Final answer:
Direct stimulation of the sympathetic nervous system during exercise causes vasoconstriction in various tissues due to the release of norepinephrine and epinephrine, which bind to alpha and beta adrenergic receptors, facilitating the 'fight or flight' response.
Step-by-step explanation:
The sympathetic nervous system plays a critical role in preparing the body for 'fight or flight' situations, which include exercise. Upon direct stimulation, sympathetic preganglionic neurons, which originate in the spinal cord, release acetylcholine (ACh) on postganglionic neurons within sympathetic ganglia. These postganglionic neurons then release NE onto target organs. Additionally, the adrenal medulla is activated by sympathetic preganglionic neurons, leading to the secretion of NE and E into the bloodstream. These catecholamines bind to alpha and beta receptors on various organ systems to induce multiple physiological responses.
For instance, they increase the heart rate and force of contraction, thereby augmenting stroke volume (SV) and decreasing end-systolic volume (ESV) in the heart. Furthermore, systemic effects also occur, such as redirecting blood flow away from the skin, GI tract, and kidneys, towards the muscles, heart, and brain, which are more immediately needed during exercise.