VPB 121: Veterinary Physiology - II (2+1)

MECHANICS OF RESPIRATION

• There is no diaphragm in birds. So, there is no division of abdominal and thoracic cavities.
• Pressure occurring during respiratory cycle is referred to as thoraco-abdominal pressure. Respiration is caused by changes in body volume.
• During inspiration, the transverse and dorso-ventral diameter of thorax increase because of the ventral cranial movement of sternum and lateral movement of ribs.
• During inspiration, some gas moves into the medio dorsal secondary bronchi, pass through the paleopulmonic parabronchi and enter into the cranial airsacs.
• The pressure increase in expiration in all air sacs and air is forced out of the air sacs, which moves through lungs to outside. Thus, gas flows through the avian lungs during both inspiration and expiration.
• During expiration, gas from the caudal airsacs passes again through the neopulmonic parabronchi and lateroventral secondary bronchi in the opposite direction and then moves into the mediodorsal secondary bronchi and passes through the paleopulmonic parabronchi in the same direction as during inspiration.
• Gases from the cranial airsacs move into the medioventral secondary bronchi and out of the lungs without passing through the gas exchange area.
• The unidirectional movement of gas through paleopulmonic parabronchi, which is the gas exchange portion of avian lungs, increases efficiency of ventilation.
• Gas exchange can occur in the paleopulmonic parabronchi during both inspiration and expiration.
• The remainder the gas moves through the neopulmonic parabronchi, lateroventeral secondary bronchi into the caudal airsacs.
• During expiration these diameters decrease. In air sacs pressure drops and volume increase during inspiration and air move through the lungs into the airsacs.