Lymphoid Tissue Flashcards
1
Q
Encapsulated lymphoid tissues
A
Thymus
Tonsils (can lack a capsule)
Lymph nodes
Spleen
2
Q
Diffuse lymphoid tissue
A
MALT
- Galt
- Balt
3
Q
Lymphoid cells
A
B cells
T cells
Macrophages
4
Q
B cells
A
- originate in bone marrow
- mature in bone marrow
- migrate to secondary structures
- can become plasma cells
5
Q
T cells
A
- originate in bone marrow
- mature in thymus
- migrate to secondary structures
6
Q
Macrophages
A
derived from monocytes
7
Q
Where do you find IgG?
A
Many locations (75% of serum immunoglobulins)
- produced in large amounts during immune responses
- the only immunoglobulin to cross placental barrier (to protect newborn from infections)
8
Q
Where do you find IgA
A
Nasal, bronchial, intestinal and prostatic secretions; also tears, colostrum, saliva and vaginal fluid
(5-10% Ig in serum)
- secreted by plasma cells in lamina propia of epithelium if GI, respiratory and urinary passages
- present in secretions in secretory form that is resistant to several enzymes; provides protection in secretions against microorganisms
9
Q
Where do you find IgM?
A
Plasma membrane of B cells or in circulating form (10% Ig in serum)
- IgM in the membrane, when bound to an antigen, causes differentiation of the B cell into an antibody-secreting plasma cell
- Secreted IgM, when bound to antigen, activates the complement system
10
Q
Where do you find IgE?
A
Surfaces of mast cells and basophils (5-10% Ig in serum)
- Only small amounts in blood since it is attached to cells via its Fc region
- They stimulate release substances (e.g. histamine), triggering an allergic reaction.
11
Q
Where do you find IgD?
A
Plasma membrane of B cells or in circulating form (0.2% Ig in serum)
12
Q
X-linked agammaglobulinemia
A
B lymphocytes do not develop, resulting in a scarcity of plasma cells and a lack of immunoglobulin production
13
Q
CVID (common variable immunodeficiency)
A
Normal B cell population but do not make enough immunoglobulins
symptoms:
- recurrent respiratory infections
- autoimmune disorders (RA, thyroiditis, Addison disease)
- GI disorders (diarrhea and malabsorption of nutrients in GI tract)
14
Q
Reticular cells
A
- Form supporting framework of lymphoid organs (lymph nodes, spleen and bone marrow)
- Synthesize reticular fibers
- May be phagocytic
15
Q
Nonencapsulated clusters of lymphoid cells or nodules
A
Diffuse lymphoid tissue
16
Q
Peyer’s patches
A
Large aggregates of lymphoid nodules in the ileum, pushing into submucosa
17
Q
Primary nodules
A
- no germinal center
- composed of mostly RESTING B CELLS as well as plasma cells, dendritic cells, macrophages and reticular cells
18
Q
Secondary nodules
A
- formed in response to antigenic challenge
- germinal center (developing B cells)
- mantle/corona (darker periphery of displaced resting b cells, memory cells, plasma cells, DCs, macrophages and reticular cells)
19
Q
Lymph node
A
- Maintains/produces B cells and T cells
- Possess memory cells (esp. T memory cells)
- Primary location for filtration of lymph
- Antigens delivered to lymph nodes by APCs are recognized by T cells, and an immune response is initiated
-contains: capsule, cortex/medulla, lymphoid nodules, hilum
20
Q
primary location for filtration of lymph
A
lymph node
21
Q
Vessels of lymph node
A
- Convex surface of lymph node receives afferent lymphatic vessels
- Concave surface (hilum) is where arterioles enter; venules and efferent lymphatic vessels exit
22
Q
Antigens delivered to lymph nodes by APCs are recognized by _________, and an immune response is initiated
A
T cells
23
Q
Lymph node cortex
A
- Lymphoid nodules (mainly B cells)
- subcapsular and cortical sinuses (sinusoids)
24
Q
Lymph node paracortex
A
- Mainly T cells
- T cells enter paracortex via “High-Endothelial Venules” (specialized post-capillary venules with a cuboidal epithelium)
- known as “thymus-dependent area”
25
What is the "thymus-dependent area" in the lymph node?
paracortex
26
Lymph node medulla
- Medullary sinuses (sinusoids) composed of reticular fibers/cells and macrophafes
- Medullary cords composed of lymphocytes and plasma cells
27
High-endothelial venule
- specialized postcapillary venule in paracortex of the lymph node
- simple cuboidal epithelium
- 90% of lymphocytes leave bloodstream and enter lymph node here by diapedesis
28
90% of lymphocytes leave the bloodstream and enter the lymph node at the __________ by ___________
High-endothelial venule, diapedesis
29
Most venules in the body have a _______________, but the High-endothelial venule has ___________
simple squamous epithelium; simple cuboidal epithelium
30
Why do lymph nodes swell?
