59 - GI Gastric Motility

Question 1

What are the three basic mechanical movements of the stomach?

Answer 1

1 - Storing
2 - Churning
3 - Emptying

Question 2

What is gastric storing?

Answer 2

Stomach fills and stores contents

Question 3

What is gastric churning?

Answer 3

Mixing and initiating digestion

Question 4

What is gastric emptying?

Answer 4

Food delivery to the duodenum

Question 5

What are the two steps to gastric storing?

Answer 5

1 - Receptive relaxation

2 - Gastric accommodation

Question 6

Describe receptive relaxation

Answer 6

• A vagovagal reflex that is initiated by swallowing
• Includes the relaxation of the stomach in anticipation of food
• The LES and proximal stomach relax
• The goal of receptive relaxation is to have a rise in gastric volume without a rise in gastric pressure
• There is NO cholinergic or adrenergic hormone signaling here

Question 7

Describe gastric accommodation

Answer 7

• Stomach relaxes in response to gastric filling - DISTENSION is the key stimulus
• Distention is sensed by mechanoreceptors
• The result is NO release which relaxes smooth muscle
• This causes the fundus of the stomach to dilate
• This is primarily regulated by the ENS, but modulated by the vagus nerve
• Again the goal here is to have a rise in gastric volume without a rise in pressure

Question 8

What are the three types of gastric churning that occurs?

Answer 8

1 - Propulsion
2 - Retropulsion
3 - Grinding

Question 9

Describe propulsion

Answer 9

• Movement of contents toward the antrum/pylorus region
• Initiated by pacemaker cells near the greater curvature of the stomach
• Note that the pylorus is still closed at this point

Question 10

Describe retropulsion

Answer 10

• Pulverization and shearing of food particles

Question 11

Describe grinding

Answer 11

• Food is trapped in antrum
• Products that are smaller than 2 mm pass through the pylorus
• Particles that are larger than 2 mm will eventually pass into duodenum during the interdigestive period (2 hours later)

Question 12

Describe factors that control the rate of gastric emptying

Answer 12

Rate of emptying

• Rate of gastric emptying depends upon the content of the ingested material
• Protein and lipids slow things down

Question 13

How is gastric emptying controlled?

Answer 13

Neuronal and hormonal regulation

Question 14

What three hormones control gastric emptying?

Answer 14

• Secretin
• CCK
• Gastrin

Question 15

What four neurotransmitters control gastric emptying?

Answer 15

• ACh
• NO
• 5-HT
• VIP

Question 16

What is the function of CCK?

Answer 16

CCK: promote digestion of food in the duodenum while limiting throwing more food (from the stomach) into the mix

CCK responds to fat – gallbladder is going to contract because it contains bile – which emulsifies fats

Cholicystokinin
As fat enters the duodenum, it stimulates the release of CCK
This feeds back and delays gastric emptying
The more fat you eat in a meal, the more CCK that is release, the more the meal will remain in the stomach to allow for adequate breakdown
This allows them to have a high surface area to be broken down more

Question 17

What is the function of secretin?

Answer 17

Released in response to high HCl in stomach

Protective in function

Question 18

Role of CCK and gastrin

Answer 18

CCK and gastrin are similar in that they impair gastric emptying to break down fat or protein, respectively, to the smallest possible form – this means more efficient digestion as smaller particles diffuse faster

Question 19

Role of NO and VIP

Answer 19

NO and VIP are the “gate-keepers” of the pyloric sphincter

Question 20

What is emesis?

Answer 20

Vomiting

- Expulsion of gastric and duodenal contents from the GI tract via the mouth

Question 21

What is emesis preceded by?

Answer 21

• Nausea
• Tachycardia
• Dizziness
• Sweating
• Mydriasis
• Retching
• Increased saliva production

Question 22

Describe the series of events of vomiting

Answer 22

• Irritation of GI mucosa
• Afferent fibers are activated
• The vomiting center of the brain is activated
• This triggers a wave of reverse peristalsis and the relaxation of the pyloric sphincter and stomach
• Forced inspiration, contraction of abdominal muscles and contraction of respiratory muscles occurs
• LES relaxes, pylorus and antrum contract
• UES relaxes
• Contents of the stomach are expelled
• Secondary peristalsis returns esophageal material back to the stomach because it senses distention of the esophagus and high acid content

Question 23

What are the key neurotransmitters that are involved in the emetic response?

Answer 23

Histamine, Ach, Serotonin (listed as 5-HT3), D2 (dopamine) are all important in emetic response.

Question 24

How do you treat motion sickness?

Answer 24

Interrupting Ach is very good at preventing motion sickness – like promethazine

Question 25

How is the physiology of the stomach altered in GERD?

Answer 25

Problems with any of the following mediators can cause an impairment leading to GERD - Histamine - Acetylcholine - Serotonin - Dopamine

Question 26

Describe gastroparesis

Answer 26

- Gastroparesis means delayed gastric emptying – frequently associated with problems of pyloric sphincter or region. - It’s commonly seen in uncontrolled diabetes mellitus (due to neuropathy) – patients with this most likely have more stomach acidity problems because if motility in the pylorus region stops it from going out the bottom end, it’s more likely to come back out the mouth as the patient eats more (food builds up). - Gastroparesis is also frequently seen in infantile pyloric stenosis

Question 27

What neurotransmitters are involved in gastroparesis?

Answer 27

- NO or VIP | - Vagal stimuli (dopamine, serotonin, histamine)

Question 28

Case study #3

Answer 28

Go read case #3

Question 29

How may diabetes contribute to the development of gastroparesis?

Answer 29

Diabetic neuropathy means loss of coordination in emptying as well as coordination in relaxation, churning, emptying. It doesn’t mean the stomach isn’t working – greater variability of what’s happening due to lack of coordination.

Question 30

Is his poor glycemic control a cause or consequence of gastroparesis?

Answer 30

Which came first, the chicken or the egg? Gastroparesis can cause diarrhea – less efficient absorption can impact retention of nutrients, ultimately impacting glycemic control. More likely though, the diabetic neuropathy caused gastroparesis – further supporting poor glycemic control. Seems kind of like a vicious cycle

Question 31

How can delayed gastric emptying cause diarrhea?

Answer 31

Think about this in the context of diabetes first. Maybe the lack of coordination means fast movement past through the duodenum (and subsequently bad absorption) but blockage at the level of pylorus. It could also mean many other things such as, releasing of the pylorus even when no food is anticipated or present – resulting in increased acid released into the duodenum and subsequent mucosal damage.