No Trachea

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					              No. 10
1.   Trachea
2.   Bronchi
3.   Lungs
4.   Pleura
5.   mediastinum
         Section 4 The Trachea
    The trachea is a tube approximately 2.0 cm in
    diameter and 11 cm long.
   Location:
    It is located in the midline of neck and upper
    thorax, and in front of the esophagus.
    It extends from the larynx at the lower border of
    the cricoid cartilage at the level of sixth cervical
    vertebra to the level of the sternal angle
    (corresponding) to the lower border of the fourth
    thoracic vertebra, where it divides into the right
    and left principal bronchi.
    Composition:
   The wall of trachea is mainly composed of
    about 15~30 C-shaped rings of hyaline
    cartilage keep the lumen of the trachea
    open.
   But the posterior wall of the trachea is
    closed by the tracheal muscle and lies
    against the anterior surface of the
    esophagus permitting the esophagus to
    expand during swallowing.
     Carina of trachea:
   It is a sagittal semilunar ridge inside
    the bifurcation of trachea, which can
    be seen through bronchoscope and
    used as a guide to the bronchi.
        Section 5 The Bronchi
   The trachea terminates at the level of
    fourth thoracic vertebra and divides into
    the right and left principal bronchi.
   The right principal bronchus is about
    2~3 cm long and is shorter, wider and
    more vertical in position than the left.
   The left principal bronchus is longer,
    about 4~5 cm long, finer and less vertical.
   So the foreign objects from the trachea
    usually pass to the right bronchus.
     Bronchial tree:
   As entering the lungs, the principal
    bronchus branches to form lobar bronchi
    which enter the lobes of lung.
   The lobar bronchi continue to branch,
    forming still smaller bronchi called the
    segmental bronchi, which are
    subdivided into the bronchioles.
   ramify into even smaller tubes called the
    terminal bronchioles.
   These branches resemble a tree and so
    are called the bronchial tree.
         Section 6 The Lungs
   The lungs are the essential organs of
    respiration.
   Healthy lungs always contain some air so
    they may float in water. In the newborn
    which has not breath, the lungs will not
    float in water. At birth the lungs are
    pinkish-white but they turn dark trey with
    age and become almost black due to
    carbonaceous deposits.
     Location:
   The lungs are situated one on each
    side within the thorax, and separated
    from each other by the heart and
    other contents of the mediastinum.
Ⅰ. The External Features of Lungs
   Each lung is shaped somewhat like a
    cone, with an apex, a base, two
    surfaces and three borders.
   The right lung is shorter than the left
    one because the right dome of the
    diaphragm is higher, and it is wider
    because the heart and pericardium
    bulge more to the left.
  1. One apex and one base
1) The apex of lung is rounded and
extends to about 2~3 above the level of
the medial one-third of the clavicle.
2) The base of lung is concave and
related to the diaphragm which separates
the right lung from the liver and the left
lung from the stomach, spleen and liver,
so the base of lung is also called the
diaphragmatic surface.
        2. Two surfaces
 The lung possesses a costal surface
and a medial surface.
 1) The costal surface is smooth,
convex and related to the inner
surface of the ribs, costal cartilages
and intercostal spaces.
 2) The medial surface is related to
the mediastinum, so it is also called
the mediastinal surface.
    The hilum of lung and root of lung:
   Near the center of the medial surface, there is a
    depression called the hilum of lung (hilus). The
    hilus is the region where the structures that form
    the root of the lung-that is, the bronchus, blood
    vessels, lymphatics and nerves-enter or leave the
    lung.
   The structures entering and emerging the hilum
    is called the root of lung, which is short broad
    pedicle and consists of the bronchi, pulmonary
    artery and veins, nerves, bronchial vessels,
    lymphatics and lymph nodes.
             3. Three borders
   The borders of lung includes anterior,
    posterior and inferiors.
   The anterior border is thin and sharp,
    having a deep notch at the forth and fifth
    intercostals spaces in the left lung, called
    the cardiac notch of left lung, beneath
    which is the lingula of left lung.
   The posterior border is round.
   The inferior border is also sharp and
    separates the base of lung from the costal
    and medial surfaces.
    Ⅱ. The Lobes and Segments of
               Lungs
     Fissures and lobes:
   Each lung is divided into superior
    and inferior lobes by an oblique
    fissure. The right lung is further
    divided by a horizontal fissure, which
    bounds a middle lobe.
