Pulmonary ventilation

Dr. K. Rama Rao
Department of Zoology
Govt, Degree College
TEKKALI; Srikakulam Dt: A.P.

1. Pulmonary Ventilation Dr. K. Rama Rao Department of Zoology Phone: [phone]

2. Pulmonary ventilation is commonly referred to as breathing. It is the process of air flowing into the lungs during inspiration (inhalation) and out of the lungs during expiration (exhalation). Air flows because of pressure differences between the atmosphere and the gases inside the lungs.

3. Air enters the respiratory system through the mouth and the nasal cavity, passing through the pharynx then larynx (where sounds are produced for speech) and finally the trachea which enters the chest cavity.

4. These passages (the nasal cavity in particular) are lined with cilia (tiny hair like structures) that act as a filter, blocking germs from entering the respiratory system as well as warming and moistening the air. 

5. At the top of the oesophagus is a plate of flexible elastic cartilage called the epiglottis which closes over the larynx as we swallow food to ensure the food travels to the stomach and not into the lungs

6. In the chest cavity the trachea splits into two smaller tubes called the left and right bronchi. These further divide into secondary bronchi which lead directly into the lungs, where they divide into many smaller tubes called bronchioles

7. The bronchioles finally connect to tiny structures called alveoli where gas exchange occurs, as can be seen in the adjacent diagram.

8. Respiratory muscles and their role in respiration When we breathe in, air flows into the lungs down what is known as a ‘pressure gradient’ from an area of high pressure to an area of low pressure.  The pressure gradient within the lungs is controlled by a muscle called the diaphragm.

9. When contracted the diaphragm flattens and pushes downwards resulting in an enlargement of the chest cavity (area within which the lungs sit) and a decrease of pressure in the lungs.  This reduction in pressure causes air to be sucked into the lungs and we breathe in, as seen in the following image.

10. As we breathe out the opposite happens as the diaphragm relaxes and pushes upwards, as seen in the right image above.  This reduces the size of the chest cavity making the pressure within the lungs higher and results in air being exhaled.  In turn the pressure gradient within the body returns to its original state and the process starts again.

11. During exercise when inspiration increases, the external intercostal muscles are recruited to help with the increase in ventilation rate.  They work to lift the ribs up and outwards, further increasing the chest cavity and enabling more air to be inspired, as seen on the image below.

12. Expiration is generally a passive process that does not require muscle contraction.  As the muscles of inspiration relax and return to their resting positions air is forced out of the lungs as the pressure within them increases.

13. However, when needed, active and or forced expiration can be completed by voluntary contraction of the abdominals and internal intercostal muscles, as seen in the above image.  This further reduces the volume within the chest cavity and more air is exhaled.

14. Pulmonary ventilation summarised The following images and table provides a usefull summary of pulmonary ventilation or 'breathing

15. Inspiration Expiration Diaphragm contracts pushing downward 2. Lungs expand as pressure Inside chest Decreases 3. Air drawn in through nose and mouth 1. Diaphragm relaxes pushing upward 2. Lungs made smaller and more pressurized by relaxing diaphragm 3. Air passes out through nose and mouth