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40 Cards in this Set
- Front
- Back
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What is the upper small intestine called?
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the duodenum
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What are the 4 functions of the upper small intestine?
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Neutralization: Upper small intestine can't deal with the acidity of chyme
Osmotic equilibration: isotonicity reached in the duodenum (even though chyme= acidic) Digestion Absorption: only in the small intestine |
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What are the motor activities of the small intestine?
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Effective mixing: mix chyme from stomach and alkaline solution and secretion coming into the SI
Slow propulsion: takes 2-6 hours to get from duodenum to the end of the SI |
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What governs intestinal contractions?
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controlled by BER with ERA spikes, more ERA spikes per BER = increased strength of contractions
stimulus for contractions is distension or ACh release |
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How is the intestinal BER different from the distal stomach?
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Frequency of contraction is different
-> it declines systematically from proximal to distal intestine |
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Describe the f of cycles of contraction per minute in the small intestine
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Duodenum: max 12 BER/min - musculature more excitable, requires less stimulus to excite contractions
-Ileum: ~8cycles/min f of contractions dec as you go to the distal portion of the SI |
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Describe the mechanism regulating intestinal motility.
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BER made by the muscle fibres in the SI has a declining f gradient (highest in the duodenum, lowest in the ileum)
-Gradient determined by series of pacemaker regions along the intestine, each with a slightly lower f than the previous one -distribution of BER in time and space in the intestine created the distribution of spikes (ERA) and contractions -.: proximal portions of the intestine exhibit more activity than the distal ones **Maximal contractile activity in the SI cannot exceed the BER f of that gut segment** |
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Compare proximal and distal regions of the SI.
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Proximal: more contractions that are also more vigorous. More resistance to flow upsream
-> f of BER is greater -> Excitability of smooth muscle is greater (need less ACh or less spikes) -> Thickness of smooth muscle is greater Distal: fewer contractions and less vigorous |
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What is the result of having more contractions that are also more vigorous proximally?
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There is a slow net aboral (proximal to distal) movement
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What is the most common type of contractile activity?
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Segmentation: standing rings of contraction
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What is segmentation?
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1) Myogenic response to physilogical distension
2) ENS organizes tbe contraction over segments (not required) 3) ANS and hormones modulate |
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Describe peristalsis in the intestine.
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Infrequent, irregular, weak, shallow
Travel only for short distances (.: need segmentation) |
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Is there segmentation in the stomach?
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No
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What is intestinal peristalsis?
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triggered by stretch from a new meal
REQUIRES ENS - series of local reflexes modulated by ANS |
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What happens to the longitudinal and circular muscles AHEAD of the bolus?
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Longitudinal: contract-> make wall a telescope over the bolus
Circular: Relax -> this decreases resistance to flow |
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What happens to the longitudinal and circular muscles BEHIND the bolus?
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Longitudinal: Relax
Circular: Contract -> narrow lumen, create P system to push contents forward |
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Does the colon absorb nutrients?
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No
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Describe colon motility.
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Similar to SI, but:
Slower More Sluggish Irregular BER waves |
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How long does it take a meal to travers the esophagus? the small intestine? the colon?
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8-10 seconds
2-6 hours 50-60 hours |
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Where are digestion and absorption completed?
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In the small intestine
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Can anything be absorbed in the colon?
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Yes: H2O and some ions, but NO NUTRIENTS
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What are the fcts of the the colon?
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Mixing: ptomotes absorption of water and ions
Propulsion: slow (50-60 h, from proximal to distal colon) Storage |
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What governs segmentation and peristalsis of colon?
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Irregular BER
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Where do mixing, propulsion and storage take place in the colon?
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Mixing: transverse colon
Propulsion: descendin colon Storage: sigmoid colon |
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What happens after taking in a new meal?
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-Stomach becomes newly distended
-Gives rise to gastroileal reflex ->results in relaxation of ileal-cecum sphincter ->peristaltic activity in cecum (moves contents across ileal-cecum sphincter, from SI to colon) -Gastro-colic reflex: elevate rectum -> relaxes internal sphincter ->relax anal sphincter -Evacuation of contents from colon-> relax external sphincter -Ileocolic reflex: go to colon |
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What does distension of the stomach lead to?
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Different reflexes
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What happens in the interdigestive period?
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Migrating Myoelectric Motor Comples (MMC) => cyclic pattern of intense activity for housekeeping
*a) Recurring at regular intervals (~90min) *b) moving sequentially over distal stomach and small intestine up to distal ileum (~2-10cm/min) |
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What does the gastro colic reflex do?
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Increases contractile activity in distal colon and push content in rectum
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What does the ileocolic reflex do?
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Induces increased activity in the distal colon
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What does the gastroileal reflex do?
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Increase activity in distal colon
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What is MMC?
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Migrating Myoelectric (motor) Complex
Total of 90 min Moves contents ahead during interdigestive period (toward the colon) |
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What happens in phase I of MMC?
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60 min
-No spike potentials -No contractions ->always have a BER, but nothing else in phase I |
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What happens in phase II of MMC?
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20 min
-Irregular spike potentials Irregular contractions |
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What happens in phase III of MMC?
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10 min
Regular spike potential Regular contractions |
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What stops MMC?
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Entry of a new meal
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Where is the MMC restricted to?
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Distal stomach and SI
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How is MMC initiated?
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by ENS. can be modulated by ANS and peptides
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How is the MMC propagated?
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Via the ENS with modulation by th ANS and gut peptides
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How is the MMC interrupted?
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Intake of a new meal
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What are the functions of the MMC?
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-Housekeeping: cleanes distal stomach and SI during interdigestive periods and sweeps it into the colon
-Gastric emptying of large, non-digestible particles: pushed out of stomachand into the SI |
