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What are the primary lymphoid organs?
- bone marrow in mammals
- bursa or fabricius in birds
When is the thymus most active and when is its maximum development?
- most active early in life
- maximum development at puberty
What are the secondary lymphoid organs?
- lymph nodes
- other lymphoid tissue (lymphocytes distributed in bronchial and GI mucosa and peyer's patches)
Where are the Peyer's patches?
in the ileum
What do the primitive hematopoietic stem cells in bone marrow give rise to?
- lymphoid cells
- erythromyeloid cells
What do lymphoid cells give rise to?
lymphocytes (B lymphocytes and T lymphocytes)
What are B lymphocytes?
mature into plasma cells which secrete antibodies (immunoglobulins)
What are T lymphocytes?
mediate cell-mediated immune reactions
What are the cell-mediated immune reactions that T-lymphocytes mediate?
- cell lysis
- produce substances that direct cell functions
What are the erythromyeloid cells?
- megakaryocytes (platelets)
- monocytes (macrophages)
What do the precursors to T lymphocytes migrate to?
migrate to the thymus (primary lymphoid organ)
Where do the precursors to B lymphocytes go?
bone marrow (primary lymphoid organ)
What happens once T and B lymphocytes enter blood circulation?
they colonize secondary lymphoid organs (lymph nodes, spleen, etc)
How do we tell the difference between T and B lymphocytes?
- cannot be distinguished by light or electron microscopy
- can test to identify certain molecules on their cell membranes
Where do T lymphocytes mature?
in the thymus
What are the subsets of T lymphocytes?
- T helper cells
- T cytotoxic cells
- T memory cells
- natural killer cells
In normal human blood, there are about _____ as many T helper cells as T cytotoxic cells.
What happens once T helper cells are activated?
they divide rapidly and secrete small proteins called cytokines that require or assist in the immune response
What are cytokines?
a group of regulatory molecules
What do T cytotoxic cells do?
mediate killing of virus-infected or tumor cells that are recognized by the body as foreign
What are T memory cells?
- inactive clones of Ag sensitized T cells - persist long-term after an infection has resolved.
- multiply upon re-exposure to "their" antigen
- speed up the immune response the next time the Ag is encountered by the body
What are natural killer cells?
- T cells that do not recognize specific Ag
- do not require previous sensitization
- are part of the innate immunity
What are B lymphocytes?
lymphocytes that will differentiate into immunoglobulins-producing plasma cells
Which cells are the site of synthesis of immunoglobulins?
What is RER and which cells have lots of this?
- rough endoplasmic reticulum
- plasma cells
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