When the body fights infection or injury, lymph nodes PRODUCE MORE CELLS and therefore often swell
Lymph nodes usually swell near the site of injury
31
When the Virchow's node is enlarged
suggestive of abdominal metastasis
32
Thymus
- Maintains T cells
- Primary location for T cell maturation
contains: capsule, cortex/medulla
33
The thymus does not possess lymphoid nodules
true - the thymus just contains a capsule and cortex/medulla
34
Cells in the cortex of thymus?
Epithelial reticular cells
Thymocytes
35
Epithelial reticular cells
(TECs) In cortex of thymus
- pale
- form meshwork within which T cells are tightly packed
- have long processes that contact other reticular cells and surround cortex, isolating it
- synthesize THYMOSIN (transforms immature T cells --> immunocomputent T cells)
36
What is thymosin?
Synthesized by epithelial reticular cells in the cortex of the thymus
-a serum thymic factor, thymopoietin for transforming immature T cells into immunocompetent T cells
37
Thymocytes
In cortex of thymus
- respond to cytokines (released by TECs) and become T cells
- migrate from cortex toward medulla as they mature (many die along the way and are phagocytosed)
- surviving T cells are naive, leave thymys and travel in blood to secondary lymphoid organs
38
What cells leave the thymus?
surviving T cells are naive; they leave the thymus and travel in blood to secondary lymphoid organs
39
Blood-thymus barrier structure
in cortex of thymus
1. capillary endothelium and basal lamina
2. perivascular connective tissue w macrophages
3. thymic epithelial reticular cells and basal lamina
40
What creates an immunologically protected region, ensuring that antigens escaping the bloodstream do NOT reach developing T cells in the cortex?
the blood-thymus barrier
41
Cells in Medulla of Thymus
Loosely packed Mature T cells and epithelial reticular cells
the loosely packed cells is why the medulla is lighter staining than the cortex
42
Where are Hassall corpuscles?
In the Medulla of Thymus
43
Hassall corpuscles
(Thymic corpuscles)
- Whorl-like accretions of epithelial reticular cells
- keratinized
- increase in # w age
- unknown function
44
Mature T cells exit the thymus via
venules and efferent lymphatic vessels from the thymic medulla
45
DiGeorge syndrome
aka Congenital thymic aplasia
-abnormal cell-mediated immunity but normal humoral immunity
CATCH 22: Cardiac defects, Abnormal facies, Thymic hypoplasia, Cleft palate, Hypocalcemia, microdeletion of chromosome 22
46
In the thymus, positive selection occurs in the
cortex
47
In the thymus, negative selection occurs in the
medulla
48
Filters blood
spleen
49
Spleen
- Maintains/produces B cells and T cells
- Filters blood
- Stores RBCs; phagocytoses damaged/aged RBCs
- Prenatal, extramedullary hematopoiesis
Contains: capsule, lymphoid nodules, hilum
50
How is the spleen different from both the thymus and lymph nodes?
it lacks a cortex and medulla
51
The spleen lacks a cortex and medulla
true
52
Does the spleen have afferent lymphatic vessels?
No. but the lymph nodes have afferent lymphatic vesseles
53
Spleen White pulp
Lymphoid nodules = B cells
Periarterial lymphatic sheath (PALS) = T cells
54
Spleen Red pulp
Interconnected network of sinusoids and splenic cords
sinusoids lined by stave cells
cords (of billroth) has plasma cells, reticular cells, blood cells and macrophages
55
Spleen White pulp and Red pulp are separated by a
marginal zone
56
The spleen is very vascular
true
57
Organization/flow of vasculature in spleen
Splenic artery --> trabecular artery -->
central artery -->
penicillar artery -->
either (1) splenic sinusoiuds or (2) splenic cords
58
Central artery is white or red pulp?
White pulp; covered by Periarterial lymphatic sheath (PALS), T cells
59
Penicillar artery and its branches are white or red pulp?
red pulp
60
The splenic artery enters the
hilum
61
Splenic sinusoids are _______ circulation
closed
62
Splenic cords are __________ circulation
open
63
Marginal zone of spleen
- between red and white pulp
- first site where blood contacts pleen parenchyma
- richly supplied by macrophages and APCs
- circulating T cells and B cells are sorted here
64
Tonsils
- Maintain/produce B cells
- Combat antigens entering via nasal/oral epithelia
Contains: capsule, lymphoid nodules
