What body cell last the Longest and turns over the least?

The cells of the nervous system. Particularly, the hormonal since they are kept in neuronal vesicles, they can last up to ten times longer than those of neurotransmitters.

There are some cells that last a whole lifetime.

This has been a subject of recent research, with only just recently reliable methods for calculating the ages of cells are becoming available.

Some early results of the research are written in summary here:
Your Body Is Younger Than You Think - New York Times

Quote:

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"About the only pieces of the body that last a lifetime, on present evidence, seem to be the neurons of the cerebral cortex, the inner lens cells of the eye and perhaps the muscle cells of the heart. The inner lens cells form in the embryo and then lapse into such inertness for the rest of their owner's lifetime that they dispense altogether with their nucleus and other cellular organelles."

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