Lymph Tissues and Organs Flashcards
What are the 3 main lines of defense of the immune system?
Protective surfaces
Innate immune system
Adaptive immune system
How does the immune system use protective surfaces?
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
What is the innate immune system?
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
What is the adaptive immune system?
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)
What are B lymphocytes?
Humoral response - cells use antibodies to recognize antigens
What are T lymphocytes?
Cellular response - cells recognize antigens directly
Parenchyma
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
Stroma
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
What is the main site of inflammatory and immune response in tissues?
CT of the stroma
What is the lymphoid system?
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
What are lymphoid organs?
Bone marrow
Thymus
Lymph nodes
Spleen
Various types of mucosa-associated lymphoid tissue
What are primarily (central) lymphoid organs?
Organs where lymphocytes differentiate, become educated and learn to distinguish self from not self
Bone marrow and thymus
What are secondary (peripheral) lymphoid organs?
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
What do we also classify lymphoid tissues based on, beside organs?
Organization - diffuse vs. nodular
Where do lymphocytes differentiate, develop, and mature to become B lymphocytes (B cells)?
Bone marrow
How does bone marrow function as a primary lymphoid organ?
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
What can clones do when a B cell is activated?
Clones can synthesize an Ig with same antigen specificity
Most clones mature into plasma cells
What do plasma cells make?
lots and lots of antibody (Ig)
What does the thymus do as a primary lymphoid organ?
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)
Where do T cells going after being released from thymus?
Thymus dependent secondary lymphatic tissues
Paracortex of lymph nodes
PALS of spleen
What is MALT?
Mucosa Associated Lymphoid Tissue
Any lymphoid tissue located within a mucous membrane lining a tract
Where is mucosa located and what is the benefit of MALT?
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
What is GALT?
Gut Associated lymphoid tissue
What is BALT?
bronchus associated lymphoid tissue
What are tonsils considered?
MALT
embedded in walls of pharynx/throat
What is diffuse lymphatic tissue? What is its structure?
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
What are solitary lymphatic nodules?
Isolated temporary structures and can appear, disappear, and reappear
What are lymphatic aggregates?
Permanent clusters of lymphatic nodules within another organ
What are secondary lymphatic nodules collectively called and what do they contain?
Peyer patches
Permanent structures in walls of ileum
Contain B cells, T cells, and macrophages
Similar aggregates in walls of appendix
What are the 3 kinds of tonsils?
Palatine tonsils
Lingual tonsils
Pharyngeal tonsils
What are the characteristics of tonsils?
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
What do lymph nodes do?
Filter lymph - remove bacteria and other antigens or pathogens
Afferent lymphatic vessles
Where lymph arrives (on convex side of node)
Hilum of lymph node
Area with blood vessels and efferent lymphatic vessels (on concave side of node)
Lymph exits node via efferent lymphatic vessels
What are lymphatic nodules?
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
What is the mantle zone and germinal center of secondary lymphatic nodules?
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
What are palatine tonsils?
Located at boundary of oral cavity and oropharynx
Covered with nonkeratinized stratified squamous epithelium
Have deep crevices called tonsillar crypts (fissures)
What are lingual tonsils?
Small bumps on the dorsal surface of posterior 1/3 of tongue
Covered with nonkeratinized stratified squamous epithelium
Have crypts
What are pharyngeal tonsil?
Located in roof of nasopharynx
Covered with ciliated pseudostratified columnar epithelium
Has pleats (no crypts) = broader folds of surface
What types of cells are in lymph nodes?
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
What is in the paracortex and what does it do?
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
How do lymphocytes enter lymph nodes?
Enter lymph nodes from the bloodstream via HEVs in the paracortex
Most lymphocytes leave lymph nodes via efferent lymphatic vessels
What is the flow of lymph?
Afferent lymphatic vessels
Subscapular sinuses
Peritrabecular sinuses
Medullary sinuses
Efferent lymphatic vessel
What is the function and structure of thymus?
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
What are the 3 types of cells in thymic cortex?
- Thymocytes
- Macrophages
- Epithelial reticular cells (Types I, II, and III)
What are thymocytes?
Immature T lymphocytes
What are the function of macrophages in the cortex?
Phagocytize any developing T cells that do not meet thymic requirements
What is the function of epithelial reticular cells (Types I, II, and III)?
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
What are the cells in the thymic medulla?
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
What do epithelial reticular cells?
Cortex: Types I, II, II - all 3 types work to create a pristine environment for the maturing thymocytes
Medulla: Types IV, V, VI
What is is the blood-thymus barrier?
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
What are the immune functions of the spleen?
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
What are the hematopoietic functions of the spleen?
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
What is the white pulp of the spleen?
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
What is the red pulp of the spleen?
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
