Testing Your Stress Levels
Understanding the Science behind the Adrenal Stress Response
Understanding the rudimentary aspects of the stress response requires knowing a few components of anatomy and hormone physiology. The basic components we will discuss are the adrenal glands and several hormones made in the adrenals, as well as they hypothalamus and pituitary glands and some of the hormones they secrete.
The Adrenal Glands
The adrenal glands are small (5 grams or about the size of 2-3 pinto beans) glandular tissues lying atop each of the kidneys. The inner portion, called the medulla, secretes epinephrine (adrenaline) and norepinephrine and is an extension of the sympathetic nervous system. The larger outer portion, called the cortex, is responsible for secreting various steroid hormones. We will consider only the cortex and its hormones in this particular discussion.
Of the nearly 30 steroid hormones produced by the adrenal cortex, the principal ones include aldosterone (a mineralocorticoil), cortisol (a glucocorticoid) and various sex hormones and their precursors (DEHA, androstenedione). The ineralocorticoids play an essential role in regulation potassium and sodium levels, water balance and, consequently, blood pressure. DHEA and its metabolites have diverse effects during the lifecycle of the individual. Finally, there is the glucocorticoid, cortisol, a key player in the adrenal glands stress response mechanism.
Cortisol is tightly regulated by feedback mechanisms in both the hypothalamus and the pituitary glands, where the original hormonal signals trigger its production. As in other systems, the hypothalamus gland, located at the base of the brain, begins the process by secretion corticotropin-releasing factor (CRF0 in response to a variety of “stressors.” CRF then triggers the anterior pituitary to release adrenocorticotropic hormone (ACTH), which travels through the blood until it reaches the adrenal glands where it induces the adrenal cortex secretion of cortisol. In turn, increasing cortisol levels slow down the production of both CRF and SCTH from their respective glands. This whole circuit is referred to as the hypothalamic-pituitary-adrenal (HPA) axis or system. Similar systems also regulate the thyroid hormones (HPT axis) and ovarian hormone production (HPO axis). Not surprisingly, stress will also cause an imbalance in thyroid and female hormone cycles as well.
Normal functioning of the HPA is known to have three attributes. First, when the system is unstressed there is a regular circadian rhythm of activity. The rhythm results in the highest cortisol levels shortly after awakening (7-8 a.m.) and progressively falling until they are lowest during the first several hours of sleep. A healthy HPA axis should have a circadian rhythm, as well as appropriate total daily secretion of cortisol. The second function of the HPA is proper feedback loops coordination. As mentioned previously, increasing amounts of cortisol should be able to shut down ACTH and CRF production, and hence reduce serum cortisol levels. Clinically appropriate challenges with corticosteroids like dexamethasone can be used to test this feedback loop. Positive tests for pituitary and adrenal cortex functions can also be performed by giving CRF or ACTH and measuring cortisol responses.
Third, and most importantly for us, is the fact that various stressors can stimulate the HPA and many can do so in a way that overrides both the circadian and feedback controls. It is this well-known phenomenon that allows the functional testing of the HPA system to give us a glimpse at the effects of stress (both acute and chronic) on the health of an individual.