View source for Lungs - Anatomy & Physiology

{{OpenPagesTop}}
==Introduction==
[[Image:Doglungdeflated.jpg|right|thumb|250px|©RVC 2008]]
[[Image:Doglunginflated.jpg|right|thumb|250px|©RVC 2008]]

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.

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

'''Left Lung''' - Cranial and Caudal lobes. 

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

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.

===Alveolar Ducts===
These have alveoli which open on all of its sides, they have no 'walls' as such. Openings to individual alveoli are guarded by [[Muscles - Anatomy & Physiology#Smooth Muscle|smooth muscle]].

===Alveolar Sacs===
These are rotunda-like areas on the end of each alveolar ducts which are usually present in clusters.

===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'' 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==

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

==Vasculature==

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]].

==Innervation==

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 [[Cranial Nerves - Anatomy & Physiology|vagus nerve]].

==Lymphatics==

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

==Histology==

'''Pneumocytes''' are a type of epithelial cells that lines the alveoli. 
*the '''Type I''' pneumocytes are simple squamous with a flattened central nucleus that protrudes into the alveolar lume
*the '''Type II''' pneumocytes are round to pyramidal-shaped cells that are found among the type I pneumocytes. The type II pneumocytes have a larger centrally placed nucleus with a prominent nucleolus and a slightly vacuolated, foamy, basophilic cytoplasm. The nucleus of these cells also has a nucleolus.


<center><gallery>
Image:Lungadultlowmag.jpg|<p>'''Lung (adult)'''</P><sup>©RVC 2008</sup>
Image:SEMAdultSheepLung.jpg|<p>'''SEM of Adult Sheep Lung'''</P><sup>©RVC 2008</sup>
Image:Bronchuslowpower.jpg|<p>'''Bronchus'''</P><sup>©RVC 2008</sup>
Image:Bronchuslowpower2.jpg|<p>'''Bronchus'''</P><sup>©RVC 2008</sup>
Image:Alveoli.jpg|<p>'''Alveoli'''</P><sup>©RVC 2008</sup>
Image:Alveoli2.jpg|<p>'''Alveoli'''</P><sup>©RVC 2008</sup>
</gallery></center>

==Species Differences==

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.

==Links==

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

{{Template:Learning
|powerpoints = [[Respiratory System Histology resource|Respiratory system histology tutorial with questions and answers]]
|dragster = [[Respiratory System Histology Resource (II)|Lung Histology Dragster]]
|videos = [[Video: Piglet Anatomy|Piglet Anatomy]]<br>[[Video: African Gray Parrot Radiograph|African Gray Parrot Radiograph]]<br>[[Video: Equine left-sided abdominal and thoracic topography dissection|Equine left-sided abdominal and thoracic topography dissection]]<br>[[Video: Equine thoracic cavity dissection|Equine thoracic cavity dissection]]<br>[[Video: Ovine right-sided abdominal and thoracic dissection|Ovine right-sided abdominal and thoracic dissection]]
|OVAM = [http://www.um.es/anatvet/interactividad/ingles/avispi/practicas/practica1.htm Dissection plans of the canine thoracic cavity]<br>[http://www.onlineveterinaryanatomy.net/sites/default/files/original_media/document/asset_9296_Dried%20dog%20lung%20PDF.pdf Labelled dried dog lung]<br>[http://www.onlineveterinaryanatomy.net/content/respiration-histology-images-lung-0 Histology - Lung 1]<br>[http://www.onlineveterinaryanatomy.net/content/respiration-histology-images-lung Histology - Lung 2]<br>[http://www.onlineveterinaryanatomy.net/content/ovine-lung-histology-0 Histology - Ovine Lung 1]<br>[http://www.onlineveterinaryanatomy.net/content/ovine-lung-histology Histology - Ovine Lung 2]<br>[http://www.onlineveterinaryanatomy.net/content/fallow-deer-lungs-0 Cast of Fallow deer lungs]<br>[http://www.onlineveterinaryanatomy.net/content/interactive-pig-anatomy-lungs-0 Interactive Pig Anatomy - Lungs]
}}

==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}}

{{review}}
{{OpenPages}}
[[Category:Respiratory System - Anatomy & Physiology]]
[[Category:A&P Done]]