Motility Of The Gastrointestinal Tract Flashcards
What is motility?
Movement of material in the gastrointestinal tract as a result of muscular contraction
What are the purposes of motility?
- moving food
- mixing food
What are the types of movement that happen in the gastrointestinal tract?
- voluntary
- involuntary
-peristalsis - segmentation
Voluntary movements:
- skeletal muscles at the end of the tract
- mouth at the beginning at the tract, for chewing & swallowing
- external anal sphincter at end, for defecation
Involuntary movements:
- smooth muscles are in the rest regions of the tract
- tonic contractions, go on for minutes / hours
- phasic contractions, last for a few seconds, contraction-relaxation cycles happen
Peristalsis:
- progressive waves of contraction
- circular muscles are behind a bolus of food, they come into contact
- moves contents from one section of the gastrointestinal tract to the next
Happens in the:
- pharynx
- oesophagus
- stomach
- intestines
Segmentation:
- short segments of intestine alternatively contract & relaxing
- this mixes food
- circular muscles contract
- longitudinal muscles relax
Happens in:
- small intestines
- colon
How is food mechanically processed in the mouth?
- Chewing
- Grinds and breaks up food
- Allows swallowing, increases the surface area for food
- Mixes food with the saliva
- Exposes food to the taste buds
Mouth to the stomach = all-or-none reflex
1st stage = oropharyngeal stage
- bolus of food in mouth
- upper esophageal sphincter is closed
- soft palate blocks the nasal cavity
- tongue blocks the oral cavity
- upper esophageal sphincter is opened
- epiglottis blocks the larynx
- bolus of food is swallowed
- upper esophageal sphincter then re-closes
2nd stage = oesophageal stage
- primary peristaltic wave
- 2-6cm travelled per second
- secondary peristaltic waves are also very effective
- moves the bolus of the food from the oesophagus to the stomach
What happens in the stomach? 3rd stage:
- Filling
- Storage
- Mixing
- Emptying
Inner layer of smooth muscles:
- strengthens stomach wall
- assists mixing & churning activities that are essential to form chyme
Filling of the stomach:
50ml to 1000ml = little change in tension in the wall, little rise in intragastric pressure
Greater than 1000 = over distended, intragastric pressure rises, discomfort occurs
Storage in the stomach:
- very weak peristalsis
- stores food in the body of the stomach
- optimal digestion & absorption by the small intestine
Mixing and emptying in the stomach:
Propulsion:
- pyloric valve closed
Mixing & emptying:
- strong antral peristalsis
- pyloric valve is slightly open
How is chyme produced?
- the stomach contents is mixed with gastric secretions
What is gastric emptying?
- chyme is propelled into the duodenum in small squirts
- via the pyloric sphincter
What is retropulsion?
- pyloric sphincter closes
- forces chyme back into the stomach
- for further mixing
What prevents reflux of the gastric contents?
- lower oesophageal sphincter
What happens in the small intestine?
- segmentation
- limited peristalsis
- most digestion & absorption takes place here
What is segmentation?
- oscillatory
- alternating contractions & relaxations of the small intestine’s smooth muscles
What does segmentation do?
- mixes chyme with the small intestine digestive juices
- chyme is brought into repeated contact with absorptive surfaces
- slowly moves the chyme through the small intestine
- ensures the nutrients will be absorbed
- frequency decreases as it goes on
- 12/min in the duodenum
- 9/min in the ileum
What is peristalsis between meals called?
Migrating motility complex
What is the migrating motility complex?
- weak, repetitive peristaltic waves from the stomach to the ileum
- sweeps undigested material, mucosal debris & bacteria to the colon
- one happens every 90 minutes
- 6-8 happen overnight
What happens in the colon?
- segmentation
- mass movements
