Simplify the expression 
.
Definitions:
Enamel
The hard, outermost layer of a tooth that protects against decay and is the hardest substance in the human body.
Photomicrograph
An image taken using a microscope to show a magnified view of a tiny object.
Duodenum
The first section of the small intestine immediately beyond the stomach, responsible for the initial breakdown and absorption of nutrients.
Esophagus
The muscular tube that connects the throat (pharynx) with the stomach, responsible for moving swallowed food and liquids.
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