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Microscopic Anatomy > Lymphoid Organs > Flashcards

Lymphoid Organs Flashcards

1
Q

What are the central lymphoid organs and what is their function?

A
  • bone marrow
  • thymus

-Production of lymphocytes

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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

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3
Q

Name some extralymphoid components?

A
  • digestive system - GALT
  • respiratory tract
  • urinary tract
  • reproductive tract
  • skin - SALT
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4
Q

What percent are B lymphocytes of circulating lymphocytes? T lymphocytes?

A

10-15%, 70-80%

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5
Q

What are three targets of CTLs?

A
  1. foreign cells
  2. Infected cells with bacteria or viruses
  3. malignant cells
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6
Q

What are the two mechanisms of killing by CTLs?

A
  1. production of perforins and granzymes

2. induction of apoptosis by FAS-FAS ligand

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7
Q

What are two types of reticular tissues in Hematopoietic organs ?

A

myeloid and lymphoid

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8
Q

Lymphocytes are what percentage of leukocytes?

A

30%

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9
Q

What type of tissue do lymphocytes reside in?

A

Reticular

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10
Q

How would you observe reticular tissue?

A

-It cant be observed in H&E preps, but you can use reduced silver salts

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11
Q

What type of collagen composes reticular tissue?

A

Type III

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12
Q

What are reticular cells?

A

Fibroblasts or dendritic cells which produce type III collagen

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13
Q

What are the functions of reticular cells

A
  1. APCs
  2. support blood cell maturation
  3. store ferritin
  4. synthesize reticular fibers and ground substance
  5. phagocytosis
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14
Q

What is the appearance of a reticular cells?

A
  • pale cytoplasm with numerous processes

- diffuse nucleus with prominent nucleolus

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15
Q

Which free cells predominate in lymphoid reticular tissue? myeloid reticular tissue?

A
  • Lymphocytes

- erythrocytes and granular leukocytes

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16
Q

Which cells are most numerous in loose lymphoid tissue?

A

Fixed reticular cells

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17
Q

Which cells are most numerous in dense lymphoid tissue?

A

free cells - lymphocytes

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18
Q

Which cells are most numerous in nodular lymphoid tissue?

A

Lymphocytes

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19
Q

Nodular lymphoid tissue lacks what?

A

A connective tissue capsule

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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

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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
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22
Q

What are the functional correlations of the three zones of the germinal center?

A
  1. dark zone - clonal expansion of B lymphocytes
  2. Light zone:
    - selection including apoptosis of self recognizing B cells
    - differentiation into plasma and memory cells
  3. Mantle zone: temporary storage of plasma and memory cells
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23
Q

When do secondary nodules exist?

A

They appear during primary antigenic response and involute after four weeks

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24
Q

What type of tissue composes the capsule of a lymph node?

A

Dense irregular tissue

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25
Q

What type of tissue composes the cortex of a lymph node?

A

Loose lymphoid tissue - subscapular and peritrabecular sinuses

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26
Q

Where are lymphatic nodules found?

A

In the cortex of lymph nodes

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27
Q

What type of tissue is the medulla of a lymph node composed of?

A

Dense lymphoid tissue - medullary cords

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28
Q

What are the 5 steps of lymph flow through a node?

A 
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
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29
Q

Where does the filtration of lymph occur?

A

In the sinuses by reticular cells

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30
Q

What is the route of a lymphocyte? 5 steps

A
  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
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31
Q

Through what cells do most lymphocytes return to nodes through ?

A

High endothelial venules

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32
Q

What organs HEVs found in?

A

lymph nodes, Tonsils and peyers patches

NOT spleen

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33
Q

What are 3 medical relevance factors of HEVs?

A
  1. They play a role in mestastisis
  2. They decrease in number with age
  3. They are involved with lymphocyte recirculation
34
Q

Where is the paracortical zone ?

A

It is located at the boundary btwn cortex and medulla, centered on opening of afferent lymphatics

35
Q

What part of the lymph node is where most HEVs are found?

A

-Paracortical zone - peripheral portion

36
Q

Describe the central portion of the paracortical zone?

A
  • few reticular fibers
  • high concentration of small lymphocytes
  • site of cellular storage and proliferation
37
Q

Describe the peripheral portion of the paracortical zone?

A
  • dense framework of reticular fibers
  • fewer lymphocytes
  • site of HEVs
  • site of rapid migration of lymphocytes
38
Q

What lymphocytes are found in the paracortical zone?

A

T lymphocytes

39
Q

Where do reticular cells in the lymph nodes originate from? What do they look like?

A

Mesenchyme

Black blobs because they are phagocytotic

40
Q

What is the embryological origin of the thymus?

