ABSTRACT
Responses of the SNS and adrenal medullae are not necessarily parallel, and each traumatic stress is unique. The SNS is most important in response to cold stress, exercise, and in counteracting hypotension (e.g., hypovolemic shock). Epinephrine secretion is elicited more by anxiety, hypoxia, and hypoglycemia. During physiologic starvation (but perhaps not cachexia) adrenal medullary secretion (mainly of epinephrine) is increased, and activity of the SNS (which is mainly responsible for thermogenesis) is depressed. This is an admirable arrangement, becuause epinephrine is useful for blood glucose homeostasis, and suppression of a tonic thermogenic influence conserves calories. The nervous system is organized so that individual compoents of the SNS, including those responsible for controlling secretory activity of adrenal chromaffin cells, can be called on singly or in any appropriate combination during physiologic stress. During fetal life there is high norepinephrine production, with epinephrine production increasing following birth (Ch. 72).
