Tutorial title - Muscles

10 important questions on Tutorial title - Muscles

What are the functions of GI movements?

1. To propel ingesta from one location to the next with propulsive motility (e.g. Peristalsis)
2. To retain ingesta at a given time for digestion, absorption, or storage via retentive motility (e.g. Sphincter contraction)
3. To break up food material physically and mix with digestive secretions
4. To circulate ingesta so that all portions come into contact with absorptive surfaces

What are the muscles of the GI system?

Smooth muscles, coupled by gap junctions and pacemaker cells (interstitial cells of Cajal)

What determines the PATTERN of contraction?

Slow waves from the ICC, located at various locations along the GI tract.
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What determines whether contraction occurs or not?

Excitatory neurotransmitters (ACh, tachykinins such as substance P) from ENS/PSNS or Inhibitory neurotransmitters (NE, NO, VIP, ATP) from ENS/SNS

What is the rate of the waves in the GI system from ICCs?

5-20 waves per minute.

Where are contractions the strongest?

Antrum/pylorus > Cardia/body

Why are contractions the strongest at the distal stomach?

They force small particles into duodenum while grinding larger particles

Why are contractions the weakest at the proximal stomach?

They are adjusting the stomach size to the contents

What is the peristaltic reflex?

After mechanoreceptors sense distension caused by ingesta, there are local reflexes through interneurons to the motor neurons in the circular and longitudinal muscle layer to contract to push food through

What is the mechanism of the peristatltic reflex?

1. Stretch stimulates circular muscle proximal to bolus (ACh, substance P)
2. Circular muscle contracts and longitudinal muscle relaxes
3. Stretch relaxes the circular muscle distal to bolus (NE, NO, VIP, ATP)
4. Longitudinal muscle contracts and circular muscle relaxes

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