HISTOLOGY OF LARYNX & 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

LARYNX

An irregular tube that connects pharynx to the trachea.

Laryngeal wall consists of:

1.- Mucosa

2.- Cartilages

3.- Intrinsic muscles

MUCOSA :

comprises of:

Epithelium

Lamina propria

- Mucosa forms 2 pairs of folds that extend into the lumen of the larynx.

- Upper pair constitutes false vocal cords (vestibular folds)

- Lower pair constitutes true vocal cords. - Large bundles of parallel elastic fibers that compose the

vocal ligament lie within the vocal folds. - Parallel to the ligaments are bundles of skeletal muscle,

vocalis muscle, which regulate the tension of the fold and its ligament.

- Epithelium lining epithelium varies in type in different parts of the larynx:

▪ stratified squamous noncornified epithelium - covers laryngeal inlet, most of

the epiglottis & true vocal cords.

▪ Typical respiratory epithelium (i.e., pseudostratified columnar ciliated epithelium with goblet cells) covers the rest of the larynx.

- Lamina propria

▪ Consists of fine connective tissue and contains: scattered lymphatic nodules

▪ many simple branched tubulo-alveolar glands of mixed variety

▪ nine cartilages:

Cartilages - There are 3 unpaired & 3 paired cartilages

Unpaired Cartilages :-

a. Epiglottis b. Thyroid. c. Cricoid

Paired Cartilages :-

a. Arytenoids. b. Thyroid.

c. Cricoid

-

- Cartilages are bounded together by the ligaments and are supported by skeletal muscles.

- In addition to supporting role, these cartilages serve as a valve, and prevents entry of swallowed food or fluid into the trachea.

- They also participate in producing sounds for phonation

EPIGLOTTIS

It consists of a plate of elastic cartilage covered on both sides by mucosa.

Epithelium

- 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.

Lamina propria

- It lodges tubulo-alveolar glands of mixed type.

- These glands are found mainly on the posterior surface, where they lie in irregular depressions

(pock marks) in the underlying elastic cartilage.

- Scattered taste buds are also found to be present between the epithelial cells on the posterior surface.

HISTOLOGY OF TRACHEA

It is thin wall tube, about 10 cm long, that extend from the base of larynx to sterna angle where it bifurcates in to two primary bronchi.

Consists of

Mucosa submucosa Adventitia

MUCOSA:

Made up of epithelium and lamina propria

- Epithelium Respiratory with numerous goblet cells.

- Lamina Propria ▪ There are 16-20 C-shaped rings of

hyaline cartilage that keep the tracheal lumen open.

▪ Gaps b/w posterior ends of each cartilage is bridged by a band of fibro-elastic ligament & bundle of smooth muscle called Trachealis.

▪ Ligament prevents over distention of lumen.

▪ Muscle allows regulation of lumen. ▪ Space b/w adjacent rings are filled by dense fibrous C.T.,

which is fused with the perichondrium.

SUBMUCOSA

- Consists of loose Connective tissue

- Contains numerous tubulo-alveolar glands. Ducts of these glands pierce L.P.to open on to the mucosal surface.

ADVENTITIA

- mainly composed of loosely arranged collagenous fibers.- It lodges small blood vessels and autonomic nerve, which

supply trachea.