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GI Week 2 > Gastric Physiology and Motility > Flashcards

Gastric Physiology and Motility Flashcards

1
Q

What are the three main functions of the stomach?

A
  1. Acts as a reservoir
  2. Emulsifies fats
  3. Grinds food
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2
Q

How many muscle layers does the stomach have?

A
  1. Longitudinal layer
  2. Circular layer
  3. Oblique layer
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3
Q

How much can the stomach store?

A

2-4 L

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4
Q

How does the stomach Accommodate when we swallow food?

A

When food enters the stomach, there is little change in pressure so it is not like an elastic balloon, instead the fundal wall undergoes a receptive relaxation as part of the swallowing reflex and in response to gastric mechanoreceptors.

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5
Q

What is the function of the Dorsal Vagal Complex?

A

It senses mechanical stimulus in the pharynx, then integrates input to alter gastric secretion and relaxation of the stomach.

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6
Q

Is vagal release of ACh during accommodation associated with contraction or relaxation of the stomach?

A

Relaxation

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7
Q

What signals does the stomach send out when it’s expanded?

A

It signals forward along the enteric nervous system to empty more distal segments

  1. Gastroileal reflex - causes ileoceccal valve to relax and transfer contents from small to large bowel
  2. Gastrocolic reflex - induces the need to defecate after ingesting a meal
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8
Q

What does low pH do in gastric digestion?

A

Low pH facilitates protein denaturation

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9
Q

What does pepsin do in gastric digestion?

A

Pepsin endopeptidase releases peptides

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10
Q

What does gastric lipase do in gastric digestions?

A

Gastric lipase (optimal at pH 3-6) produces free fatty acids (pancreatic lipase is active at higher pH and is used with more bicarbonate around)

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11
Q

What are mechanical movements important for in gastric digestion?

A

Emulsification and reducing the size of any solids

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12
Q

Gastic absorption is. ..

A

. . .Minimal.

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13
Q

What substances can be absorbed by diffusion?

A

Lipid soluble substances like alcohol and aspirin

-There is no active transport

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14
Q

Absorption of what substances is associated with gastritis?

A

Lipid soluble substances like alcohol and aspirin

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15
Q

How small must food be to pass through the pylorus?

A

Less than 2 mm in diameter.

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16
Q

What does the emptying of liquids from the stomach require?

A

Emptying of liquids involves proximal stomach (tonic)

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17
Q

What does the emptying of solids from the stomach require?

A

Emptying of solids involves antral pump (phasic).

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18
Q

What do gastric motility patterns use to mix, triturate and sieve gastric contents?

A

Phasic contractions (3 cycles/minute)

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19
Q

What is the cycle of phasic stomach contraction?

A
  1. A circumferential contraction (A) sweeps toward the pylorus resulting in anterograde and retrograde propulsion of material
  2. As contraction A subsides, a second contraction, B, mixes contents further.
  3. Contraction B is sufficient to cause transient and partial opening of the pylorus, allowing small particles to exit the stomach. Larger particles are propelled back into eh stomach to be further dispersed by contraction C.
  4. Further cycles of contraction against a closed pylorus continue mixing and grinding until all of the meal is emptied from the stomach.
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20
Q

When does the pylorus contract and why?

A

It contracts during antral contraction to limit the movement of chyme into the duodenum creating retroperistalsis

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21
Q

What is the BER?

A

Peristalsis occurs at the Basic Electrical Rhythm (BER) and is 3 to 5 waves per minute in the stomach.

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22
Q

What does the BER establish?

A

The maximum frequency of the wave that is propagated over the stomach

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23
Q

How can the amplitude of the BER be altered?

A

By neural (ACh causes calcium influx) and hormonal (Gastrin) input

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24
Q

What determines the magnitude of a stomach contraction?

A

The number of action potentials on the crests of slow waves determines the magnitude of the contraction

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25
Q

How do contractions change as they approach the closed pyloric sphincter?

A

They strengthen and speed up!

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26
Q

What influences the magnitude of contractions?

A

Magnitude increases - parasympathetic

Magnitude decreases - sympathetic

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27
Q

What causes Rapid emptying of the stomach?

A

Rapid emptying is caused by tonic contraction 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) and peristaltic duodenal contractions (5).

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28
Q

What causes Delayed emptying of the stomach?

A

Delayed emptying due to feedback inhibition 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) and segmenting duodenal contractions (10).

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29
Q

What does the rate of gastric emptying depend on?

A

The composition of the meal. Glucose solution leaves first, then protein solution, then solid meal.

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30
Q

What feedback mechanism is associated with gastric emptying?

A

When food first enters the duodenum, a variety of neural, hormonal and mechanical signals feedback to slow gastric emptying by diminishing the intensity of the contractile wave.

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31
Q

What is the active ingredient in Slimful (brownie or strawberry chews!)?

A

Konjac Flour

32
Q

How does Konjac Flour work?

A

It’s a potent dietary fiber, creates a thick gel in the stomach that delays gastric emptying and keeps you feeling full. Study showed a weight loss of 5.5 lbs over 2 months. Note: can lead to blockages of the esophagus and is the same concept as eating more fruits and vegetables

33
Q

What things inhibit gastric contractions and gastric emptying?

A
  • Acid in the duodenum via neural (enteric and vagal) and hormonal (secretin and somatostatin) mechanisms
  • Fat in the duodenum via hormonal (CCK) mechanisms and via enteric neural mechanisms
  • Osmolality of the duodenal contents via enteric neural mechanisms and perhaps hormonal mechanisms (GIP)
34
Q

What delays emptying of the stomach?

A

Feedback from the small intestine

35
Q

What causes greater pyloric emptying?

