The key difference between primary and secondary peristalsis is that primary peristalsis is a type of esophageal peristalsis induced by swallowing, while secondary peristalsis is a type of esophageal peristalsis induced by esophageal distension.
Esophageal peristalsis is a process in which ingested food bolus push through the esophagus towards the stomach due to the sequential contraction of circular muscles in the esophagus. Esophageal longitudinal muscles may also play an important role in esophageal peristalsis. Esophageal peristalsis is mainly of two types: primary and secondary. Primary peristalsis is also known as deglutition, whereas secondary peristalsis is also known as local distension.
CONTENTS
1. Overview and Key Difference
2. What is Primary Peristalsis (or Deglutition)
3. What is Secondary Peristalsis (or Local Distension)
4. Similarities – Primary and Secondary Peristalsis
5. Primary vs. Secondary Peristalsis in Tabular Form
6. Summary – Primary vs. Secondary Peristalsis
What is Primary Peristalsis?
Primary peristalsis involves complex reflex neural activities. The time duration of primary peristalsis is around 8 to 10 seconds, and it is unidirectional. The initial phase of primary peristalsis is voluntary. In this phase, the food is chewed, mixed with saliva, and formed into a bolus. The receptors in the posterior pharynx are then activated to initiate the involuntary phase of primary peristalsis. In the involuntary phase, there is a sequenced contraction of numerous head and neck muscles. The food bolus is pushed towards the esophagus by pharyngeal constrictor muscles. Simultaneously, there is an activation of muscles that lift the palate and close off and elevate the larynx. This happens to prevent the misdirection of the bolus into the nasopharynx and larynx.
Later, the upper esophageal sphincter (UES) opens immediately upon activation of the primary peristalsis reflex, allowing food bolus to pass through the esophagus. UES then rapidly closes to prevent the retrograde passage of the food bolus. The oropharyngeal phase of primary peristalsis helps to propel the food bolus into the esophagus, while the esophageal phase of primary peristalsis takes over when the food bolus is in the esophagus. In the esophageal phase of the primary peristalsis, there is a sequential contraction of circular muscles of the esophageal body. This causes a peristaltic wave that pushes the food bolus toward the stomach. The peristaltic wave also results in the relaxation and opening of the lower esophageal sphincter (LES). Furthermore, the swallowing center is located in the medulla oblongata and lower pons. Following vagotomy, it typically continues to regulate primary peristalsis.
What is Secondary Peristalsis?
Secondary peristalsis is initiated by esophageal distension. If the food bolus gets stuck or moves slower than expected in the primary peristalsis due to poor lubrication, then the stretch receptors in the esophageal lining are stimulated. This creates a local reflex response that initiates a secondary peristaltic wave around the food bolus. In the secondary peristalsis, the food bolus is further forced down the esophagus, and these secondary peristaltic waves continue indefinitely. Therefore, secondary peristalsis continues until the bolus enters the stomach.
Once the food bolus reaches the stomach, both the primary and secondary peristalsis of esophageal peristalsis are inhibited. Moreover, the fat present in the food and the dilution of food with gastric juice inhibits or reduces esophageal peristalsis. Furthermore, secondary peristalsis is controlled by the efferent nervous system and remains unaffected by vagotomy.
What are the Similarities Between Primary and Secondary Peristalsis?
- Primary and secondary are two types of esophageal peristalsis.
- Both peristalses push food bolus to the stomach.
- They are unidirectional.
- Both peristalses are inhibited once the food bolus comes to the stomach by fat present in the food or by the dilution of food with gastric juice.
- Problems with both peristalses lead to diseases.
What is the Difference Between Primary and Secondary Peristalsis?
Primary peristalsis is a type of esophageal peristalsis that is induced by swallowing, while secondary peristalsis is a type of esophageal peristalsis that is induced by the esophageal distention. Thus, this is the key difference between primary and secondary peristalsis. Furthermore, primary peristalsis is the most prominent type of esophageal peristalsis.
The infographic below presents the differences between primary and secondary peristalsis in tabular form for side-by-side comparison.
Summary – Primary vs Secondary Peristalsis
Esophageal peristalsis is a result of the sequential or peristaltic contraction of circular muscles in the esophageal body. It can be initiated by either sucking and swallowing or local distention. Primary and secondary are two different types of esophageal peristalsis. Primary peristalsis is induced by swallowing, while secondary peristalsis is induced by esophageal distension. Moreover, primary peristalsis is the most prominent type of esophageal peristalsis, whereas secondary peristalsis is a less prominent type of esophageal peristalsis. So, tis summarizes the difference between primary and secondary peristalsis.
Reference:
1. “Peristalsis.” StatPearls – NCBI Bookshelf.
2. Sifrim, Daniel, and Jozef Janssens. “Secondary Peristaltic Contractions, like Primary Peristalsis, Are Preceded by Inhibition in the Human Esophageal Body.” Karger Publishers.
Image Courtesy:
1. “2404 PeristalsisN” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “2401 Components of the Digestive System” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia