How Stress Responses Impact Physiological Systems in Adverse Ways

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Muscle tension

Migraine headache is associated with chronic muscle tension in the shoulders, neck and head.

Cardiovascular

The stress response increases sympathetic activity which affects the cardiovascular system through adrenergic stimulation. Catecholamines (adrenaline/noradrenaline) released from the adrenal medulla is primarily involved in this stress response. Catecholamines cause an increase in heart rate and stronger heart contractions. This in turn increases stroke volume which leads to increased blood pressure (hypertension).

• Stress increases serum lipid levels (cholesterol → atherosclerosis, coronary heart diseases)

• Increased heart rate, blood pressure and myocardial contractility lead to increased oxygen demand within the narrowed coronary artery → myocardial ischemia

• ADH → water retention → vascular damage

• Increased stroke volume → vascular damage

• Vascular injury (endothelial cells) → increased platelet and leukocyte adhesion, vascular smooth muscle cell migration and proliferation → atherogenesis, vasoconstriction, coagulation

Respiratory

Hyperventilation

Bronchodilation

Gastrointestinal

• ANS regulates contractions in GI tract via efferent autonomic nerve fibers that run along the mesenteric artery terminate on smooth muscle cells.

• Sympathetic innervation- noradrenaline binds to adrenergic receptors and reduces gut motility and secretion

• Chronic stress → prolonged reduction in gut motility and secretion → chronic GI pain and IBS

The immune system

Chronic stress → increase in cytokine production → activation of HPA axis. The three “inflammatory cytokines” that activate the HPA axis are IL-6, IL1 and TNF-, main one being IL-6.

• IL-6: produced by T cells, macrophages, endothelial cells. Actions: T and B cell growth and differentiation, production of neutrophils, acute phase protein, major elevations of ACTH and cortisol

• NF-kB: transcription factor that initiates an immune response and helps cytokines pass the BBB (cytokines in brain activates HPA axis and alters neuroplasticity)

• Both HPA axis and sympathetic system appear to be chronically activated in melancholic depression.

• Chronic stress/chronic activation of the HPA axis has been linked to anorexia nervosa, panic anxiety, depression, obsessive-compulsive disorder, chronic active alcoholism, alcohol and narcotic withdrawal.

Neuro

Chronic stress → chronic activation of paraventricular neurons → ADH (which potentiates the actions of CRH and ACTH) → adrenal activation (cortisol, adrenaline.. etc)

CRH plays a central role in the regulation of HPA axis