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Neural and Endocrine Control of Digestive Processes
Production of Saliva
| Salivary Glands are stimulated to produce and release saliva. |
|
Efferent messages are sent via PNS fibers in cranial nerves VII and IX) |
| Contractions of Masseter and Temporalis muscles in chewing stimulates Pressoreceptors . Afferent messages of chewing are sent to the salivatory nuclei. |
| Chemoreception with Taste Buds. Afferent messages of taste via the Facial, Glossopharyngeal and Vagus nerves (CN VII, IX and X) are sent to the salivatory nuclei. |
| Presence of Food in the Mouth |
| Salivatory Nuclei in the Pons and Medulla |
| Hypothalamus - Low Blood Sugar Produces Hunger Drive |
| Cerebral Cortex |
| SIght, Smell or Thought of Food |
Neural and Endocrine Regulation of Digestion
| Cerebrum |
| Sight, smell, taste or thought of food |
I. Cephalic Phase (lasts about 8 minutes)
Before food has reached the stomach,
sensory messages of food will begin to
prepare the stomach for food. The result
of this sensory input is the production of
gastric juice from the stomach lining. The
chief means of stimulating the stomach lining
is through the vagus nerve.
II. Gastric Phase (lasts 3 to 4 hours)
| Submucosal plexi of the stomach wall are stimulated |
This phase is characterized by:
The overall effect of a, b and c above is to lower the pH of the stomach chyme and reduce the distention of the stomach wall due to the passage of acid chyme through the pyloric sphincter into the duodenum. The entrance of chyme into the small intestine brings on the last component of the control of gastric digestion, namely, the Intestinal Phase.
III. Intestinal Phase of Gastric Digestion - Duration is several hours
The combined result of the hormonal and neural portions of the intestinal phase is to insure that the stomach doesn't empty more chyme into the small intestine than can be processed by the duodenum at one time.
The release of secretin and cholecystokinin by duodenal enterendocrine cells coordinates the functions of the small intestine and the accessory organs of digestion with the stomach as see in the table below.
| Digestive organ | Effects of Secretin | Effects of Cholecystokinin |
| Stomach | Inhibits gastric secretion and peristalsis | Inhibits gastric secretion and peristalsis |
| Pancreas | Release of pancreatic juice rich in sodium bicarbonate | Release of pancreatic juice rich in enzymes |
| Liver | Release of bile to the small intestine by way of the hepatic ducts | No significant effect |
| Gall Bladder | No significant effect | Contraction of gall bladder and relaxation of the sphincter of Oddi |
| Intestinal Mucosa | Release of digestive juice and Brunner's gland mucous | Same as secretin |
| Stimulates the duodenum due to distension and the entrance of chyme containing glucose and fatty acids |
| cholecystokinin |
| secretin |
| Duodenal enteroendocrine cells release two hormones |
| Entrance of acid chyme into the duodenum |
| Inhibits the emptying of the stomach by reducing peristalsis and closing the pyloric sphincter |
| Inhibits the release of gastric juice |
| Directly stimulates |
|
a. Increased gastric juice secretion |
|
3. Presence of proteins and amino acids in incoming food stimulates enteroendocrine (G) cells releasing the hormone gastrin. This results in |
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2. An increase in the pH of the stomach contents as foods buffer the gastric juice. |
|
1. Distension of the stomach as
food enters. |
| Neural enterogastric reflex |
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c. Relaxation of the pyloric sphincter |
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b. Increased peristalsis of the stomach wall |
| Parasympathetic impulses via the vagus nerve |
| Medulla Oblongata |
