Final answer:
The sympathetic nervous system shuts down unnecessary organ functions during a threat by decreasing blood flow to the digestive system and kidneys, and by releasing epinephrine and norepinephrine for a systemic 'fight-or-flight' response.
Step-by-step explanation:
The sympathetic nervous system (SNS) prepares the body to react to threats in a 'fight-or-flight' response by shutting down unnecessary organ functions. This includes reducing blood flow to the digestive system, which is accomplished through vasoconstriction of blood vessels. Another effect is the reduction of glomerular flow in the kidneys, limiting filtration to redirect blood to more critical structures during stress. Additionally, the SNS triggers the release of epinephrine and norepinephrine from the adrenal medulla, which causes a systemic increase in blood pressure and redirects blood towards muscles and away from the kidneys and other non-critical systems during emergencies.
The extensive projections of the SNS allow it to influence diverse organ systems simultaneously, ensuring an integrated and efficient response to stress. Pre-ganglionic sympathetic neurons have multiple targets and may connect to chain ganglia, pass through them, or project directly to organs such as the adrenal medulla. These connections facilitate the coordination of the systemic changes required in a sympathetic response, including increased heart rate, respiratory rate, muscle perfusion, sweat gland activity, and the inhibition of gastrointestinal activity.