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GI Physiology > Lecture 10 - Gastric Motility > Flashcards

Lecture 10 - Gastric Motility Flashcards

1
Q

What is helicobacter pylori is essential for what?

A

gastric ulcers

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2
Q

What happens to proteins in the presence of pepsin?

A

proteins lose their functions

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3
Q

What does the acidity in the gastric lumen do?

A

it converts the protease precursor pepsinogen to pepsin

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4
Q

What is the relaxation of the gastric reservoir regulated by?

A
  1. ) Receptive relaxation
    - mechanical stimuli in the pharynx, when we swallow something, send signal to vagus centre, and then relax the muscle
  2. ) Adaptive relaxation
    - tension receptors in the gastric wall send signal to vagus centre and then it relaxes the stomach
  3. ) Feedback relaxation
    - nutrients in the first section of the duodenum send signal to vagus centre which causes relaxation. This reduces the flow of nutrients.
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5
Q

What formula represents the relationship between the pressure and the volume in hollow viscera?

A

P = T / R

R = square root of volume

T = P X square root of volume

increase tension = increase pressure

decrease in radius = increase in pressure

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6
Q

In the stomach if the volume increases what happens to the pressure?

A

It also increases

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7
Q

we need ……… to relax gastric wall, specifically the …… to stimulate the gastroesophageal reflex

A

neuronal activity and vagus nerve

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8
Q

Waves of smooth muscle contraction in the stomach cause what?

A

it mixes and propels the ingested contents of the gastric lumen, but only a small amount enters the small intestine as a result of each wave cycle.

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9
Q

The stomach can be divided into how many anatomical and functional parts and what are these parts?

A

Anatomical:

  • Fundus
  • corpus
  • antrum
  • pylorus

functional:
- gastric reservoir tonic contractions
- gastric pump phasic contractions

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10
Q

How is digesta transported to the antral pump?

A

2 mechanisms:

  1. ) tonic contraction
  2. ) peristaltic waves in the region of the gastric corpus
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11
Q

When a meal is swallowed, the smooth muscle in the stomach wall relaxes causing the stomachs volume to increase from …. to ….. with little increase in ……

A

from 50ml to 1.5 L with little increase in pressure

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12
Q

Stomach’s relaxing is mediated by?

A

parasympathetic nerves innervating the stomach’s enteric nerve plexuses, with coordination provided by the afferent vagal input from the stomach and efferent input by the swallowing centre in the brain.

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13
Q

What do the stomach’s mediators do to relax the stomach?

A

They cause the release of NO and serotonin to mediate relaxation.

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14
Q

What is a peristaltic wave and how does it work?

A
  • each wave begins in the stomach and only produces a small ripple as it proceeds towards the antrum of the stomach.
  • this contraction is too weak to produce much mixing of the luminal contents with acid and pepsin
  • once a peristaltic wave reaches the pyloric sphincter, it causes it to contract and close, expelling some food into the duodenum with each wave.
  • overall not a powerful mixer of the food that goes in
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15
Q

What is retropulsion in the stomach?

A
  • when the pyloric sphincter closes and most of the contents in the antrum are formed backwards towards the body of the stomach
  • this generates strong shear forces that help disperse food and improve mixing of chyme
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16
Q

What is responsible for gastric peristaltic waves?

A
  • generated by pace maker cells in the longitudinal smooth muscle layer
  • these smooth muscle cells undergo spontaneous depolarisation- depolarisation cycles (slow waves) known as basic electrical rhythm of the stomach.
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17
Q

What is the rate for gastric peristaltic waves?

A
  • 3 a minute
18
Q

The slow waves are conducted through where ?

A

They are conducted through hap junctions along the stomach’s longitudinal muscle layer and they also induce similar slow waves overlying the circular muscle layer.

19
Q

Without neuronal and hormonal inputs what would happen to the depolarisation that contract the stomach ?

A

The depolarisation would be too small to cause significant contractions

20
Q

What controls the force of contraction and rate of contractions?

A

rate - intrinsic basic electrical rhythm and remains essentially constant

force - neuronal and hormonal input to the astral smooth muscle which determines how much food is pushed to the duodenum.

21
Q

What do the neuronal and hormonal outputs do in the depolarisation of the antrum?

A

they further depolarise the membrane bringing it closer to the threshold.

