Difference between revisions of "Lungs - Anatomy & Physiology"
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==Introduction== | ==Introduction== | ||
[[Image:Doglungdeflated.jpg|right|thumb|250px|©RVC 2008]] | [[Image:Doglungdeflated.jpg|right|thumb|250px|©RVC 2008]] | ||
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'''Right Lung''' - Cranial, Caudal, Middle and Accessory lobes. The cranial lobe is further divided by an external fissure. | '''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. | + | The bulk of the lung consists of [[Bronchi and Bronchioles - Anatomy & Physiology|bronchi]], [[Anatomy of Blood Vessels - Anatomy & Physiology|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=== | ===Alveolar Ducts=== | ||
| − | These have alveoli which open on all of | + | These have alveoli which open on all of it's sides, they have no 'walls' as such. Openings to individual alveoli are guarded by [[Muscles - Anatomy & Physiology#Smooth Muscle|smooth muscle]]. |
===Alveolar Sacs=== | ===Alveolar Sacs=== | ||
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===Alveoli=== | ===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'' | + | 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== | ==Function== | ||
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==Histology== | ==Histology== | ||
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==Links== | ==Links== | ||
| − | Click here for more information on [[ | + | Click here for more information on [[Lungs - Pathology|pathology of the lungs]]. |
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==References== | ==References== | ||
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{{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}} | ||
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[[Category:Respiratory System - Anatomy & Physiology]] | [[Category:Respiratory System - Anatomy & Physiology]] | ||
[[Category:A&P Done]] | [[Category:A&P Done]] | ||
Revision as of 18:17, 29 December 2010
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Introduction
The lungs are the site for 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 inspiration and expiration.
The lungs, along with the larynx and trachea, develop from a ventral respiratory tract. After separation from the developing oesophagus, two lung buds develop, which undergo divisions as they grow, forming the beginnings of the bronchial tree. This process is not completed at the time of parturition.
Structure
The left and right lungs lie within their pleural sac and are only attached by their roots, to the 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. The apex of the lungs is their cranial point.
In most species, the lungs are divided into lobes by the 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, blood vessels and connective tissue. The terminal 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 it's sides, they have no 'walls' as such. Openings to individual alveoli are guarded by 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 inspiration and 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 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.
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 right atrium via the azygous vein. More often the blood from the bronchi drains directly to the left atrium.
Innervation
Nervous supply to the lung is via the pulmonary plexus within the mediastinum. The pulmonary plexus consists of sympathetic fibres largely from the stellate ganglion, and parasympathetic fibres from the vagus nerve.
Lymphatics
Lymph drains to the tracheobronchial and mediastinal lymph nodes.
Histology
Lung (adult)
©RVC 2008
SEM of Adult Sheep Lung
©RVC 2008
Bronchus
©RVC 2008
Bronchus
©RVC 2008
Alveoli
©RVC 2008
Alveoli
©RVC 2008
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 has many fundamental differences to mammalian respiration. The respiratory systems of non-homeotherms are also very different to that of mammals.
Links
Click here for more information on pathology of the lungs.
References
Dyce, K.M., Sack, W.O. and Wensing, C.J.G. (2002) Textbook of Veterinary Anatomy. 3rd ed. Philadelphia: Saunders.