Motility disorders, intestinal

Gastrointestinal tract. Serotonin released from myenteric neurons or enterochromaffin cells acts on 5-HT3 and 5-HT4 receptors to enhance bowel motility and enteral fluid secretion Cisapride is a proldnetic agent that promotes propulsive motor activity in the stomach and in small and large intestines. It is used in motility disorders. Its mechanism of action is unclear, but stimulation of 5HT4 receptors may be important... 

Clinical conditions with intestinal motility disorders 108... 

CLINICAL CONDITIONS WITH INTESTINAL MOTILITY DISORDERS... 

The proximal small intestine (duodenum and jejunum) normally contains few bacteria. Most ingested bacteria do not survive the acidic environment of the stomach and therefore few live organisms normally enter the small bowel. The motfiity of the jejunum prevents fecal-type organisms from progressing up into the jejunum from the cecum. The ileum normally contains some fecal-type bacteria. Colonization of the upper small bowel is described as bacterial overgrowth and usually occurs as a consequence of other abnormalities (structural or motility disorders) of the small intestine (see Box 48-4). Use of PPIs is associated with an increased risk of bacterial colonization. 

Patients with Crohn s disease, ischemic bowel disease, severe GI motility disorders, extensive intestinal obstruction, and congenital bowel dysfimction have been maintained successfully with home PN. ... 

In vivo, 5-HT4 agonists are clearly prokinetic [44,133] and display a wide range of therapeutic applications in gastrointestinal motility disorders. ether or not their therapeutic actions are entirely mediated by 5-HT4-RS is not clear. In isolated human stomach, renzapride has been shown to potentiate electrically-evoked contractions [84]. This effect was antagonized by mM concentrations of tropisetron, suggesting that 5-HT4-RS are involved [85]. 5-HT4-RS are also present in human small intestinal mucosa [86] where the non neuronal electrogenic secretory effect of 5-HT appears to be mediated by 5-HT4-RS. 

The healthy small intestine contains only a small bacterial population, unlike the colon. However, an acute infection of the mucosa by a virus, bacterium or other parasite can reduce its motility, allowing a huge proliferation of the resident bacteria. Absorption of both macro- and micronutrients is impaired, resulting in the disorder known as sprue. Folic acid is particularly poorly absorbed, causing reduced rates of repair of mucosal cells. Hence, the damage persists and worsens to create a vicious circle. Treatment involves administration of an antibiotic to kill the bacteria and folic acid to allow damaged tissue to recover. The clinical presentation includes bulky stools, steatorrhoea (fatty faeces) and weight loss. 

The depressant effect of EOs on smooth muscle in the small intestine is consistent with the therapeutic uses of these aromatic plants as gastrointestinal anti-spasmodics and carminatives [224]. In vitro studies showed that EOs produced the inhibition of gastric motility, and are thus the basis of the treatment of some gastrointestinal disorders [225, 226]. 

A9-Tetrahydrocannabinol (A9-THC) is considered to be the predominant compound in preparations of C. sativa (marijuana, hashish, bhang) that is responsible for the central nervous system effects in humans. The recognized central nervous system responses to these preparations include alterations in cognition and memory, euphoria, and sedation. Potential therapeutic applications of cannabis preparations that are of either historical or contemporary interest include analgesia, attenuation of the nausea and vomiting of cancer chemotherapy, appetite stimulation, decreased intestinal motility of diarrhea, decreased bronchial constriction of asthma, decreased intraocular pressure of glaucoma, antirheumatic and antipyretic actions, and treatment of convulsant disorders. These effects have been reviewed recently (Howlett, 1995). 

Q2 Constipation is a condition in which faecal material moves too slowly through the large intestine. As a result too much water is reabsorbed hard, dry faeces which are difficult to move and very abrasive are produced. Infrequent or difficult defecation is a common problem in the elderly as ageing is associated with a decline in both secretory activity and motility in the gut. Constipation could develop because of emotional problems, inactive or sedentary lifestyle, lack of fibre and fluid in the diet, intestinal muscle weakness, a neurogenic disorder or an iatrogenic effect. Iatrogenic conditions are those caused by drugs or other medical treatments. 

Diarrhoea associated with deranged motility. In order for nutrients and water to be efficiently absorbed, the intestinal contents must be adequately exposed to the mucosal epithelium and retained long enough to allow absorption. Disorders in motility that accelerate transit time can decrease absorption, resulting in diarrhoea. Alterations in intestinal motility (usually increased propulsion) are observed in many types of diarrhoea. What is not usually clear, and is very difficult to demonstrate, is whether primary alterations in motility are the cause of diarrhoea or simply an effect. 

Diarrhoea results from an imbalance between secretion and reabsorption of fluid and electrolytes it has numerous causes, including infections with enteric organisms (which may stimulate secretion or damage absorption), inflammatory bowel disease and nutrient malabsorption due to disease. It also commonly occurs as a manifestation of disordered gut motility in the absence of demonstrable disease (see below). Rarely it is due to secretory tumours of the alimentary tract, e.g. carcinoid tumour or vipoma (a tumour which secretes VIP, vasoactive intestinal peptide). 

Altered gastrointestinal motility can result from many disorders, not all of which primarily affect the gut. For instance, endotoxemia, regardless of its origin, can depress intestinal motility. Motility is also probably affected by diet, subclinical endoparasitism and even exercise. 

Large-colon impaction is characterized by distention of the large intestine with desiccated digesta. All segments of the large colon can be involved but the pelvic flexure and right dorsal colon are the most frequent sites of impaction. Impactions of the large colon are probably a combination of motility and fluid-balance disorders and most cases are treated with laxatives or hydration solutions. 

While enhanced signalling at CBi receptors contributes to the production of reduced intestinal motility typical of paralytic ileus, in small intestine inflammation and cholera toxin-induced hyper-secretion and diarrhoea it affords tonic protection against the symptoms of the disorders. 

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