A
  • epithelial lining of 3rd and 4th branchial (pharyngeal pouches)
  • mesenchyme
41
Q

Describe what occurs to the thymus after birth

A

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
Q

What type of tissue is the capsule of the thymus composed of?

A

Dense connective tissue

43
Q

What is the histological organization of the thymus?

A

Connective tissue septae subdivide organ into two main lobes and numerous lobules

44
Q

What is the composition of the cortex of a thymic lobule?

A

Dense darkly stained lymphoid tissue with lymphocytes (thymocytes) predominating

45
Q

What occurs at the cortex of a thymic lobule?

A

Thymocyte proliferation, apoptosis, selection

46
Q

What is the composition of the medulla of a thymic lobule?

A

-lightly stained loose lymphoid tissue with epithelial-reticular cells

47
Q

What occurs at the medulla of a thymic lobule?

A

Thymocyte maturation

48
Q

Why are thymic epithelial reticular cells different?

A
  • they originate from endoderm of the 3rd and 4th pouches
  • they are not phagocytic
  • they do not make reticular fibers
49
Q

What is the secretory function of thymic epithelial reticular cells?

A

They produce thymosins (polypeptides) which promote the differentiation of T lymphocytes. and thymopoietin which supports the lymphoid system

50
Q

What forms the supporting framework or cytoreticulum of the thymus?

A

epithelial reticular cells with desmosomes and tonofilaments

51
Q

What structure is unique to the thymic medulla and what are they composed of?

A

Hassals corpuscles composed of concentrically arranged epithelial reticular cells

52
Q

What cells contribute to the blood-thymus barrier, making the thymus an immunologically priveledged site?

A

epithelial-reticular cells

53
Q

Do dendritic (reticular cells of mesenchymal origin) exist in the thymus?

A

Yes - they clean up the debris of T cell selection

54
Q

Where is the largest accumulation of lymphatic tissue in the body?

A

The spleen

55
Q

What tissue composes the capsule of the spleen?

A

Dense irregular connective tissue

56
Q

What is the histological organization of the spleen?

A

Branching network of trabeculae arises from the capsule, and pulp in between

57
Q

Where is smooth muscle found in the spleen?

A

In the capsule and the trabeculae

58
Q

Which pulp comprises more of the splenic parenchyma?

A

Red pulp - 80%

59
Q

What two structures make up the red pulp of the spleen?

A

Splenic sinuses and cords

60
Q

What are the function of splenic cords?

A

It is the site of destruction of RBCs and storage of blood

61
Q

What two structures is the white splenic pulp made up of and what lymphocytes are found there?

A

PALS- T

lymphatic nodules - B cells

62
Q

Where is the marginal zone in the spleen?

A

At the junction of the red and white pulp

63
Q

What does the marginal zone of the spleen contain?

A

lymphocytes, dendritic cells, macrophages

64
Q

What is the marginal zone of the spleen the site of?

A

initiation of immune responses to blood-borne antigens

65
Q

Describe the 9 steps of blood flow through the spleen

A
  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
Q

What is the function of the central arteries of the spleen?

A

They are actually arterioles in PALS and lymphatic nodules, which supply lymphatic tissue including
the marginal zone

67
Q

What are penicilli

A

straight branches of central arteries into red pulp

68
Q

What are the open and closed theories of splenic circulation and which is more common?

A

open: capillaries to cords to sinuses - slower
closed: capillaries to sinuses - faster

Most blood uses the open route

69
Q

What are splenic sinuses?

A

Wide vascular channels btwn endothelial cells with a discontinuous basement membrane

70
Q

Where are macrophages located in the spleen?

A

In the cords outside the basement membrane of splenic sinuses

71
Q

What are the functions of the spleen?

A
  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
Q

What do tonsils consist of ?

A

Lymphatic nodules embedded in dense lymphoid tissue

73
Q

Where are the tonsils located in general?

A

Aperture where oral cavity communicates with the pharynx

74
Q

When do the tonsils reach their maximal development?

A

Childhood

75
Q

Which tonsils are located in the lateral walls of the oropharynx?

A

Palantine

76
Q

Which tonsils are covered by straitified epithelium and which by pseudostratified ciliated columnar epithelium?

A

strat – lingual and palantine

pseudo - pharyngeal - respiratory epithelium!

77
Q

Which tonsils have crypts (invagination of epithelium)?

A

Palantine - many
lingual - single large
pharyngeal - pleats or surface folds instead

78
Q

What do crypts contain?

A

desquamated epithelial cells, lymphocytes, bacteria - detritus

79
Q

Where are the pharyngeal tonsils located?

A

Roof of nasopharynx

80
Q

Where are the lingual tonsils located?

A

base of the tongue

81
Q

What are the functions of tonsils?

A
  1. detection and response to pathogens in the oral cavity

2. production of lymphocytes

Microscopic Anatomy (3 decks)

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