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What are the organs of the lymphoreticular system?

Thymus, lymph node, mucosa-associated lymphoid tissue (MALT), spleen


The immune system provides highly specific responses to what specifically?

To antigens with the destruction of the antigen


What was the original definition of an antigen?

Any molecule that binds specifically to an antibody


What does the term antigen now also refer to?

Any molecule or molecular fragment that can be bound by a major histocompatability complex (MHC) and presented to a T helper cell


What is the function of a MHC - major histocompatability complex?

The function of MHC molecules is to bind peptide fragments derived from pathogens and display them on the cell surface for recognition by the appropriate T cells.


What are the the types of lymphocytes?

B lymphocytes and t lymphocytes


What is the function of the b lymphocytes?

To produce antibodies


What is the function of the t lymphocytes?

They have several subtypes and act as suppressor cells, cytotoxic cells and helper cells


What are antigen presenting cells?

They include macrophages and the b lymphocytes control the activation of the t cells. An antigen-presenting cell is a cell that displays antigen complexed with major histocompatibility complexes (MHCs) on their surfaces


Why are the b lymphocytes called b lymphocytes?

Because they are formed from a stem cell, into a pre-b cell and the pre-b cell matures into a fully functional b cell in the red bone marrow


Why are the t lymphocytes called t lymphocytes?

Because they are formed from a stem cell into a pre t cell in the red bone marrow. but then the pre-t cell matures into a fully functional t cell in the thymus


Roughly what percentage of white blood cells in circulation are lymphocytes?



The number of lymphocytes in circulation increase in response to what?

In response to a viral infection


How would you describe lymphocytes under a microscope

they have a round/oval nuclei with dense chromatin and nucleoli which are not usually visible and often very little cytoplasm


How does the size of a lymphocyte compare to the size of red blood cells?

red blood cells are about 7 microns in diameter - about the size of a lymphocyte nucleus


What are the two types of lymphocytes?

t and b


what are the three types of t lymphocyte?

t helper cells, cytotoxic t cells and suppressor t cells


what do t helper cells do

they help other lymphocytes perform functions


what do cytotoxic t cells do

they kill virally infected and malignant cells


what do suppressor t cells do

they switch off the immune system when the stimulating antigen is removed


what do b lymphocytes do

they produce antibodies following maturation to plasma cells


what is a plasma cell

a fully differentiated B-lymphocyte (white blood cell) which produces a single type of antibody.


what types of cells are included in the antigen presenting cells category

macrophage monocyte type cells and dendritic cells


what do antigen presenting cells do?

the antigen is taken up by the apc and processed. processed antigen is then bound to a major histocompatability complex and the mhc-peptide complex is exposed to the outside world


how would you describe the dendritic cell morphology

finger like projections


what are the four organs of the lymphoid system

thymus, lymph nodes, mucosa-associated lymphoid tissue, spleen


what is the thymus

a flattened lymphoid organ


where is the thymus located

in the upper anterior mediastinum and lower part of the neck


when is the thymus most active and when does it undergo involution

most active during childhood, heaviest at puberty and then undergoes involution


what does the thymus consist of

its got a right and left lobe, its got septae and its made of lobules