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functions of motility in GI tract

Propulsion - at a controlled rate

Mechanical digestion - increase SA

Mixing - food, secretions and enzymes

Exposure to absorptive surfaces -> intimate contact


Basic electrical rhythm (slow wave)

  • These are spontaneous variations in membrane potential (pacemakers)
  • If they surpass threshold, we get action potentials and therefore contraction of smooth muscle


regulation of motility

  • BER determines the frequency of contractions
  • Strength of contraction regulated by nervous and hormonal reflexes
  • depolarise or hyperpolarise RMP to make it easier or harder to get to threshold


role of enteric nervous system 

  • determines type of motility that occurs: peristalsis or segmentation
  • modified by stretch, nerves, hormones, loacl feedback loops


fasting motility pattern

  • migrating motor complex
  • coordinated movement from stomach to SI to LI for 4-5 hours after a meal
  • repeated every 2 hours
  • 3 period: inactivity, intermittent activity, intense activity
  • function = housekeeping


feeding motility patterns in GI tract

  • storage
  • peristalsis
  • segmentation


features of storage

Mainly stomach

Relaxation of smooth muscle (-> distension)


features of peristalsis

Esophagus, stomach, small & large intestine


Proximal squeeze, distal relax


features of segmentation

Small and large intestine

Mixing & exposure to absorptive surfaces - churning and squishing

Alternate contraction and relaxation of circular muscle


function of swallowing (deglutition)

rapid transfer of material from mouth to stomach via oesophagus



function of chewing (mastication)

Reduce size of food  

Mix food with saliva  



motility in esophagus

  • Oesophageal peristalsis transfers food from the mouth (following mastication and deglutition) to the stomach  
  • May or may not be aided by gravity (i.e. still happens when we’re upside down)  
  • Oesophageal sphincters prevent backflow of food 


control of chewing

  • Under both voluntary and reflex control  
  • We have to voluntarily masticate (skeletal muscle)
  • Reflexes control the strength, frequency, occlusion (how the teeth match up during biting), and side of chewing 


control of swallowing

  • Initiated voluntarily but proceeds via reflexes (involuntary) 
  • Involves the coordination of multiple muscles in order to pass the food to the stomach, whilst still protecting the airway  


fasting stage of gastric motility

shrinks to small volume, MMC


fed stage of gastric motility

  • storage in proximal stomach 
  • peristalsis 
  • controlled delivery of chyme to the duodenum


storage in stomach

  • nervous reflex initiated by swallowing
  • relaxation of proximal gastric smooth muscle leads to increase in volume - distension of rugae


peristalsis in stomach

  • initiated on greater curvature that spread to antrum
  • propulsion moves food down to antrum
  • retropulsion moves food back from pyloric sphincter - helps mix food with secretions, and also mechanical digestion


controlled delivery of chyme to duodenum

  • rate depends on composition of food (solids slower than liquids, fats move slowly)
  • gastric inhibitory polypeptide (hormone) and enterogastric reflex (neural) are feedback from duodenum that influence gastric emptying


functions of small intestine motility

  • Facilitate the chemical digestion of food
  • Facilitate the absorption of nutrients, salts, and water  
  • Mix chyme with intestinal secretions
  • Exposure chyme to absorptive surfaces 
  • Propel chyme along the GI tract 


fed small intestine motility

Mainly segmentation to aid in contact digestion and mixing of chyme with digestive enzymes and other chemicals  

Also peristalsis to propel chyme through the small intestine 


functions of large intestine motility

Temporary storage of faeces  

Regulation of the salt and water content of faeces 


motility patterns in large intestine


Segmentation to aid in mixing and slow propulsion  

Peristalsis to move masses of faeces into the rectum for defecation. Occurs 3-4 times per day 


what is chemical digestion

chemical hydrolysis of food by digestive enzymes into molecules that can cross epithelial lining of GI tract


functions of secretions in GI tract

digest food

dilute food

maintain optimal pH

protect and lubricate GI tract


features of digestive enzymes


organic catalysts

display specificity (i.e. they will only act on a specific substrate).

Function optimally at a specific pH (different for different enzymes)


two stages of chemical digestion

  1. luminal digestion - initial digestion of food in the lumen of the GI tract
  2. contact digestion - completion of chemical digestion by brush border enzymes in the small intestine


luminal enzymes secreted by salivary glands, chief cells of stomach and acinar cells of pancreas

salivary glands: amylase

chief cells of stomach: pepsinogen

acinar cells of pancreas: trypsinogen, chymotrypsinogen, lipase and amylse


composition of carbohydrates

composed of chains of monosaccharides 

main polysaccharides in our diet are starch and glycogen - joined by alpha-1,4-glycosidic bonds

a lof of cellulose in in our diet which we cant digest because our digestive enzymes cannot cleave beta-1,4-glycosidic bonds

some disaccharides such as sucrose, lactose and maltose


luminal digestion of carbohydrates

Polysaccharides are converted to disaccharides by salivary and pancreatic amylase (in lumen)