zigya tab
 Diffusion of gases occur in the alveolar region only and not in the other part of respiratory system, why ?

Alveoli have thin walls, have layer of mucus on inner side and have rich supply of blood. Each alveolus is made up of highly-permeable and thin layers. The barrier between the alveoli and the capillaries is thin and the diffusion of gases takes place from higher partial pressure to lower partial pressure. The pO2 of blood is lesser than alveolar air and pCO2 of blood is greater than alveolar air. Thus, alveoli support the diffusion of gase.  
Since the other region do not provide the necessary conditions like thin and permeable membrane, difference in the partial pressure of the gases across the membrane etc., they do not supprt the diffusion of gases as alveoli. 



What will be the pO2 and pCO2 in the atmospheric air compared to those in the alveolar air ?
(i) pO2 lesser, pCO2 higher
(ii) pO
2 higher, pCO2 higher
(iii) pO
2 higher, pCO2 higher
(iv) pO
2lesser, pCO2 lesser.

    ii. PO2 higher PCO2 lower.
    ii. PO2 higher PCO2 lower.

    How is respiration regulated ?

    The respiration is regulated in the following ways :

    The neural system is involved in regulating the respiration. 

    i. Respiratory rhythm centre - A specialised centre present in the medulla region of the brain is primarily responsible for the regulation of respiration.

    ii. Pneumotaxic centre - in the pons region of the brain moderates the functions of the respiratory rhythm centre. Neural signal from this centre can reduce the duration of inspiration and thereby alter the respiratory rate.

    iii. A chemosensitive area situated adjacent to the rhythm centre which is highly sensitive to CO2 and hydrogen ions. Increase in these substances can activate the centre which signals the rhythm centre to make the necessary adjustments in the respiratory process by which these substances can be eliminated.

    iv. Aortic arch and carotid artery receptore also recognise changes in CO2 and H+ concentration and send necessary signals to the rhythm centre for necessary actions. Oxygen plays a vital role in the regulation of respiratory rhythm.


    Define vital capacity. What is its significance?

    Vital capacity : (V.C) It is the total volume of air that can be expelled from the lungs after first filling the lungs to the maximum and then exhaling the same to the maximum :

    VC = TV + IRV + ERV

    = 500 + 2000 to 2500 + 1000 to 1500 = 3500 to 4500 ml.

    Significance of V.C. : Vital capacity of a person gives important clues for diagnosing a lung problem. Measurement of this capacity helps the doctor to decide about the possible causes of the diseases and about the line of treatment. It determines the stamina of sportsmen and mountain climbers. The greater the vital capacity more is energy available to body. Sportsperson or mountain dwellers have higher vital capacity. Young persons have more vital capacity than aged.


    Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern ? 

    Oxygen dissociation curve is the sigmoid curve obtained when the percentage saturation of haemoglobin with O2 is plotted against the partial pressure of oxygen pO2.  It helps in the study of the effect of factors like pCO2, H+ concentration etc. on binding of oxygen with haemoglobin. What is oxygen dissociation curve ?
Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern ? 

    The binding of oxygen to haemoglobin is in such a way that the binding of the first oxygen oxygen molecule binds to the haemoglobin, it increases the affinity for the second molecule of oxygen to bind. Subsequently, haemoglobin attracts more oxygen and this gives the curve a sigmoid shape.