Hering-Breuer reflex is mediated by :(Repeat Q 46 2009)

Ans: a (Pulmonary stretch receptors)Ref: Ganong, 22nd ed Pg. 678Hering Breur reflex is mediated by pulmonary stretch receptor.Hering Breuer inflation reflexIt is the cutting down of inspiration before the lung volume increases very much: as in case of physical exercise.1) expiration time increased2) Lung operates at low volume: wastage of energy prevented.Operates when lungs are deflated very much & it stimulates respiration.It usually does not operate in normal condition: helps to open up an atelectatic portion.RECEPTORSSITESTIMULIEFFECT1) pulmonary stretch receptor2) lung irritant receptorSmooth muscle of small airway (slowly adapting)B/w epithelial lining respiratory tract (rapidly adapting)Stretch via vagi (myelinated)ExogenousSmoke, SO2 via vagiEndogenous (myelinated)Histamine, PG- Hering breuer reflex- cough.Branch ospasm- ? mucus secretion3) J receptorsJuxtacapillaryPul. Capillary via vagiEngorgement(unmyelinated))Pul, edemaCapsaicin, bradykinin- apnoea followed by tachypnoea- bradycardia- bronchospasm- hypotension4) chest wall proprioceptors (load detecting R)Muscle spindles in inspiratory musclesReceptors in thoracic cage. - regulate the amount and force of muscle contraction