Physiological Pathways of Stress response
Hypothalamus and Pituitary gland are close neighbors and collaborators!
Hypothalamus is the stress "commanding general" despite its small size. It receives "intelligence" information from two sources. 1- Brain cortex provides it with outside information i.e. whether there is an external threat or demand. 2- Brain limbic system (the emotional part of the brain that stores long term memory, fear, anger, sadness, happy feelings and emotional attachments) provides it with information about internal needs and demands .This is how perceived threats, fears, worries and bad memories cause the same stress response as real threats.
Hypothalamus then analyzes the extent of threats or demands and issues orders to sympathetic nervous system, adrenal medulla (inner part) and pituitary gland to start body's stress response pathways.
Adrenal medulla, by direct order from hypothalamus, releases large amounts of potent hormones, adrenaline and noradrenaline. Pituitary gland then releases hormones from its front part (anterior pituitary) to stimulate adrenal cortex (ACTH or Adreno-Cortical Stimulating Hormone) and thyroid gland (TSH or Thyroid Stimulating Hormone). The back part (posterior pituitary) secrets Vasopressin to directly affect smooth muscles in small blood vessels, kidney tubules and uterus. Adrenal cortex , in response to ACTH, releases extra amounts of cortisol and aldosterone. Thyroid gland, in response to TSH, increases its hormone (thyroxin) output.
Stress hormones cause increased heart rate and blood pressure, decreased urine output, increased blood sugar, decreased brain cognitive function, dilated pupils, increased sweating, increased bowel contractility, increased stomach acid production, increased metabolic rate, reduced immune function and increased protein breakdown. Muscle tension is not hormonal. It is a direct cortical to skeletal system pathway which occurs when a threat (real or perceived) is detected.
While the pituitary gland is busy pumping out stress hormones, its other non-stress hormone production is suppressed. These include Prolactin, Gonadotropin and growth hormone. Therefore chronic stress also leads to sexual dysfunction, loss of libido, cessation of milk production and breast development, protein breakdown, loss of tissue integrity, premature births and miscarriages.