Large constricting snakes will sometimes constrict and kill prey that are too large to swallow. Arterioles also constrict and dilate in response to different chemical concentrations. Phenylephrine selectively binds to alpha-1 receptors which cause blood vessels to constrict. The coronary arteries can constrict as a response to various stimuli, mostly chemical. Therefore, ACE indirectly increases blood pressure by causing blood vessels to constrict. Triptans, medications which treat migraines, block serotonin receptors and constrict blood vessels. Yarn can restrict sap production on trees and constrict growth. When the passageways are irritated by some allergen, these muscles can constrict. Soon after fracture, blood vessels constrict, stopping further bleeding. This tension can constrict circulation, sending pain signals to the brain. Second, "blood vessels in the extremities constrict". Standard designs constrict chest movement during breathing. The stenosis can constrict the spinal canal giving rise to a neurological deficit. A correctly adjusted martingale does not constrict the dog's neck when pulled taut. By moving a finger toward a person's face to induce accommodation, their pupils should constrict.