   The right lung therefore has three
    lobes, whereas the left has only two.
     Bronchopulmonary segments:
   Each lung is subdivided by connective
    tissue partitions into smaller units called
    bronchopulmonary segments.
   Each bronchopulmonary segment
    represents the portion of the lung that is
    supplied by a specific tertiary bronchus.
    Each lung has ten segments.
   The bronchopulmonary segments are
    important surgically because a diseased
    segment can be removed without having
    to remove an entire lobe or the entire lung.
    Also, disease does not spread so easily
    across the partitions that separate the
    segments, so pathology tends to be
    confined to one or several segments
    rather than spreading freely throughout
    the lungs.
         Section 7 The Pleura
   Each lung is enclosed in a double-walled
    the pleura. Both layers of the pleura are
    formed of serous membrane that lines the
    inner surface of the thorax and the
    surface of the thorax and the surfaces of
    lungs.
   The portion of the pleura that adheres
    firmly to the lungs is the visceral pleura.
   The portion that lines the walls of the
    thoracic cavity is the parietal pleura.
        Ⅰ. The Parietal Pleura
   The serous membrane lining the
    inner surface of chest wall is called
    the parietal pleura.
   According to the regions the parietal
    pleura is divided into four portions:
     ① the costal pleura,
     ② he diaphragmatic pleura,
     ③ the mediastinal pleura ,
     ④ the cupola of pleura.
        Ⅱ. The Visceral Pleura
   The pleura is reflected from the
    mediastinum to the surface of lung, where
    it is called visceral pleura covering the
    lungs and extending into the fissures of
    lung.
   Below the root of lung the mediastinal
    pleura extends as a double layer to the
    mediastinal surface of lung. This double
    layer is called the pulmonary ligament.
      Ⅲ. The Pleural Cavity and
             Recesses
 Ⅰ) The Pleural Cavity
 The visceral and parietal layers are
  continuous at the hilus of the lung.
  between the two layers of the pleura is an
  extremely narrow pleural cavity, which is
  filled with pleural fluid. The pleural fluid
  is secreted by the pleura, and it acts as a
  lubricant to reduce the friction between
  the two layers during respiratory
  movements.
 The two pleural cavities are separated
  from each other by the mediastinum.
     Ⅱ) The Pleural Recesses
     Costodiaphragmatic recess:
   In quiet breathing the inferior border of
    the lung does not completely extend the
    inferior margin of the pleural reflexion, so
    that the costal and diaphragmatic pleurae
    are in contact with each other here, the
    intervening narrow slit termed the
    costodiaphragmatic recess. In quiet
    respiration the lower limit of lung is about
    5 cm above the lower limit of the pleura.
     Costomediastinal recess:
   A similar condition present behind
    the sternum, between the costal and
    mediastinal pleurae it is termed the
    costomediastinal recess.
    Ⅳ. The Projection of the Inferior
    Margins of Lungs and Pleurae
   On the surface of the body, the
    projection of the inferior margins of
    the lungs and pleurae are shown in
    table 1:
   The inferior margins of pleurae is the
    costodiaphragmatic lines of reflexion
    of the pleurae
     Table 1 The inferior margins of
           lungs and pleurae

            Midclavicular   Midaxillary   Posterior median
            line            line          line
Inferior    6th fib         8th rib       On the level of T10
margin of                                 spinal process
lungs
Inferior    8th rib         10th rib      On the level of T12
margin of                                 spinal process
pleurae
     Section 8 The Mediastinum
   The mediastinum is generally defined as
    the interval between the right and left
    pleural sacs.
    Location:
   It extends from the sternum in front to
    vertebral column behind, and from the
    thoracic inlet above to the diaphragm
    below.
   Its lateral wall is the mediastinal pleura of
    both sides.
    Division:
   The mediastium is divided into superior and
    inferior mediastina by the line drawn
    horizontally from the sternal angle to the lower
    border of 4th thoracic vertebra.
   The inferior mediastinum is subdivided into an
    anterior mediastinum in front of pericardium, a
    middle mediastinum containing the
    pericardium with heart and great vessels, and the
    posterior mediastinum between pericardium
    and vertebral column.
   The posterior mediastinum extends to the lower
    border of the 8th thoracic vertebra, its main
    contents are the bronchi, esophagus, vagus and
    phrenic nerves, thoracic duct etc.

				
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posted:8/12/2011
language:English
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