RESPIRATORY REFLEXES ::
Pulmonary Irritant Reflexes ::
The lungs are sensitive to wide range of chemicals dust limt smoke etc on sensitisation they communicate with respiratory centres via vagal nerves These promote reflex constriction of air passages coughing and sneezing
The Hering Breuer Reflex (Inflational Reflex ) ::
The conducting passages and visceral pleural contains stretch receptors which get stimulated when lungs are over inflated The impulses from these receptors are sent to medulary centres and result in termination of inspiration and allow expiration This reflex is mainly for preventing lung damage and is thus protective
INTERNAL RESPIRATION
Exchange of gases ::
The exchange of gases at the cellular level in lungs and tissue is described as internal respiration Two gases namely oxygen (o2) and carbon dioxide (CO2) are transported between lungs and tissues through blood These exchange mechanisms work on the priniciple of biophysics that gases try to equalise the pressure on either side by the process of diffusion if there is pressure gradient
Exchange of gases in alveoli :::
The inspired air has po2 (partial pressure of o2) in blood as 158.2 mmHg whereas pCO2 (Partial pressure of CO2) AS 0.3 mmHg The blood coming from right ventricle of heart (i.e.through pulmonary arteries ) has po2 as 40.0mmHg and pCO2 as 46.0 mmhg Thus in the alveoli because of the differences in partial pressure there is quick diffusion of o2 from inspired air to the blood and of CO2 from the blood to the air in the lungs as a result the air to be expired has pO2 as 116.0 mmHg and pCO2 as 26.8mmHg whereas the blood going out from lungs to heart will have high amount of O2 (pO2 100mmHg ) and low amount of CO2 (PCO2 40.0mmHg )
Exchange of gases at tissue level ::;
Similarly when the blood reaches various tissues there is exchange of O2 from the blood to tissues and of CO2 from tissue to blood The reason is again the pressure gradient The pO2 is about 40.0mmHg and pCO2 is about 46.0 mmHg in the tissues as compared to 100 mmHg and 40.0 mmHg pO2 and PCO2 in the arterial blood respectively At the lung level as well as at the cellular level the gaseous exchanges take place are on the basis of diffusion
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