Stress Response

What is the stress response?

This is the body's response to any external or internal threat (i.e. stress) that it receives. It involves three phases:

   1.   Alarm Phase

The alarm phase involves the high activity of the sympathetic nervous system (fight or flight). It is when norepinephrine and epinephrine are released, as well as glucocorticoids from the zona fasiculata. It results in:

• Decreased digestion
• Decreased urine production
• Increased heart rate
• Increased sweating
• Increased respiratory rate
• Changes in blood circulation
• Mobilisation of glucose stores

   2.   Resistance Phase

The resistance phase is when the stress remains for more than a few hours. It involves the use of alternative energy stores for organs, reserving glucose for the nervous system. The release of glucocorticoids and thyroid hormone dominates in the resistance phase, but NE and E are still released from the adrenal medulla. Glucagon is released also from the pancreas. This has the following effects:

• Conservation of glucose for NS
• Mobilisation of lipids and amino acids for organ energy supply
• Increase in blood glucose concentration
• Conservation of salts and water, loss of K+ and H+

   3.    Exhaustion Phase

This is when the resistance phase lasts from weeks to months. It involves:

• Organ failure
• Homeostatic regulation breaks down
• Aldosterone is released to conserve Na+ but secrete K+ (lack of K+ damages organs)
• Exhaustion of lipid reserves
• Inability to produce glucocorticoids
• Failure of electrolyte imbalance