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==Introduction==

==Introduction==

The avian respiratory system contains some fundamental differences to the mammalian system.

The avian respiratory system contains some fundamental differences to the mammalian system.

==Avian Nasopharynx and Oropharynx==

==Avian Nasal Cavity and Oropharynx==

The nostrils of the bird, which lead into the [[Nasal Cavity - Anatomy & Physiology|nasal cavity]], may have a flap of horn to protect them, known as the ''Operculum''. The Oral Cavity and the Nasal Cavity of the bird are interconnecting via a slit in the [[Hard Palate|hard palate]] called the ''Choana''. Birds lack a [[Soft Palate|soft palate]].

The nostrils of the bird, which lead into the [[Nasal Cavity - Anatomy & Physiology|nasal cavity]], may have a flap of horn to protect them, known as the ''Operculum''. The Oral Cavity and the Nasal Cavity of the bird are interconnecting via a slit in the [[Hard Palate|hard palate]] called the ''choana''. Birds lack a [[Soft Palate|soft palate]].

[[Image:Avianheadsaggitalsection.jpg|right|thumb|250px|©Nottingham 2008 ''Saggital Section of an Avian skull showing the conchae.]]

[[Image:Avianheadsaggitalsection.jpg|right|thumb|250px|©Nottingham 2008 ''Saggital Section of an Avian skull showing the conchae.]]

There are Rostral, Middle and Caudal Conchae arising from the lateral wall, filling part of the [[Nasal Cavity - Anatomy & Physiology|nasal cavity]]. The '''rostral conchae''' in the vestibular region are lined with stratified squamous epithelium. The '''middle conchae''' in the respiratory region are lined with [[Respiratory Epithelium - Anatomy & Physiology|respiratory Epithelium]]. The '''caudal conchae''' in the [[Nose - Anatomy & Physiology|olfactory]] region are lined with [[Nose - Anatomy & Physiology|olfactory]] epithelium. The '''Infraorbital Sinus''' is a triangular cavity under the skin, rostroventral to the eye. Some marine birds have a ''Salt Gland'' (nasal gland) which excretes sodium.

There are rostral, middle and caudal conchae arising from the lateral wall, filling part of the [[Nasal Cavity - Anatomy & Physiology|nasal cavity]]. The '''rostral conchae''' in the vestibular region are lined with stratified squamous epithelium. The '''middle conchae''' in the respiratory region are lined with [[Respiratory Epithelium - Anatomy & Physiology|respiratory epithelium]]. The '''caudal conchae''' in the [[Nose - Anatomy & Physiology|olfactory]] region are lined with [[Nose - Anatomy & Physiology|olfactory]] epithelium. The '''infraorbital sinus''' is a triangular cavity under the skin, rostroventral to the eye. Some marine birds have a ''salt gland'' (nasal gland) which excretes sodium.

==Avian Larynx==

==Avian Larynx==

The [[Larynx - Anatomy & Physiology|larynx]] is on the floor of the [[Oropharynx - Anatomy & Physiology|oropharynx]] supported by '''Cricoid''' and paired '''Arytenoid''' Cartilages which are different in structure to those in mammals. There is no [[Epiglottis|epiglottis.]] and there are no vocal folds - birds vocalise using a [[Syrinx - Anatomy & Physiology|syrinx]].

The [[Larynx - Anatomy & Physiology|larynx]] is on the floor of the [[Oropharynx - Anatomy & Physiology|oropharynx]] supported by '''cricoid''' and paired '''arytenoid''' cartilages which are different in structure to those in mammals. There is no [[Larynx - Anatomy & Physiology#epiglottis|epiglottis]] and there are no vocal folds - birds vocalise using a [[Syrinx - Anatomy & Physiology|syrinx]].

