Question

Describe the mechanisms, anatomy, and physiology of INHALATION in the bird lung and in the human lung.

Answer 1

Mechanism and physiology

• Human inhale by moving the diaphragm to lower the air pressure in the chest cavity and pull air into lungs.
• The human chest cavity is always at a lower pressure than the outside environment usually 760mmHg at the sea level.
• But birds have air sac that store and pump the air through the stationary lungs.
• Unlike in mammals , air flows in one direction through bird lungs.With the help of this airsac , which help in taking oxygen during exhalation.
• Birds can breathe at much higher level than mammals because of more efficient lung structure.
• Avian respiratory system play an important role in thermoregulation.
• When fresh air is first inhaled through a bird’s nares (nostrils), it travels through the trachea (a large tube extending from the throat), which splits into left and right primary bronchi (a.k.a. mesobronchi, with each bronchus leading to a lung).
• The inhaled air travels down each primary bronchus and then divides: some air enters the lungs where gas exchange occurs, while the remaining air fills the posterior (rear) air sacs.
• Then, during the first exhalation, the fresh air in the posterior sacs enters the lungs and undergoes gas exchange. The spent air in the lungs is displaced by this incoming air and flows out the body through the trachea.
• During second inhalation , fresh air again enters both the posterior sacs and the lungs.
• Spent air in the lungs is again displaced by incoming air, but it cannot exit through the trachea because fresh air is flowing inward.
• Inorder to counter act that , the spent air from the lungs enters anterior (forward) air sacs. '
• Then during the second exhalation, the spent air in the anterior sacs and in the lungs flows out through the trachea, and fresh air in the posterior sacs enters the lungs for gas exchange.
• Birds having relatively small lungs plus nine air sacs that play an important role in respiration.
• Air sac in bird's lung permit unidirectional flow of air .In human air flow is  bidirectional , which causes mixing of oxygen and carbon dioxide gases, hence avalilability of oxygen decreases .But in case of birds due to unidirectional flow ,more oxygen is available which will be diffuse more rapidly into blood.

Anatomy

• Each human lung is divide into lobes by a fissure .Both lungs have oblique fissure while right lung have transverse fissure.Human lung are spongy.
• Lungs are covered with a membrane called pleura , which is filled with a space called pleural cavity
• The oblique fissure in the left lung separates the superior and the inferior lobe. The oblique and horizontal fissure divides the lungs into superior, middle and inferior lobes.
• All the respiratory passage from the trachea to respiratory bronchiole are called tracheobronchial tree.Each bronchus enters the lung at a notch called the hilum.
• Lungs and airway are innervated by branches of sympathetic trunk and vagus nerve.
• Arterial supply of lungs include pulmonary artery and bonchial artery .
• Avian lungs are relatively  compact , unlobed and donont have capacity to expand due to the close arrangement between the finite gas exchange structures.
• Birds donot have pleural cavity .
• One primary bronchus from  the trachea enter into lung and it communicate with abdominal air sac.
• Bronchus then divide into secondary bronchus , which is divided into 400-500 parabronchi .
• The parabronchichi give rise to atria. The atria form infundibulae from which the air capillaries emerge.
• Through the walls of air capillaries gas exchange occurs.