Lymphoid Organs Flashcards
1
Q
What are the central lymphoid organs and what is their function?
A
- bone marrow
- thymus
-Production of lymphocytes
2
Q
What are the secondary lymphoid organs and their function?
A
- lymph nodes
- spleen
- tonsils
- peyers patches
-microenvt for interxn of lymphocytes and antigens
3
Q
Name some extralymphoid components?
A
- digestive system - GALT
- respiratory tract
- urinary tract
- reproductive tract
- skin - SALT
4
Q
What percent are B lymphocytes of circulating lymphocytes? T lymphocytes?
A
10-15%, 70-80%
5
Q
What are three targets of CTLs?
A
- foreign cells
- Infected cells with bacteria or viruses
- malignant cells
6
Q
What are the two mechanisms of killing by CTLs?
A
- production of perforins and granzymes
2. induction of apoptosis by FAS-FAS ligand
7
Q
What are two types of reticular tissues in Hematopoietic organs ?
A
myeloid and lymphoid
8
Q
Lymphocytes are what percentage of leukocytes?
A
30%
9
Q
What type of tissue do lymphocytes reside in?
A
Reticular
10
Q
How would you observe reticular tissue?
A
-It cant be observed in H&E preps, but you can use reduced silver salts
11
Q
What type of collagen composes reticular tissue?
A
Type III
12
Q
What are reticular cells?
A
Fibroblasts or dendritic cells which produce type III collagen
13
Q
What are the functions of reticular cells
A
- APCs
- support blood cell maturation
- store ferritin
- synthesize reticular fibers and ground substance
- phagocytosis
14
Q
What is the appearance of a reticular cells?
A
- pale cytoplasm with numerous processes
- diffuse nucleus with prominent nucleolus
15
Q
Which free cells predominate in lymphoid reticular tissue? myeloid reticular tissue?
A
- Lymphocytes
- erythrocytes and granular leukocytes
16
Q
Which cells are most numerous in loose lymphoid tissue?
A
Fixed reticular cells
17
Q
Which cells are most numerous in dense lymphoid tissue?
A
free cells - lymphocytes
18
Q
Which cells are most numerous in nodular lymphoid tissue?
A
Lymphocytes
19
Q
Nodular lymphoid tissue lacks what?
A
A connective tissue capsule
20
Q
What is the visual difference between primary nodules and secondary nodules?
A
Secondary nodules have germinal centers - dark zone, light zone, mantle zone
21
Q
What are the 3 layers of a germinal center and what do they contain?
A
- dark zone - dividing B lymphocytes
- light zone - nondividing B lymphocytes, T helper cells
- mantle - young plasma cells and memory B cells
22
Q
What are the functional correlations of the three zones of the germinal center?
A
- dark zone - clonal expansion of B lymphocytes
- Light zone:
- selection including apoptosis of self recognizing B cells
- differentiation into plasma and memory cells - Mantle zone: temporary storage of plasma and memory cells
23
Q
When do secondary nodules exist?
A
They appear during primary antigenic response and involute after four weeks
24
Q
What type of tissue composes the capsule of a lymph node?
A
Dense irregular tissue
25
What type of tissue composes the cortex of a lymph node?
Loose lymphoid tissue - subscapular and peritrabecular sinuses
26
Where are lymphatic nodules found?
In the cortex of lymph nodes
27
What type of tissue is the medulla of a lymph node composed of?
Dense lymphoid tissue - medullary cords
28
What are the 5 steps of lymph flow through a node?
```
1. Afferent lymphatics
enter at multiple sites on CONVEX (big) surface
valves open towards node
2. subscapular sinus
3. peritrabecular (intermediate sinuses)
4. medullar sinuses
5. Efferent lymphatics
leave node at the HILUS
valves point away from hilus
```
29
Where does the filtration of lymph occur?
In the sinuses by reticular cells
30
What is the route of a lymphocyte? 5 steps
1. produced in germinal centers
2. forced to periphery of nodules
3. enter sinuses
4. leave node by way of efferent lymphatics
5. enter blood circulatory system by way of thoracic duct
31
Through what cells do most lymphocytes return to nodes through ?
High endothelial venules
32
What organs HEVs found in?
lymph nodes, Tonsils and peyers patches
NOT spleen
33
What are 3 medical relevance factors of HEVs?
1. They play a role in mestastisis
2. They decrease in number with age
3. They are involved with lymphocyte recirculation
34
Where is the paracortical zone ?
It is located at the boundary btwn cortex and medulla, centered on opening of afferent lymphatics
35
What part of the lymph node is where most HEVs are found?
-Paracortical zone - peripheral portion
36
Describe the central portion of the paracortical zone?
- few reticular fibers
- high concentration of small lymphocytes
- site of cellular storage and proliferation
37
Describe the peripheral portion of the paracortical zone?
- dense framework of reticular fibers
- fewer lymphocytes
- site of HEVs
- site of rapid migration of lymphocytes
38
What lymphocytes are found in the paracortical zone?