==Avian Trachea==

==Avian Trachea==

The avian [[Trachea - Anatomy & Physiology|trachea]] is composed of tightly stacked [[Bones and Cartilage - Anatomy & Physiology|cartilages]] which are shaped similarly to signet rings. These are complete with no dorsal space as in the mammalian [[Trachea - Anatomy & Physiology|trachea]]. They overlap considerably. The trachea can be palpated on the right side of the neck; it runs alongside the [[Oesophagus - Anatomy & Physiology|oesophagus]]. The trachea is lined with [[Respiratory Epithelium - Anatomy & Physiology|respiratory epithelium]]. The trachea bifurcates into two main [[Bronchi and Bronchioles - Anatomy & Physiology|bronchi]] as in mammals. The [[Syrinx - Anatomy & Physiology|syrinx]] is formed by this terminal part of the trachea.

The avian [[Trachea - Anatomy & Physiology|trachea]] is composed of tightly stacked [[Cartilage - Anatomy & Physiology|cartilages]] which are shaped similarly to signet rings. They are complete with no dorsal space as in the mammalian trachea and overlap considerably. The trachea can be palpated on the right side of the neck; it runs alongside the [[Oesophagus - Anatomy & Physiology|oesophagus]]. The trachea is lined with [[Respiratory Epithelium - Anatomy & Physiology|respiratory epithelium]]. The trachea bifurcates into two main [[Bronchi and Bronchioles - Anatomy & Physiology|bronchi]] as in mammals. The [[Syrinx - Anatomy & Physiology|syrinx]] is formed by this terminal part of the trachea.

==Avian Lungs==

==Avian Lungs==

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 as the lungs do not expand, thus the membranes are not necessary. 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 [[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 close arrangement between the finite gas exchange structures, i.e.the air capillaries and blood capillaries and scanty connective tissue. 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 as the lungs do not expand, thus the membranes are not necessary. One '''primary bronchus''' from the [[Trachea - Anatomy & Physiology|trachea]] enters each lung, narrowing as it travels through, and communicates with the '''abdominal air sac'''. This bronchus gives off branches as it travels through the lung, known as '''secondary bronchi'''. Each of these gives off a further 400-500 '''parabronchi'''. The parabronchichi give rise to '''atria'''. The atria form '''infundibulae''' from which the '''air capillaries''' emerge.  It is in the walls of the latter structures that [[Gas Exchange - Anatomy & Physiology|gaseous exchange]] takes place.

==Air Sacs==

==Air Sacs==

Birds lack a [[Diaphragm - Anatomy & Physiology|diaphragm]], and their thoracic and abdominal cavities are continuous. 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. The air sacs create unidirectional flow of air to maximise oxygen extraction and reduce heat production during flight.

Birds lack a [[Diaphragm - Anatomy & Physiology|diaphragm]], and their thoracic and abdominal cavities are continuous. The bird has a number of thin walled, easily distensible '''air sacs''' which can extend to approximately 10x the volume of the [[Lungs - Anatomy & Physiology|lungs]]. Theye are present within body cavities, and extend into some specific [[Bones - Anatomy & Physiology|bones]] to take the place of the [[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. The air sacs create unidirectional flow of air to maximise oxygen extraction and reduce heat production during flight.

The chicken has 8 air sacs:  

The chicken has 8 air sacs:  

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

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

:'''Abdominal''' (x2) - these are the largest air sacs and fill the caudodorsal region of the abdomen, in contact with [[Small Intestine Overview - Anatomy & Physiology|small]] and [[Large Intestine - Anatomy & Physiology|large intestines]], [[Renal Anatomy - Anatomy & Physiology#Common Anatomy|kidneys]] and [[:Category:Avian Reproduction|reproductive]] organs. In addition, these airsacs utilise space within the acetabulum and synsacrum.  

'''Clavicular''' - lies within the thoracic inlet, surrounding the [[Heart - Anatomy & Physiology|heart]], and within the humerus in the [[Forelimb - Anatomy & Physiology|forelimb]].

The cervical, clavicular and cranial thoracic air sacs form one functional group - '''cranial''' and the caudal thoracic and abdominal air sacs forming another, '''caudal''' functional group. The air sacs have a vital role in [[Ventilation - Anatomy & Physiology|ventilation]], but do not have the capacity for [[Gas Exchange - Anatomy & Physiology|gaseous exchange]].

