The pharynx, also known as the throat, is a cone-shaped empty cylinder that rises up out of the rear of the nose, reaches out to the neck and finishes in the windpipe and throat. As per the body size, a pharynx can be up to 5 inches long. It is associated along the side with the middle ear and serves as the path for both stomach-related and respiratory tract.
Muscles of Pharynx
It is a musculomembranous structure that carries out many essential roles related to respiration and digestion. The pharynx is attached to the foundation of the skull with thick strands of muscles and connective tissues. Both longitudinal and circular muscles are found in the walls of the pharynx. The circular muscles of the pharynx form constrictions that help in the swallowing of food and prevent the entry of air.
The longitudinal muscles of the pharynx help in lifting the walls of the pharynx during the process of swallowing.
|Note: There are no muscle fibres present at the roof of the pharynx.|
- It is a funnel-shaped structure that is broad at the upper end and is situated just below the lower surface of the skull.
- It narrows down at the lower end and is found at the level of the sixth cervical vertebrae.
- The pharyngeal wall is composed of muscle fibres, lymphoid tissue, mucosal and submucosal membranes.
- The nasopharynx is composed of columnar and ciliated epithelial cells that are interspersed with goblet cells. The other pharynx structures are covered with non-keratinised stratified squamous epithelium.
- At the roof of the pharynx, where no muscle fibres are present, there is a thick layer of the submucosal membrane.
Divisions of the Pharynx
The pharynx structure is divided into three main regions. Let us look at each of them separately.
The nasopharynx or nasal pharynx lies in the anterior portion of the nasal cavity. The nasal pharynx is the site of air passage for the respiratory tract. On the lateral surfaces of the nasopharynx are present tube-like structures on either side called the eustachian tubes.
The tubes are surrounded by elevated mucus membranes called tubal elevations. These tubes are connected to the middle ear and function to equalise the pressure and facilitate the drainage of middle ear secretions. The nasopharynx also houses lymphoid tissues called adenoids or pharyngeal tonsils that function as the first line of defence against pathogens entering the oral cavity.
The oropharynx or oral pharynx is connected with the nasopharynx by a passage-like structure called the isthmus. It is located behind the opening of the oral cavity and continues till the epiglottis (a flap-like structure that directs the food to the oesophagus).
Laryngopharynx, hypopharynx, or laryngeal pharynx, is the third pharynx structure that begins at the epiglottis and extends to the oesophagus. The laryngeal pharynx receives the bolus (soft mass of food) from the oral pharynx and directs it to the oesophagus for digestion purposes. It also receives air from the above two regions and directs it towards the inlet of the larynx to the trachea for respiration.
The pharynx serves as a site for both digestion and respiratory purposes. It helps in directing food and air to the oesophagus and larynx, respectively.
Development of Pharynx
All vertebrates possess pharynx. It is developed during the fourth and fifth weeks of gestation. The pharyngeal apparatus are present on either side of the head in a developing embryo. These apparatus consist of clefts, pouches and membranes that help in the development of the head and neck. The pharynx arises from the arches of the pharyngeal apparatus.
Pharynx and Kidney
End-stage renal disease (ESRD) is a serious condition where the affected person’s kidney stops functioning, and they need to go for lifetime dialysis or kidney transplantation to continue their life. Sleep apnea is a condition that is seen very commonly in people affected with ESRD. The pharynx and the associated respiratory tract narrow down during sleep apnea which leads to difficulty in breathing.
A human kidney is divided into medulla and cortex, the nephron being the functional unit. A simple kidney diagram will help you to understand the mechanism of filtration and excretion by the kidney. In ESRD, the nephrons are slowly destructed, and the glomerular filtration rate is decreased progressively. Hypertension and diabetes mellitus are the leading causes of ESRD.
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