GI motility

Motility in mouth/pharynx

deglutition → voluntary → involuntary

motility in esophagus

primary and secondary peristalsis

Motility in stomach

Receptive relaxation and antral mixing

What is receptive relaxation known as?

Tonic proximal

What is antral mixing known as

phasic peristalsis

What is motility in small intestine

segmentation and slow peristalsis

Motility in colon

Haustral mixing and mass movements

Rectum/anus motility

sphincter tone and defecation reflex

What failures of motility cause symptoms?

Pressure, sphincter opening/closing, neural coordination

Steps of deglutition

Trigger, protection, transfer, reset

What occurs during trigger of deglutition

tongue pushes against hard palate, moving food bolus into pharynx

What kind of movement is trigger of deglutition

Voluntary

What happens during protection step of deglutition

soft palate elevates to prevent food from entering the nasal passages

What kind of action is deglutition: protection

involuntary

What happens during deglutition: transfer

Epiglottis covers the glottis protecting the trachea, and the upper esophageal sphincter relaxes | Shutting the vocal cords

What is the process of epiglottis covering the glottis known as?

apnea

What kind of movement is deglutition: transder

involuntary

What happens during deglutition: reset

food descends into the esophagus, and upper esophageal sphincter regains tone

What kind of movement is food descending into the esophagus

Involuntary

What is the UES at rest?

Tonically closed

What happens to UES during swallowing

relaxation and then striated muscle contraction

What regulates the UES

cholinergic → nAChR

How does swallowing occur in the UES?

ACh added to open pharnyx, and removed to open UES

How does the esophagus look without stimulation

quiescent

What happens during swallowing in the esophageal body

Contraction behind, relaxation ahead

What happens to the muscle behind the bolus in the esophagus

ACh M3-AChR causes contraction

What is given to esophageal body in front of bolus

NO/VIP

LES at rest?

Tonically closed

Where does the esophagus pass through diaphragm

At the level of the LES

Why can a hernia increased acid reflux?

The lack of support from the diaphragm tonically will result in less tone, allowing reflux

What is in the LES to allow for swallowing

NO/VIP relaxes it

How is the LES regulated

ACh (M3R) ensures closure, while NE (a1) maintains basal closure

What is achalasia

impaired LES relaxation + loss of distal peristalsis

What does achalasia cause symptom-wise?

Dysphagia and megaesophagus

What does a skeletal muscle on a graph look like

Sharp peak

What does smooth muscle on a graph look like

smooth peak

When does the LES open?

During peak force at mouth

What is a vagotomy?

Cutting of vagal nerve, abolishing primary peristalsis

What activates secondary peristalsis of esophagus?

Food gets stuck, resulting in distension + increased pH

What regulates secondary peristalsis?

Enteric nervous system

What does an inability to ingest solids indicate?

Obstruction

Examples of esophageal obstruction

esophageal stricuture/cancer, external compression

what does an inability to swallow solids and liquids

Motility disorder/neuromuscular issue

Examples of motility diorder/neuromuscular issues?

Achalasia, esophageal spasm, ineffective esophageal motility

What does a trouble with initiation of swallowing/aspiration indicate?

Oropharyngeal/neuromuscular issue

Examples of oropharyngeal/neuromuscular issue

stroke and multiple sclerosis

How does stomach look during fasted state?

Quiescent except for MMC

What happens in the stomach once food enters

receptive relaxation and accommodation

What does receptive relaxation and accommodation result in

Minimal rise in intragastric pressure

What does receptive relaxation mean

vasovagal swallowing, resulting in the release of ENS inhibitory neurons

What happens during stomach accommodation?

Distension, which inhibits ENS independent of vagal input

What promotes relaxation during food entrance into stomach

CCK

What begins peristalsis stomach

antral peristaltic waves begin mixing gastric contents and moving chyme towards the pylorus

What sets the contraction timing for stomach peristalsis

ICC sets a rate of 3/min

What can increase antral peristalsis?

ACh and Gastrin

What is antral systole

antral peristalsis drives emptying via a pump

What does narrowing cause antral systole

Solids stay back via retropulsion

How does ENS promote pyloric relaxation?

employs NO/VIP to relax and allow emptying

What does enterogastric reflex control

how fast food goes from stomach to duodonum

What circumstances induce enterogastric reflex

Increased acidity (dec pH), increased fat, increased amino acids, hypertonicity (salt), distension

what is the short enterogastric reflex

Reduce ACh to antrum, and reduce NO/VIP to pylorus

What are long enterogastric reflex

Less vagal, more sympathetic

How are long reflexes achieved for enterogastric

Activation of a2 to antrum, and a1 to pylorus

What are enterogastrones

CCK and GLIP-1

What stimulates CCK entergastric

FFAs and AAs

What stimulates GLP-1 enterogastric

CHO, FFA, AA

Is GLP or CCK high response?

CCK

What are secondary enterogastrones (not official term)

Secretin and GIP decrease gastrin and acid secretion

What is gastroparesis

delayed gastric emptying without obstruction

What typically causes gastroparesis

Diabetic autonomic vagal neuropathy

What increases motility with serotonin

agonist

What increases motility with dopamine

antagonist

What is dumping syndrome

High amount of gastric emptying

What causes dumping syndrome

gastric surgery

What is the mechanism of dumping syndrome

Hyperosmotic chyme draws fluid into bowel, causing hypovolemia

What kinds of food empty slower

Solids, high calorie, fat, hypertonic, high fiber

What foods are more filling (fullness and satiety)

Fat and protein

What is starling’s law of the gut

distension causes contraction proximal to ACh and substance P, and relaxation distal to the bolus

Why is peristalsis reflex preserved after extrensic innervation

ENS

What is the intestino-intestinal reflex

severe distension inhibits bowel activity

What mediates the intestino-intestinal reflex

extrinsic nerves

What is gastroileal reflex

meal ingestion increases ileal peristalsis

What is a stimulatory chemical modulator?

Motilin, serotonin, prostaglandins, gastrin, CCK, insulin

What are inhibitory chemical modulators

epinephrine, secretin, glucagon

What do slow waves set

contraction frequency

What is higher in the duodenum compared to the illieum

Segmentation rate

Phase 1 of MMC

No spike potentials or contractions

Phase II of MMC

Small, irregular spike potentials and weak contractions that don’t go the whole length of the SI

What stimulates phase II

Ghrelin induces phase II via the Vagus nerve

What can impair phase II?

Vagotomy

What happens in Phase II of MMC

Large spike potentials and strong contractions that propagte the intestinal length, serving as the housekeeper of the gut

What is the primary regulator of phase II

Motilin

What helps the transition to phase three

Ghrelin

Major vomiting input: Pharyngeal stimulation

Glossopharyngeal afferents

Major vomiting input: GI

Vagal afferents

Major vomiting input: Blood-Borne emetogens

area postrema

Major vomiting input: Motion sickness

Vestibular pathways

Major vomiting input: Pain/fear

higher centers

Medullary integration of vomiting

Inputs converge on the brainstem emetic network

What area detects emetic stimuli?

Area postrema