QS Study

Hering Breuer Reflex

Definition: The rate and depth of respiration are controlled by the reflex which is transmitted from the stretch receptor of the lungs to the respiratory center via vegus nerve is called Hering – Breuer reflex. Pulmonary stretch receptors present in the smooth muscle of the airways respond to excessive stretching of the lung during large inspirations. The reflex may determine breathing rate and depth in newborns and in adult humans when tidal volume is more than 1 L, as when exercising. It has two parts:

(A) Hering Breuer inflation reflex (M/A)

  1. Overstretching of the lung due to increased tidal volume is greater than about 1.5 L.
  2. Stimulation of the stretch receptor located in the bronchioles throughout the lungs.
  3. Transmission of signals from the stretch receptor into the dorsal respiratory groups of neurons through the vagi.
  4. ‘Switch off’ the inspiratory ramp and thus stops further inspiration.

Fig: Hering Breuer Reflex

(B) Hering Breuer deflation reflex –

During expiration, the stretch receptor becomes outstretch. The inhibitory impulse from this receptor ceases and apneustic center is stimulated. As a result, respiration takes place again. It is initiated either by stimulation of stretch receptors or stimulation of proprioceptors activated by lung deflation. These reflexes appear to play a more minor role in humans than in non-human mammals.

Importance

(i) A protective mechanism for preventing over inflation.

(ii) Maintain the tidal volume within a certain range.

(iii) Essential for conversion of continuous inspiration into rhythmic inspiration.li