Lymphoid organs Flashcards
What are two antigen presenting cells
Macrophages and dendritic cells
Central (primary) lymphoid organs
Bone marrow
thymus
production of lymphocytes
Peripheral (secondary) lymphoid organs
Lymph nodes Spleen Tonsils Peyer's patches microenvironment for interaction of lymphocytes and antigens
Aggregates of lymphoid tissue in non-lymphoid organs
Digestive system (GALT) respiratory tract urinary tract reproductive tract skin (SALT)
Recirculation of lymphocytes
From blood to lymphoid organs and back to blood
- facilitates antigen recognition, lymphocyte proliferation and differentiation
- ensures rapid response to antigens
- connects three components of the immune system– Primary/secondary/extralymphoid
B lymphocytes
Differentiate into plasma cells
humoral immunity
production of antibodies
T lymphocytes
70-80% of circulating lymphocytes
cytotoxic lymphocytes
Cell-mediated immunological responses
T-cell
against foreign cells
against bacterial or viral infected cells
against malignant cells
T-cell mechanisms of killing
Production of perforin and granzymes
induction of apoptosis
Reticular fibers
Cant be observed in H&E
reduce silver salts
composed of Type III collagen
Reticular cells
originate from mesenchyme functions -synthesize and maintain reticular fibers and ground substance -macrophage -trophic role in blood cell maturation -storage place of ferritin -antigen presentation (dendritic cells)
loose lymphoid tissue
Open meshwork of cells and fibers fixed cells (reticular cells) most numerous
dense lymphoid tissue
Denser meshwork of cells and fibers free cells (lymphocytes) most numerous
Nodular lymphoid tissue
Lymphocytes predominate
occurs in the form of spherical aggregates of cells
lack of connective tissue capsule
Primary and secondary nodules
Primary nodules
Tightly packed small lymphocytes
not under antigenic challenge
Secondary nodules
Have germinal centers
- subdivision- dark zone–dividing B lymphocytes
- light zone- non-dividing B lymphocytes and T helpers
Mantle zone- young plasma cells and memory B cells
-place of storage
Follicular dendritic cells and reticular fibers form framework
Function of Secondary nodules
- Proliferation of activated B lymphocytes occurs in dark zone
- selection of B lymphocytes occurs in light zone
- apoptosis of B lymphocytes occurs in light zone
- surviving B lymphocytes begin differentiation into plasma cells and memory B cells in light zone
- temporary storage of young plasma cells and memory B cells takes place in mantle
These appear during primary antigenic response and involute after about 4 weeks
General characteristic of lymph nodes
Blood vessels enter and leave at hilus
Efferent lymphatics leave at hilus
Connective tissue trabeculae
Provide structural support
subdivide node into incomplete compartments
Cortex
loose lymphoid tissue (sinuses)
Lymphatic nodules- may or may not have germinal centers
-contain mostly B lymphocytes
Medulla
composed of dense lymphoid tissue (medullary cords)
-populated largely by B lymphocytes and plasma cells
Medullary sinuses
Communicate with peritrabecular sinuses and efferent lymphatics
permeable walls- permit free passage of wandering cells
Flow of lymph through node
Afferent lymphatics -enter node @ multiple sites on convex surface -valves open toward node Subcapsular sinus peritrabecular sinuses medullary sinuses efferent lymphatics -leave node @ hilus -valves point away from hilus
filtration of lymph
occurs in sinuses
reticular cells are phagocytes- reticular cell failure facilitates spread of infection and/or metastases
Lymphocyte circulation
produced in germinal centers forced to periphery of nodules enter sinuses leave node by way of efferent lymphatics enter blood circulatory system by way of thoracic duct
High endothelial venules
have cell adhesion molecules
- selectins
- intergrins
- carbohydrates
- immunoglobulin superfamily members
- clever- 1
Play a role in lymphocyte recirculation
decrease in number with age
may be involved in metastasis of lymphoid malignancies
recirculation is critical to efficient immune surveillance
Permits lymphocytes to encounter antigens
facilitates communication with other leukocyte types
allows targeting of lymphocytes
paracortical zone
site of most HEVs
under thymic influence
-populated mostly by T lymphocytes
function of lymph nodes
Filtration of lymph
production and selection of B lymphocytes
Play a role in the immune response to lymph-borne antigens
Cortex of thymus
dense lymphoid tisse
lymphocytes predominate
site of thymocyte proliferation, apoptosis, and selection
Medulla of thymus
Loose lymphoid tissue
rich in epithelial-reticular cells
site of thymocyte maturation
Thymocytes
predominate in cortical regions
proliferate and undergo selection in cortex
populate T dependent regions of other lymphoid organs
Epithelial reticular cells
Originate in endodermal lining of 3rd and 4th brachial pouches not phagocytic do not manufacture reticular fibers Have a secretory function -produce polypeptides promoting the differentiation of T lymphocytes -thymopoietin provide supporting framework form hassall's corpuscles contribute to blood-thymus barrier
reticular cell of mesenchymal origin- dendritic cells
phagocytic
clean up debris resulting from T cell selection
Functions of thymus
Development of T lymphocytes
- under influence of thymosin
- sensitive to radiation and chemotherapy
supports the development of the lymphoid system
-produces thymopoietin
General characteristics of the Spleen
largest accumulation of lymphatic tissue in body
complex filter interposed in bloodstream
Red pulp of spleen
large quantity of blood
two structures
-splenic sinuses- discontinuous BM with macrophages on outside- allow free exchange btwn cords and sinuses
-splenic cords- site of destruction of RBCs, site of storage of blood
White pulp of spleen
composed of lymphoid tissue periarterial lymphatic sheath (PALS) -T dependent area Lymphatic nodules -located within the PALS -contain mostly B lymphocytes -May or May not have germinal centers
Marginal zone of spleen
junction of red and white pulp
where most arterial blood runs through
contains- lymphocytes, dendritic cells and macrophages
site of initiation of immune responses to blood-borne antigens
Pattern of blood flow through spleen
Splenic artery enters @ hilus trabecular arteries central arteries penicilli capillaries splenic sinuses red pulp veins trabecular veins splenic vein leaves the spleen @ hilus
functions of spleen
production of lymphocytes
plays role in immune response to blood-borne pathogens
destruction of RBCs- in red pulp
storage of blood
Palatine tonsils
Located in the lateral walls of the oropharynx
covered by stratified squamous epithelium
epithelium invaginated to form numerous deep crypts
surrounded by thick capsule of dense, irregular connective tissue
Pharyngeal tonsil
Located in the roof of the nasopharynx
covered by pseudo stratified ciliated columnar epithelium
presence of numerous surface folds rather than deep crypts
surrounded by a thin capsule of dense, irregular CT
Lingual tonsils
located @ base of the tongue
covered by stratified squamous epithelium
each lingual tonsil has a single large crypt
function of tonsils
Detection and response to pathogens in the oral cavity
production of lymphocytes
