Within a second of the brain perceiving something stressful, it sends cortiocotropin-releasing hormone (CRH) to the pituitary, which within five seconds sends a hormone to the adrenals which immediately puts cortisol into the blood stream. When the stressor is removed, cortisol levels drop and the body returns to normal activity.

The effects of stress hormones tend to accumulate. Chronic stress can cause either an over activation or an under activation of the HPA ( hypothalamic-pituitary-adrenal) axis, depending on the individual. Over activation of the HPA axis may increase long term levels of the stress hormone cortisol.

The sympathetic nervous system (SNS)
The parasympathetic nervous system maintains a resting digesting state.The Sympathetic Nervous System (SNS) activates the body for extreme physical activity, strength and endurance (“fight or flight”). The body cannot be in both states at once.

Long term maintenance processes like blood flow through the digestive system are reduced or shut down. Blood flow to the deliberating front of the brain and viscera diminishes and is increased to the musculature, lungs and the sensory, reactive rear of the brain.

The pituitary gland and brain secrete endorphins so in the heat of the moment after injury we feel less pain.

adrenal glands
Once the adrenal switch is thrown growth systems close down and self protection is prioritised. Active negative emotions take over.

The brain components of the sympathetic nervous system connect directly through the spinal chord to the adrenal glands which trigger the secretion of the stress hormones adrenaline and noradrenaline into the blood stream preparing the body for action. People who cannot secrete cortisol or adrenaline have difficulty mobilising to even run up a flight of stairs.

Beta receptors on the heart muscle trigger a faster and stronger beat.

Receptors in the walls of the coronary arteries, dilate them allowing more blood to the heart..

The hormone glucagon increases, which mobilises glucose stored in muscle and liver as glycogen providing immediate increase in energy for immediate action. If this is not used it causes fluctuations of blood sugar levels, which contributes to cardiovascular disease, diabetes, anxiety and insomnia.

Liver and spleen are affected

Peripheral vasoconstriction and muscle tone ncreases. Blood flows away from the hands and feet and metabolic organs to the heart lungs and muscle. Muscles tense and hands and feet become colder.

Blood clotting time decreases.

Tears and digestive secretions are inhibited t. Butterflies in the stomach

Digestion slows or stops.

Sexual function shuts down – lubrication and erection are inhibited.

Bladder relaxes.

Pupils dilate.

Sensory alertness and reactive rear brain mental activity increases.

Front brain deliberative activity decreases.

Blood pressure increases.

Respiration rate increases. Breathing becomes shallower or breathing is in gulps.

Sweating increases. Hands feel cold and clammy.

If stress continues long enough adrenal fatigue sets in and compromises the body’s ability to respond to stress.

Mobilises for endurance and sets the body up for long-term stress. Activated through the hypothalamic-pituitary-adrenal axis (HPA-axis).

Stimulates the production of extra nutrients such as glucose and fatty acids increasing blood glucose levels.

Suppresses the immune system - attaches to receptors on immune system cells, depressing the cell’s ability to function (on the other hand a short burst of stress may stimulate the immune system)

Prevents the formation of T lymphocytes (white blood cells that attack viruses and foreign protein),

May destroy some lymphocytes.

Inhibits the release of interleukins and interferons, essential components of the immune systems.

Breaks down tissues

Activates an enzyme that promotes fat storage in fat cells (adipocytes). There are more cortisol receptors in intra-abdominal adipocytes, so fat accumulates at the waist.

Increases insulin and decreases female hormones.

Stress promotes excessive pursuit of rewards like binge eating and drug addiction because high levels of the stress hormone corticotropin-releasing factor (CRF) in the nucleus accumbens amplifies rewards cues.