Final answer:
Hormones, neural stimulation by the ANS, and local factors regulate the contraction of smooth muscle.
Step-by-step explanation:
The three things that can regulate the contraction of smooth muscle are hormones, neural stimulation by the autonomic nervous system (ANS), and local factors.
Hormones can affect the contraction of smooth muscles. For example, adrenaline can increase the rate at which cardiac muscle contracts, thereby speeding up the heartbeat.
Neural stimulation by the ANS can also regulate smooth muscle contraction. The autonomic nervous system sends electrical impulses to smooth muscles, causing them to contract.
Lastly, local factors such as stretching can trigger the contraction of smooth muscles. For example, stretching the muscle in the walls of visceral organs can cause them to contract.