During the stage of exhaustion, individuals may begin to suffer depression, the suppression of their immune response, severe fatigue, or even a fatal heart attack. If the stress continues for a longer term however, the body responds with symptoms quite different than the fight-or-flight response. If a person is starving for example, the body may send signals to the gastrointestinal tract to maximize the absorption of nutrients from food. If the stress is not soon relieved, the body adapts to the stress in the second stage called the stage of resistance. The section on the adrenal medulla covers this response in more detail. Once this stress is relieved, the body quickly returns to normal. Their function is to prepare the body for extreme physical exertion. This is short-term stress, the fight-or-flight response, mediated by the hormones epinephrine and norepinephrine from the adrenal medulla via the SAM pathway. Stage one of GAS is called the alarm reaction. The body responds in different ways to short-term stress and long-term stress following a pattern known as the general adaptation syndrome (GAS).

Psychological stresses include the perception of a physical threat, a fight with a loved one, or just a bad day at school. Physical stresses include exposing the body to injury, walking outside in cold and wet conditions without a coat on, or malnutrition. Stress can be either physical or psychological or both. One of the major functions of the adrenal gland is to respond to stress. The medulla is stimulated to secrete the amine hormones epinephrine and norepinephrine. The sympathomedullary (SAM) pathway involves the stimulation of the medulla by impulses from the hypothalamus via neurons from the thoracic spinal cord. It is really an extension of the autonomic nervous system, which regulates homeostasis in the body.

The adrenal medulla is neuroendocrine tissue composed of postganglionic sympathetic nervous system (SNS) neurons. This pathway will be discussed in more detail below.

ACTH then stimulates the adrenal cortex to produce the hormone cortisol. The HPA axis involves the stimulation of hormone release of adrenocorticotropic hormone (ACTH) from the pituitary by the hypothalamus. The adrenal cortex, as a component of the hypothalamic-pituitary-adrenal (HPA) axis, secretes steroid hormones important for the regulation of the long-term stress response, blood pressure and blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation. Each region secretes its own set of hormones. The cortex itself is divided into three zones: the zona glomerulosa, the zona fasciculata, and the zona reticularis. The adrenal gland consists of an outer cortex of glandular tissue and an inner medulla of nervous tissue. View the University of Michigan WebScope at to explore the tissue sample in greater detail.

Definition of adrenal gland