22
Q

How does gastrin affect gastric motility?

A

if there is gastrin in high concentrations then that can increase the force of antral smooth muscle contractions.

23
Q

How does distension of the stomach affect the force of antral contractions?

A

it increase the force of antral contractions through a long and short reflex that is triggered by mechanoreceptors in the stomach wall. Hence after a large meal the the force of initial stomach contractions is greater which results in a greater emptying per contraction.

24
Q

What inhibits gastric emptying and what is it called ?

A

enterogastric reflex:

  • Distention of the duodenum
  • presence of fat, high acidity (low pH) or hypertonic solutions int eh lumen of the duodenum.

These factors also inhibit acid and pepsin secretion in the stomach.

25
Q

What is the most potent chemical stimuli that inhibits gastric emptying and what impact does this have on us?

A
  • fat
  • This prevents overfilling of the duodenum and the rate at which the duodenum is filled has some clinical implications
  • these include the fact that we have to consider what we eat when we are taking oral medications because if we have a meal that is rich in fat, this will slow oral drug absorption because it will take longer for it to reach the small intestine through the pyloric sphincter.
26
Q

How does a hypertonic solution inhibit gastric emptying?

A
  • prevents fluid in the duodenum from becoming too hypertonic
  • it slows the rate of entry of chyme
  • which decreases the delivery rate of large molecules that can rapidly be broken down into many small molecules by enzymes in the small intestine.
27
Q

How do the autonomic neutrons affect gastric motility?

A
  • autonomic neurons activated by CNS
  • independent of the reflexes that originate in the stomach and duodenum which impact gastric motility
  • increase in parasympathetic will increase gastric motility
  • increase in sympathetic will reduce gastric motility
28
Q

What are the phases of the gastric pump?

A
  1. ) Phase of propulsion
  2. ) Phase of emptying
  3. ) Phase of retropulsion
29
Q

What happens in the phase of propulsion?

A
  1. ) Contraction of the proximal antrum
  2. ) propulsion of chyme into relaxing terminal antrum and duodenal contraction
30
Q

What happens in the phase of emptying?

A
  1. ) Contraction of the middle antrum
  2. ) transpyloric and retrograde flow and duodenal relaxation
31
Q

What happens in the phase of retropulsion?

A
  1. ) contraction of the terminal antrum
  2. ) jet like back flow with grinding (mixes food up) and duodenal contraction
32
Q

what is the sieving function ?

A

When liquids and small particles leave the stomach much faster than larger particles.

33
Q

sieving function effect in the different phases of gastric pump?

A

Phase of propulsion - rapid flow of liquids with suspended small particels and delayed flow of large particles towards the pylorrus

Phase of emptying - emptying of liquids with small particles whereas large particles arre retained in teh buldge of the terminal of the antrum

Phase of retropulsion - retropulsion of large particles and clearing of the terminal antrum

34
Q

When do the contractions of the duodenum stop?

A

during contratctions of the antrum

35
Q

Pyloric activity is modulated by ….. inhibitory and …. excitatory reflexes

A

antral inhibitory and duodenal excitatory relexes

36
Q

What does the pyloric sphincter prevent?

A

duodenogastric reflux

37
Q

Duodenal stimuli like oleic acid inhibit what?

A
  • antral contractions
  • evoke duodenal contractions
  • increase pyloric tone
  • elicit frequent pyloric contractiosn.
38
Q

Rapid vs delayed gastric emptying?

A

Rapid emptying -

  • tonic contractions of the reservoir (1a)
  • deep peristaltic waves along the gastric body (1b)
  • deep constrictions of the antral waves (2)
  • a wide opening of the pylorus (3)
  • a duodenal receptive relaxation (4)
  • peristaltic duodenal contractions (5).

Delayed emptying :

  • feedback inhibition is caused by a prolonged relaxation of the reservoir (6a)
  • shallow peristaltic waves along the gastric body ( 6b)
  • shallow antral waves (7)
  • a small pyloric opening (8)
  • a lacking duodenal relaxation (9)
  • segmenting duodenal contractions (10).
39
Q

At what velocities are solids, liquids and chyme emptied?

A

liquids - exponential

solid - begins after sufficient grinding (lag phase)

viscous chyme - liner fashion

40
Q
A

GI Physiology (16 decks)

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