stress physiology

Once the adrenal switch is thrown growth systems are shut down and self protection is prioritised. Negative emotions take over. Blood supply shuts down to the deliberating front of the brain and viscera and is transferred to the musculature, lungs and the sensory, reactive rear of the brain. This fight/flight response activates the body for extreme physical activity strength and endurance.

The sympathetic nervous system (SNS)
The “fight-flight” response of the SNS prepares the body for action in contrast to the “rest and digest” parasympathetic nervous system (PNS). The body cannot be fully in both states at once.

The digestive system slows and the pituitary gland and brain secrete endorphins to reduce pain. After accidents or injury we usually feel little discomfort in the heat of the moment. Long term maintenance processes like blood flow through the digestive system are reduced or shut down and short-term emergency processes like blood flow to the muscular system are activated.

adrenal glands
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..

•

Increases the hormone glucagon, 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 can contribute to cardiovascular disease, diabetes, anxiety and insomnia.

•

Liver and spleen are affected

•

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

•

Decreases blood clotting time.

•

Inhibits tears and digestive secretions. Butterflies in the stomach

•

shuts down digestion

•

shuts down sexual function – inhibits lubrication/erection.

•

Relaxes the bladder.

•

Dilates pupils.

•

Increases sensory alertness and reactive rear brain mental activity.

•

Decreases front brain deliberative activity.

•

Increases blood pressure.

•

Increases respiration rate. Breathing becomes shallower or breathe in gulps.

•

Increases sweating. Hands feel cold and clammy.

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

cortisol
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.

When the brain perceives something stressful, within a second it sends cortiocotropin-releasing hormone (CRH) to the pituitary, which within five seconds sends a hormone to the adrenals which immediately puts out 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 axis, depending on the individual. Over activation of the HPA axis may result in increased and sustained levels of the stress hormone cortisol.

Stress promotes excessive pursuits 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.


copyright (C) John Brasted 2008
updated 06/11/11