Changes

The lungs are the site for 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 inspiration and expiration.

The lungs are the site for 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 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 by birth.

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]].

==Structure==

==Structure==

*The left and right lungs lie within their 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 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. The apex of the lungs is the cranial point.

*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 bronchial tree:

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

**Left Lung = Cranial and Caudal lobes.  

**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''']]

**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''']]

*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.

*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''': 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 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 [[Muscles - Anatomy & Physiology#Smooth Muscle|smooth muscle]].

**'''Alveolar Sacs''': These are rotunda-like areas on the end of the alveolar ducts, usually there are clusters of these at the end of each duct.

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

**'''Alveoli''': These 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.

**'''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==