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|linkpage =Cardiorespiratory System - Anatomy & Physiology

[[Image:Doglungdeflated.jpg|right|thumb|250px|©RVC 2008]]

|linktext =Cardiorespiratory System

[[Image:Doglunginflated.jpg|right|thumb|250px|©RVC 2008]]

|maplink = Cardiorespiratory (Content Map) - Anatomy & Physiology

 

|pagetype =Anatomy

The lungs are the site for [[Gas Exchange - Anatomy & Physiology|gaseous exchange]], and are situated within the thoracic cavity. They occupy approximately 5% of the body volume in mammals when relaxed, and their elastic nature allows them to expand and contract with the processes of [[Ventilation - Anatomy & Physiology#Inspiration|inspiration]] and [[Ventilation - Anatomy & Physiology#Expiration|expiration]].

 

The lungs, along with the [[Larynx - Anatomy & Physiology|larynx]] and [[Trachea - Anatomy & Physiology|trachea]], develop from a ventral respiratory tract. After separation from the developing [[Oesophagus - Anatomy & Physiology|oesophagus]], two lung buds develop, which undergo divisions as they grow, forming the beginnings of the [[Bronchi and Bronchioles - Anatomy & Physiology|bronchial]] tree. This process is not completed at the time of [[Normal Parturition - Anatomy & Physiology|parturition]].

 

==Structure==

 

The left and right lungs lie within their [[Pleural Cavity and Membranes - Anatomy & Physiology|pleural]] sac and are only attached by their roots, to the [[Mediastinum - Anatomy & Physiology|mediastinum]], so they are fairly free within the thoracic cavity. The right lung is always larger than the left, due to the positioning of the [[Heart - Anatomy & Physiology|heart]]. The apex of the lungs is their cranial point.

[[Image:Doglungdeflated.jpg|right|thumb|250px|©RVC 2008]]

In most species, the lungs are divided into lobes by the [[Bronchi and Bronchioles - Anatomy & Physiology|bronchial]] tree:

'''Right Lung''' - Cranial, Caudal, Middle and Accessory lobes. The cranial lobe is further divided by an external fissure.

The lungs are the site for [[Gas Exchange - Anatomy & Physiology|gaseous exchange]], and are situated within the thoracic cavity. They occupy approximatley 5% of the body volume in mammals when relaxed, but generally have no fixed size or shape since their volume is constantly changing with the processes of [[Ventilation - Anatomy & Physiology#Inspiration|inspiration]] and [[Ventilation - Anatomy & Physiology#Expiration|expiration]].

The lungs, along with the [[Larynx - Anatomy & Physiology|larynx]] and [[Trachea - Anatomy & Physiology|trachea]], develop from a ventral respiratory tract. After separation from the developing [[Oesophagus - Anatomy & Physiology|oesophagus]], two lung buds develop, which undergo divisions as they grow, forming the beginnings of the [[Bronchi and bronchioles - Anatomy & Physiology|bronchial]] tree. This process is not completed by [[Parturition - Normal Parturition - Anatomy & Physiology|parturition]].

The bulk of the lung consists of [[Bronchi and Bronchioles - Anatomy & Physiology|bronchi]], blood vessels and connective tissue. The terminal [[Bronchi and Bronchioles - Anatomy & Physiology|bronchioles]] have alveoli scattered along their length, and are continued by alveolar ducts, alveolar sacs and finally alveoli.

==Structure==

===Alveolar Ducts===

===Alveoli===

Alveoli are minute, polygonal chambers, whose diameter changes with the processes of [[Ventilation - Anatomy & Physiology#Inspiration|inspiration]] and [[Ventilation - Anatomy & Physiology#Expiration|expiration]], and varies by species. The wall of the alveoli is extremely thin, consisting of 2 irregular layers of epithelial sheets, 'sandwiching' a network of capillaries. Thus the ''Blood-Gas Barrier'' at the thinnest portions is a tripartite structure consisting of  the pulmonary capillary endothelium, a common basal lamina and the alveolar epithelium- ideal for [[Gas Exchange - Anatomy & Physiology|gaseous exchange]]. The alveolar interstitium is formed from connective tissue fibres and cells, which include collagen fibrils and elastin fibres.

