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 oflung.

They are also accompanied by pulmonary vessels and bronchial vessels.

The primary bronchi subdivide within lunginto secondary or lobar bronchi.

The lobar bronchi divide into tertiary orsegmental bronchi which are 10 inright lung and 8 in the left.

Segmental bronchi go on dividing until they become 1mm in diameter, nowknown 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.

EPITHELIUMOF 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