Respiratory Epithelium, Larynx and Trachea
LEARNING OBJECTIVES
At the end of the lecture the student shouldbe able to know :
• Different layers of larynx
•
Histological characteristics of each layer of larynx
•
Histological classification of laryngeal cartilage
•
Structure of trachea and its layer
•
Different layers of trachea and their histological characteristics
LECTURE OUTLINE
The respiratory system includes the lungs and a system of tubes that links the sites of gas exchange with the external environment.
A ventilation mechanism,
Respiratory System
Consists of Lungs and Respiratory Passages.
Conducting portion
Respiratory portion
Functions of Respiratory Epithelium
Exchange of O2 and CO2 between the blood and inhaled air across the alveoli
Olfaction
Phonation
Conducting Portion
Respiratory Portion
Respiratory Epithelium
Following types of epithelia line the respiratory system:
Ciliated Pseudo stratified Columnar epithelium-conducting portion up to the large bronchioles.
Ciliated Simple cuboidal epithelium-terminal bronchioles
Simple squamous epithelium-alveoli.
Bronchial Wall Constituents
Cilia
Goblet cells
Glands
Cartilage
Smooth muscle fibers
Elastic fibers
Cell Types
Electron microscopy reveals Six types of cells present in epithelia lining the conducting portion .
Ciliated columnar cells

Goblet cells
Brush cells
Basal (short) cells
Small granular cells
Clara cells
LARYNX
The respiratory system is composed of two main parts:
1. A system of progressively smaller, structurally and functionally complex tube known as airway .
2. A respiratory unit at the distal end of airway, where gases are exchanged between the airway and circulating blood.
Airway (conducting part)

It starts from nasal cavity, continues in the nasopharynx, larynx, trachea, bronchi, bronchioles and terminal bronchioles.

Its function is to clean, moisten and warm the inhaled air and conduct it to respiratory part.
Respiratory unit

Here exchange of gases takes place.

It is composed of respiratory bronchioles, alveolar ducts, alveolar sacs and pulmonary alveoli
Trachea divides into two primary (main) bronchi which enter in the substance of lung.
They are also accompanied by pulmonary vessels and bronchial vessels.
The primary bronchi subdivide within lung into secondary or lobar bronchi.
The lobar bronchi divide into tertiary or segmental bronchi which are 10 in right lung and
8 in the left.
Segmental bronchi go on dividing until they become 1mm in diameter, now known as bronchioles.
Bronchioles continue to divide and when they have reduced to 0.5 mm they are known as terminal bronchioles

LARYNX
An irregular tube that connects pharynx to the trachea.
Laryngeal wall consists of: 1.-
Mucosa 2.-
Cartilages 3.-
Intrinsic muscles
LARYNGEAL MUCOSA
Comprises of:
Epithelium
Lamina propria
Mucosa forms 2 pairs of folds
Upper pair constitutes false vocal cords (vestibular folds)
Lower pair constitutes true vocal cords .
Epithelium
Varies in type in different parts of the larynx:
Stratified squamous noncornified epithelium
Laryngeal inlet
Most of the epiglottis
True vocal cords
Typical respiratory epithelium covers the rest of the larynx.
Lamina propria
Consists of fine connective tissue and contains
TRUE VOCAL CORDS
FALSE VOCAL CORDS
LARYNGEAL CARTILAGES
Unpaired Cartilages:-
Epiglottis
Thyroid.
Cricoid
Paired Cartilages:-
Arytenoids.
Thyroid.
Cricoid
HISTOLOGICAL CLASSIFICATION OF LARYNGEAL CARTILAGES
Hyaline Cartilages
Thyroid
Cricoid
Most of arytenoids
Subject to calcified in old age.

ELASTIC CARTILAGES OF LARYNX
Epiglottis
Cuneiforms,
Corniculates
Tips of arytenoids
EPIGLOTTIS
Unpaired cartilage
Elastic; covered on both side by mucosa comprising of epithelium and lamina propria.
EPITHELIUM OF EPIGLOTTIS
Anterior (lingual) surface and upper part of posterior (laryngeal) surface are covered by stratified squamous noncornified epithelium.
Lower half of the posterior surface is covered by the respiratory epithelium.
EPIGLOTTIS LAMINA PROPRIA
Contains tubulo-alveolar glands of mixed type. mainly on the posterior surface
Scattered taste buds are present between the epithelial cells on the posterior surface
TRACHEA
Thin wall tube, about 10 cm long, Extends from the base of larynx to sternal angle
Bifurcates in to two primary bronchi.
HISTOLOGY OF TRACHEA
Consists of
Mucosa
Epithelium
Lamina propria submucosa
Adventitia
MUCOSA OF TRACHEA
Made up of epithelium and lamina propria
Epithelium
Respiratory with numerous goblet cells.
TRACHEA LAMINA PROPRIA
16-20 C-shaped rings of hyaline cartilage

SUBMUCOSA
Consists of loose Connective tissue
Contains numerous tubulo-alveolar glands that open on to the mucosal surface
ADVENTITIA
Mainly composed of loosely arranged collagenous fibers
Lodges small blood vessels and autonomic nerve, which supply trachea