Download The upper respiratory tract

The upper respiratory tract
<< introduction to respiratory system
The Upper Respiratory Tract
The organs of upper respiratory tract include the following:
Nose: The nose is the only externally visible part of the respiratory system. Protruding
prominently from the face, the nose serves as a vent for air exchange. The structures of the
nose are divided into the
External nose and the Internal nasal cavity. The external
nose
consists of a supporting framework of bone and hyaline cartilage covered with muscle and skin.
The external openings of the nose, the
external nares
or
nostrils
,
are bounded laterally by the flared
alae
. The
nasal cavity
lies in and posterior to the external nose. During breathing, air enters the nasal cavity by
passing through the external nares. The nasal cavity is divided equally into right and left halves
by a midline nasal septum. The nasal cavity is continuous posteriorly with the nasal portion of
the pharynx through the
internal nares
, also called the
posterior nares
or
choanae
. The portion of the nasal cavity just superior to the nostrils, called the
vestibule
, is lined with skin containing subaceous and sweat glands and numerous hair follicles. The
hairs, or
vibrissae
( vibro = to quiver), filter coarse particles (lint, dust, pollen) from inspired air. The remainder of
the nasal cavity is lined with two types of mucous membrane. The
olfactory mucosa
,
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The upper respiratory tract
lining the slitlike superior region of the nasal cavity, contains the receptors for the sense of
smell. The
respiratory mucosa
, is a pseudostratified ciliated columnar epithelium. The ciliated cells of the respiratory mucosa
create a gentle current that moves the sheet of contaminated mucus posteriorly toward the
throat (pharynx), where it is swallowed and digested by stomach juices.
Therefore, the nose (1) provides an airway for respiration, (2) moistens and warms entering air,
(3) filters inspired air and cleanses it of foreign matter, (4) serves as a resonating chamber for
speech, and (5) houses the olfactory (smell) receptors.
Pharynx: The pharynx is a funnel-shaped four to five inch fibromuscular tube that conducts air
from the nasal cavity to the larynx . Its three anatomical regions are described below. The
pharynx resembles a short length of garden hose and extends about 5 inches from the base of
the skull to the level of the sixth cervical vertebra.
Based on location, the pharynx has three regions, the nasopharynx is lying posterior to the
nasal cavity and connected to the cavity through posterior nares or choanae. It serves only as
an air passageway. The
lini
ng epithelium
of nasopharynx is the same pseudostratified columnar ciliated type. Goblet cells in the
epithelium secrete mucus, which further cleans, warms, and moistens incoming air before it
moves deeper into the respiratory tract. The
oropharynx
lies posterior to the oral cavity. It extends inferiorly from the soft palate to the epiglottis. Given
this location, both swallowed food and inhaled air pass through it. The oropharynx is lined with a
more
protective epithelium
that is nonkeratinized stratified squamous type. The
laryngopharynx
also serves as a common pathway for food and air. It lies directly posterior to the upright
epiglottis
and extends to the larynx, where the respiratory and digestive pathways diverge.
Larynx: The larynx or commonly known voice box, is a short tube (about 2 inches) located in
the throat, below the base of the
hyoid bone
and
tongue
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The upper respiratory tract
and anterior to the
esophagus
. Making up its walls are
nine supportive cartilages
, interconnecting ligaments, intrinsic and extrinsic muscles, and a mucosal lining. as a primary
function, the larynx provides a carefully guarded passageway between the pharynx and lower
respiratory tract organs. During the process of swallowing, movements of the
cartilages
close the entrance to the larynx so food and drink can not enter the respiratory passages. The
larynx also houses the
vocal folds
and ligaments that produce the voice.
All the laryngeal cartilages except for the epiglottis are hyaline cartilages. The large,
shield-shaped
thyroid
cartilage
is formed by the fusion of two cartilage plates. The midline laryngeal prominence, which marks
the fusion point, is obvious externally as the
Adam's apple
.
Inferior to the thyroid cartilage is the signet ring-shaped
cricoid cartilage
, which is anchored to the
trachea
inferiorly.
Three pairs of small cartilages, the arytenoid, cunieform, and corniculate cartilages, form part of
the lateral and posterior walls of the larynx. The most important of these are the
pyramid-shaped arytenoid cartilages, which anchor the
vocal cords
.
The ninth cartilage, the flexible, spoon-shaped epiglottis is composed of elastic cartilage. A
small
ligament attaches the narrow end
of epiglottic cartilage to the back of the thyroid cartilage.
During the process of swallowing, as the larynx continues to move upward, the epiglottis flattens
against the surface of the tongue. This downward movement causes the epiglottis to
cover
the laryngeal opening.
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The upper respiratory tract
Lying under the laryngael mucoa on each side are the vocal ligaments, which attach the
arytenoid cartilages to the thyroid cartilage. These ligaments composed largely of elastic fibers,
form the core of mucosal folds called the vocal folds or
true vocal cords
, which appear pearly white because of their avascular nature..
The medial opening between the two vocal cords through which air passes is the
glottis
.
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