22.3 control of digestive system // enteric nervous system

GI tract has its own nervous system, referred to as

also called gut brain

enteric nervous system 

• Gut brain is made up of ———- that communicate extensively with each other

  • Major nerve supply to GI tract wall that controls motility

• Major nerve supply to GI tract wall that controls motility

enteric neurons

Enteric neurons make up bulk of two main interconnecting intrinsic nerve plexuses:

• Submucosal nerve plexus - Regulates glands and smooth muscle in mucosa

• Myenteric nerve plexus - Controls GI tract motility

Autonomic Control: 

• Parasympathetic system enhances digestive process

• Sympathetic system inhibits digestion

Three key concepts regulate GI activity

1. Digestive activity is provoked by a range of mechanical and chemical stimuli

2. Effectors of digestive activity are smooth muscle and glands

3. Neurons (intrinsic and extrinsic) and hormones control digestive activity

Hormonal controls

Hormones from cells in stomach and small intestine stimulate target cells in same or different organs to secrete or contract

1. Digestive activity is provoked by a range of mechanical and chemical stimuli

• Receptors located in walls of GI tract organs

• Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion

2. Effectors of digestive activity are smooth muscle and glands

• When stimulated, receptors initiate reflexes that stimulate smooth muscle to mix and move lumen contents 

• Reflexes can also activate or inhibit digestive glands that secrete digestive juices or hormones

3. Neurons (intrinsic and extrinsic) and hormones control digestive activity

• Intrinsic controls: involve short reflexes (enteric nervous system)

• Extrinsic controls: involve autonomic nervous system