How Stress Responses Impact Physiological Systems in Adverse Ways

How stress responses impact physiological systems in adverse ways

Stress: experiences that are challenging, emotionally and physically

• Hans Selye believed stress to be nonspecific- a stimulus that threatens homeostasis

• Bruce McEwan and Jaap Koolhaas believe that stress "should be restricted to conditions where an environmental demand exceeds the natural regulatory capacity of an organism"

• Stressors could be acute (car accident, sprained ankle) or chronic (ongoing sleep deprivation, arthritis)

The adaptive stress response is characterised by both behavioural and physical changes, including heightened attention and alertness and suppression of sexual and feeding behaviours. The latter lead to the conservation and/or redirection of energy e.g. oxygen and nutrients to the CNS where it is needed most for the “fight or flight” response.

General adaptation syndrome (GAS)

1. Alarm stage (6-48 hrs): modulated by adrenaline and noradrenaline

2. Resistance stage (> 48 hrs): cortisol

3. Exhaustion stage (>1-3 months): muscle wasting, atrophy of tissues of the immune system, hyperglycemia, vascular damage… etc

Endocrine- adrenal glands

Sympathetic activation leads to the production and release of the following hormones (release mediated through HPA axis):

• Glucocorticoids from the adrenal cortex (cortisol)

• Catecholamines from the adrenal medulla (adrenaline/noradrenaline)

• Mineralocorticoids from the adrenal cortex

Liver

Increased production of glucose through the actions of adrenaline and cortisol. Leading to:

• Increased serum glucose levels (hyperglycemia)

• Increased glycogenolysis and gluconeogenesis

Growth and reproduction

Are directly linked to the stress system and are both influenced by the HPA axis.

• CRH suppresses the secretion of GnRH by either direct hypothalamic stimulation or via stimulation of POMC peptide secreting neurons.

• Stress-induced suppression of GH suppression (reversible)

o E.g. Psychosocial dwarfism (PD): severe childhood or adolescent store stature or delayed puberty due to emotional deprivation or psychological harassment

o Patients have low GH secretion and dysfunctional thyroid axis

o Decreased GH secretion is reversible after child is no longer exposed to that environment

Thyroid

• Stress system suppresses the secretion of TSH and decreased conversion of T4 (relatively inactive) to T3 in peripheral tissues → suppression thyroid axis function

Musculoskeletal