The first phase of ingestion, called the cephalic phas , is controlled by the neural response to the stimulus provided by food. All aspects—such as sight, sense, and smell—trigger the neural responses resulting in salivation and secretion of gastric juices. The gastric and salivary secretion in the cephalic phase can also take place due to the thought of food.
Right now, if you think about a piece of chocolate or a crispy potato chip, the increase in salivation is a cephalic phase response to the thought. The central nervous system prepares the stomach to receive food. The gastric phase begins once the food arrives in the stomach. It builds on the stimulation provided during the cephalic phase. Gastric acids and enzymes process the ingested materials. The gastric phase is stimulated by 1 distension of the stomach, 2 a decrease in the pH of the gastric contents, and 3 the presence of undigested material.
This phase consists of local, hormonal, and neural responses. These responses stimulate secretions and powerful contractions. The intestinal phase begins when chyme enters the small intestine triggering digestive secretions. This phase controls the rate of gastric emptying. In addition to gastrin emptying, when chyme enters the small intestine, it triggers other hormonal and neural events that coordinate the activities of the intestinal tract, pancreas, liver, and gallbladder.
The endocrine system controls the response of the various glands in the body and the release of hormones at the appropriate times. One of the important factors under hormonal control is the stomach acid environment. During the gastric phase, the hormone gastrin is secreted by G cells in the stomach in response to the presence of proteins. Gastrin stimulates the release of stomach acid, or hydrochloric acid HCl which aids in the digestion of the proteins.
However, when the stomach is emptied, the acidic environment need not be maintained and a hormone called somatostatin stops the release of hydrochloric acid. This is controlled by a negative feedback mechanism. In the duodenum, digestive secretions from the liver, pancreas, and gallbladder play an important role in digesting chyme during the intestinal phase. In order to neutralize the acidic chyme, a hormone called secretin stimulates the pancreas to produce alkaline bicarbonate solution and deliver it to the duodenum.
In response, the following reflexes are initiated:. Neural response: Stimuli that arouse digestion are relayed to the hypothalamus, which in turn initiates nerve impulses in the parasympathetic vagus nerve. These impulses innervate nerve networks of the GI tract enteric nervous system , which promote contraction of smooth muscle which causes peristalsis and secretion of gastric juice. Stimuli that repress digestion emotions of fear or anxiety, for example innervate sympathetic fibers that suppress muscle contraction and secretion.
The gastric phase describes those stimuli that originate from the stomach. These stimuli include distention of the stomach which activates stretch receptors , low acidity high pH , and the presence of peptides.
General effects: The stomach and small intestine prepare for the digestion of chyme, and gastric emptying is promoted. The intestinal phase describes stimuli originating in the small intestine.
These include distention of the duodenum, high acidity low pH , and the presence of chyme especially fatty acids and carbohydrates. Neural response: Gastric secretion and gastric motility are inhibited enterogastric reflex. When the stomach is full, the part of the brain that detects satiety signals fullness. There are three overlapping phases of gastric control: the cephalic phase, the gastric phase, and the intestinal phase.
Each requires many enzymes and is under neural control as well. Salivation : Seeing a plate of food triggers the secretion of saliva in the mouth and the production of hydrochloric acid in the stomach. The response to food begins even before food enters the mouth. The first phase of ingestion, called the cephalic phase, is controlled by the neural response to the stimulus provided by food.
All aspects, such as sight, sense, and smell, trigger the neural responses resulting in salivation and secretion of gastric juices. The gastric and salivary secretion in the cephalic phase can also take place at the thought of food.
Right now, if you think about a piece of chocolate or a crispy potato chip, the increase in salivation is a cephalic phase response to the thought. The central nervous system prepares the stomach to receive food. The gastric phase begins once the food arrives in the stomach. It builds on the stimulation provided during the cephalic phase. Gastric acids and enzymes process the ingested materials. The gastric phase is stimulated by 1 distension of the stomach, 2 a decrease in the pH of the gastric contents, and 3 the presence of undigested material.
This phase consists of local, hormonal, and neural responses. These responses stimulate secretions and powerful contractions. The intestinal phase begins when chyme enters the small intestine, triggering digestive secretions. This phase controls the rate of gastric emptying.
In addition to gastric emptying, when chyme enters the small intestine, it triggers other hormonal and neural events that coordinate the activities of the intestinal tract, pancreas, liver, and gallbladder. The endocrine system controls the release of hormones responsible for starting, stopping, slowing, and quickening digestive processes. The endocrine system controls the response of the various glands in the body and the release of hormones at the appropriate times.
The system is made of a series of glands that produce chemicals called hormones.
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