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Chapter 18: Problem 30

Describe the reflexes controlling the stomach, liver, gallbladder, and pancreas that are triggered by the arrival of chyme in the duodenum.

Short Answer

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The arrival of chyme in the duodenum triggers several reflexes controlling the stomach, liver, gallbladder, and pancreas. In the stomach, the enterogastric reflex reduces gastric motility and secretion, while gastric inhibitory peptide (GIP) is secreted to further inhibit gastric activity. The liver and gallbladder respond to the presence of chyme by secreting bile-promoting hormones, secretin and cholecystokinin (CCK), with the latter also causing gallbladder contraction. Lastly, the pancreas is stimulated by secretin to release bicarbonate, neutralizing the chyme, and by CCK to secrete digestive enzymes such as trypsin, chymotrypsin, and lipase for breaking down proteins, fats, and carbohydrates for absorption.

Step by step solution

01

Define chyme and its arrival in the duodenum

Chyme is a semi-fluid mass of partially digested food that is released from the stomach into the small intestine, specifically into the duodenum. The duodenum is the first part of the small intestine, and it plays a crucial role in digesting food and neutralizing stomach acids before the food moves further down the small intestine.
02

Reflexes controlling the stomach

The arrival of chyme in the duodenum triggers several reflexes in the stomach, which help control digestion: 1. Enterogastric reflex: This reflex reduces gastric motility and secretion of gastric juices in response to the presence of chyme in the duodenum. This delay allows the duodenum time to process the chyme and prevents an excessive amount of chyme from entering the duodenum at once. 2. Gastric inhibitory peptide (GIP) secretion: GIP is a hormone that inhibits gastric secretion and motility, allowing the chyme to be processed by the duodenum without overwhelming it.
03

Reflexes controlling the liver and gallbladder

The presence of chyme in the duodenum triggers reflexes in the liver and gallbladder, which aid digestion by releasing bile: 1. Secretin secretion: The arrival of acidic chyme in the duodenum stimulates the release of secretin, a hormone that promotes bile secretion by the liver. 2. Cholecystokinin (CCK) secretion: Fats and proteins in the chyme stimulate the release of CCK, a hormone that causes the gallbladder to contract and release stored bile into the duodenum. Bile helps in emulsifying and breaking down fats for absorption.
04

Reflexes controlling the pancreas

The arrival of chyme in the duodenum also triggers reflexes in the pancreas, leading to the secretion of digestive enzymes and bicarbonate: 1. Secretin effect on the pancreas: Secretin stimulates the pancreas to release bicarbonate, which neutralizes the acidic chyme and provides the optimal pH for the pancreatic enzymes to function. 2. Cholecystokinin effect on the pancreas: CCK also stimulates the pancreas to secrete digestive enzymes such as trypsin, chymotrypsin, and lipase into the duodenum. These enzymes help in breaking down proteins, fats, and carbohydrates for absorption.

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