Lymph Tissues and Organs

Question 1

What are the 3 main lines of defense of the immune system?

Answer 1

Protective surfaces

Innate immune system

Adaptive immune system

Question 2

How does the immune system use protective surfaces?

Answer 2

First line of defense

Physical barrier

Keep out pathogens as long as they stay intact

Breaches in skin or mucosal linings allow pathogens into deeper tissues

Question 3

What is the innate immune system?

Answer 3

Rapid reactions to infection, but cannot learn

Cells - neutrophils, eosiniophils, basophils, mast cells, macrophages, natural killer cells

Cells equipped with generic protein tools to fight pathogens - bacteriocidal enzymes for example

Cells able to mobilize rapidly

Question 4

What is the adaptive immune system?

Answer 4

Slow to respond to infections, but able to learn

Second and subsequent encounters with pathogens elicit greater, more specific and faster responses

Takes 3-5 days to mount a response - needs large number of lymphocytes with specificity for a particular pathogen (or antigen)

Main cells - B lymphocytes (b cells) and T lymphocytes (T cells)

Question 5

What are B lymphocytes?

Answer 5

Humoral response - cells use antibodies to recognize antigens

Question 6

What are T lymphocytes?

Answer 6

Cellular response - cells recognize antigens directly

Question 7

Parenchyma

Answer 7

Parts of a gland or organ that are specialized for that gland or organ’s unique function - differs depending on structure

Ex. Lung parenchyma - airways and alveoli

Question 8

Stroma

Answer 8

Support tissue - usually CT proper

Any CT that covers, subdivides, and or physically supports functional cells in parenchyma

Usually has vessels and nerves that supply parenchyma in generic way

Question 9

What is the main site of inflammatory and immune response in tissues?

Answer 9

CT of the stroma

Question 10

What is the lymphoid system?

Answer 10

All places where lymphoid cells proliferate, differentiate, and mature into immunocompetent cells, or where they mount immune responses

Lymphoid cells - B and T cells

Lymphatic tissues can form temporarily within other tissues or organs and can also form permanent structure (=lympoid organs)

Lymphoid organs

Question 11

What are lymphoid organs?

Answer 11

Bone marrow

Thymus

Lymph nodes

Spleen

Various types of mucosa-associated lymphoid tissue

Question 12

What are primarily (central) lymphoid organs?

Answer 12

Organs where lymphocytes differentiate, become educated and learn to distinguish self from not self

Bone marrow and thymus

Question 13

What are secondary (peripheral) lymphoid organs?

Answer 13

Organs and tissues where mature B cells and T cells encounter foreign antigens/pathogens, become activated in response to antigens, and where immune responses take place

Lymph nodes, spleen, and MALT tissues with nodules

Question 14

What do we also classify lymphoid tissues based on, beside organs?

Answer 14

Organization - diffuse vs. nodular

Question 15

Where do lymphocytes differentiate, develop, and mature to become B lymphocytes (B cells)?

Answer 15

Bone marrow

Question 16

How does bone marrow function as a primary lymphoid organ?

Answer 16

Bone marrow releases mature (unactivated) B cells into blood and they travel to secondary lymphatic organs that have nodules.

B cells in secondary organs are activated when an antigen binds a surface immunoglobulin and then it undergoes mitosis to form clones

Question 17

What can clones do when a B cell is activated?

Answer 17

Clones can synthesize an Ig with same antigen specificity

Most clones mature into plasma cells

Question 18

What do plasma cells make?

Answer 18

lots and lots of antibody (Ig)

Question 19

What does the thymus do as a primary lymphoid organ?

Answer 19

Precuror of T cells start out in bone marrow and go to thymus

Differentiate into thymus into immunincompetent T cells - thymocytes

Thymocytes mature into immunocompenetent lymphocytes in thymus

Mature in thymus and called T lymphocytes (T cells)

Thymus released T cells (unactivated) into blood and they travel to 2 thymus dependent secondary lymphatic tissues (paracortex of lymph nodes and PALS of spleen)

Question 20

Where do T cells going after being released from thymus?

