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What is Hering Breur reflex is mediated by and explain in detail?
Ans: a (pulmonary stretch receptors) Ref: Ganong 22nd ed/p.678Hering Breur reflex is mediated by Pulmonary stretch receptorHering 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.Hering Breuer deflation reflex:-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