Coupon Accepted Successfully!


Gastrointestinal Motility


A. Peristalsis

This is a reflex contraction of the gut wall to stretch (e.g. by food). It is present throughout the GIT (from the oesophagus to the rectum). Stretching the gut wall causes a wave of contraction and relaxation viz. an area of circular contraction behind the stretch and an area of relaxation in front of it. The wave moves from an oral to caudal direction and helps in moving the contents of the GIT (at a rate of 2 to 25 cm/s).


B. Cause/mechanism :

Peristalsis occurs due to the integrated activity of the intrinsic i.e. the enteric nervous system; however, the input from the extrinsic autonomic nervous system can increase/decrease it. If a segment of intestine is removed and the cut ends are joined in their original position, peristalsis still occurs. However, if the ends are reversed and then joined, peristalsis does not occur.       


C. Possible sequence of events

Stretch → releases serotonin stimulates the myenteric plexus from the myenteric plexus, cholinergic neurons go two directions :

  1. In a retrograde direction to activate neurons that release substance P and acetylcholine these cause the contraction.                   
  2. In an anterograde direction to activate neurons that release NO, VIP and ATP → these cause the relaxation in front of the stimulus.

D. BER (Basic Electric Rhythm)
  1. Definition :
    The smooth muscle of the GIT show a spontaneous, rhythmic fluctuations in their membrane potentials (between –65 mV to –45 mV); this is called basic electrical rhythm or BER.
  1. Site
    BER is present throughout GIT except the oesophagus and proximal portion of the stomach.
  1. Cause
    BER is caused by pacemaker cells called the interstitial cells of Cajal.
Location of the cells of Cajal :
a. stomach and small intestine → outer circular muscle layer near the myenteric plexus
b. colon   submucosal border of the outer circular muscle layer

Rate of BER:
BER Rate (per min)
Stomach 4
Duodenum 12
Proximal Jejunum 12
Distal Ileum 8
Caecum 9
Sigmoid Colon 16 (MAXIMUM MOTILITY)
BER: Absent in Oesophagus and proximal colon

Note : The rate decreases in the stomach and small intestine and increases in the large intestine.

E. Function:
  1. Coordination of peristalsis and other motor activity of the GIT. Proof : vagotomy or transection of the stomac wall causes the peristalsis in the stomach to become irregular.
  2. The BER by itself rarely causes muscle contraction; however, the spike potentials superimposed on the most depolarizing portions of the BER waves cause contraction and increases muscle tension. The depolarizing phase of these spike potentials is due to calcium influx and their repolarisation phase is due to potassium efflux.

F. Factors affecting BER:
Acetylcholine increases the number of spike potentials (and thus increases muscle tension) whereas epinephrine decreases the number of spike potentials (and thus decreases muscle tension)

G. Migrating motor complex
  1. Definition :
The motor and electrical activity of smooth muscle in GIT that occur during fasting  (between periods of digestion) are called migrating motor complex or MMC. They are so called because the motor activity starts from the stomach and migrates to the distal ileum.
  1. Rate
During the period of fasting, MMCs move down the GIT at a regular rate of approximately 5 cm/min. They are completely inhibited by a meal; they resume 90 to 120 minutes after the meal.and occur at intervals of about 90 minutes till the next meal.
  1. Phases of the MMCs
Phase I : This is the first phase; it is the quiescent period with no spike potentials and no contractions
Phase II : this is a period of irregular spike potentials and contractions               
Phase III : this is the last phase; it is a period of regular spike potentials and contractions

This is not fully clear. There is an increase in pancreatic and gastric secretion as well as bile flow during each MMC. The function of MMC may be to clear the contents of the stomach and small intestine in between the meals. On taking foodMMC stops immediately and is replaced by peristalsis and other forms of BER and spike potentials.

  1. Gastroileal
  2. Gastrocolic
  3. Enterogastric
  4. Intestino – intestinal
  5. Rectosphincteric
  6. Colono – ileal

Test Your Skills Now!
Take a Quiz now
Reviewer Name