Answer 20

Thymus dependent secondary lymphatic tissues

Paracortex of lymph nodes

PALS of spleen

Question 21

What is MALT?

Answer 21

Mucosa Associated Lymphoid Tissue

Any lymphoid tissue located within a mucous membrane lining a tract

Question 22

Where is mucosa located and what is the benefit of MALT?

Answer 22

Walls of respiratory tract, GI, and GU tracts

Prominent near orifices, major transitions within tracts and near where trachea splits into primary bronchi

Antigens or pathogens get through epithelial lining of a tract are immediately confronted by immunocompetent lymphocytes in tissues below

Question 23

What is GALT?

Answer 23

Gut Associated lymphoid tissue

Question 24

What is BALT?

Answer 24

bronchus associated lymphoid tissue

Question 25

What are tonsils considered?

Answer 25

MALT

embedded in walls of pharynx/throat

Question 26

What is diffuse lymphatic tissue? What is its structure?

Answer 26

Least organized lymphatic tissue

Always forms within some other organ

Unorganized clusters of lymphocytes - never forms lymphatic nodules (follicles), temporary aggregations

Cells: B cells, T cells, plasma cells, monocytes/macrophages

Stroma: No capulse, reticular CT may be present to suspend and support cells

Question 27

What are solitary lymphatic nodules?

Answer 27

Isolated temporary structures and can appear, disappear, and reappear

Question 28

What are lymphatic aggregates?

Answer 28

Permanent clusters of lymphatic nodules within another organ

Question 29

What are secondary lymphatic nodules collectively called and what do they contain?

Answer 29

Peyer patches

Permanent structures in walls of ileum

Contain B cells, T cells, and macrophages

Similar aggregates in walls of appendix

Question 30

What are the 3 kinds of tonsils?

Answer 30

Palatine tonsils

Lingual tonsils

Pharyngeal tonsils

Question 31

What are the characteristics of tonsils?

Answer 31

All 3 types are MALT and contain lymphatic aggregates

Stroma: surfaces covered with epithelium and partial/incomplete CT capsules with long septa. Capsules physically protect underlying tissue and may provide some protection vs spread of tonsillar infections

Cells: B cells and T cells

Question 32

What do lymph nodes do?

Answer 32

Filter lymph - remove bacteria and other antigens or pathogens

Question 33

Afferent lymphatic vessles

Answer 33

Where lymph arrives (on convex side of node)

Question 34

Hilum of lymph node

Answer 34

Area with blood vessels and efferent lymphatic vessels (on concave side of node)

Lymph exits node via efferent lymphatic vessels

Question 35

What are lymphatic nodules?

Answer 35

Dense spherical aggregations of lymphocytes with some organization

Sites of initial immune responses

2 types - primary and secondary

Can be solitary or form aggregates

Always present in the tonsils, lymph nodes, and spleen

Question 36

What is the mantle zone and germinal center of secondary lymphatic nodules?

Answer 36

Mantle zone - smaller but mature lymphoctyes

Germinal center - most are activated B cells (many dividing to form new clones), some follicular dendritic cells (antigen presenting cell)

Germinal center site where lymphocyte clones are produced - mitotic figures

Question 37

What are palatine tonsils?

Answer 37

Located at boundary of oral cavity and oropharynx

Covered with nonkeratinized stratified squamous epithelium

Have deep crevices called tonsillar crypts (fissures)

Question 38

What are lingual tonsils?

Answer 38

Small bumps on the dorsal surface of posterior 1/3 of tongue

Covered with nonkeratinized stratified squamous epithelium

Have crypts

Question 39

What are pharyngeal tonsil?

