Regulation of Digestion

Nervous system effects
- Control of muscular and glandular activity by local nerves in alimentary canal
- Long-distance regulation by the brain

Secreted mainly by cells scattered throughout the epithelium of stomach and small intestine
Target cells in pancreas and gallbladder
Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis.
Glucagon: increases blood glucose levels by stimulating conversion of glycogen to glucose in the liver and the breakdown of fat and protein into glucose
Insulin: reduces blood glucose levels by promoting the cellular uptake of glucose, slowing glycogen breakdown in the liver, promoting fat storage
Leptin: produced by adipose (fat) tissue; suppresses appetite as its level increases.
- When body fat decreases, leptin levels fall, and appetite increases.
PYY: secreted by the small intestine after meals; acts as an appetite suppressant that counters the appetite stimulant ghrelin.
Ghrelin: secreted by the stomach wall; triggers feelings of hunger.
- In dieters who lose weight, ghrelin levels increase, which may be one reason it’s so hard to stay on a diet.
Insulin: secreted by the pancreas when there’s a rise in blood sugar level after a meal; suppresses appetite by acting on the brain.

The human body imposes a limit in the amount of fat it stores or uses up.
A complex feedback mechanism regulates the storage and use of fat.
- The hormone leptin is produced by the adipose tissue.
- High leptin level cues the brain to depress appetite and to increase energy-consuming muscular activity and body-heat production.
- Loss of body fat decreases the leptin levels in the blood, and the brain is signaled to increase appetite and weight gain.
- Genes are involved in fat homeostasis.