What is Receptive Relaxation? 

Receptive relaxation refers to the relaxation of the muscles in the upper portion of the stomach that occurs before the food particles enter the esophagus. This receptive relaxation helps in the movement of the food. This receptive relaxation is achieved with the help of the peristaltic movement of the stomach. Peristalsis, or the peristaltic movement, is defined as a series of wave-like contractions in the muscle that helps move the food through the gastrointestinal tract.  

Stomach 

The stomach has two ends, namely the cardiac and pyloric ends. These ends are present with greater and lesser curvature. The upper end of the stomach consist of a sphincter termed the cardiac sphincter. This sphincter is significant in connecting the stomach region to the duodenum. There are about four stomach parts that are classified anatomically. They are the pyloric portion, the fundus, the cardiac region, and the body. 

• The dome-shaped structure located above the horizontal plane drawn at the cardiac notch’s level is named the fundus or gastric fundus. 
• The cardiac part specifically relates to the cardiac sphincter, and it is represented as the area that exists around the orifice. 
• The stomach’s body is considered the abdomen’s major part between the stomach and the pyloric antrum. 
• The pyloric part is characterized as the funnel-shaped outflow and is further classified into three parts. These are namely pyloric antrum, pyloric canal, and pylorus. 

Peristalsis 

An involuntary movement of the muscles in the gastrointestinal tract is called peristalsis. It occurs in a circular and longitude manner. The involuntary movement occurs as wave-like contractions for propelling food from the esophagus region to reach the stomach. The peristalsis begins at the period when food is being swallowed and enters the region of the esophagus. This movement continues to take place throughout the esophagus, stomach, and intestines. The peristaltic wave could be long and continuous or short and local based on the source that is responsible for causing it and its location. 

This wave tends to diminish when the stomach is completely full. The contraction tends to be weak in the stomach’s beginning which gets stronger as it eventually reaches the stomach’s distal part. This contraction results in the proper mixing of food in the stomach region and its propulsion towards the region of the intestines. 

Gastric Motility  

The motility of the gastric region is defined as the function of the musculature in the gastric region. It is composed of three layers of smooth muscle fibers, namely a middle circular layer, an outer longitudinal, and an inner oblique layer. From the aspect of gastric contractions, the region of the stomach can be classified into two regions, namely the oral and the caudal regions. 

• The stomach’s oral region includes the proximal body and the fundus. This particular region is significant for receiving the food content that is being ingested. 
• The stomach’s caudal region comprises the antrum and the distal part of the stomach. This region is significant for the contractions that help in mixing the food. 

Receptive Relaxation 

The term receptive relaxation represents the relaxation mechanism of the muscles in the smooth muscles. This mechanism takes place when the entry of food into the stomach occurs through the esophagus. An oral region is considered the food content’s storage unit before it gets mixed in the caudal region of the stomach. The food bolus is defined as the food that has been chewed and mixed in the mouth with the help of saliva. The passage of each bolus of the specific food has the capability to stimulate the oral area’s stretch receptors. This stretching, in turn, produces relaxation. At the finishing stage of the meal, approximately one to two liters of food content could be accommodated in the region of the stomach because of the receptive relaxation. Cholecystokinin, which is defined as a gut hormone that gets released after a meal, tends to participate in the process of receptive relaxation by increasing the oral stomach’s distensibility. 

Vasovagal Reflex 

The process of receptive relaxation falls under the vasovagal reflex. This relaxation is because that the vagus nerve mainly controls this relaxation. When the food intake occurs, the stomach muscles are relaxed by activating the vagus nerve to accommodate the bolus. This is possible when the receptor signal received from the stomach travel to the brain region and returns to the stomach. The afferent and efferent nerve that carries messages towards the central nervous system and brings the messages away from the central nervous system is the vagus nerve. If the innervation of the vagal nerve is disrupted in any manner, the relaxation in the stomach cannot take place. As a result, it causes symptoms, including vomiting, as the proximal region of the stomach becomes incapable of accommodating the ingested food. Thus, receptive relaxation is considered a vasovagal reflex that is specifically initiated by the distention of the abdomen. This is further synchronized with the primary movements of peristalsis in the esophagus. 

Context and Applications 

This topic is significant in the professional exams for both undergraduate and graduate courses and research side, especially for courses such as: 

• Bachelors in zoology 
• Bachelors in General physiology 
• Masters in Human physiology 
• Masters in anatomy and physiology 

Related Concepts 

• Vagovagal reflex 
• Digestive system 

Practice Problem 

• Question: Why vagus nerve is important for receptive relaxation? 

Solution: The vagovagal reflex is specifically active during the stomach’s receptive relaxation, and it is the response for the swallowing of food. These vagal afferents are active during the gastric phase of the digestion of the food that gets entered into the intestine. The Vagal represents the vagus nerve. It is a long nerve from the brain region and is then extended through the neck and thorax into the abdomen region.  The vagus nerve has several functions: it regulates the internal organ system, digestion, reflex conditions, respiration, swallowing, and vomiting. 

• Question: What is chyme? 

Solution: Chyme is a semisolid material. It is partially digested food formed in the stomach. It is basically acidic in nature. Acid chyme is emptied from the stomach as it takes about three to four hours of time. This slow process is useful for the absorption and digestion of food materials from the small intestine.  Gastric emptying occurs due to the peristaltic contraction in the body and the pyloric part and relaxation of the pyloric sphincter.