Answer 39

Located in roof of nasopharynx

Covered with ciliated pseudostratified columnar epithelium

Has pleats (no crypts) = broader folds of surface

Question 40

What types of cells are in lymph nodes?

Answer 40

B cells

T cells

Plasma cellss

Stellate reticular cells - synthesize and secrete collagen III fibers and ground substance for ECM

Dendritic cells - antigen-presenting cells and monitor stroma for foreign substances

Macrophages - phagocytic cells, line sinuses, antigen presenting cells

Question 41

What is in the paracortex and what does it do?

Answer 41

High endothelial venules - special postcapillary venules lined by cuboidal endothelial cells, instead of the ormal simple squamous endothelial cells

Specialized venules that allow B and T cells to pass through their walls and enter lymph node tissue faster/more easily

Question 42

How do lymphocytes enter lymph nodes?

Answer 42

Enter lymph nodes from the bloodstream via HEVs in the paracortex

Most lymphocytes leave lymph nodes via efferent lymphatic vessels

Question 43

What is the flow of lymph?

Answer 43

Afferent lymphatic vessels

Subscapular sinuses

Peritrabecular sinuses

Medullary sinuses

Efferent lymphatic vessel

Question 44

What is the function and structure of thymus?

Answer 44

Primary lymphoid organ - site where T cells mature and become immunocompetent

Stroma: capsule surrounds both lobes, trabeculae partially subdivide thymus into thymic lobules, thymus lacks afferent lymphatic vessels

Parenchyma: medulla and cortex

Question 45

What are the 3 types of cells in thymic cortex?

Answer 45

1. Thymocytes
2. Macrophages
3. Epithelial reticular cells (Types I, II, and III)

Question 46

What are thymocytes?

Answer 46

Immature T lymphocytes

Question 47

What are the function of macrophages in the cortex?

Answer 47

Phagocytize any developing T cells that do not meet thymic requirements

Question 48

What is the function of epithelial reticular cells (Types I, II, and III)?

Answer 48

Form a 3D cellular framework that seals off the cortex and physically supports the thymocytes

Some are also “teachers” that present self-antigens and foreign antigens to thymocytes

Question 49

What are the cells in the thymic medulla?

Answer 49

Epithelial reticular cells (Types IV, V, VI) - seal off boundaries and form the 3D cellular framework that supports the developing T cells

Thymocytes

Some macrophages

mature T cells

Question 50

What do epithelial reticular cells?

Answer 50

Cortex: Types I, II, II - all 3 types work to create a pristine environment for the maturing thymocytes

Medulla: Types IV, V, VI

Question 51

What is is the blood-thymus barrier?

Answer 51

Ensures blood borne antigens do not get into cortical tissues where thymocytes are developing

Isolates developing thymocytes and protects them from unregulated or premature exposure to antigens circulating in blood

Creates an immunologically protected region within the thymic cortex

Increased permeability of the blood-thymic barrier or premature exposure of thymocytes to antigens results in impaired immunity

Question 52

What are the immune functions of the spleen?

Answer 52

Site of B cell and T cell proliferation

Site where dendritic cells and macrophages present antigens

Formation of antibodies that bind to antigens circulating in the blood

Site where antigens are removed from blood

Question 53

What are the hematopoietic functions of the spleen?

Answer 53

Filters cellular components of blood

Inspects RBCs - removes old/damaged RBCs from circulation

Recycles iron from destroyed RBCs

Removed old/damaged platelets from circulation

Hematopoiesis site

Question 54

What is the white pulp of the spleen?

Answer 54

Splenic nodules - lymphatic nodules that lie along the paths of central arteries, most cells are B cells

Periarterial lymphatic sheath - sheath of T cells around the central artery

Question 55

What is the red pulp of the spleen?

Answer 55

Splenic cords (cords of Billroth) - branching cords of splenic tissue and splenic macrophages monitor RBCs remove old and damaged RBCs from circulation

Splenic sinuses - blood filled sinusoidal capillaries