The bodies reponse to stress - Acute stress

Acute stress - The sympathomedullary pathway 

Immediate stressors arouse the autonomic nervous system (ANS). It is called autonomic because it governs itself. This system is necessary because some bodily functions, such as your heartbeat, might not work as well as they need to if you had to think about them. The ANS is divided into the sympathetic branch and the parasympathetic branch. The SNS arouses an animal to be ready for fight or flight, the parasympathetic branch returns the animal to a state of relaxation. A key part of this response is the sympathetic adrenal medullary system (SAM); together the SNS and SAM system make up the sympathomedullary pathway.

The SNS:

Neurons from the SNS travel to virtually every organ and gland within the body, preparing the body for the rapid action necessary when an animal is under threat. Responses include an increase in heart rate, blood pressure and cardiac output, increased pupil size and metabolic changes such as the mobilisation of fat and glycogen in the bloodstream. Noradrenaline is released by the SNS to activate these internal body organs.

The SAM system:

At the same time that the SNS is activated, the SAM system alerts the animal through the release of adrenaline into the bloodstream where it is transported rapidly throughout the body to prepare the animal for fight or flight. The SAM system is regulated by the SNS and also the adrenal medulla.

The adrenal medulla:

Each adrenal gland has two distinct zones, the adrenal medulla, in the centre of the gland and the adrenal cortex around the outside. Neurons of the SNS travel to the medulla, so that when it is activated it releases adrenaline into the bloodstream. Once in the blood, adrenaline has widespread effects on the body's physiological systems e.g. boosting the supply of oxygen and glucose to the brain and muscles, and suppressing non-emergency bodily processes such as digestion.