gland, (kokuji)
腺 centers on a biological gland: an organ that secretes substances. As a kokuji created in Japan, it has no extended abstract meanings.
腺 is a Japanese kokuji created in the Edo period for medical terminology. It combines ⺼ (flesh/body part) with 泉 (spring/fountain), suggesting a body part that secretes fluid like a spring.
The flesh radical ⺼ indicates a body part, and 泉 is a spring. Picture a gland as a spring inside the body that releases fluids.
For セン, imagine a gland sending out secretions: send -> セン, and the gland sends fluids like a spring.
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thyroid (gland)
prostate (gland)
gland
mammary gland
tear gland; lacrimal gland
tonsil
sweat gland
thymus
gonad; sexual gland
adenoma
apocrine sweat gland
apocrine gland
eccrine gland
Cowper's gland; bulbourethral gland
Cowper's fluid; pre-ejaculate; pre-cum
sinus gland
Skene's gland (possibly responsible for female ejaculation)
Bartholin's glands
meibomian gland
Mehlis' gland