factors influencing the bronchial muscle tone

• In general the smooth muscle of the bronchial walls causes bronchodilation during inspiration and bronchoconstrictions during expiration . 

• Autonomic nerve fibers also innervate the bronchial smooth muscle with cholinergic parasympathetic stimulation causing bronchoconstriction and beta adrenergic sympathetic stimulation causing bronchodilation.( Direct control of bronchioles by sympathetic nerve fibers is relatively weak because few of these fibers penetrate to the central portions of the lung . However the bronchial tree is very much exposed to circulating norephinephrine and epinephrine by sympathetic stimulation of the adrenal medulla ) 

• Stimulation of sensory receptors in the airways by irritants and chemicals such as sulfurdioxide produces reflex bronchoconstriction that is mediated via the cholinergic pathways . 

• Cool air causes bronchoconstriction and so exercise , possibly because the increased respiration cool the airways . 

• Leukotriens cause bronchoconstriction 

• There is also a circadian rhythm in bronchial tone , with a maximal constriction at about 6.00 AM and maximal dilation at about 6.00PM 

• Substance P and adenosine also casue bronchoconstriction, VIP produce bronchodilation

Labels: Physiology SEQ, Revision, RS, RS Revision, RS SEQs