Bronchial calibre is reduced by:

(Ref: Katzung 14th ed. pg. 130)Sympathetic and parasympathetic fibers present widely on the viscera, control their function.Sympathetic fibers stimulate/constrict heart (increase in HR) and inhibit/Relax all other organs (e.g. Bronchodilation, decreased GI motility, mydriasis, etc.)# Receptor of sympathetic fibres are: b1 (present on heart mainly) and b2 (present on lungs, muscle, liver, etc.)# Stimulation of b2 receptor will cause bronchodilation/ Increased bronchial calibreParasympathetic fibers inhibit/Relax heart (decreased HR) and stimulate/constrict all other organs (bronchoconstriction/reduced bronchial caliber (bronchoconstriction), increased GI motility, miosis, etc.)# Receptors of parasympathetic fibres are M1, M2 and M3# M1 is located mainly in gastric glands and CNS, M2 is located on heart and M3 is located on all other areas like eyes, glands, bladder, intestine, etc.