Final answer:
Smooth muscle contraction can be triggered by electricity, local metabolic factors, drugs, hormones like epinephrine, temperature changes, and stretch. These involuntary contractions are regulated by the autonomic nervous system, hormones, and local chemicals, with visceral smooth muscle also responding to stretch.
Step-by-step explanation:
The contraction of smooth muscle can be caused by various stimuli including electricity, local metabolic factors, drugs, hormones like epinephrine, temperature changes, and stretch. When considering the ways in which these triggers can elicit a response from smooth muscles, it's notable that this muscle type operates under involuntary control, being largely regulated by the autonomic nervous system (ANS), hormones, and local chemical signals.
For instance, the hormone adrenaline, associated with the fight-or-flight response, can cause smooth muscles in the blood vessels to contract, affecting blood flow. The stretching of smooth muscle, particularly in the walls of visceral organs, can also initiate contraction. Unlike multiunit smooth muscle cells, which do not typically respond to stretch due to the absence of gap junctions and are primarily stimulated by autonomic nerves and hormones, visceral smooth muscle can respond to stretching with contraction.