GI PHYSIOLOGY I - INTRODUCTION AND MOTILITY Flashcards
what is the function of the GI tract?
obtain nutrients and replace fluid and salt
TRUE/FALSE: the enteric nervous system can act independently of the central and autonomic nervous system
True
what are the basic principles needed for regulation of the GI system to serve its function?
- conditions in intestinal lumen are regulated
- there are receptors in the wall of GI tract to respond to: stretch, change in composition, pH, osmolarity, amino acids, sugars, fats
- smooth muscles and glands being effectors: these reflex according to receptors stimulation - e.g. smooth muscle contraction and gland secretion
- there are nervous and hormonal regulation of GI function
what is central nervous system pathway like?
- co-ordinates activity over long distances
- modulates activity of enteric nervous system BUT no direct innervation
what stimulates the motility and secretion?
parasympathetic nervous system of CNS
what inhibits motility and secretion?
sympathetic nervous system of CNS
what regulates the secretion and motility in the enteric nervous system?
- submucosal plexus regulates secretion
- myenteric plexus regulates motility
what is ENS like?
- involved in local reflex
- totally self contained
simply describe the pathway of the CNS work on the GI physiology
- external stimuli: see, smell, emotional state, etc.
- CNS integrate the external stimuli
- 2 reflexes of the CNS involves parasympathetic and sympathetic
- parasympathetic when rest and digest, stimulate GI function (secretion and motility) using acetylecholine
- sympathetic inhibit the GI function
- enteric nervous system included and act as ‘middleman’ betwwen CNS and GIT
- long reflex path sends internal stimuli to CNS so it can generates a respond to that internal stimuli
describe the pathway of how Enteric Nervous System acts on GIT?
- GI lumen contents act as internal stimuli
- the receptors detect conditions in the GI tract (conditions such as the stretchiness and chemical composition within)
- ENS respond via short LOCAL reflex pathways through: myenteric plexus or submucosal plexus
TRUE/FALSE: GI tract is the largest endocrine organ of the body
true
define paracrine
signalling that acts directly on next door cells, unlike endocrine which needs to be signal via bloodstream
what do sensor cells also be called?
enteroendocrine cells
describe the enteroendoccrine cells of the GIT?
- epithelial cells
- detect luminal content and release hormone
what are the 4 critical GI hormones?
- gastrin
- gastric inhibitory peptide (GIP)
- secretin
- cholescytokinin (CCK)
what are the 2 types of GI motility?
- tonic: sustained and long
- phasic: waves of contraction and relaxation in a short period of time
what is the pattern that is a combination of 2 or more simpler patterns
retropulsion
TRUE/FASLE: relaxation sometimes can be a motility patter such as storage in the stomach
true
what type of muscle supports GI motility?
smooth muscle
what are the properties of the smooth muscle that assist the GI motility?
- spontaneously active
- contracts without external input
- contains pacemaker cells
- strength of contraction regulated by nervous and hormonal input
list the frequency of contraction of each GI region
- stomach: 3 per min
- duodenum: 12 per min
- ileum: 9 per min
what are the 2 broad types of motility patterns that are not tonic or phasic
- fasting (migrating motor complex)
- feeding
describe the characteristic of fasting?
- 4 hours after a meal
- repeats every 2h until eat
- housekeeping
- repeating pattern that helps clear undigested material and helps epithelial cells turnover
what happens during feeding (eating)?
- storage
- propulsion/movement
- mixing
where does storage happen?
stomach and colon
where does propulsion and movement happen?
esophagus, stomach, small and large intestine
where does mixing happen?
stomach, small and large intestin
what happens to the muscles in order to support storage?
relaxation of smooth muscles –> increase volume without change in pressure
what type of movement majorily happens along the tube?
peristalsis
what kind of mixing happening in stomach, small and large intestine?
- stomach: retropulsion
- small and large intestine: segmentation
this is a reminder to review peristalsis and segmentation from lecture 24
what does chewing do?
- reduce size of food, allows ingestion
- mixes food with saliva
- taste
chewing is a ______1______ activity with ______2______ muscle, which has _____3______ control of ______4______, _____5_____/ _______6_______
1: voluntary
2: skeletal
3: reflex
4: strength
5: frequency
6: rhythm
describe swallowing
- rapid transfer of material from mouth to stomach
- initiated at will, proceeds reflexively
which part of stomach responsible for:
1: storage?
2: mechanical digestion?
3: mixing?
4: controlled delivery to duodenum?
1: fundus and body of stomach
2: antrum
3: antrum
4: pyloric sphincter
during fasting, how much did stomach shrink into?
approximately 50mL in volume
what does migrating motor complex in stomach means?
- occurs 4h after a meal
- continues until eat with 2h of inactivity
- 50min of uncoordinated activity
- 10min of coordinated activity
what does ‘housekeeping’ function of stomach mean?
- removes residual secretions
- removes undigested material
- promotes epithelial cell turnover
which nerve controls/regulates the receptive relaxation and gastric accommodation of stomach during storage phase of feeding?
vagus nerve
how does stomach increase volume but not change the pressure?
relax the rugae
what type of propulsion/movement happens in stomach?
peristalsis
describe the peristalsis pathway of the stomach
- initiated on greater curvature and spreads to antrum
- 3 contractions per min
- first 60 mins following meal gentle
- 60-300 min more intense activity
what assist the super strong squeeze of the stomach
an extra third layer of muscle
what is retropulsion during mixing and mechanical breakdown of the feeding stage of the stomach?
combination of peristalsis and closure of the pyloric sphincter
what is the event happen during gastric emptying
combination of peristalsis and periodic opening (relaxation of the pyloric sphincter)
what regulates the gastric emptying?
feedback from duodenum
TRUE/FALSE: the rate of gastric emptying is completely independent from the digestive capacity of intestines
false
what factors affect the gastric emptying?
- size of meal: larger the size, faster the emptying
- composition of meal
what speeds up the gastric emptying?
- larger meal
- fluid (faster than solids)
what slows down the gastric emptying?
- fats
- acids
why does fluid helps speed up the gastric emptying?
reduction in size of food particles –> increase in surface area of food –> fasting digestion
why do fats and acids slows down the process of gastric emptying?
- fats: difficult to digest and need support of bile salt
- acids: need to neutralise
what is the function of small intestine motility?
- mixing with secretions from pancreas, liver and SI
- controlled movement/propulsion
- exposure of products of digestion to absorptive surfaces
what is the motility pattern between meals in small intestine?
migrating motor complex
what is the motility pattern after meals in small intestine?
segmentation and some peristalsis
what is a special characteristic of large intestinal motility
- large period of inactivity BUT mass movement: 1-2 times/day following meals
what type of motility appears in colon?
segmentation and peristaltic wave
what does segmentation and peristaltic wave do in colon?
- segmentation: exposure to absorptive surface for water and salt absorption
- peristaltic wave: drives faeces into rectum to initiate defecation
the mixing of stomach contents is facilitated by the process of?
retropulsion
