The Migrating Motor Complex (MMC) And Why It Is Important For Our Health

Jul 19, 2022 | Digestive System, Nutrition | 1 comment

Migrating Motor Complex

What Is The Migrating Motor Complex (MMC)?

The Migrating Motor Complex (MMC), is a recurring motility pattern that occurs in the stomach and small intestine that helps move food matter through the digestive system. The MMC begins after 90 to 230 minutes without food consumption, and works to clean the digestive tract of residual food, cellular debris, and leftover secretions. The MMC cycle has four distinct phases, and takes around 90 to 120 minutes on average to complete a full cycle. It is regulated by electrical activity in the enteric nervous system, with the vagus nerve also being a primary driver of the cycle. [1] [2] [3]

The MMC can be thought of as a natural and inbuilt maintenance mechanism for our gastrointestinal tract. If you imagine an office or workplace that has a cleaning staff arrive after hours, this is a good metaphor for the Migrating Motor Complex. But like those cleaning teams, the mechanism can only get to work once everything is quiet. When the small intestine detects the presence of a meal with sufficient calorific content, this triggers a reaction that halts the process. At this point, the digestive tract switches back in to the postprandial pattern (the ‘food digesting’ state). Another 90 to 230 minutes without food must pass before the MMC can restart. [4]

Often around two to three hours after meals, it is common for people to be able to physically feel the MMC in action as their stomach begins to gurgle and rumble. The MMC’s action is often mistaken for signs of hunger, as the sensations feel similar. Next time your stomach starts to rumble after a meal and you think you might be hungry again, check in on the time and see how long has elapsed since you ate. If it is around two to three hours after eating, then this is most likely the MMC in action.

What Does The Migrating Motor Complex do?

The Migrating Motor Complex is essentially a maintenance mechanism to keep our digestive system healthy. The nerve stimulation triggers the downward movement of food matter, and provides a natural flushing mechanism that helps push food waste, parasites, undigestible matter, and bacteria out of the stomach and small intestine. The debris and pathogens then move in to the large intestine where they can dealt with and eventually be removed from the body in faecal matter.

A Diagram Showing The Gastrointestinal Tract Where The Migrating Motor Complex Travels From The Stomach To The End Of The Small Intestine
The Migrating Motor Complex Sends Propulsive Contractions From The Stomach To The Ileum

At the lower end of the stomach there is a region called the Pyloric Antrum. A band of smooth muscle called the Pyloric Sphincter closes during the digestion of food to keep food matter in the stomach until it is sufficiently digested. Once the food matter is digested, the Pyloric Sphincter opens, and allows the material to travel in to the small intestine via the duodenum.

The MMC begins as large amplitude propulsive contractions that start in the Pyloric Antrum. These propulsive contractions move down through the duodenum and on through to the small intestine to the ileum. The ileum is the final section of the small intestine, and is the connection point in to the large intestines.

When the MMC is active, it’s impulse activity creates sequential waves along the walls of the intestine, with the impulses having distinct upper and lower boundaries. This area of effect is called the ‘Activity Front’. The Activity Front advances down through the intestinal tract at a slow rate, gradually slowing down further as it approaches the ileum. Professor Jackie D. Wood, an expert on the ENS, notes that ‘the entire activity front slowly migrates down through the intestine, sweeping the lumen clean as it moves toward the junction with the colon’. [5]

Why Is The Migrating Motor Complex Important?

Due to how many different muscles and nerves are involved in the Migrating Motor Complex, it is an intricate and delicate mechanism. In instances where individuals have an impaired or non-existent MMC, it often leads to chronic and serious digestive issues. If we use the metaphor of the MMC as housekeeping staff, then you can imagine what would happen over long periods of time if no cleaning or maintenance was done!

A Diagram Of Pathogens Which The Migrating Motor Complex Helps To Flush Out Of The Stomach And Small Intestine
The Migrating Motor Complex Helps To Flush Pathogens Out Of The Stomach And Small Intestine

There are many ways that the MMC can be interrupted, including through disease, genetic defects, or damage to the Enteric Nervous System (ENS). The ENS is a mesh-like system of neurons that is responsible the functioning of the gastrointestinal tract. The ENS “functions as a minibrain, and controls smooth muscle, secretory glands and the vasculature of the gastrointestinal tract.” Without a functional and healthy ENS, the Migrator Motor Complex cannot function. [5]

The vagus nerve is the longest nerve in the human body and is responsible for controlling many unconscious bodily functions. It is a vital nerve for the respiratory system, immune system, and digestive system. The vagus nerve also plays a role in the Migrating Motor Complex, where it plays a role in the early stages of the impulses in the stomach. It has been found that some patients who have had a vagotomy (removal of part of the vagus nerve) still exhibited MMC impulses in the small intestine, but not in the stomach. [6] This suggests that there is a complex electrical interplay in the nervous system that allows the MMC to function properly.

It has been found that individuals who suffer disruption or damage to this system are far more likely to develop Small Intestinal Bacterial Overgrowth (SIBO). [6] This is because ordinarily, the MMC would flush these bacteria through the digestive system and out of the body. Without this mechanism in place, food matter and bacteria can end up stagnating in the small intestine. This then leads to bacteria populations reaching abnormally high volumes and numbers, which can produce a wide range of unpleasant effects in the host individual.

The large intestine has different bacteria strains, and a much higher volume of bacteria than the small intestine. The progressive flushing mechanism of the MMC helps to prevent bacteria strains from the colon moving up into the terminal ileum, where they could begin to colonise the small intestine.

