Lymphoid Organs :
Lymphoid organs refer to the anatomical aspects of the
immune system, whereas immunity refers to the
functional aspect of lymphoid organs. Lymphoid organs
are classified as:
1-Primary(generative) lymphoid
organs: Where
lymphocytes first express antigen receptors and attain
phenotypic and functional maturity. The major primary
lymphoid organs are thymus and bone marrow.
2-Secondary(peripheral) lymphoid organs: Where
lymphocytes respond to foreign antigens. These organs
include spleen, lymph nodes, and mucosa-associated
lymphoid tissues(MALT).
Lymphoid Organs :
Lymphoid organs refer to the anatomical aspects of the
immune system, whereas immunity refers to the
functional aspect of lymphoid organs. Lymphoid organs
are classified as:
1-Primary(generative) lymphoid
organs: Where
lymphocytes first express antigen receptors and attain
phenotypic and functional maturity. The major primary
lymphoid organs are thymus and bone marrow.
2-Secondary(peripheral) lymphoid organs: Where
lymphocytes respond to foreign antigens. These organs
include spleen, lymph nodes, and mucosa-associated
lymphoid tissues(MALT).
Thymus:
The thymus is the site of T cell maturation and
education (learn to discriminate between self and nonself antigens) by process positive and negative selection
.The lymphocytes (thymocytes) are T cells at various
stages of maturation .The most immature T cells enter
the thymic cortex through the blood vessels .Maturation
begins in the cortex ,then thymocytes migrate toward the
medulla ,so that the medulla contains mostly mature T
cells. After puberty, Thymus atrophies.