The hypothalamus-pituitary axis and stress
How the different glands of the endocrine system can have an effect on on another.
Just as we may travel the same path or road many times day after day, consider that the body orchestrates the same journey for our hormones to travel along day after day. This internal information highway is known as the hypothalamus-pituitary axis. Metaphorically let’s consider the hypothalamus as home base, it’s the number one destination along our internal circuitry pathway. Just as we always return back home, information is always fed back to the hypothalamus ‘home’ and it responds accordingly. If we think of our homes as the place we restore our sense of balance and harmony in life, the hypothalamus is also looking to maintain consistent balance, or homeostasis, physiologically. The hypothalamus is constantly receiving information via feedback loops in order to take appropriate action, either to stimulate or inhibit certain hormones.
The hypothalamus is located at the base of the brain and it’s quite small, almond size-ish, yet plays a massive role in co-ordinating hormone release/ function and overall operation of major physiological processes. The hypothalamus acts as the connecting friend between the endocrine and nervous system, it co-ordinates functions that both systems are involved in, e.g.; stress response, mood, emotional state, sleep cycles, reproduction, libido, thirst and appetite, digestive secretions, metabolism and weight control, body temperature, blood pressure and heart rate. Very close by in the brain lives the pituitary gland which is pea-sized, also tiny. Think of the pituitary as the good friend or family member that lives just around the corner, that you rely on to always be there for you. Once receiving a message from the hypothalamus via neuro-hormones, the pituitary gland releases its own set of hormones into the bloodstream and targets specific cells and other glands of the endocrine system.
The hormones released by the pituitary include:
· Adrenocorticotropic hormone, which stimulates the adrenal glands to secrete steroid hormones, principally cortisol.
· Growth hormone, which regulates growth, metabolism and body composition via acting on the liver, bones, adipose tissue (fat) and muscle. It also has an effect on sleep and memory.
· Luteinising hormone and follicle stimulating hormone, also known as gonadotrophins. They act on the ovaries or testes to stimulate sex hormone production, and egg and sperm maturity.
· Prolactin, which stimulates milk production in the mammary glands
· Thyroid stimulating hormone, which stimulates the thyroid gland to secrete thyroid hormones.
Understanding these hormones and the glands they correspond to gives rise to 3 major organ destinations, of the endocrine system, that all feed back into the hypothalamus-pituitary (HP) axis:
- HPA axis; this highway channel feeds into the destination of the adrenal glands, this is our stress response and fight/ fight pathway
- HPT axis; this feeds information into the thyroid gland and controls our thyroid function (metabolism, body temperature, mood, sleep, and heart rate)
- HPG axis; this connects into the gonads, specifically the testes for men (HPT) and ovaries for women (HPO) and controls the menstrual cycle for women and for both sexes libido, fertility and reproductive health
We see that two main destinations on all these axis, are the hypothalamus and pituitary. Because of the shared hypothalamus-pituitary function between all three, when one gland and it’s corresponding axis is thrown out of balance, there can be a detrimental effect on the others. Chronic stress and trauma, related to hyper-stimulation or over-activity of the HPA axis, also adversely affects thyroid function and the HPT axis as well as reproductive and menstrual health of the HPO axis. Research has shown that chronic stress and an increase of cortisol from the adrenal glands can create an over or under function of the thyroid gland, causing hypo/hyper-thyroidism, as well as the disruption of the ovaries which releases estrogen and progesterone, creating menstrual dysfunction, and in men disruption of the testes and testosterone inhibition.
Consider then that the underlying root cause and treatment focus for issues around fertility, menstrual health and thyroid dysfunction comes back to chronic stress and dysfunction of the HPA axis.