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==Introduction==

==Introduction==

 

The trachea bifurcates at the levels of the 4th-6th intercostal space, approximately halfway between the thoracic inlet and the [[Diaphragm - Anatomy & Physiology|diaphragm]]. It divides into two '''principle bronchi''', tubes which conduct air into the lungs, and they divide into two '''lobar bronchi''' for the left lung, and into four lobar bronchi for the right lung. These further divide into smaller bronchi and bronchioles within the lung tissue.  

The trachea bifurcates at the levels of the 4th-6th intercostal space, approximately halfway between the thoracic inlet and the [[Diaphragm - Anatomy & Physiology|diaphragm]]. It divides into two Principle 'Bronchi', tubes which conduct air into the lungs. These further divide into smaller bronchi and bronchioles within the lung tissue.

The initial division after entry to the lung is known as the '''Principle Bronchi''', and this further divides into two ''Lobar Bronchi' for the left lung, and into four ''Lobar Bronchi'' for the right lung.

==Structure==

==Structure==

*The structure of the larger bronchi is identical to that of the [[Trachea - Anatomy & Physiology|trachea]]. On the smaller bronchi the C-shaped cartilage rings are gradually replaced by irregular ''plaques'' of cartilage. Bronchioles have no cartilage at all.  

The structure of the larger bronchi is identical to that of the [[Trachea - Anatomy & Physiology|trachea]]. On the smaller bronchi the C-shaped cartilage rings are gradually replaced by irregular ''plaques'' of cartilage. Bronchioles have no cartilage at all.  

*The bronchioles are less than 1mm in diameter, and undergo further divisions, the last of which is characterised by the loss of goblet cells.

The bronchioles are less than 1mm in diameter, and undergo further divisions, the last of which is characterised by the loss of goblet cells.

==Function==

==Function==

*The bronchi and bronchioles are parts of the ''''Conduction Zone'''' of the respiratory system - allowing the passage of air from the external environment into the lungs where gaseous exchange can take place. The '''Conduction Zone''' is also known as '''dead space''', and no gaseous exchange can take place in this area.

The bronchi and bronchioles are parts of the ''''Conduction Zone'''' of the respiratory system - allowing the passage of air from the external environment into the lungs where gaseous exchange can take place. The conduction zone is also known as '''dead space''', and no gaseous exchange can take place in this area. Some of the Bronchioles have alveoli scattered along their length, and thus form part of the ''''Respiratory Zone'''' - the site for gaseous exchange.

*Some of the Bronchioles have alveoli scattered along their length, and thus form part of the ''''Respiratory Zone'''' - the site for gaseous exchange.

 

 

Between species the diameter of the bronchi and bronchioles vary greatly and more significantly than the variations of the [[Trachea - Anatomy & Physiology|trachea]]. The number of bronchial divisions before bronchioles are present varies by species - small mammals such as mice may have only 4/5 generations, whereas 12+ may be necessary in larger animals. [[Avian Respiration - Anatomy & Physiology|Avian respiration]] is very different to that of mammals. The [[Respiration in Non-Homeotherms - Anatomy & Physiology|respiratory systems of non-homeotherms]] are also very different to that of mammals.

==Histology==

==Histology==

[[Image:Bronchiole Histology.jpg|right|thumb|300px|©Nottingham 2008]]

[[Image:Bronchiole Histology.jpg|right|thumb|300px|©Nottingham 2008]]

*The histology of the '''Bronchi''' is almost identical to that of the [[Trachea - Anatomy & Physiology|trachea]] - the lumen of the bronchus is lined by a pseudostratified epithelium, including goblet cells and serous cells.

The histology of the '''bronchi''' is almost identical to that of the [[Trachea - Anatomy & Physiology|trachea]]. The lumen of the bronchus is lined by a '''pseudostratified epithelium''', including goblet cells and serous cells. Beneath the narrow layer of connective tissue under the epithelium lie well-developed spiral bands of [[Muscles - Anatomy & Physiology#Smooth Muscle|smooth muscle]].

Beneath the narrow layer of connective tissue under the epithelium lie well-developed spiral bands of [[Muscles - Anatomy & Physiology#Smooth Muscle|smooth muscle]].

*'''Respiratory Bronchioles''' have few alveoli scattered along the length, at the entrance of which is ''simple squamous'' epithelium, and bronchial [[Muscles - Anatomy & Physiology#Smooth Muscle|smooth muscle]] bundles.

*Between species the diameter of the bronchi and bronchioles vary greatly and more significantly than the variations of the [[Trachea - Anatomy & Physiology|trachea]].

The '''respiratory bronchioles''' have few alveoli scattered along the length, at the entrance of which is ''simple squamous'' epithelium, and bronchial [[Muscles - Anatomy & Physiology#Smooth Muscle|smooth muscle]] bundles.

*The number of bronchial divisions before bronchioles are present varies by species - small mammals such as mice may have only 4/5 generations, whereas 12+ may be necessary in larger animals.

*[[Avian Respiration - Anatomy & Physiology|Avian Respiration]] is very different to that of mammals.

*The [[Respiration in Non-Homeotherms - Anatomy & Physiology|Respiratory Systems of non-Homeotherms]] are also very different to that of mammals.

==Links==

==Links==

[[Bronchi and Bronchioles - Pathology]]

 

'''Click here for information on [[:Category:Bronchi and Bronchioles - Pathology|pathology of bronchi and bronchioles]]'''

==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}}

 

 

*{{citation|initiallast = Budras|initialfirst = K.D|2last = McCarthy|2first = P.H|3last = Fricke|3first = W|finallast = Richter|finalfirst = R|year = 2002|title = Anatomy of the Dog|ed =4th|city = Hannover|pub = Schlutersche GmbH & Co. KG, Verlag und Druckerei}}

[[Category:Respiratory System - Anatomy & Physiology]]