In this blog, we will see how the stress affects the body and how is the complete stress response brought about.

The pathways and consequent changes that are brought about by the stress are collectively known as the stress response.

What exactly is this Stress Response?

Firstly, Stress is a biological and psychological response, which is experienced on encountering a threat.

A stressor is the stimulus (or threat) that causes stress, e.g. exam, divorce, death of loved one, moving house, loss of job.

A stressor can activate the hypothalamus, which is in charge of the stress response. On activation hypothalamus sends signals to two other structures: the pituitary gland, and the adrenal via sympathetic nervous system.

  • The long term stress responses are regulated by the Hypothalamic Pituitary-Adrenal (HPA) system and
  • The short-term responses (The Fight or Flight Response) are produced via the Sympathomedullary Pathway (SAM).

1. The Hypothalamic Pituitary-Adrenal (HPA) System (Long term Response)

Stress causes hypothalamus to secrete corticotrophin releasing hormone (CRH). This stimulates the anterior pituitary to secrete adrenocorticotropin hormone (ACTH) into the systemic circulation. This, induces the adrenal glands to synthesize and secrete glucocorticoids.

The Hypothalamic Pituitary-Adrenal (HPA) System

Cortisol has a number of functions including releasing stored glucose from the liver (for energy). Hence it helps the body to maintain steady supplies of blood sugar and cope with prolonged stressor.

2. Sympathomedullary Pathway (SAM) (Short term/ Fight or Flight Response)

The hypothalamus also activates the adrenal medulla. The adrenal medulla is part of the autonomic nervous system (ANS). The adrenal medulla secretes the hormone adrenaline which prepares the body for a fight or

Adrenaline lead to the arousal of the sympathetic nervous system and reduced activity in the parasympathetic nervous system. Adrenaline creates changes in the body such as decreases (in digestion) and increases (sweating, increased pulse and blood pressure). Once the ‘threat’ is over the parasympathetic branch takes control and brings the body back into a balanced state. No ill effects are experienced from the short-term response to stress and has survival value in an evolutionary context.

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Psychoneuroimmunology, The Interface Between Behavior, Brain, and Immunity. Steven F. Maier, Linda R. Watkins, and Monika Fleshner. December 1994, American Psychologist. Vol. 49. No. 12, 1004-1017.

The energetics of immunity: a neuroendocrine link between energy balance and immune function. Gregory E. Demas. Hormones and Behavior 45 (2004) 173–180.

Evolutionary Origins and Functions of the Stress Response. (2000) Randolph M. Nesse and Elizabeth A. Young. Encyclopedia of Stress. Volume 2. 79-84