'''Caudal Thoracic''' (x2) - located between the body wall and the thoracic air sacs.  

[[Ventilation - Anatomy & Physiology|Ventilation]] in birds is strikingly different to that of mammals in that air flows through the lungs in the same direction during both [[Ventilation - Anatomy & Physiology#Inspiration|inspiration]] and [[Ventilation - Anatomy & Physiology#Expiration|expiration]]. In addition, both the intaking of air and the expelling of air are active processes, requiring [[Muscles - Anatomy & Physiology|muscle]] contraction.

'''Abdominal''' (x2) - these are the largest air sacs and fill the caudodorsal region of the abdomen, in contact with [[Small Intestine Overview - Anatomy & Physiology|small]] and [[Large Intestine - Anatomy & Physiology|large intestines]], [[Macroscopic Renal Anatomy - Anatomy & Physiology#Common Anatomy|kidneys]] and [[Reproductive System - Anatomy & Physiology|reproductive]] organs. In addition these airsacs utilise space within the acetabulum and synsacrum. The Cervical, Clavicular and Cranial Thoracic air sacs form one functional group - '''Cranial''', with the Caudal Thoracic and Abdominal Air sacs forming another, '''Caudal''' functional group. The air sacs have a vital role in [[Ventilation - Anatomy & Physiology|ventilation]], but do not have the capacity for [[Gas Exchange - Anatomy & Physiology|gaseous exchange]].

During '''inspiration''', the [[Ribs and Sternum - Anatomy & Physiology|ribs]] are drawn forwards and the [[Ribs and Sternum - Anatomy & Physiology|sternum]] lowered, the caudal air sacs receiving fresh air. Simultaneously, the Cranial air sacs receive air which was inhaled at the previous inhalation which is drawn from the lungs, this air has lost much of its oxygen content.  

 

[[Ventilation - Anatomy & Physiology|Ventilation]] in birds is strikingly different to that of mammals in that air flows through the lungs in the same direction during both [[Ventilation - Anatomy & Physiology#Inspiration|inspiration]] and [[Ventilation - Anatomy & Physiology#Expiration|expiration]]. In addition, both the intaking of air and the expelling of air are active processes, requiring [[Muscles - Anatomy & Physiology|muscle]] contraction.  During Inspiration, the [[Ribs and Sternum - Anatomy & Physiology|ribs]] are drawn forwards and the [[Ribs and Sternum - Anatomy & Physiology|sternum]] lowered, the Caudal air sacs receiving fresh air. Simultaneously, the Cranial air sacs receive air which was inhaled at the previous inhalation which is drawn from the lungs, this air has lost much of it's oxygen content. During Expiration, the [[Ribs and Sternum - Anatomy & Physiology|sternum]] is drawn caudal and dorsal, the air sacs are compressed, air from the caudal air sac passes through the [[Lungs - Anatomy & Physiology|lungs]], while the air in the cranial air sac leaves via the [[Trachea - Anatomy & Physiology|trachea]]. Thus, oxygenated air passes through the lungs on both [[Ventilation - Anatomy & Physiology#Inspiration|inspiration]] and [[Ventilation - Anatomy & Physiology#Expiration|expiration]].

During '''expiration''', the [[Ribs and Sternum - Anatomy & Physiology|sternum]] is drawn caudal and dorsal, the air sacs are compressed, air from the caudal air sac passes through the [[Lungs - Anatomy & Physiology|lungs]], while the air in the cranial air sac leaves via the [[Trachea - Anatomy & Physiology|trachea]]. Thus, oxygenated air passes through the lungs on both [[Ventilation - Anatomy & Physiology#Inspiration|inspiration]] and [[Ventilation - Anatomy & Physiology#Expiration|expiration]].

==Avian Gas Exchange==

==Avian Gas Exchange==

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.

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.

==References==

==References==

[[Category:Avian Respiratory System - Anatomy & Physiology]]

[[Category:Avian Respiratory System - Anatomy & Physiology]]

[[Category:To Do - AimeeHicks]][[Category:To Do - Review]]

[[Category:A&P Done]]