Digestive System Flashcards

Flashcards covering the regulation of digestion, including nervous and hormonal control, gastric phases, and reflexes.

Why is control of digestion necessary?

To create conditions in the GI tract to maximize digestion and absorption, and to slow down gut movements and secretions during the post-absorptive phase to conserve energy.

Which activities within the digestive system need to be regulated?

Salivary secretion, gastric juice secretion and stomach motility, secretion of bile and pancreatic juice into the small intestine and motility, and movements of the large intestine.

What are the two key systems that mediate responses in digestive reflexes?

Nervous System and Endocrine System

What are the two networks of neurons within the enteric nervous system?

Submucosal plexus (controls secretions) and Myenteric plexus (controls motility)

How do parasympathetic and sympathetic nerves from the CNS affect GIT activity through the vagus nerve?

Increased parasympathetic activity increases GIT activity, while increased sympathetic activity decreases GIT activity.

What type of control regulates salivary secretion?

Entirely nervous; no hormones are involved. The salivary center is in the medulla oblongata.

What are the three main hormones involved in endocrine control of digestion?

Gastrin, Cholecystokinin (CCK), and Secretin

What are the three overlapping phases of gastric secretion?

Cephalic Phase, Gastric Phase, and Intestinal Phase

What are the characteristics of the Cephalic Phase of gastric activity?

Occurs before food arrives in the stomach, prepares the stomach for digestion, increases gastric juice production, is under neural control, and lasts for minutes.

What are the characteristics of the Gastric Phase of gastric activity?

Starts when food reaches the stomach, increases gastric secretion and motility, involves both neural and hormonal control, and lasts 3-4 hours.

What are the characteristics of the Intestinal Phase of gastric activity?

Chyme gradually leaves the stomach and enters the duodenum, decreasing gastric secretion and motility, increasing bile secretion and pancreatic juice. CCK and Secretin are the main hormones involved.

How does cholecystokinin (CCK) affect digestion?

Fats and peptides in chyme increase CCK, leading to contraction of the gall bladder, increased pancreatic enzymes, increased bile, and increased fat and protein digestion (also decreasing gastric activity and relaxing the hepatopancreatic sphincter).

How does Secretin affect digestion?

Acidic Chyme in the duodenum increases secretin. This leads to increased bicarbonate-rich pancreatic juice, which neutralizes acidic chyme (also decreasing gastric secretion and motility).

What are the effects of the Enterogastric Reflex?

Decreases gastric juice and motility (slowing stomach emptying), increases segmentation in SI to mix chyme, and contraction of the pyloric sphincter, temporarily preventing more chyme from entering the SI.

What is the Gastroileal reflex?

Stomach fills and stretch receptors activate, causing peristalsis in the SI and relaxation of the ileocaecal sphincter, pushing remnants into the LI (caecum).

What is the Gastrocolic Reflex?

Distention of the stomach while or immediately after eating causes powerful peristaltic contractions from the middle of the colon (3-4 times/d), forcing feces into the rectum and initiating the defecation reflex.