The small intestine is not completely sterile, but has a much lower volume of bacteria than the large intestine. The concentration of bacteria in the small intestine of normal individuals rarely exceeds 1000 organisms/ml. [7] As large intestine bacteria are not supposed to be in the small intestine, their presence there can cause significant issues and potentially lead to chronic infections. Such scenarios often produce symptoms such as diarrhoea, constipation, bloating, abdominal pain, and nutrient deficiencies.

Keeping pathogens moving in the correct direction is a key role of the Migrating Motor Complex, but the MMC is far more than just a cleaning mechanism. It also helps to push food through the digestive tract, aiding digestion, nutrient absorption, and preventing blockages. It has been found that a weak or absent MMC can often lead to Gastroparesis, whereby the stomach cannot empty itself of food properly. Gastroparesis can lead to a range of negative effects including bloating and nausea. Patients without a fully functioning MMC are also at a much higher risk of Intestinal Pseudo-obstruction, a painful condition which can lead to a buildup of partially digested food in the intestines. [6]

Fasting And The Migrating Motor Complex

It is possible utilise the MMC when planning our meals and snacks. As the MMC is stopped by food consumption, individuals can deliberately time their food intake in accordance with the MMC and it’s natural rhythms. By avoiding snacking between meals, or cutting out foods for certain periods of the day, (such as in the case of Intermittent fasting) this allows the MMC to get to work and move through debris out of the stomach and small intestine.

A Clock Surrounded By Food To Illustrate That Meal Times Can Be Structured Around The Patterns Of The MMC
Meal Times Can Be Structured Around The Patterns Of The MMC

Many people go through an extended overnight fast in order to allow the MMC time to do it’s job efficiently. This practice predates the discovery or naming of the Migrating Motor Complex, suggesting an intuitive and traditional connection spanning thousands of years. Intermittent fasting has gained popularity in recent years, and is much easier than it sounds, as it can be done simply by not eating anything after dinner. This helps to give plenty of time for the MMC to do it’s work until food is consumed again at breakfast. This structuring of meals can give periods of around 12-14 hours for the MMC to get to work in flushing through what it needs to.

The MMC also operates whilst we sleep, though there are subtle differences in the patterns between the waking and sleep states. Gastroenterologist William L. Hasler notes that “MMC complexes migrate 2.5 times faster during the day, but exhibit greater contractile amplitudes at night.” [8] For this reason, an extended fast after dinner may help provide the required time for the Migrating Motor Complex to work efficiently and optimally.

It is worth noting however, that there is variability in onset time and duration of the MMC between individuals. Many factors can effect the operation of the MMC such as gastric emptying rate, gender, and medications. Because of these individual differences, it is best to get to know your own body and work out what your own unique digestive patterns are.

Conclusion

The Migrating Motor Complex is a crucial aspect of our digestive function that is not frequently discussed. Many people remain unaware of it’s existence, despite it doing it’s work every day. It is important for us to get to know the signs and sensations of the Migrating Motor Complex, as many individuals mistake the sensations for hunger, which leads them to grab a snack. As the MMC is stopped by eating, this constant interruption prevents the MMC from being able to properly do it’s job in cleaning out unwanted debris and pathogens from the stomach and small intestine.

When seeking to treat digestive disorders, we must have a good understanding of the Migrating Motor Complex and it’s functions. Nerve damage or enteric nervous system malfunction can play a key role in the onset of digestive disorders due to the importance of the MMC. Medications that change how nerves operate including sedatives or serotonin modulators can also impact the MMC for this reason and must not be forgotten in the wider picture when building up a diagnostic profile.

Even for healthy individuals, the Migrating Motor Complex is a crucial part of our lives and one we should strive to work with. Learning about the MMC and adjusting eating habits accordingly can provide many benefits in keeping the digestive system in top condition. As the digestive tract is where we absorb our nutrients (and therefore receive our energy and vitality) it is certainly worth doing what we can to keep it healthy. A healthy digestive system goes a long way to making us feel more energised, healthy, and happy!


[References]

1. Deloose E, Tack J. Redefining the functional roles of the gastrointestinal migrating motor complex and motilin in small bacterial overgrowth and hunger signaling. Am J Physiol Gastrointest Liver Physiol. 2016 Feb 15;310(4):G228-33. doi: 10.1152/ajpgi.00212.2015. Epub 2015 Dec 10. PMID: 26660537.

2. Sarna SK. Cyclic motor activity; migrating motor complex: 1985. Gastroenterology. 1985 Oct;89(4):894-913. doi: 10.1016/0016-5085(85)90589-x. PMID: 3896912.

3. Miyano Y, Sakata I, Kuroda K, Aizawa S, Tanaka T, Jogahara T, Kurotani R, Sakai T. The role of the vagus nerve in the migrating motor complex and ghrelin- and motilin-induced gastric contraction in suncus. PLoS One. 2013 May 28;8(5):e64777. doi: 10.1371/journal.pone.0064777. PMID: 23724093; PMCID: PMC3665597.

4. Jan Tack, in Physiology of the Gastrointestinal Tract (Fifth Edition), 2012 – Neurophysiologic Mechanisms of Gastric Reservoir Function

5. Jackie D. Wood, in Reference Module in Neuroscience and Biobehavioral Psychology, 2017

6. Deloose E, Janssen P, Depoortere I, Tack J. The migrating motor complex: control mechanisms and its role in health and disease. Nat Rev Gastroenterol Hepatol. 2012 Mar 27;9(5):271-85. doi: 10.1038/nrgastro.2012.57. PMID: 22450306.

7. Sorathia SJ, Rivas JM. Small Intestinal Bacterial Overgrowth. [Updated 2021 Jul 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546634/

8. William L. Hasler, in Physiology of the Gastrointestinal Tract (Fourth Edition), 2006

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Written by Keymer Health

July 19, 2022

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