Here's why:

* Endocrine glands produce and secrete hormones directly into the bloodstream, where they travel to target organs and tissues.

* Parathyroid glands produce parathyroid hormone (PTH), which plays a crucial role in regulating calcium levels in the blood.

While the parathyroid glands are located near the thyroid gland in the neck, they are functionally distinct and belong to the endocrine system.