Bowel Movement
Bowel Movement and Stool Characteristics
The occurrence of strong and coordinated contractions (mass movements) allows the migration of stool from distal colonic segments into the rectum. These contractions occur more frequently in the morning after awakening and after a meal (gastrocolic reflex). In contrast, colonic motility is reduced at night to avoid incontinence (Andrews & Storr, 2011) The volume and consistency of the feces are other important factors affecting anal continence. Leakage of gas or liquid stools is more difficult to control, while hard stools are difficult to expel even in the presence of damaged or poorly functioning anal sphincters(Giannini et al., 2014).
Defecation Sensory perception and physiological coordination …show more content…
The enteric nervous system is composed of the myenteric plexus (Auerbach’s plexus) and the submucosal plexus (Meissner’s plexus), and it consists of a network of nervous fibers, ganglion cells (sensory and effectors neurons), and interneurons richly interconnected by reflex arcs located in the wall of the gastrointestinal tract and directed to innervate smooth muscle cells. The effector neurons of the myenteric plexus may be excitatory or inhibitory according to the substances released in contact with smooth muscle cells. Excitatory neurons release acetylcholine, substance P, and other tachykinins, while inhibitory neurons release vasoactive intestinal peptide and nitric oxide, which cause relaxation of smooth muscle cells As a result of this organization, the enteric nervous system acts like a semi-autonomous system: it is able to coordinate most of the activities, even in the absence of an extrinsic control. Extrinsic innervation is provided by the sympathetic and parasympathetic nerves, which have only a modulatory function on the contractile activity. Sympathetic innervation originates from postganglionic fibers of the hypogastric plexus and it has an inhibitory effect on the motor function, making connections with neurons of the enteric nervous system, which in turn sends fibers to smooth muscle cells, inhibiting the contraction. On the other hand, parasympathetic fibers, which originate from the sacral plexus (S2–S4) and run into the pudendal nerve, send preganglionic fibers to neurons of the intramural plexus, which in turn sends fibers to smooth muscle cells, stimulating the contractile function. Also important are the intrinsic reflexes located in the colon and rectal wall, as well as throughout the gastrointestinal tract; the colocolonic reflex is finely organized so
The occurrence of strong and coordinated contractions (mass movements) allows the migration of stool from distal colonic segments into the rectum. These contractions occur more frequently in the morning after awakening and after a meal (gastrocolic reflex). In contrast, colonic motility is reduced at night to avoid incontinence (Andrews & Storr, 2011) The volume and consistency of the feces are other important factors affecting anal continence. Leakage of gas or liquid stools is more difficult to control, while hard stools are difficult to expel even in the presence of damaged or poorly functioning anal sphincters(Giannini et al., 2014).
Defecation Sensory perception and physiological coordination …show more content…
The enteric nervous system is composed of the myenteric plexus (Auerbach’s plexus) and the submucosal plexus (Meissner’s plexus), and it consists of a network of nervous fibers, ganglion cells (sensory and effectors neurons), and interneurons richly interconnected by reflex arcs located in the wall of the gastrointestinal tract and directed to innervate smooth muscle cells. The effector neurons of the myenteric plexus may be excitatory or inhibitory according to the substances released in contact with smooth muscle cells. Excitatory neurons release acetylcholine, substance P, and other tachykinins, while inhibitory neurons release vasoactive intestinal peptide and nitric oxide, which cause relaxation of smooth muscle cells As a result of this organization, the enteric nervous system acts like a semi-autonomous system: it is able to coordinate most of the activities, even in the absence of an extrinsic control. Extrinsic innervation is provided by the sympathetic and parasympathetic nerves, which have only a modulatory function on the contractile activity. Sympathetic innervation originates from postganglionic fibers of the hypogastric plexus and it has an inhibitory effect on the motor function, making connections with neurons of the enteric nervous system, which in turn sends fibers to smooth muscle cells, inhibiting the contraction. On the other hand, parasympathetic fibers, which originate from the sacral plexus (S2–S4) and run into the pudendal nerve, send preganglionic fibers to neurons of the intramural plexus, which in turn sends fibers to smooth muscle cells, stimulating the contractile function. Also important are the intrinsic reflexes located in the colon and rectal wall, as well as throughout the gastrointestinal tract; the colocolonic reflex is finely organized so