**'''Left Lung''' = Cranial and Caudal lobes.

**'''Right Lung''' = Cranial, Caudal, Middle and Accessory lobes. The cranial lobe is further divided by an external fissure.[[Image:Routeofairthroughrespiratorysystem.jpg|right|thumb|200px|'''Schematic Diagram showing the route air takes through the respiratory system''']]

**'''Alveoli''': These are minute, polygonal chambers, whose diameter changes with the processes of [[Ventilation - Anatomy & Physiology#Inspiration|inspiration]] and [[Ventilation - Anatomy & Physiology#Expiration|expiration]], and varies by species. The wall of the alveoli is extremely thin, consisting of 2 irregular layers of epithelial sheets, 'sandwiching' a network of capillaries. Thus the ''Blood-Gas Barrier'' is just a single basal lamina - ideal for [[Gas Exchange - Anatomy & Physiology|gaseous exchange]]. The alveolar interstitium is formed from connective tissue fibres and cells, which include collagen fibrils and elastin fibres.

==Function==

==Function==

*[[Gas Exchange - Anatomy & Physiology|Gas Exchange]]

The main function of the lungs is [[Gas Exchange - Anatomy & Physiology|gas exchange]].

==Vasculature==

==Vasculature==

*The '''Pulmonary Arteries''' follow the bronchi while the '''Pulmonary veins''' sometimes run separately.  

The '''pulmonary arteries''' follow the bronchi, while the '''pulmonary veins''' sometimes run separately. '''Bronchial arteries''' from the aorta supply the bronchi, and '''bronchial veins''' may drain this blood to the [[Heart Structure - Anatomy & Physiology#Right Atrium|right atrium]] via the '''azygous vein'''. More often the blood from the bronchi drains directly to the [[Heart Structure - Anatomy & Physiology#Left Atrium|left atrium]].

*'''Bronchial arteries''' from the Aorta supply the bronchi, and '''Bronchial veins''' may drain this blood to the [[Structure of the Heart - Anatomy & Physiology#Right Atrium|right atrium]] via the '''Azygous Vein'''. More often the blood from the bronchi drains directly to the [[Structure of the Heart - Anatomy & Physiology#Left Atrium|left atrium]].

==Innervation==

==Innervation==

* Nervous supply to the lung is via the '''Pulmonary Plexus''' within the [[Mediastinum - Anatomy & Physiology|mediastinum]].

Nervous supply to the lung is via the '''pulmonary plexus''' within the [[Mediastinum - Anatomy & Physiology|mediastinum]].

*The Pulmonary Plexus consists of Sympathetic Fibres largely from the Stellate Ganglion, and Parasympathetic Fibres from the [[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|Vagus nerve]].

The pulmonary plexus consists of sympathetic fibres largely from the '''stellate ganglion''', and parasympathetic fibres from the [[Cranial Nerves - Anatomy & Physiology|vagus nerve]].

==Lymphatics==

==Lymphatics==

* Lymph drains to the '''Tracheobronchial''' and '''Mediastinal''' [[Lymph Nodes - Anatomy & Physiology|lymph nodes]].

Lymph drains to the '''tracheobronchial''' and '''mediastinal''' [[Lymph Nodes - Anatomy & Physiology|lymph nodes]].

==Histology==

==Histology==

<center><gallery>

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==Species Differences==

==Species Differences==

* Externally the lungs of the '''Horse''' show almost no lobation. Internally the right lung of the horse lacks a Middle Lobe.

The lungs of the '''horse''' show almost no lobation, and the right lung of the horse lacks a middle lobe. In comparison to this, the lungs of '''ruminants''' and '''pigs''' are obviously lobed. The fissures between the lobes (''interlobar fissures'') are deeper in the '''dog and cat''' lung compared to other species. [[Avian Respiration - Anatomy & Physiology|Avian respiration]] has many fundamental differences to mammalian respiration. The [[Respiration in Non-Homeotherms - Anatomy & Physiology|respiratory systems of non-homeotherms]] are also very different to that of mammals.

*The lungs of '''Ruminants''' and '''Pigs''' are obviously lobed.

*The fissures between lobes (''Interlobar fissures'') are deeper in the dog and cat lung compared to other species.

*[[Avian Respiration - Anatomy & Physiology|Avian Respiration]] has many fundamental differences to mammalian respiration.

==Links==

==Links==

[[Lungs - Pathology]]

Click here for more information on [[:Category:Lungs - Pathology|pathology of the lungs]].

==References==

==References==

*{{citation|initiallast = Dyce|initialfirst = K.M|2last = Sack|2first = W.O|finallast = Wensing|finalfirst = C.J.G|year = 2002|title = Textbook of Veterinary Anatomy|ed =3rd|city = Philadelphia|pub = Saunders}}

{{citation|initiallast = Dyce|initialfirst = K.M|2last = Sack|2first = W.O|finallast = Wensing|finalfirst = C.J.G|year = 2002|title = Textbook of Veterinary Anatomy|ed =3rd|city = Philadelphia|pub = Saunders}}