Peristaltic waves

Each day most persons experience a strong peristaltic wave known as the gastrocolic reflex. A bowel movement usually follows. When the urge to have a bowel movement occurs, it should not be ignored. Some people put off having a stool for various reasons, which may lead to more difficulty in passing stool. Time should be planned daily to attempt having a stool. A busy lifestyle should not be allowed to interfere with normal bowel function. 

Contents within the colon are propelled down the tract not by peristaltic waves but by a mass movement, which occurs only several times a day, being most abundant the first hour after breakfast as a result of a duodenocolonic reflex. The greatest proportion of time moving down the GIT is spent by a meal moving through the colon. In the presence of a diarrheal condition, fluid absorption is incomplete, which results in a watery stool. 

Fig. 23.3. Tablet movement during a static view (30-s duration). Note the movement from position 1 to position 3 during successive peristaltic waves. M, external marker.

Avoid alcohol (increases amplitude of the lower esophageal sphincter, peristaltic waves, and frequency of contraction). 

Another strategy rehes on the strong peristaltic waves in the colon that lead to a temporarily increased luminal pressure (pressure-controlled drug release). Pressure-sensitive drug formulations release the drug as soon as a certain pressure limit is attained, i.e. destruction force is exceeded. 

Atropine decreases the tone and motility of all parts of gastrointestinal tract. It also decreases the amplitude of contraction and frequency of peristaltic wave of stomach and intestines. Atropine also exerts a weak antispasmodic action on biliary tract and gall bladder. 

Figure 8. Original tracings showing the effects of (R)a-methylhistamine (MHA, pM), thioperamide (TH, pM), the selective a2 adrenoceptor agonist UK-14304 (UK, nM) and the a2-adrenoceptor antagonist idazoxan (ID, pM) on different in vitro assays from the guinea pig ileum A) Electrically-evoked longitudinal contractions of the whole ileum B) Peristaltic waves of the perfused ileum, C) Reflex-evoked circular muscle contractions Vertical calibrations represent (A and C) centimeters of isotonic contractions or (B) changes in perfusion pressure. Horizontal calibration is the chart speed, w = washing of the preparation...

Peristaltic waves of the type seen in the small intestine only rarely occur in other parts of the colon. Instead, most propulsion occurs by (1) the haustral contractions discussed previously and (2) mass movements. 

Ordinarily, defecation results from the defecation reflexes, which can be described as follows. When the feces enter the rectum, distension of the rectal wall initiates afferent signals that spread through the myenteric plexus to initiate peristaltic waves in the descending colon, sigmoid, and rectum, forcing feces toward the anus. As the peristaltic wave approaches the anus, the internal anal sphincter is inhibited by the usual phenomenon of receptive relaxation, and if the external anal sphincter is relaxed, defecation will occur. This overall effect is the intrinsic defecation reflex of the colon itself. 

Among newly developed colon-specific drug delivery systems, pressure-controlled delivery capsules (PCDCs) [161] can be mentioned. Their mechanism of action is based on the relatively strong peristaltic waves taking place in the colon and leading to an increased luminal pressure. They consist of a capsular-shaped suppositories coated with a water-insoluble polymer (ethyl cellulose). Once taken orally, PCDCs behave like an ethyl cellulose balloon, because the suppository base liquefies at body temperature. In the upper GI tract, PCDCs are not directly subjected to the luminal pressures since sufficient fluid is present in the stomach and small intestine. The reabsorption of water in the colon provokes an increase of the luminal content viscosity. As a result, increased intestinal pressures directly affect the system via colonic peristalsis. Consequently, PCDCs mpture and drug release in the colon take place. 

The gut contains a collection of nerves called the enteric nervous system. Various activities of the gut, such as peristaltic contractions, and certain activities of the pancreas and gall bladder, are controlled in a manner that is relatively independent of the central nervous system. The central nervous system consists of the brain and spinal cord. Five type,s of activity are controlled by the enteric nervous system (1) contraction of smooth muscles that create the peristaltic waves used to mix and propel food through the intestines (2) release of juices by secretory cells (5) release of hormones from endocrine ceils of the gut (4) patterns of blood flow through the arteries of the gut (variations in blood flow occur because of the opening of blood vessels (vasodilation) or the dosing of blood vessels (vasoconstriction)] and (5) activities of immune cells of the gut (GoyaI and Hirano, 1996). 

Pressure-controlled systems. These systems rely on the strong peristaltic waves in the colon that temporarily increase the luminal pressure. 

The mouth is the normal point of entry of food and drink. There, solid food is reduced in size by mastication, blended with saliva, and temperature-moderated before being swallowed. Conditions that interfere with any of these processes (e.g., tooth loss) can affect food choice and hence the nutritional status and health of the individual. The esophagus is a muscular tube through which masticated food is transported from the mouth to the stomach. It consists of both striated muscle (upper one third) and smooth muscle (lower two thirds). These muscles undergo periodic contractions in the form of peristaltic waves that push the swallowed boluses toward the stomach. The esophagus has no digestive function but secretes mucus to protect the esophageal mucosa from excoriation. 

Morphine reduces the activity of the entire gastrointestinal tract in that it reduces the secretion of hydrochloric acid, diminishes the motility of the stomach, and increases the tone of the upper part of the duodenum. These actions may delay passage of the stomach contents into the duodenum. Both pancreatic and biliary secretions are diminished, and this may also hinder digestion, hi the large intestine, the propulsive peristaltic wave in the colon is reduced, the muscle tone including that of the anal sphincter is increased, and the gastrocohc reflex (defecation reflex) is reduced. These actions, in combination, cause constipation, which seems to be a chronic problem among addicts. 

Large Intestine Propulsive peristaltic waves in the colon are diminished or abolished after administration of morphine, and tone is increased to the point of spasm. The resulting delay in the passage of bowel contents causes considerable desiccation of the feces, which, in turn, retards their advance through the colon. The amplitude of the nonpropulsive type of rhythmic contractions of the colon usually is enhanced. The tone of the anal sphincter is augmented, and reflex relaxation in response to rectal distension is reduced. These actions, combined with inattention to the normal sensory stimuli for defecation reflex owing to the central actions of the drug, contribute to morphine-induced constipation. 

The diagnosis can be made by physical examination by palpating the typical olive in the epigastrium. Peristaltic waves may also be seen on the abdominal wall. 

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