Overview of Digestive System

1. Structures of Digestive System
1. alimentary canal (gastrointestinal [GI] tract)
• digestion - break down molecules
• absorption - move into circulatory system
• mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
2. accessory digestive organs
• function - assist in breakdown and absorption of foodstuffs
• teeth, tongue, gallbladder, salivary glands, liver, pancreas
2. Primary Functions of Digestive System
1. ingestion - getting food into the GI tract (eating)
2. propulsion - moving food along the tract
• swallowing and peristalsis (wave-like motion)
3. mechanical digestion - the physical grinding and churning of foodstuffs to breakdown and expose to enzymes and the surface of the GI tract
4. chemical digestion - breakdown of larger molecules into absorbable parts by enzymatic action
5. absorption - transport of digested molecules, vitamins, minerals, water, into blood
6. defecation - elimination of unused foodstuff (feces)
3. Control of Conditions in the GI Tract
1. mechanoreceptors and chemoreceptors respond to:
• stretching of the lumen by foodstuffs
• solute concentration and pH within the lumen
• presence of digestible and digested molecules
2. actions initiated by these receptors:
• activate/inhibit secretions into the lumen
• activate/inhibit muscular "mixing" activity
• activate/inhibit secretion of hormones
• activate/inhibit local "nerve plexuses"
3. types of digestive reflex processes:
• short reflex - controlled by "nerve plexus" within the GI tract (enteric plexus)
• long reflex - those involving the CNS and extrinsic autonomic nerves

Category: Physiology Notes