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The trachea begins at the lower edge of the cricoid cartilage of the larynx [3] at the level of sixth cervical vertebra (C6) [2] and ends at the carina, the point where the trachea branches into left and right main bronchi., [2] at the level of the fourth thoracic vertebra (T4), [2] although its position may change with breathing. [3]
The carina of the trachea is located at the level of the sternal angle and the fifth thoracic vertebra (at rest). The right main bronchus is wider, shorter, and more vertical than the left main bronchus, [ 3 ] its mean length is 1.09 cm. [ 4 ] It enters the root of the right lung at approximately the fifth thoracic vertebra.
The carina is a cartilaginous ridge separating the left and right main bronchi that is formed by the inferior-ward and posterior-ward prolongation of the inferior-most tracheal cartilage. [2] The carina occurs at the lower end of the trachea - usually at the level of the 4th to 5th thoracic vertebra.
The trachea is the largest tube in the respiratory tract and consists of tracheal rings of hyaline cartilage. It branches off into two bronchial tubes, a left and a right main bronchus. The bronchi branch off into smaller sections inside the lungs, called bronchioles. These bronchioles give rise to the air sacs in the lungs called the alveoli. [10]
The fifth thoracic vertebra, together with the fourth, is at the same level as the sternal angle. The human trachea divides into two main bronchi at the level of the 5th thoracic vertebra, but may also end higher or lower, depending on breathing. The thoracic spinal nerve 5 (T5) passes inferior to it.
In the fourth week of development, the respiratory diverticulum, [1] starts to grow from the ventral (front) side of the foregut into the mesoderm that surrounds it, forming the lung bud. Around the 28th day, during the separation of the lung bud from the foregut it forms the trachea and splits into two bronchial buds, one on each side. [1] [2]
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The trachea is an area of dead space: the oxygen-poor air it contains at the end of exhalation is the first air to re-enter the posterior air sacs and lungs. In comparison to the mammalian respiratory tract , the dead space volume in a bird is, on average, 4.5 times greater than it is in mammals of the same size.