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Full text of "Diseases Of The Nose Throat And Ear"

ANATOMY AND PHYSIOLOGY OF THE LARYNX         147

columnar ciliated over the rest of the larynx. This latter type comrnonK
undergoes squamous metaplasia in response particularly to atmospheric
pollution and smoking.

The supraglottis is rich in mucous glands and lymphatics and so metastases
are commoner in supraglottic tumours than others. There are no mucous
glands in the glottis and very few in the subglottis. This latter compartment
has a much poorer lymph drainage than the supraglottis accounting for the
fact that only 1 in 5 patients with subglottic cancer have metastatic lymph
nodes.

The mucosa of the glottis and supraglottis is firmly bound down to the
underlying tissue, but not so in the subglottic region. Here, the laxity of the
tissue allows a dangerous degree of oedema, especially in children, where the
diameter of the area is relatively smaller than in the adult. In this situation, a
degree of oedema, which would not cause too much trouble to an adult, could
be fatal in childhood.

LARYNGEAL COMPARTMENTS

The larynx is divided into three different compartments, namely, the glottis,
supraglottis and subglottis. This division is not only of academic anatomical
interest but is of prime importance in the staging and treatment of cancer of
the larynx.

The glottis is basically composed of the vocal cords from the extreme lateral
edge of the cord to the inferior border of the medial surface of the cord.
Anteriorly it extends from the anterior commissure (which is where the vocal
cords meet) to the posterior commissure (where the arytenoids meet).
Approximately half the length of the glottis is formed by the arytenoid
body and vocal process (i.e. cartilage) and half by the membranous vocal
cord.

The subglottis extends from the lower border of the glottis to the inferior
border of the cricoid. Below this is the trachea. The subglottis is dome shaped
and is relatively small and restricted.

The supraglottis extends from the upper border of the glottis inferiorly (the
ventricle of the larynx) to the hyoid bone superiorly being bounded laterally
by the ary-epiglottic folds; the pyriform fossa, which is part of the pharynx,
begins at the edge of the ary-epiglottic folds. The suprahyoid epiglottis and
vallecula are considered part of the oropharynx.

PHYSIOLOGY

The functions of the larynx are: (i) to protect the lung, (ii) to control air-flow
and (iii) to initiate phonation. The protective function is well known to all who
have choked on a crumb and have experienced the laryngeal spasm which
follows. It is provided by three sphincter-like actions: (a) the approximation
of the ary-epiglottic folds assisted by the epiglottis which tilts posteriorly, (b)
the apposition of the false cords (ventricular folds) and (c) the closure of the
vocal cords (folds) to prevent the entry of foreign material. During this phase
respiration is arrested but once the foreign particle is ejected into the
hypopharynx a long inspiration occurs.