Question

Overstretching of lungs can be prevented by:

• A. Bohr’s effect
• B. Haldane’s effect
• C. Herring-Breuer reflex
• D. None of the above

Answer 1

The correct option is C Herring-Breuer reflex

There are stretch receptors present in the walls of the terminal bronchioles and atria. When maximum air gets filled in the alveoli, these receptors are activated. This activates Hering Breuer reflex arch, which sends inhibitory signals to the inspiratory centre (present in medulla) to switch off the inspiration. Inspiratory group or centre is responsible for the stimulation of the external intercostal muscles and diaphragm to inspire. Hering-Breuer reflex prevents the alveoli from overstretching or bursting. Hence this is also called a protective reflex. It is only required when the normal mechanism to switch off inspiration doesn’t work.
The relationship between partial pressure (pressure exerted by the gas present in a mixture of gases) of oxygen and percent saturation of haemoglobin is represented as oxygen haemoglobin dissociation curve. Percent saturation of haemoglobin refers to the percentage ratio of the oxygen content in the haemoglobin to the oxygen content in the haemoglobin during saturation. It is sigmoid in shape. A rise in the partial pressure of carbon dioxide or a decrease in the pH results in a decrease in the oxygen affinity of haemoglobin. This raises the value of partial pressure of oxygen required to saturate 50% of haemoglobin to form oxyhaemoglobin. This effect is called the Bohr’s effect.
The effect of oxyhaemoglobin dissociation or association on carbon dioxide transport is called Haldane’s effect.