|T he halved joint is frequently known as half-lapping, and sometimes as checking and half-checking. In the majority of cases it is made by halving the two pieces, i.e., by cutting half the depth of the wood away. There are, however, exception... Read more of The Halved Joint at Wood Workings.ca|| Informational|
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Anatomy Of Larynx Trachea Bronchi And Esophagus Endoscopically Considered
Category: ANATOMY OF LARYNX, TRACHEA, BRONCHI AND ESOPHAGUS, ENDOSCOPICALLY CONSIDERED
Source: A Manual Of Peroral Endoscopy And Laryngeal Surgery
The larynx is a cartilaginous box, triangular in cross-section, with
the apex of the triangle directed anteriorly. It is readily felt in
the neck and is a landmark for the operation of tracheotomy. We are
concerned endoscopically with four of its cartilaginous structures:
the epiglottis, the two arytenoid cartilages, and the cricoid
cartilage. The epiglottis, the first landmark in direct
laryngoscopy, is a leaf-like projection springing from the
anterointernal surface of the larynx and having for its function the
directing of the bolus of food into the pyriform sinuses. It does not
close the larynx in the trap-door manner formerly taught; a fact
easily demonstrated by the simple insertion of the direct laryngoscope
and further demonstrated by the absence of dysphagia when the
epiglottis is surgically removed, or is destroyed by ulceration.
Closure of the larynx is accomplished by the approximation of the
ventricular bands, arytenoids and aryepiglottic folds, the latter
having a sphincter-like action, and by the raising and tilting of the
larynx. The arytenoids form the upper posterior boundary of the
larynx and our particular interest in them is directed toward their
motility, for the rotation of the arytenoids at the cricoarytenoid
articulations determines the movements of the cords and the production
of voice. Approximation of the arytenoids is a part of the mechanism
of closure of the larynx.
The cricoid cartilage was regarded by esophagoscopists as the chief
obstruction encountered on the introduction of the esophagoscope. As
shown by the author, it is the cricopharyngeal fold, and the
inconceivably powerful pull of the cricopharyngeal muscle on the
cricoid cartilage, that causes the difficulty. The cricoid is pulled
so powerfully back against the cervical spine, that it is hard to
believe that this muscles is inserted into the median raphe and not
into the spine itself (Fig. 68).
The ventricular bands or false vocal cords vicariously phonate in
the absence of the true cords, and assist in the protective function
of the larynx. They form the floor of the ventricles of the larynx,
which are recesses on either side, between the false and true cords,
and contain numerous mucous glands the secretion from which lubricates
the cords. The ventricles are not visible by mirror laryngoscopy, but
are readily exposed in their depths by lifting the respective
ventricular bands with the tip of the laryngoscope. The vocal cords,
which appear white, flat, and ribbon-like in the mirror, when viewed
directly assume a reddish color, and reveal their true shelf-like
formation. In the subglottic area the tissues are vascular, and, in
children especially, they are prone to swell when traumatized, a fact
which should be always in mind to emphasize the importance of
gentleness in bronchoscopy, and furthermore, the necessity of avoiding
this region in tracheotomy because of the danger of producing chronic
laryngeal stenosis by the reaction of these tissues to the presence of
the tracheotomic cannula.
The trachea just below its entrance into the thorax deviates
slightly to the right, to allow room for the aorta. At the level of
the second costal cartilage, the third in children, it bifurcates into
the right and left main bronchi. Posteriorly the bifurcation
corresponds to about the fourth or fifth thoracic vertebra, the
trachea being elastic, and displaced by various movements. The
endoscopic appearance of the trachea is that of a tube flattened on
its posterior wall. In two locations it normally often assumes a more
or less oval outline; in the cervical region, due to pressure of the
thyroid gland; and in the intrathoracic portion just above the
bifurcation where it is crossed by the aorta. This latter flattening
is rhythmically increased with each pulsation. Under pathological
conditions, the tracheal outline may be variously altered, even to
obliteration of the lumen. The mucosa of the trachea and bronchi is
moist and glistening, whitish in circular ridges corresponding to the
cartilaginous rings, and reddish in the intervening grooves.
The right bronchus is shorter, wider, and more nearly vertical than
its fellow of the opposite side, and is practically the continuation
of the trachea, while the left bronchus might be considered as a
branch. The deviation of the right main bronchus is about 25 degrees,
and its length unbranched in the adult is about 2.5 cm. The deviation
of the left main bronchus is about 75 degrees and its adult length is
about 5 cm. The right bronchus considered as a stem, may be said to
give off three branches, the epiarterial, upper- or superior-lobe
bronchus; the middle-lobe bronchus; and the continuation downward,
called the lower- or inferior-lobe bronchus, which gives off dorsal,
ventral and lateral branches. The left main bronchus gives off first
the upper-or superior-lobe bronchus, the continuation being the
lower-or inferior-lobe bronchus, consisting of a stem with dorsal,
ventral and lateral branches.
[FIG. 44.--Tracheo-bronchial tree. LM, Left main bronchus; SL,
superior lobe bronchus; ML, middle lobe bronchus; IL, inferior lobe
The septum between the right and left main bronchi, termed the carina,
is situated to the left of the midtracheal line. It is recognized
endoscopically as a short, shining ridge running sagitally, or, as the
patient lies in the recumbent position, we speak of it as being
vertical. On either side are seen the openings of the right and left
main bronchi. In Fig. 44, it will be seen that the lower border of the
carina is on a level with the upper portion of the orifice of the
right superior-lobe bronchus; with the carina as a landmark and by
displacing with the bronchoscope the lateral wall of the right main
bronchus, a second, smaller, vertical spur appears, and a view of the
orifice of the right upper-lobe bronchus is obtained, though a lumen
image cannot be presented. On passing down the right stem bronchus
(patient recumbent) a horizontal partition or spur is found with the
lumen of the middle-lobe bronchus extending toward the ventral surface
of the body. All below this opening of the right middle-lobe bronchus
constitutes the lower-lobe bronchus and its branches.
[FIG. 45.--Bronchoscopic views.
S; Superior lobe bronchus; SL, superior lobe bronchus; I, inferior
lobe bronchus; M, middle lobe bronchus.]
 Coming back to the carina and passing down the left bronchus, the
relatively great distance from the carina to the upper-lobe bronchus
is noted. The spur dividing the orifices of the left upper- and
lower-lobe bronchi is oblique in direction, and it is possible to see
more of the lumen of the left upper-lobe bronchus than of its
homologue on the right. Below this are seen the lower-lobe bronchus
and its divisions (Fig. 45).
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