Bowel function, mechanisms

Analogous or neurologically similar mechanisms operate in normal bladder and bowel function, and some... 

FIGURE 51.1 Mechanisms of urinary and bowel function and dysfunction. ANS, autonomic nervous system CNS, central nervous system. 

The safety and efficacy of senna have been reviewed (4). Its rhein-anthrone-induced laxative effects occur through two distinct mechanisms, an increase in intestinal fluid transport, which causes accumulation of fluid intralumm-ally, and an increase in intestinal motihty. Senna can cause mild abdominal complaints, such as cramps or pain. Other adverse effects are discoloration of the urine and hemorrhoidal congestion. Prolonged use and overdose can result in diarrhea, extreme loss of electrolytes, especially potassium, damage to the surface epithelium, and impairment of bowel function by damage to autonomic nerves. Abuse of senna has also been associated with melanosis coli, but resolution occurs 8-11 months after withdrawal. Tolerance and genotoxicity do not seem to be problems associated with senna, especially when used periodically in therapeutic doses. 

Zinc supplementation to these patients led to complete clearance of skin lesions and restoration of normal bowel function, which had previously resisted various dietary and drug regimens. This original observation was quickly confirmed in other cases with equally good results. The underlying mechanism of the zinc deficiency in these patients is most likely attributable to malabsorption. The cause of poor absorption is obscure, but an abnormality of Paneth s cells may be involved. These observations should provide a great stimulus to all interested in zinc metabolism to look for manifestations of zinc deficiency in other disorders, either natural or induced, in both children and adults. 

The complementary activity of upgraded sympathetic activity has nearly the opposite effects, at least as far as the mechanical effects. Sphincters that would ordinarily be more likely to be open in effect close. Motility of the contents is radically reduced. All of this is expected, given that increased sympathetic activity is beneficial for fight or flight behaviors. Circulation to the locomotive components of the body, the arms and legs, becomes increased and is decreased to the viscera. Decreased bowel function, increased water absorption caused by increased transit time and timer surface contact, and a more solid production of fecal matter are effects. The patient may likewise have pain and discomfort from increased and trapped flatus. In some severe instances, dehiscence and rupture may occur. 

The motility of the small bowel has been studied in great detail in experimental, physiological and clinical research [21, 71, 106, 107,109], and the patterns are well defined in man [21, 23, 110], Although a standard test of intestinal motor activity with regard to the efficiency of mechanical luminal clearance is not yet established for clinical use, means to evaluate this function have been proposed. 

FGIDs present with variable combinations of chronic or recurring GI symptoms not explained by overt biochemical or structural abnormalities and encompass conditions like functional dyspepsia (FD), irritable bowel syndrome (IBS) and chronic idiopathic constipation [1], A variety of mechanisms that could explain the etiology of FGIDs are currently under investigation and include, but are not limited to altered GI motility, visceral hypersensitivity and post-infectious abnormalities [2],... 

The 5-HT3 receptors are found in both the peripheral nervous system and central nervous system (CNS), where they mediate last synaptic transmission at synapses (3). In the CNS, they are located predominantly at intemeurones, where they modulate the release of a range of neurotransmitters (4-9). There is some evidence that 5-HT3 receptors play roles in brain reward mechanisms and in neurological phenomena such as anxiety, psychosis, nociception, and cognitive function (10,11), and in the first few years following the discovery of these receptors, there was also much interest in the therapeutic potential of 5-HT3 receptor antagonists for antipsychotic, antinociceptive, and other psychiatric disorders (12-15). This potential has not yet been realized, but there is still active research in this area (16), and their current major therapeutic target is against emesis in cancer chemotherapy and irritable bowel syndrome (17,18). 

Despite evidence for a role of delta opioid receptors in modulating mechanical activity in isolated intestinal preparations, there have been few studies to confirm their role in vivo. These receptors appear to play a minor role in modulating basal motility in the rat and dog small intestine [99,100]. However, it is possible that the function of delta opioid receptors in intestinal motor function may be unmasked in states of inflammation, volume distention, or increased enteric neural activity. Indeed, the antimotility potency of delta opioid agonists is increased in the inflamed bowel [101]. 

In this fenfe the ftimulus of the blood produces the contractions of the heart and the fubftances we take into our ftomach and bowels ftimulatc them to perform their neceflary functions. The rays of light excite the retina into animal motion by their ftimulus j at the fame time that thofe rays of light themfelves are phyfically converged to a focus by the ina live humours of the eye. The vibrations of the air ftimulate the auditory nerve into animal a(Tion while it is probable that the tympanum of the ear at the fame time undergoes a mechanical vibration. 

Identification of the mechanism utilized by the dietary supplement to maintain structure and function. That is, fiber maintains bowel regularity. ... 

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