T lymphocytes
39
Where do reticular cells in the lymph nodes originate from? What do they look like?
Mesenchyme
| Black blobs because they are phagocytotic
40
What is the embryological origin of the thymus?
- epithelial lining of 3rd and 4th branchial (pharyngeal pouches)
- mesenchyme
41
Describe what occurs to the thymus after birth
It is fully developed at birth and begins to involute at about two years of age - parenchyma is replaced by fat and fibrous tissue
42
What type of tissue is the capsule of the thymus composed of?
Dense connective tissue
43
What is the histological organization of the thymus?
Connective tissue septae subdivide organ into two main lobes and numerous lobules
44
What is the composition of the cortex of a thymic lobule?
Dense darkly stained lymphoid tissue with lymphocytes (thymocytes) predominating
45
What occurs at the cortex of a thymic lobule?
Thymocyte proliferation, apoptosis, selection
46
What is the composition of the medulla of a thymic lobule?
-lightly stained loose lymphoid tissue with epithelial-reticular cells
47
What occurs at the medulla of a thymic lobule?
Thymocyte maturation
48
Why are thymic epithelial reticular cells different?
- they originate from endoderm of the 3rd and 4th pouches
- they are not phagocytic
- they do not make reticular fibers
49
What is the secretory function of thymic epithelial reticular cells?
They produce thymosins (polypeptides) which promote the differentiation of T lymphocytes. and thymopoietin which supports the lymphoid system
50
What forms the supporting framework or cytoreticulum of the thymus?
epithelial reticular cells with desmosomes and tonofilaments
51
What structure is unique to the thymic medulla and what are they composed of?
Hassals corpuscles composed of concentrically arranged epithelial reticular cells
52
What cells contribute to the blood-thymus barrier, making the thymus an immunologically priveledged site?
epithelial-reticular cells
53
Do dendritic (reticular cells of mesenchymal origin) exist in the thymus?
Yes - they clean up the debris of T cell selection
54
Where is the largest accumulation of lymphatic tissue in the body?
The spleen
55
What tissue composes the capsule of the spleen?
Dense irregular connective tissue
56
What is the histological organization of the spleen?
Branching network of trabeculae arises from the capsule, and pulp in between
57
Where is smooth muscle found in the spleen?
In the capsule and the trabeculae
58
Which pulp comprises more of the splenic parenchyma?
Red pulp - 80%
59
What two structures make up the red pulp of the spleen?
Splenic sinuses and cords
60
What are the function of splenic cords?
It is the site of destruction of RBCs and storage of blood
61
What two structures is the white splenic pulp made up of and what lymphocytes are found there?
PALS- T
| lymphatic nodules - B cells
62
Where is the marginal zone in the spleen?
At the junction of the red and white pulp
63
What does the marginal zone of the spleen contain?
lymphocytes, dendritic cells, macrophages
64
What is the marginal zone of the spleen the site of?
initiation of immune responses to blood-borne antigens
65
Describe the 9 steps of blood flow through the spleen
1. Splenic artery enters at hilus
2. trabecular arteries
3. central arteries
4. penicilli
5. capillaries
6. splenic sinuses
7. Pulp veins
8. Trabecular veins
9. splenic vein leaves the spleen at the hilus
66
What is the function of the central arteries of the spleen?
They are actually arterioles in PALS and lymphatic nodules, which supply lymphatic tissue including
the marginal zone
67
What are penicilli
straight branches of central arteries into red pulp
68
What are the open and closed theories of splenic circulation and which is more common?
open: capillaries to cords to sinuses - slower
closed: capillaries to sinuses - faster
Most blood uses the open route
69
What are splenic sinuses?
Wide vascular channels btwn endothelial cells with a discontinuous basement membrane
70
Where are macrophages located in the spleen?
In the cords outside the basement membrane of splenic sinuses
71
What are the functions of the spleen?
1. Produces lymphocytes at secondary nodules
2. Plays a role in the immune response to blood-borne antigens - dendrites, T and B cells
3. Destruction of RBCs - macrophages
4. Storage of blood -red pulp
72
What do tonsils consist of ?
Lymphatic nodules embedded in dense lymphoid tissue
73
Where are the tonsils located in general?
Aperture where oral cavity communicates with the pharynx
74
When do the tonsils reach their maximal development?
Childhood
75
Which tonsils are located in the lateral walls of the oropharynx?
Palantine
76
Which tonsils are covered by straitified epithelium and which by pseudostratified ciliated columnar epithelium?
strat -- lingual and palantine
| pseudo - pharyngeal - respiratory epithelium!
77
Which tonsils have crypts (invagination of epithelium)?
Palantine - many
lingual - single large
pharyngeal - pleats or surface folds instead
78
What do crypts contain?
desquamated epithelial cells, lymphocytes, bacteria - detritus
79
Where are the pharyngeal tonsils located?
Roof of nasopharynx
80
Where are the lingual tonsils located?
base of the tongue
81
What are the functions of tonsils?
1. detection and response to pathogens in the oral cavity
| 2. production of lymphocytes
