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==Introduction==

==Introduction==

The trachea bifurcates at the levels of the 4th-6th intercostal space, approximatley halfway between the thoracic inlet and the diaphragm, dividing into two Principle 'Bronchi', tubes which conduct air into the lngs. These further divide into smaller bronchi and bronchioles.

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 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 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 teh 'Respiratory Zone' - a site for gaseous exchange.

 

==Histology==

==Histology==

[[Image:Bronchiole Histology.jpg|right|thumb|350px|©Nottingham 2008]]

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

 

The '''Bronchioles''' have no [[Cartilage - Anatomy & Physiology#Types of Cartilage|cartilage]] rings but have well developed [[Muscles - Anatomy & Physiology|muscular]] walls to enclose the lumen. The epithelium is reduced to cuboidal, and in the normal animal it contains no mucus secreting glands. There are many [[Lymph Nodes - Anatomy & Physiology|lymphoid]] nodules beneath the epithelial layer.

*The '''Bronchioles''' have no cartilage rings but have well developed muscular walls to enclose the lumen. The epithelium is reduced to cuboidal, and in the normal animal it contains no mucus secreting glands. There are many lymphoid nodules beneath the epithelial layer.

*'''Respiratory Bronchioles''' have few alveoli scattered along the length, at the entrance of which is ''simple squamous'' epithelium, and bronchial smooth muscle bundles.

==Species Differences==

 

==Links==

*Betweeh species the diameter of the bronchi and bronchioles vary greatly and more significantly than the variations of the trachea.

'''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]]