To save someone else a search, HPTA is, according to Wikipedia: The hypothalamic–pituitary–gonadal axis (HPG axis) refers to the hypothalamus, pituitary gland,

To save someone else a search, HPTA is, according to Wikipedia: The hypothalamic–pituitary–gonadal axis (HPG axis) refers to the hypothalamus, pituitary gland, and gonadal glands as if these individual endocrine glands were a single entity. Because these glands often act in concert, physiologists and endocrinologists find it convenient and descriptive to speak of them as a single system.