Anatomy & Physiology of the Throat

The Pharynx

The nose and mouth open into the pharynx, which is the common passage for air and food leading to the larynx and oesophagus.

The pharynx is divided into 3 parts:

• Nasopharynx
• Oropharynx
• Laryngopharynx
  

It extends from the base of skull to upper oesophagus (level with 6th vertebra) behind the cricoid cartilage.

It is attached to:

• Base of skull
• Tongue
• Mandible
• Skeleton of larynx
  

The wall of the pharynx has 4 layers:

• Mucous membrane
• Submucosa
• Pharyngeal muscles
• Fascia

The Nasopharynx

The nasopharynx or postnasal space lies behind the nasal cavity and extends from the base of the skull to the level of the soft palate.

It has five opens:

• The two posterior nares
• Downwards into the oropharynx
• The orifices of the two pharyngotympanic (Eustachian) tubes.
  These protrude into the nasopharynx to form an elevation on the lateral walls.
  

The Oropharynx

The oropharynx lies behind the mouth between the soft palate and the upper edge of the epiglottis. It is continuous above with the nasopharynx and below with the laryngopharynx at the level of the hyoid bone.
Anteriorly the uvula, soft palate, anterior tonsillar pillars and part of the tongue border the opening into the mouth. At the base of the tongue lies the lingual tonsil.

The laryngopharynx (hypopharynx)

The laryngopharynx lies behind the larynx and extends from the level of the hyoid to the cricoid cartilage. It is continuous below with the oesophagus. The anterior wall opens into the larynx at the level of the ary-epiglottic folds. Laterally the larygopharynx extends to form two recesses called pyriform fossa.

The lymphoid tissue of the pharynx

There are superficial masses of lymphoid tissue in the pharyngeal mucosa, which form a ring that acts as a filter, protecting the body against infecting organisms that might enter it from the nose or mouth. This ring of lymphoid tissue is called "Waldeyer's Ring"

It consists of:

1. Faucial or Palatine tonsils
   The faucial tonsils consist of lymphoid tissue with 8 - 20 tubular crypts, which frequently branch in the depth of the tonsil, lymphocytes normally collect in the crypts. It is covered with stratified squamous epithelium and desquamated epithelial cells. The faucial tonsil is enclosed in a capsule, which enables complete enucleation of all tonsillar material by splitting the capsule.
2. Pharyngeal tonsil (Adenoid)
   The pharyngeal tonsil lies on the roof and upper posterior wall of the nasopharynx. It contains many tubular crypts extending from the surface. Its surface has five or more fissures running from front to back, the lymphoid follicles being arranged along the sides of these fissures and crypts. The adenoid is covered with ciliated mucous membrane that keeps the fissures swept clean of debris.
   There is no defined fibrous tissue capsule separating the pharyngeal tonsil from the superior constrictor muscle, so that complete surgical removal is not always and re-growth frequently occurs.
3. Lingual tonsil
   The lingual tonsil lies at the back of the tongue, immediately above the epiglottis.
4. Lymphoid nodules
   Scattered lymphoid nodules occur on the posterior and lateral walls of the pharynx.

The lymphatics of the pharynx are numerous and drain into the anterior cervical lymph glands, in front of the sternomastoid muscle, except those from the nasopharynx and posterior oropharynx, which drain into the posterior cervical lymph glands, behind the same muscle.

The Larynx

The main function of the larynx is to act as a sphincter to protect the lower airway from contamination by food, liquid and secretions. A second function is the production of sound vibrations, which are then modified by the pharynx, tongue, lips, teeth and mouth to produce voice. Thirdly it aids the production of an effective cough.
The larynx is made up of a more or less rigid framework of cartilages held together by ligaments. It is a box like structure approximately 32mm wide and 25mm in depth. It is lined with mucous membrane and is continuous with the pharynx above and the trachea below. The larynx is separated from the 4th, 5th, 6th cervical vertebrae by the laryngopharynx. The position of the larynx can be seen and felt in the front of the neck as the 'Adams apple', or laryngeal prominence.

Laryngeal cartilages

1. Thyroid cartilage.
   The largest cartilage at the front and side of the larynx. It has two 'wings' or alae that meet at an angle anteriorly to form the laryngeal prominence. It is the difference in this angle in men and women that accounts for the voice differences.
2. Cricoid cartilage.
   The cricoid cartilage lies below the thyroid cartilage and is shaped like a signet ring with the lamina forming the posterior part of the larynx. It is the strongest and only complete ring of cartilage in the larynx and trachea.
3. Arytenoid cartilage
   The right and left arytenoids cartilages are perched on the cricoid cartilage. They give attachment for the vocal folds and muscles.

The laryngeal cartilages articulate by small synovial joints. Sheets and bands of fibrous tissue, containing many elastic fibres, attach them to each other. The upper horns of the thyroid cartilage articulate indirectly with the hyoid bone, from which the larynx is suspended.

The hyoid bone

The hyoid bone is a V-shaped bone above the larynx and is 'slung' from the jaw by a thick muscle, and the tongue is attached to the posterior aspect of the hyoid. Other muscles attach the larynx to the hyoid.

The epiglottis

The epiglottis is a leaf-shaped structure of yellow elastic cartilage; its 'stem' is attached to the posterior aspect of the thyroid cartilage at the junction of the two thyroid plates. It curves upwards behind the tongue and the hyoid bone and cannot move forwards. Small muscles from the arytenoid cartilage pass to the sides of the epiglottis. In swallowing the arytenoid cartilages are pulled forward, the tongue presses the epiglottis over the narrowed orifice of the larynx and food slides over the smooth mucous membrane into the oesophagus.
The function of the epiglottis is to protect the airway by covering the entrance to the larynx during swallowing.

The glottis

The glottis is the area that contains the vocal folds, supported by the cartilaginous framework of the larynx. Above the glottis is the supra-glottis and below the sub-glottis.

The vocal folds

The vocal folds are folds of tissue on either side of the cavity of the larynx. They are suspended in the front to the thyroid cartilage, behind by the arytenoids and they rest on the cricoid.

There are two pairs:

• The false vocal folds
  The false vocal folds are protective folds of connective tissue passing from halfway up the anterior border of the arytenoid cartilages forward to reach the angle of the union between the two laminae of the thyroid cartilage.
  
• The true vocal folds
  The true vocal folds pass from the base of the arytenoid cartilages to points just below the false vocal folds. They are composed of elastic tissue and project further into the cavity of the larynx than the false vocal folds. They are pearly white in colour due to their poor blood supply. Their function is with phonation and protection of the airway.

The arytenoids can move backwards and forwards as well as sliding towards and away from each other. This means that the position and tension of the vocal folds can be changed and thus change the pitch of the resulting sound.

Nerve and lymphatic supply to the glottis

Supra-glottis

Sub-glottis

Vocal folds

Has virtually no lymphatic drainage therefore a small glottic carcinoma has a good prognosis.

Angela Griggs