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Avian Respiration - Anatomy & Physiology (view source)

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==Avian Lungs==

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*Avian [[Lungs - Anatomy & Physiology|lungs]] are relatively ~~small~~, with a bird's lungs being approximately 50% as large as the lung of a mammal of a similar size. The lungs are unlobed and do not have the capacity to expand.

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*Avian [[Lungs - Anatomy & Physiology|lungs]] are relatively compact, with a bird's lungs being approximately 50% as large as the lung of a mammal of a similar size. The lungs are unlobed and do not have the capacity to expand due to the fact that they contain cartilage.

*The lungs are positioned in the craniodorsal region of the body, and are deeply indented by both the thoracic [[Spinal Column - Anatomy & Physiology#Vertebrae and Joints|vertebrae]] and [[Ribs and Sternum - Anatomy & Physiology|ribs]].

*Birds do not have a [[Pleural cavity and membranes|pleural cavity]] as the lungs do not expand, thus the membranes are not necessary.

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*One '''Primary Bronchi''' from the [[Trachea - Anatomy & Physiology|trachea]] enters each lung, narrowing as it travels through, and communicates with the '''Abdominal Air Sac'''. This bronchi gives off branches as it travels through the lung, known as '''Secondary Bronchi'''. Each of these gives off a further 400-500 '''Parabronchi''' in the walls of which, [[Gas Exchange - Anatomy & Physiology|gaseous exchange]] takes place.

==Air Sacs==

*Birds lack a [[Diaphragm - Anatomy & Physiology|diaphragm]], and their thoracic and abdominal cavities are continuous.

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*The bird has a number of thin walled, easily distensible '''Air Sacs''' which can extend to approximatley 10x the volume of the [[Lungs - Anatomy & Physiology|lungs]]. These are present within body cavities, and extend into some specific [[Bones and Cartilage - Anatomy & Physiology|bones]], to take the place of [[Bone Marrow - Anatomy & Physiology|bone marrow]]. This has the added function of reducing the weight of the bone, as they are essentially filled with air.

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*The bird has a number of thin walled, easily distensible '''Air Sacs''' which can extend to approximatley 10x the volume of the [[Lungs - Anatomy & Physiology|lungs]]. These are present within body cavities, and extend into some specific [[Bones and Cartilage - Anatomy & Physiology|bones]], to take the place of [[Bone Marrow - Anatomy & Physiology|bone marrow]]. This has the added function of reducing the weight of the bone, as they are essentially filled with air.

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*The air sacs create unidirectional flow of air to maximise oxygen extraction and reduce heat production during flight.

*The chicken has 8 air sacs:

**'''Cervical''' - this extends within the cervical and thoracic [[Spinal Column - Anatomy & Physiology#Vertebrae and Joints|vertebrae]].

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==Avian Gas Exchange==

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*One '''Primary Bronchi''' from the [[Trachea - Anatomy & Physiology|trachea]] enters each lung, narrowing as it travels through, and communicates with the '''Abdominal Air Sac'''. This bronchi gives off branches as it travels through the lung, known as '''Secondary Bronchi'''. Each of these gives off a further 400-500 '''Parabronchi''' in the walls of which, [[Gas Exchange - Anatomy & Physiology|gaseous exchange]] takes place.

*Avian Gas exchange takes place not in alveoli, as in mammals, but within '''Air Capillaries''' which are extensions of the parabronchial lumen. They are an interconnecting network of loops, and closely intertwine with Blood Capillaries.

*The Air Capillaries and Blood Capillaries are arranged so that flow is ''crosscurrent''. This makes the [[Gas Exchange - Anatomy & Physiology|gaseous exchange]] which occurs from one to the other extremely efficient.

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