SWALLOWING DR. ADEL HUSSIEN DR. AHMED ALANTARY

Objectives: The student should know: - The normal swallowing process and its stages. - Mechanism of each stage of swallowing and control. - Protective reflexes accompanying the processes of swallowing. Reference: Guyton and Hall Textbook of Medical Physiology, 12th edition, Chapter 63 pages: Chapter 66 page: 799. Ganong’s Review of Medical Physiology, 24 th edition Chapter 27 pages:

The Pharynx: Anatomically it is divide into 3 regions 1- Nasopharynx: lies behind the Nose (posterior nasal openings) 2- Oropharynx: lies behind oral cavity 3- Laryngopharynx: lies behind larynx

The Oesophagus: It extends from the lower end of the Pharynx to the upper end of the stomach It has 2 sphincters: Upper Oesophageal Sphincter (UES): usually closed in between Meals to prevent excessive air entry to the GIT. Lower Oesophageal Sphincter (LES or cardiac sphincter): close the upper end of the stomach In between meals and so it helps to prevent regurgitation of acidic contents to the oesophagus.

Swallowing (Deglutition) Swallowing is the passage of food from the mouth to the stomach It is divided into three stages or phas:es 1- Buccal stage (Oral). 2- Pharyngeal stage. 3- Esophageal stage.

(1) Buccal stage Stage in which food passes from the mouth to the pharynx It is voluntary stage (what is meant by voluntary?) Mechanism: - Lips and jaws are closed. - Food bolus collected on the upper surface of the tongue - Contraction of myelohyoid muscle leads to upward and backward movement of the tongue pushing the food bolus towards the pharynx (oropharynx)

(2) Pharyngeal stage In which food passes from the pharynx to the oesophagus It is involuntary stage (what is meant by involuntary?). Mechanism: - Food stimulates the swallowing receptors around the opening of the pharynx. - This stimulation send impulses along the afferent nerve (5 th cranial nerve). - These impulses reach the swallowing center in the medulla oblongata - The swallowing center send impulses through efferent nerves (9 th and 10 th cranial nerves to the following structures:

1- Mouth cavity is shut behind the food bolus to prevent regurgitation of food to the oral cavity by the following actions: a- the tongue moved upward to be in contact with the hard palate. b- Approximation of the tonsillar pillars. 2- protective reflexes: to prevent food from entering into the respiratory passage and include the followings: a- Closure of the larynx by: - Epiglottis - Root of the tongue - Approximation of vocal cords

b- Closure of posterior nasal opening by elevation of soft palate to prevent regurgitation of food to the nose c- Temporary inhibition of respiration (Apnea) 3- Contraction of pharyngeal muscles and relaxation of upper esophageal sphincter leading to passage of food to the esophagus.

(3) Oesophageal stage In which food passes from the oesophagus to the stomach It is involuntary stage Mechanism: - Immediately after semisolid food enters the oesophagus a peristaltic wave starts leading to pushing the food down to the stomach - Fluid food passes with oesophagus relaxed until whole amount passes then a wave of contraction develops pushing the remaining fluid into the stomach. Notice: Decreased LES pressure leads to regurgitation of acidic gastric contents into the oesophagus Heartburn (reflux oesophagitis) Coffee, fat, chocolates and citrus juices may produce heart burn by decreasing LES pressure.

LES The LES is made up of three components: 1- The esophageal smooth muscle is more prominent at the junction with the stomach (intrinsic sphincter). 2- Fibers of the crural portion of the diaphragm, a skeletal muscle, surround the esophagus at this point (extrinsic sphincter). and exert a pinchcock-like action on the esophagus. 3- In addition, the oblique or sling fibers of the stomach wall create a flap valve that helps close off the esophagogastric junction and prevent regurgitation when intragastric pressure rises.

The tone of the LES is under neural control. Release of acetylcholine from vagal endings causes the intrinsic sphincter to contract, and release of NO and VIP from interneurons innervated by other vagal fibers causes it to relax.