Thymus, Bone Marrow: Immune System development

[regeneration]

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I'm a bit confused as to how development/differentiation works:

All blood cells "arise" from the bone marrow, but T-Cells differentiate in the Thymus while B-cells remain and differentiate in the bone marrow? Other WBCs reside in the spleen and lymph nodes in the lymph?

Can someone clarify for me where things are arising vs. maturing vs. where they are being stored, and how the thymus, bone marrow, spleen, and lymph nodes come into play?

 

[Trayshawn]

Correct me if I'm wrong but...

I believe all blood originates in the bone marrow. Thats where hematopoietic stem cells exist.
Immature T cells migrate to the thymus for maturation. Everything else matures in the bone marrow. After maturation, they all enter circulation. Many of them them reach lymph nodes (through the lymphatic system) where they act kind of like customs at an airport for whatever tries to pass through there. Both B cells and T cells (and all the other WBCs like NK cells, dendritic cells, nuetrophils, eosinophils etc...) can atleast in part be found in those lymph nodes. The spleen is pretty much just one big lymph node.

 

[image187]

Correct me if I'm wrong but...

I believe all blood originates in the bone marrow. Thats where hematopoietic stem cells exist.
Immature T cells migrate to the thymus for maturation. Everything else matures in the bone marrow. After maturation, they all enter circulation. Many of them them reach lymph nodes (through the lymphatic system) where they act kind of like customs at an airport for whatever tries to pass through there. Both B cells and T cells (and all the other WBCs like NK cells, dendritic cells, nuetrophils, eosinophils etc...) can atleast in part be found in those lymph nodes. The spleen is pretty much just one big lymph node.

more or less correct as far as lymphocyte maturation. But other immune cells differentiate and mostly mature in the bone marrow and then end up fully maturing in the peripheral circulation (e.g. macrophages come from precursor monocytes out in the peripheral tissues, etc ... )

 

[theCLE]

Cool fact: less than 10% of T cells leave the thymus after maturation/receiving CD4 or 8- because these are the only ones that have the correct MHC to actually help out the immune system. Also, the thymus destroys cells that react to self. (all probably irrelevant to mcat)