Migrating motor complex, also known as migrating myoelectric complex, migratory motor complex, migratory myoelectric complex and MMC, is a pattern of electrical activity observed in the
gastrointestinal tract
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organ (biology), organs of the digestive syste ...
in a regular cycle during
fasting
Fasting is the abstention from eating and sometimes drinking. From a purely physiological context, "fasting" may refer to the metabolic status of a person who has not eaten overnight (see " Breakfast"), or to the metabolic state achieved after ...
. MMC was discovered and characterized in fasting dogs in 1969 by Dr. Joseph H. Szurszewski at the
Mayo Clinic
The Mayo Clinic () is a nonprofit American academic medical center focused on integrated health care, education, and research. It employs over 4,500 physicians and scientists, along with another 58,400 administrative and allied health staff, ...
.
He also showed that this activity stops upon eating a meal, and suggested that it induces a motor activity that acts as a "interdigestive housekeeper" in the small intestine.
These motor complexes trigger
peristaltic waves, which facilitate transportation of indigestible substances such as
bone
A bone is a Stiffness, rigid Organ (biology), organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red blood cell, red and white blood cells, store minerals, provid ...
,
fiber
Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...
, and
foreign bodies
A foreign body (FB) is any object originating outside the body of an organism. In machinery, it can mean any unwanted intruding object.
Most references to foreign bodies involve propulsion through natural orifices into hollow organs.
Foreign bo ...
from the
stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
, through the
small intestine
The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...
, past the
ileocecal sphincter, and into the
colon. MMC activity varies widely across individuals and within an individual when measured on different days. The MMC occurs every 90–230 minutes during the interdigestive phase (i.e., between meals) and is responsible for the
rumbling experienced when hungry. It also serves to transport
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
from the small intestine to the large intestine and to inhibit the migration of colonic bacteria into the
terminal ileum
The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine ma ...
; an impairment to the MMC typically results in
small intestinal bacterial overgrowth
Small intestinal bacterial overgrowth (SIBO), also termed bacterial overgrowth, or small bowel bacterial overgrowth syndrome (SBBOS), is a disorder of excessive bacterial growth in the small intestine. Unlike the colon (or large bowel), which is r ...
.
Phases
The MMC originates mostly in the stomach—although ~25% will arise from the
duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine m ...
or proximal
jejunum
The jejunum is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialised for the absorption by enterocytes of small nutrient molecules which have been previous ...
—and can travel to the distal end of the
ileum
The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine ma ...
.
They consist of four distinct phases:
* Phase I – A prolonged period of quiescence (40–60% of total time);
* Phase II – Increased frequency of action potentials and smooth muscle contractility (20–30% of total time);
* Phase III – A few minutes of peak electrical and mechanical activity (5–10 minutes);
* Phase IV – Declining activity which merges with the next Phase I.
Regulation
Movements of the small bowel are believed to be controlled by the central and enteric nervous systems, intestinal muscles, and numerous peptides and hormones. For example, the MMC is thought to be initiated by
motilin
Motilin is a 22-amino acid polypeptide hormone in the motilin family that, in humans, is encoded by the ''MLN'' gene.
Motilin is secreted by endocrine Mo cells (also referred to as M cells, which are not the same as the M cells, or microfold ce ...
, and it does not directly depend on extrinsic nerves.
Additionally, gastrin, insulin, cholecystokinin, glucagon, and secretin have been reported to disrupt the MMC.
Eating interrupts the MMC. For example, one study found that a continental breakfast of 450 Kcal causes the MMC to disappear for 213 ± 48 minutes. The number of calories and nature of food determine the length of the disruption with fats causing a longer disruption than carbohydrates which in turn cause a longer disruption than protein.
Most of the cleaning waves in the MMC happen at night while we are asleep. For many people this will be sufficient enough to help maintain a healthy, balanced environment in the digestive tract. For others, it may be beneficial to space out food intake to allow for a couple cleaning waves to occur between meals throughout the day as well.
Impairment
Autoimmunity following infection by a pathogen producing
CdtB, such as ''
C. jejuni
''Campylobacter jejuni'' () is a species of pathogenic bacteria, one of the most common causes of food poisoning in Europe and in the US. The vast majority of cases occur as isolated events, not as part of recognized outbreaks. Active surveillan ...
'', may be the leading cause of MMC impairment.
Narcotic
The term narcotic (, from ancient Greek ναρκῶ ''narkō'', "to make numb") originally referred medically to any psychoactive compound with numbing or paralyzing properties. In the United States, it has since become associated with opiates ...
s are also known to impair the MMC. Stress has been shown to reduce MMC activity as well.
Patients with
SIBO and
IBS have on average a third as many MMC phase III events with those events being roughly 30% shorter on average.
Therapeutic stimuli
Drugs used to enhance gastrointestinal motility are generally referred to as
prokinetics
A prokinetic agent (also gastroprokinetic agent, gastrokinetic agent or propulsive) is a type of drug which enhances gastrointestinal motility by increasing the frequency or strength of contractions, but without disrupting their rhythm. They are us ...
. Serotonin induces phase III of the MMC, and so serotonin receptor agonists are commonly administered as prokinetics. Motilin administration causes phase III contractions, and so motilin agonists are another common prokinetic.
Eradication of bacterial overgrowth has been shown to partially restore MMC activity.
An
elemental diet An elemental diet is a diet that proposes the ingestion, or in more severe cases use of a gastric feeding tube or intravenous feeding, of liquid nutrients in an easily assimilated form. It is usually composed of amino acids, fats, sugars, vitamins, ...
has been hypothesized to partially restore MMC function.
References
External links
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{{Gastrointestinal physiology
Digestive system