GI 4

Question 1

Which part of the receptive relaxation is part of the deglutition reflex

Answer 1

There are 3 ways to get this relaxation, only one of which is part of the deglutition reflex and mediated by the deglutition centre, and thats the one triggered by the distension of the pharynx, so the distension that occurs in anticipation to the food due to the reflex
The other mechanisms are in response to the food arriving, not to anticipation of its arrival

Question 2

How are the muscles of the stomach relaxed in the receptive relaxation

Answer 2

The ENS neurons release NANC peptides onto the smooth muscle cells leading to their hyperpolarization, little to no contracting which is what is required for such a relaxation
The order of the release of the NANC peptides can come from ANS as well as directly from the ENS circuitry

Question 3

What separates the stomach from the duodenum (SI)

Answer 3

The pyloric sphincter, separates specifically the pylorus of the stomach from the duodenum

Question 4

What’s the main contractile activity of the distal stomach

Answer 4

Peristalsis for pushing food down as well as chopping it up

Question 5

What determines how strong a peristaltic contraction in the stomach will be (brief)

Answer 5

Magnitude is contingent on the size/magnitude of the stimulus, so the more local distension aka stretch we have the stronger the contraction will be
Neural intervention as well as hormones will also contribute

Question 6

What controls the frequency, direction and velocity of peristaltic contraction in the stomach (brief)

Answer 6

The electrical characteristic of the smooth muscle in the distal stomach

Question 7

Compare the electrophysiology resting state of proximal and distal stomach

Answer 7

At rest, the proximal stomach is forever at -55mV because it doesnt contract
The distal stomach does contract and its resting state is also -55mV but with rhythmic waves of partial depolarization, meaning it rhythmically depolarizes to -45mV but that doesnt pass threshold, not unless theres an outside factor like local distension

Question 8

BER

Answer 8

Basic electrical rhythm of the distal stomach
The distal stomach isn’t ever perfectly at rest, it has small partial depolarizations, rhythmically not random, which defines its basic electrical rhythm
It doesnt change unless theres an outside stimulus, otherwise its permanently like that
It occurs synchronously but only circumferencially, the different circumferences partially depolarizes at different rhythms (like its not one uniform depolarization across the entire stomach, its organized in circumferential waves)
Refer to slide 149

Question 9

What are spikes

Answer 9

A little extra electrical activity leading to spikes on the partial depolarizations, potentially ones strong enough to depolarize the muscle fibre for contraction
These spikes affect all the circumferencial rings in a staggered way, makes sense since they dont all have the partial depolarization at the same time

Question 10

What’s the relationship between spikes and amplitude

Answer 10

The more spikes there are for a given partial depolarization the higher the amplitude, which we said to be the strength of contraction
Note that we get more spikes if theres more distension

Question 11

What’s the maximum frequency of stomach contraction

Answer 11

The largest amount of times the stomach can contract in a minute, specific to the stomach its 3x/min because thats how many partial depolarizations we have, caps there because we cannot have a depol with first the partial depolarization

Question 12

What sets the BER

Answer 12

The ICC, the interstitial cells of Cajal, non-neuronal, non-muscular cells, kind of an intermediate between neuronal cells and smooth muscle, function as pacemakers and coordinate groups of muscle cells

Question 13

What causes spikes

Answer 13

Can be triggered by release of Ach or local distension, triggering of stretch receptors
They only occur at the peak of the BER and are Ca dependent, and they’re proportional to the magnitude of contraction

Question 14

What is antral systole

Answer 14

Antral systole is the state in which the distal stomach is going through a wave of contraction leading to a closed (contracted) pyloric sphincter, basically acting as a wall in which the contents bounce back off of to continue mixing and being broken down

Question 15

Pyloric sphincter

Answer 15

Weird because its always open at rest, unlike all other sphincters, and its closed by antral systole aka antral peristalsis, also has a very narrow lumen such that only things of 1-2mm can pass, meaning its ok for it to be always open because only the sufficiently digested can pass

Question 16

What is retropulsive flow

Answer 16

What happens when the bolus of food that hasnt been sufficiently digested gets caught up in the contraction of the distal stomach, is pushing to the pyloric sphincter in antral peristalsis but ricochets and bounced right off, due to not being able to pass through the small lumen (also contracted)
This causes a lot of disruption and breakage of the chyme

Question 17

How does the gastric emptying of liquids work

Answer 17

Happens usually according to the pressure gradient, so if the pressure pf the stomach is higher than that of the duodenum, should pass
Note: receptive relaxation helps balance these pressure really well but there’s always a little but of unbalance
Think of the delat P as small and allowing a small amount of fluid to trickle thru the 1-2mm lumen of teh pyloric sphincter at rest

Question 18

How does the gastric emptying of solids work

Answer 18

The meal/food is stored in the funding reservoir (proximal stomach) while the distal stomach is the antral pump (moves the contents forward according to a certain frequency and volume)
So we know that the frequency is set by the BER, 3x/min, but stroke volume is determined by other factors, which affect how easily the contents are pumped and with what force (amplitude)

Question 19

What determines stroke volume of the antral pump

Answer 19

The fluidity of teh chyme: the more fluid and digested it is the faster it’ll be able to flow through the sphincter
Also the magnitude, number of spikes per peak

Question 20

What causes antral peristalsis

Answer 20

Can be caused by distension leading to spikes leading to contraction waves, peristaltic waves, the contraction specifically is triggered by excitatory effector ENS neurons releasing Ach on muscle cells and the ENS neurons themselves can be activated by the ANS (vagal-vagal) or by the ENS sensory receptors directly (intramural)
Does not happen before the meal arrives

Question 21

What affect does the duodenum have on the stomach and its practices

Answer 21

It slows gastric emptying and antral peristalsis
Makes sense because the acidic content is hard to deal with so small doses are best, so it has protective mechansisms (can be hormonal or neural) by which it can slow teh emptying an peristalsis
It sends the chill out signals when it senses: distension, pH of less than 3, high osmolarity (time required to absorb), chemical composition (as in fat, carb, protein, that has an affect on desired rate of emptying)

Question 22

How does chemical composition affect digestion time in duodenum

Answer 22

Fat takes longer than protein takes longer than carbs, so if you eat smtg fat dense you’ll digest it slower because duodenum can sense that, knows it’ll take a long time, and slows gastric emptying