A while ago (in this post about Reishi mushroom) I wonder/mused about why the thymus gland loses most of its mass by the time we turn age 7 or 8, given that it is the central tenet of the immune system. During this weekend’s endocrine system workshop with Matthew Wood, at Mary Pat Palmer’s Philo School of Herbal Energetics, I finally found out why. Matthew explained to us that the thymus gland is relatively gigantic in the body of babies and young children because its job is to establish the immune system in early life, and that this establishing is completed by age 7. It is only after the thymus has done its job that it shrivels down to about a quarter of its original size. The thymus remains an important part of the immune system after this initial stage, continuing to produce T cells and macrophages and such when we need them, but its foundational building work has been completed.
Matthew also explained that this establishing of the immune system is a process of discerning between what is ourselves and what is not ourselves, because of course the immune system responds to threats, and we cannot know what constitutes a threat until we know what belongs in our bodies and what does not. By helping us discern and establish the boundaries that make us who we are, the thymus also plays a role in self-identity, which is largely established by age 7 or 8. (Strangely, at dinner the night before I had been talking with two friends about their first memories of having a sense of self, and that both of them felt this happening to them at around age 7. A most bizarre prefiguring/coincidence, even moreso to me because I don’t have any kind of memory like this, and sometimes think I am still 95% cosmos.) The thymus lives on top of the heart, resting on the pericardium, which is the protective membrane that surrounds the heart. Matthew pointed out that the Heart in astrology is the Self – it is who you are. And the Heart in Chinese medicine is the body’s Emperor, where the quality of Spirit/Shen lives (which in Chinese medicine constitutes all the intangible parts of yourself, so also carries the connotation of personality and self-identity). So it completely makes sense that the thymus, so intimately connected to the Heart, has this function of establishing self-identity.
I am so comforted to know the mystery of the incredible shrinking thymus. Thank you Matthew!