Adrenal gland
The adrenal gland was a part of the endocrine system that regulated the body's stress responses and produced adrenaline and cortisol.

According to Dr. Phlox in 2151, the scent of the Nausicaan adrenal gland gave off a fragrance not unlike the scent of Ensign Socorro after performing exercise. () 

In 2266, navigator Bailey mentioned to Spock that his raising of his voice did not indicate that he was scared, but that he just had a Human thing called "an adrenaline gland". Spock remarked that it was most inconvenient and suggested that he have his removed. ()

The parasitic beings that infested Starfleet Command in 2364 used their tendrils to stimulate the adrenal glands of their Human victims, generating great strength. ()

One of The Doctor's planned "Hints for Healthful Living" segments on A Briefing with Neelix in 2372 was titled "Uncovering the hidden mysteries of the adrenal gland." When Neelix postponed his segment two times, The Doctor was willing to let go of the adrenal gland topic in favor of "The Klingon glottis, friend or foe?". ()

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Glands