Download Elastic cartilages

Histology 2016-2017
Department of Anatomy &Histology:
Dr.Rajaa Ali
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Respiratory System II
PARANASAL SINUSES
● Paranasal sinuses are air-filled spaces in the bones around the nasal
cavity.
● There are our pairs o paranasal sinuses—frontal, sphenoidal , ethmoidal
and maxillary; they are present in the bones with the corresponding names.
● They open into the nasal cavity.
● They are lined by the respiratory mucosa.
PHARYNX
GENERAL FEATURES
 Pharynx is a fibromuscular tube extending from the base of the skull
to the level of the sixth cervical vertebra where it becomes
continuous with the oesophagus.
 It lies behind the nasal cavity (nasopharynx), oral cavity
(oropharynx) and larynx (laryngopharynx).
STRUCTURE
Pharynx is composed of the following four coats:
1. Mucosa
 This comprises epithelium and lamina propria. The epithelium is
pseudostratifi ed ciliated columnar type in the nasopharynx and
stratified squamous type in the oropharynx and laryngopharynx.
 Aggregation of lymphatic nodules in the lamina propria of the
posterior wall and around the opening of the auditory tube in the
nasopharynx results in the formation of pharyngeal and tubal
tonsils, respectively.
 The palatine tonsil present in the lateral wall of the oropharynx and
the lingual tonsil in the pharyngeal part of tongue, are already dealt
with under lymphatic system.
2. Submucosa
It is formed by loose areolar connective tissue (pharyngobasilar fascia).
3. Muscle coat
 This layer is formed by skeletal muscle arranged into inner
longitudinal and outer circular layers.
 The circular layer is formed by the constrictors of pharynx.
4. Adventitia
It is formed by fibroelastic connective tissue (buccopharyngeal fascia).
LARYNX
● The larynx connects the oropharynx and the trachea. It is the component
of the conductive part of the respiratory system, and it is also responsible
or sound production.
● The interior of the larynx has two olds—vestibular and vocal olds—
projecting into the lumen (Fig.1).
● The vestibular old ( alse vocal cord) is lined by respiratory epithelium.
Underneath the epithelium, in the lamina propria, there are numerous
serous and mucous glands; the ducts o these glands open into the luminal
surface of the larynx.
● The vocal old (true vocal cord) is lined by stratifed squamous nonkeratinised epithelium which provides protection from physical injury
during its movement.
 The remaining parts of the interior of the larynx are lined by the
respiratory mucosa.
● Underneath the lamina propria , laryngeal cartilages are present.
• These are thyroid, cricoid, epiglottis, corniculate and cuneiform
cartilages; they are present in the wall o the larynx and form its
skeletal framework.
• The thyroid, cricoid and most of arytenoid consist of hyaline
cartilage .
• whereas the epiglottis, corniculate and cuneiform are elastic
cartilage.
Fig.1: histological section through the larynax
The cartilages are either hyaline or elastic in nature. These are:
Hyaline cartilages
 Thyroid (unpaired)
 Cricoid (unpaired)
 Arytenoid (paired)
Elastic cartilages
 Epiglottis (unpaired)
 Cuneiform (paired)
 Corniculate (paired)
Epiglottis (Fig.)
● The epiglottis has upper and lower ends, anterior and posterior surfaces
and two lateral borders (fig.2 )
Fig. 2 : epiglottis
●The lingual surface (or anterior surface) and upper part of the laryngeal
surface (or posterior surface) are covered by stratified squamous nonkeratinised epithelium, and the rest of the laryngeal surface is covered by
respiratory epithelium.
 The upper part of the laryngeal surface, where the epithelium is
stratified squamous non-keratinised, shows the presence of some
taste buds.
● Lamina propria consists of connective tissue with numerous serous and
mucous glands (fig. 3 ).
● Elastic cartilage is present underneath the lamina propria and provides
the skeletal framework to the epiglottis.
Fig .3 : histological section through the epiglottis
TRACHEA (Fig. 4 ,5 ,6 )
● The luminal surface of the trachea is lined by respiratory epithelium.
● Lamina propria is present underneath the epithelium.
● underneath the lamina propria, there is the submucosa with serous and
mucous glands; the ducts of these glands open on the luminal surface of
the epithelium.
● Beneath the submucosa, there is ‘C’-shaped hyaline cartilage. The ends
of the ‘C’-shaped cartilage are on the posterior aspect of the trachea. The
two ends of these cartilages are joined by smooth muscle called trachealis
(Fig.4).
Fig. 4 : transfere section through the trachae
Fig. 5 : histological section through the trachae
Fig. 6 : histological section through the trachea
 Trachea divides into principal bronchi in the thorax at the level
of T4
 Each principal bronchus enters the lung at the hilum.
 The structure of principal bronchus is similar to that of trachea.
Primary or Principal Bronchus .
The primary bronchus is similar to the trachea with a few differences
which are as follows:
● The cells o respiratory epithelium are shorter and have less number
of goblet cells.
● Between the lamina propria and the submucosa, there are bundles of
spirally arranged smooth muscle, completely encircling the bronchus.
● Glands in submucosa are less in number compared to those in the
submucosa of trachea.
● Cartilaginous rings completely encircle the bronchus.