AVIAN PHYSIOLOGY
Respiratory System
Doç. Dr. Dr. Yasemin SALGIRLI DEMİRBAŞ
Resident ECAWBM (BM)
• Delivers oxygen from the air to the tissues and removes carbon dioxide.
• Helps thermoregulation
• Main differences: (1) Presence of air sacs and air spaces, (2) Lungs structure,
(3) Unidirectional flow
FUNCTIONS OF THE RESPIRATORY SYSTEM
• Parts in the head regions include the nasal openings, nasal cavities and the pharyngeal region of the mouth.
• The cranial larynx (superior larynx or glottis), located in this pharyngeal region, is the opening to the trachea (windpipe).
• The pharyngeal region also has the openings of the esophagus.
• The cranial larynx is normally open to allow air passage, but it closes when feed is passing down the throat so that the feed goes down the esophagus and does not enter the trachea.
PARTS OF THE RESPIRATORY
SYSTEM
• Trachea conducts air from the nares and mouth to the bronchi
• Another functions of trachea: warming, moisturizing, and screening particulate matter from inspired gas.
• Anatomically, significant differences exist between the avian trachea and the mammalian trachea.
• Avian tracheal cartilages are complete rings unlike the incomplete C shaped rings of mammals. ‐
• The syrinx (or caudal larynx), located near the end of the trachea, is the avian's voice box.
• Avians do not have vocal cords to produce sound. «Voice" is produced by air pressure on a valve and modified by muscle tension.
TRACHEA
• The typical bird trachea is 2.7 times longer and 1.29 times wider than that of a comparably sized mammal - resistance to airflow through the trachea in birds is comparable to that in mammals .
• Tracheal volume, is about 4.5 times greater than that of comparably sized mammals.
• The impact of the larger tracheal dead space volume is reduced in at least three ways‐ :
1. Birds have a relatively low respiratory frequency - minute tracheal ventilation rate is only about 1.5–1.9 times greater than that of comparably sized mammals
2. Tidal volume in birds is larger (about 1.7 times ) than that of a comparably sized mammal;
3. The large expansible volume and greater compliance of the respiratory system means that birds expend less energy when breathing compared with mammals
• They are able to overcome any limitations imposed by the larger tracheal dead space.
TRACHEA
• Bronchial system of birds consists of only three orders of branching before the gas exchange surfaces are ‐ reached:
1. a primary bronchus (extrapulmonary and intrapulmonary), 2. secondary bronchi, and
3. tertiary bronchi, more commonly referred to as parabronchi:
They can be several millimeters long and 0.5-2.0 mm in diameter (depending on the size of the bird)
Their walls contain hundreds of tiny, branching 'air capillaries' surrounded by a profuse network of blood capillaries.
Exchange of gases between the lungs and the blood occurs within these air capilleries.
Cross-current arrangement (Blood flows at right angles to parabronchi) increases amount of O2 entering blood.
After passing through the parabronchi, air moves into the ventrobronchi.
BRONCHI
• a) The avian 'unidirectional' respiratory system where gases are exchanged between the lungs and the blood in the parabronchi.
• b). The mammals 'bidirectional' respiratory system where gas exchange occurs in small dead-end sacs called alveoli.
Comparison of avian and mammals respiratory
system:
• The air sacs function as bellows, to ventilate the lungs with fresh air with higher O2 content during both inspiration and expiration.
• The pulmonary air flow is continuous and unidirectional through respiratory cycle.
• The air sacs is thin walled, about 10 times the volume of the lungs.
• It situated between the internal organs in the thoracic and abdomen.
• The air sac extend into the proximal bones of the extrimities, and the skull.
Replacing bone marrow with air makes the bird lighter.
• Histologically, the air sacs are poorly vascularized and do not significantly contribute to gas exchange
AIR SACS
• Most species of the birds have nine air sacs:
• One interclavicular sac
• Two cervical sacs
• Two anterior thoracic sacs
• Two posterior thoracic sacs
• Two abdominal sacs
• The volume of the air sacs is distributed approximately equally between the cranial and caudal groups.
• During ventilation all air sacs are effectively ventilated, with the possible exception of the cervical air sacs, and the ratio of ventilation to volume is similar for each air sac.
AIR SACS
Anterior sacs
Posterior sacs
