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==Introduction==

==Introduction==

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 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 [[Parturition - Normal Parturition - Anatomy & Physiology|parturition]].

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 [[Parturition - Normal Parturition - Anatomy & Physiology|parturition]].

==Structure==

==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 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.

*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:

*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.

**'''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]], [[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.

*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 [[Muscles - Anatomy & Physiology#Smooth Muscle|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 each alveolar ducts which are usually present in clusters.

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