Lecture 24: Introduction to GI Physiology and Motility Flashcards
(34 cards)
what is the overall function of the GI tract?
- obtain nutrients required for growth and energy
- replace fluid and salts lost in urine, feces, sweating, breathing
what does the CNS, ENS and hormones do?
regulates motility and secretion
what does motility do?
- carries out mechanical digestion
- aids chemical digestion
- aids absorption
what does secretion do?
- aids mechanical digestion
- essential for chemical digestion
- aids absorption
what is the path food takes in the GI tract?
- food is ingested
- undergoes mechanical digestion
- which essential for chemical digestion
- which is essential for absorption
-which leads to excretion of waste
what happens to the conditions of the intestinal lumen?
conditions of intestinal lumen are regulated
what do receptors in the GI tract wall respond to?
- stretch (food in lumen)
- change in composition such as pH, osmolarity, amino acids, sugars, fats
what are the effectors?
smooth muscle and glands
- reflexes stimulated by receptors stimulate smooth muscle contraction and glands secretion
what type of regulation is GI function under?
nervous and hormonal regulation
what is the nervous regulation of GI function?
- central nervous system
- enteric nervous system
how does the central nervous system regulate GI function?
- coordinates activity over long distances
- parasympathetic nervous system stimulates motility and secretion
- sympathetic nervous system inhibits motility and secretion
- modulates activity of the enteric nervous system
how does the enteric nervous system regulate GI function?
ENS consists of
- submucosal plexus which regulates secretion
- myenteric plexus which regulates motility
- involved in local reflexes (peristalsis and segmentation)
- completely self contained in GI tract
what is the hormonal regulation of GI function?
- GI tract is the largest endocrine organ in the body
- has endocrine and paracrine functions
- critical hormones are: gastrin, ghrelin, secretin, cholecystokinin
what are tonic contractions?
sustained contractions for minutes to hours e.g. sphincters
what are phasic contractions?
waves of contraction and relaxation over seconds (e.g. peristalsis)
define motility/motility pattern?
any pattern of contraction or relaxation of GI tract smooth muscle
- some motility patterns are a combination of two or more simpler patterns (e.g. retropulsion)
- sometimes relaxation can be a motility pattern (e.g. storage in stomach)
define movement/propulsion?
motility patterns that specifically move or propel GI contents along the tract
what is the basis of GI motility?
smooth muscle which is spontaneously active
- meaning it contracts without external input
- strength of contraction regulated by nervous and hormonal input
what is the frequency of contraction property in each region?
stomach - 3/min
duodenum - 12/min
ileum - 9/min
what are the features of the fasting motility pattern?
migrating motor complex
- 4 hours after a meal
- repeats every 2 hours until eat again
- housekeeping role
what are the features of the feeding motility pattern?
Storage
- occurs in stomach and colon
- relaxation of smooth muscle allows volume to increase without a change in pressure
Propulsion/Movement
- occurs in esophagus, stomach, small and large intestine
- peristalsis
Mixing
- Stomach (retropulsion)
- Small and large intestine (segmentation)
what is peristalsis?
- bolus of food arrive in digestive system
- circular muscle contract behind bolus
- longitudinal muscles head of bolus contract
- contraction in circular muscle layer pushes bolus forward
what is segmentation?
Alternate patterns of contraction to push food together and apart
what are the features of chewing?
- reduces size of food
- allows ingestion and reduces size
- mixes food with saliva for taste
- under voluntary control (skeletal muscle)
- involuntary control of strength, frequency and rhythm
