulate a T cell response be taken up by?
how will this activate a T cell response?
taken up by dendritic cells in the cortex, that will bring these antigens into the T cell region of the inner cortex and activate a T cell response
74
what cells will seek out and destroy antigens in the tissue
activated T cells (helper) and cytotoxic T cells
75
what do T helper cells do
provide help to B cells that reponse to T dependent antigens
76
what do follicular dendritic cells do
trap antigens complexed to antibodies or complement and display them on their surfaces for recognition by B lymphocytes
-play an important role in the selection of activated B cells whose antigen receptors bind the displayed antigens w /high affinity
77
what are the palpable lymph nodes
cervical
inguinal
auxillary lymph nodes
78
what is the englargement of a lymph node referred to as
lymphadenopathy
79
what is erythema
redness due to capillary congestion
80
what can cause the pre-auricular node to swell (adenopathy)
endoviral infection
| less common in bacterial infections
81
what type of infection is chlamydial conjunctivitis
| -almost always exhibits a palpable pre-auricular node
bacterial inclusion
82
if an antigen fails to be filtered out by the lymph nodes, how is it filtered
enter the blood stream and is filtered by the spleen
83
what is the spleen the major site for
phagocytosis of antibody-coated microbes
84
without the spleen what would one be more susceptible to
infectious encapsulated bacteria
85
what support the variety of cells in the spleen
connective tissue capsule that sends trabeculae into the parenchyma of the organ and the reticular fiber framework
86
what are the 2 main types of tissue in the spleen
red pulp: sinusoids and rest of blood cells
| white pulp: WBCs, T and B cells
87
what is the functinon of the red pulp
| what is the function of the white pulp
red: mainly involved in clearing the blood of old and dying blood cells and particulate matter
white: contains lymphatic tissue capable of responding to antigenic stimulation
88
where is the bulk of lymphatic tissue located around
located around small arterioles so it is called periarteriolar lymphatic sheath (PALS)
89
where are the Tcell and B cells areas of PALS
T cell areas being close to central arteriole
| B cell areas being found more peripherally
90
how are the B cell areas of PALS organized
as theyare in lymph nodes: w/ areas of primary and/or secondary follicles present, depending on state of antigen
91
what is the marginal zone
the PALS are surround by a rim of lymphocytes and macrophages called the marginal zone where it is thought that antigens first enter the white pulp
92
where do the arterioles ultimately end
directly or indirectly in vascular sinuses w/in the region of the red pulp where macrophages clear the blood of old and dying cells
93
what do blood cells that are not cleared by macrophages do
re-enter splenic venules and exit the spleen by way of the splenic vein
94
what encapsulated bactera does the spleen remove
act removal of encapsulated bacteria haemophilus influenza and streptococcal pneumonia
95
how to lymphocytes circulate throughout the body, tissues, and lymph compartments
insinuating themselves btwn the endothelial cells of post capillary venules by a process called diapedesis
96
what do post-capillary venules have on their cell wall isntaed of squamous endothelial cells for the migration of lymphocytes into lymph nodes, spleen and mucosal lymphoid tissue
lined by high-walled cuboidal endothelial cells referred to as high endothelial venules (HEV)
97
how are lymphocytes guided to the HEVS
by their interaction w/ vascular addressins on the surface of the endo cells (act as homing beacons for the lymphocytes)
98
how to lymphocytes bind to addressins
integrins which also play a role in tissue migration of cells during embryogeness, tumor metastasis, and wound healing
99
do lymphocytes need high endo-walled vessels to enter nonlymphatic tissue?
no
