The smooth muscle in the wall of the gastrointestinal tract provides the force to move digesta through the tract; gastrointestinal motility is the general term used to describe the activity of this smooth muscle by three mechanisms: (1) autonomic nervous system, (2) gastrointestinal hormones, and (3) enteric nervous system.
Gastrointestinal hormones are released from endocrine cells in the epithelial lining of the gastrointestinal tract (enteroendocrine cells) and may stimulate or inhibit gastrointestinal smooth muscle. The release of these hormones is usually in response to digesta in the lumen of the tract. Thus, these hormones are a means of local regulation that is coordinated with the ingestion and digestion of food.
The enteric nervous system consists of neural plexuses between layers of smooth muscle in the wall of the tract (fig.21-1). These plexuses contain complete neurons (dendrites, cell bodies, and axons) that can from complete neural and reflex circuits in the wall of the tract so that neural regulation can be independent of external innervation. The presence of food and distension of gastrointestinal tract segments act as stimuli to initiate activity of the enteric nervous system. The three regulatory mechanisms (autonomic nervous system, gastrointestinal hormones, and enteric nervous system) also regulate secretions from glands in the wall of the gastrointestinal tract (Fig.21-1) and the intestinal accessory organs (salivary glands, liver, and pancreas).
All three of these mechanisms may regulate a given intestinal segment or accessory organ, but the relative importance of each varies among the segment of the gastrointestinal tract and the accessory organs. For example, salivary secretion is almost entirely regulated by autonomic nervous system, whereas gastrointestinal hormones are primary in initiation of bile secretion
The smooth muscle in the wall of the gastrointestinal tract provides the force to move digesta through the tract; gastrointestinal motility is the general term used to describe the activity of this smooth muscle by three mechanisms: (1) autonomic nervous system, (2) gastrointestinal hormones, and (3) enteric nervous system.
Gastrointestinal hormones are released from endocrine cells in the epithelial lining of the gastrointestinal tract (enteroendocrine cells) and may stimulate or inhibit gastrointestinal smooth muscle. The release of these hormones is usually in response to digesta in the lumen of the tract. Thus, these hormones are a means of local regulation that is coordinated with the ingestion and digestion of food.
The enteric nervous system consists of neural plexuses between layers of smooth muscle in the wall of the tract (fig.21-1). These plexuses contain complete neurons (dendrites, cell bodies, and axons) that can from complete neural and reflex circuits in the wall of the tract so that neural regulation can be independent of external innervation. The presence of food and distension of gastrointestinal tract segments act as stimuli to initiate activity of the enteric nervous system. The three regulatory mechanisms (autonomic nervous system, gastrointestinal hormones, and enteric nervous system) also regulate secretions from glands in the wall of the gastrointestinal tract (Fig.21-1) and the intestinal accessory organs (salivary glands, liver, and pancreas).
All three of these mechanisms may regulate a given intestinal segment or accessory organ, but the relative importance of each varies among the segment of the gastrointestinal tract and the accessory organs. For example, salivary secretion is almost entirely regulated by autonomic nervous system, whereas gastrointestinal hormones are primary in initiation of bile secretion
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