Esophageal phase of deglutition is caused by?
Correct Answer: Primary peristalsis
Description: ANSWER: (B) Primary peristalsisREF: Guyton 12th ed page 763-765STAGES OF DEGLUTITIONIn general, swallowing can be divided into:Voluntary stage, which initiates the swallowing process. When the food is ready for swallowing, it is "voluntarily" squeezed or rolled posteriorly into the pharynx by pressure of the tongue upward and backward against the palate. From here on, swallowing becomes entirely or almost entirely automatic and ordinarily cannot be stopped.Pharyngeal stage, which is involuntary and constitutes passage of food through the pharynx into the esophagus. The trachea is closed, the esophagus is opened, and a fast peristaltic wave initiated by the nervous system of the pharynx forces the bolus of food into the upper esophagus, the entire process occurring in less than 2 seconds. The pharyngeal stage of swallowing is principally a reflex act. It is almost always initiated by voluntary movement of food into the back of the mouth, wThich in turn excites involuntary pharyngeal sensory receptors to elicit the swallowing reflex. The entire pharyngeal stage of swallowing usually occurs in less than 6 secondsEsophageal stage, another involuntary phase that transports food from the pharynx to the stomach. The esophagus functions primarily to conduct food rapidly from the pharynx to the stomach audits movements are organised for this purpose. The esophagus normally exhibits two types of peristaltic movements.Primary peristalsis is simply a continuation of the peristaltic wave that begins in the pharynx and spreads into the esophagus during the vharyngealstage ofdeglution. This wave passes all the way from the pharynx to the stomach in about 8 to 10 seconds. Food swallowed by a person who is in the upright position is usually transmitted to the lourer end of the esophagus even more rapidly than the peristaltic wave itself, in about 5 to 8 seconds, because of the additional effect of gravity pulling the food downward.Secondary peristalsis: If the primary peristaltic wave fails to move into the stomach all the food that has entered the esophagus, secondary peristaltic waves result from distention of the esophagus itself by the retained food; these wraves continue until all the food has emptied into the stomach. The secondary peristaltic waves are initiated partly by intrinsic neural circuits in the myenteric nervous system and partly by reflexes that begin in the pharynx and are then transmitted upward through vagal afferent fibers to the medulla and back again to the esophagus through glossopharyngeal and vagal efferent nerve fibers.
Category:
Physiology
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