Question

Which of the following activity does not take place during pulmonary respiration?

• A. Movement of buccal cavity
• B. Contraction and relaxation of sternohyal and pterohyal muscles
• C. Successive opening and closing of mouth and external nostrils
• D. All of the above
• E. No activity takes place

Answer 1

The correct option is C Successive opening and closing of mouth and external nostrils

Successive opening and closing of mouth and external nostrils do not take place during pulmonary respiration.

The mechanism of pulmonary respiration: It includes breathing movement, exchange of gases, in lungs, transport of gases by blood and exchange of gases by tissue.

The medulla oblongata (with the inspiratory centre and expiratory centre) and pons varolli (with pneumotoxic centre) are the breathing centre that regulates the breathing mechanism. Inspiratory centre stimulates inspiratory muscle (diaphragm) to control the rhythm of respiration. Expiratory centre remains inactive during normal breathing but it controls both expiration and inspiration during exercise. Pneumotoxic centre controls the switch off point of the breathing sending signal to inspiratory centre. The medulla’s control centre detects low pH of tissue fluid during formation of more carbonic acids, the centre increases the rate of breathing to eleiminate the excess CO2. The concentration of O2 has little effect on breathing centers. However, when O2 level is severely depressed, O2 sensors in the aorta and carotid arteries send signals to breathing control center to increase the breathing rate.

The main purpose of the respiratory system is to provide oxygen to the tissues and to remove carbon dioxide from them. This entire process is achieved through the following steps:

• Breathing or pulmonary ventilation leading to exchange of oxygen and carbon dioxide between the atmospheric air and the lungs
  
• Exchange of gases at the alveolar surface
  
• Transport and exchange of gases in the tissues
  
• Cellular respiration