| Definition of Stress | In what way does modern life contribute to stress | Effects of stress on the human body |
The human body has evolved to react effectively to dangerous situations. Stress results when the behavioural response (“flight or fight”) is suppressed because it is not deemed acceptable in modern society. Regardless of conscious suppression or social conditioning, situations that are sub-consciously perceived as dangerous will trigger automatic responses through two mechanisms: the nervous system and the endocrine system.
The nervous system relays electrochemical signals from sensory nerves to the brain, which determines that a dangerous situation is present and sends signals via the autonomic sympathetic nervous system to other systems in the body to react to the danger. The transmission of signals through nerves is almost instantaneous and allows for very rapid reactions to threatening situations. However the systems of the body soon become acclimatised to rapid nerve signals, so if the threat of danger persists, the hormones of endocrine system continue stimulating the body.
The organs of the endocrine system that are activated during threatening situations are the hypothalamus, the pituitary gland and the adrenal glands. The hypothalamus, in the brain, detects a dangerous situation and sends a nervous signal to the pituitary gland. The pituitary gland releases adrenocorticotropic hormone (ACTH) into the blood. When the ACTH reaches the adrenal glands adrenalin and noradrenalin are released into the blood by the adrenal medulla.
The effects of stimulation by the sympathetic nervous system and the adrenal hormones are similar and ensure that extra oxygen and glucose is made available to the organs which will respond directly to the danger: the brain, the skeletal muscles and the heart. Circulation is increased through dilation of the blood vessels and increased blood pressure. Breathing becomes more rapid and shallower. In the liver cortisol converts glycogen to glucose, which is released into the blood. The digestive system is shut down and blood is diverted away from the skin and stomach. Urine and faeces are excreted which lighten the body.
When the threat has been resolved (or perceived to be resolved) the body stops producing ACTH which stops production of adrenalin and noradrenalin. The parasympathetic autonomic nervous system sends signals to the organs that reverse the action of the sympathetic nervous system. Gradually the body calms down and returns to homeostatis.
If the stressful condition is not resolved quickly (and this can often happen in modern times as neither fight nor flight is an appropriate response) the adrenal glands increase their output of the hormone cortisol. This releases fatty acids into the blood to provide extra reserves of energy, but also has the effect of suppressing the immune system, leaving the person susceptible to a wide range of ailments that are the recognised signs and symptoms of stress. Unless the body is regularly allowed to relax and undo the build up of tension, the cumulative effect of much small stimulation can result in exhaustion and serious long-term illness.