New answers tagged hematology
Here are some figures from Cellular and Molecular Immunology, 8th Edition: Hopefully they're helpful in some way.
Researchers have puzzled over the selective explanation for the ABO polymorphism at least back to the 1950s. Multiple lines of more recent evidence, including the very old age of the ABO polymorphism and (perhaps) multiple convergent evolution events, suggest that the ABO polymorphism is maintained by balancing selection (E.g. Saitou and Yamamoto 1997, ...
While organs are generally considered to have a single, specified function (or perhaps a group of closely-related functions), blood (the fluid inside the vessels, not the vessels themselves) has many different functions: deliver $O_2$ from lungs to cells remove waste $CO_2$ from cells to lungs respond to injury by clotting carry multiple different types of ...
Blood is considered a type of connective tissue (sometimes). However, an organ is formed of multiple different tissues. Thus, blood is a tissue, not an organ.
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