Meditation, Prefrontal Cortex and Dzogchen
From what I understand the original authors of the Tantras mapped out the system of Tsa or Nadis within the human body with their clairvoyance as a guide, and saw that each organ & gland (Pineal, Pituitary, Ovaries & Gonads, Thyroid, Thymus, Thalamus, Hypothalamus, etc.) is a junction of Nadis with its corresponding energetic center or Cakra/Chakra within the Vajra Body.
See also: The Bliss of Inner Fire: Heart Practice of the Six Yogas of Naropa
by Lama Yeshe, pages 180 and 277 of Longhcenpa's Mind in Comfort and Ease: The Vision of Enlightenment in the Great Perfection
by H.H. the Dalai Lama, and also the DVD that accompanies a book on Tsa-Lung called Awakening the Sacred Body
by Geshe Tenzin Wangyal Rinpoche (this DVD also has the Inner Refuge prayers for Qualities and Activity
related to the Chakras and mentions their corresponding Kaya), and see if you can "connect the dots".
Hint: The Higher Two Truths
(not "the two lies"
), Seven Kayas, and Seven (main) Cakras.
It is also said that individuals with an abundance of melanin
generally have less Pineal Gland calcification, so it seems that us non-melanated folks have to work harder to keep our Pineal Glands in shape (that is get to bed before midnight and have a regular sleep schedule, eat all organically grown food if possible, take herbs, Chulen, Sorig, Dhutse, etc., regularly practice Tsa-Lung or Yantra Yoga, correctly practice Karmamudra or at least follow the sexual-advice of Tibetan Medicine