A

Greater peristalsis and pressure, faster the emptying and greater pyloric opening

36
Q

What happens at low pH?

A

There is slower emptying and large particles decrease!

37
Q

What is the Migrating Motor Complex (MMC)?

A

It has housekeeping function to remove indigestible material during fasting induced by motilin.

38
Q

What is Phase I of the MMC?

A

Quiescence 20-60 minutes

39
Q

What is Phase II of the MMC?

A

Irregular, Peristaltic Contractions 10-30 minutes. Increase in gastric, pancreatic juices to eliminate bacteria.

40
Q

What is Phase III of the MMC?

A

Intense contractions for 5-10 minutes. Pylorus opens fully. Stimulated by some prokinetic drugs - macrolides (erythromycin). May be hunger contractions.

41
Q

What is Aspirin Bezoar?

A

300 partially digested pills

42
Q

What does the MMC often cause?

A

Can be noisy sources of growling

43
Q

How might you suppress the MMC?

A

Eating a small amount

44
Q

What is Pyloric Stenosis?

A

Congenital condition where pylorus fails to relax after a meal, leading to malnutrition and dehydration.

45
Q

How do you treat Pyloric Stenosis?

A

Surgical myotomy

46
Q

What is Gastroparesis?

A

Reduced gastric emptying

47
Q

What is the most common cause of Gastroparesis?

A

It is often due to diabetic neuropathy involving the vagus and enteric nerves in the stomach such that the stomach fails to generate enough force to empty the stomach.

48
Q

What are other causes of Gastroparesis?

A

Drugs and cancer treatments

49
Q

What does Gastroparesis result in?

A

Nausea, vomiting, bloating, poor digestion, weight loss, malnutrition, impaired absorption of medications, and impaired glycemic control.

50
Q

How do you treat Gastroparesis?

A

Prokinetic drugs

51
Q

What is dumping syndrome?

A

Rapid gastric emptying

52
Q

What is dumping syndrome often a result of?

A

Gastric bypass surgery, vagotomy and high sugar-containing meals

53
Q

What is the physiology behind dumping syndrome?

A

Rapid entry of gastric contents into the duodenum represents an osmotic challenge, water moves into the lumen resulting in hypovolemia and reduced blood pressure.

54
Q

What are the symptoms that result from the physiology of dumping syndrome?

A

Nausea, weakness, dizziness, sweating, shakiness, diarrhea, heart palpitations

55
Q

How can Peptic Ulcer Disease cause abnormal motility?

A

Scarring and ulcers near the pylorus can delay emptying or in duodenal ulcers can lead to rapid gastric emptying due to loss of duodenal negative feedback mechanisms

56
Q

What is Emesis?

A

Vomiting. Expulsion of contents of one’s stomach and intestinal contents through reverse peristalsis in the intestine.

57
Q

What often precedes Emesis?

A

Nausea - sensation that vomiting will occur, can be associated with loss of appetite

58
Q

What can forceful vomiting cause?

A

Mallory-Weiss tears in esophageal mucosa causing self-limiting haematemesis.

59
Q

What are different causes of vomiting?

A

Gastritis, Poisoning, Brain tumors, Increased intracranial pressure, Migraine, Vestibular problems, Bowel obstruction, Appendicitis

60
Q

What are emetic stimulants?

A

They include stimulation of the pharynx, sensory input from higher centers, vestibular information, irritants or blockage in the GI tract, and blood-borne emetics.

61
Q

What coordinates vomiting (emesis) mechanisms?

A

Vomiting center in brainstem medulla.

62
Q

What happens before vomiting?

A

Increased salvation to protect enamel of teeth from dental erosion, sweating and tachycardia.

63
Q

What is Retroperistalsis?

A

It is starting from the middle of the small intestine (why bile is present in vomit), sweeping up the contents of the digestive tract into the stomach, through the relaxed pyloric sphincter.

64
Q

What is Rectching?

A

It includes contraction of abdominal muscles, relaxation of esophagus but not vomiting (gaging/belching combined) –> movement of material into esophagus, not yet expelling vomitus

65
Q

What happens in order for you to vomit and not aspirate?

A
  • Epiglottis closes off larynx
  • Hyoid moves upward and forward opening upper esophageal sphincter
  • Soft palate is drawn upwards
  • Diaphragm and abdominal muscles contract, propelling stomach contents into the esophagus
66
Q

What happens when inebriated or unconscious individuals vomit?

A

Protective mechanisms may fail causing aspiration of vomitus leading to pneumonia.

67
Q

What are consequences of vomiting?

A

Dehydration, hypokalemia, and hyponatremia.

68
Q

The NTs that regulate vomiting are. . .

A

. . .poorly understood.

69
Q

What types of drugs are used to suppress vomiting?

A

Inhibitors of dopamine, histamine and serotonin

70
Q

What allows the stomach to function as a reservoir?

A

Receptive relaxation of the proximal stomach

71
Q

How does the stomach grind the meal?

A

The antral stomach uses phasic contractions driven by the basal electrical rhythm of the stomach to grind the meal.

72
Q

What does emptying the stomach involve?

A

Tonic contractions of the proximal portions and pylorus opens only partially and intermittently in response to feedback from the duodenum.

73
Q

How quickly do different substances leave the stomach (sugars vs fats)?

A

Sugars leave most quickly, and fats leave slowly permitting emulsification.

74
Q

During fasting, what phase of the MMC is stimulated by the GI hormone motilin?

A

Phase II - at this stage the MMC acts to remove undigested material

75
Q

What does vomiting require?

A

Somatic and gastrointestinal muscles, and involves retrograde propulsion of the gastric contents out of the body

GI Week 2 (9 decks)

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