GI phys Lecture 1

Question 1

Where is the myenteric plexus located?

Where is the submucosal plexus located?

Answer 1

Myenteric plexus: lies between longitudinal muscle layer and circular muscle layer: more to do with contractions

Submucosal plexus: lies between circular muscle layer and muscularis mucosa: more to do with secretions

These layers are connected

Question 2

Enteric Neurons and Neurotransmitters pathways

Answer 2

1.) Sensory Neuron, then interneuron, then secretomotor neuron, then neurotransmitters to target cells

Question 3

Gastrin

source, stimulus, actions

Answer 3

Source: G cells stomach
Stimulus: small peptides, AAs, gastric distention
Actions: Stimulates secretion of HCl, maintains integrity of gastric mucosa

Question 4

Cholecystokinin (CCK)

source, stimulus, and function

Answer 4

source: I cells, small intestine
Stimulus: associated with peptides, amino acids, fatty acids (biproducts of digestion)
actions: stimulates gallbladder contractions, pancreatic secretions

Question 5

Secretin

Source, stimulus, function

Answer 5

Source: S cells small intestine
Stimulus: pH <4.5 in duodenum
Action: stimulates secretion of bicarbonate HCO3- by liver and pancreas (bicarbonate is a buffer) to try and neutralize low pH

Question 6

Glucose-dependent insulinotropic peptide: (GIP)

Source, stimulus, function

Answer 6

Source: K cells, upper intestine
Stimulus: FAs, AAs, glucose (biproducts of digestion)
Actions: Will stimulate an early release of insulin, inhibits gastric emptying / inhibits secretion of HCl

Question 7

Motilin

Source, stimulus, function

Answer 7

It is the only fasting state hormone of the 5. (the other 4 are fed-state hormones).

Source: M cells, upper intestine
Stimulus: fasting
Actions: stimulates interdigestive migrating motor complexes (IMMC)

Question 8

Esophageal dysfunction:
Dysphagia
Achalasia
GERD (gastro esophageal reflex disease)

Answer 8

Dysphagia: Difficulty in swallowing
Achalasia: LES (Lower esophageal sphincter) will not relax
GERD: acid enters lower esophagus, heartburn

Question 9

Factors affecting gastric emptying:

Answer 9

Gastric volume
osmolarity of gastric contents
acid conditions in DUODENUM * (Secretin stimulated by low pH. Secretin will delay gastric emptying)
Caloric content of meal More calories = longer time to empty*
food particle size

This occuring in antral pump

Question 10

Visceral smooth muscle contractions, 2 dif types,

Answer 10

Phasic pattern: depend on frequency of slow waves

Tonic pattern: sphincters. Always contracting until signal to relax occurs

Question 11

Parasympathetic / Sympathetic relation towards GI

Answer 11

Parasympathetic: Sacral spinal cord, Vagal nerve. Preganglionic. Promotes normal GI function.

Sympathetic: Thoracolumbar region. Typically opposes normal GI function, but you need balance of both para / symp.

Brain can affect gut through autonomic. But important part is enteric nervous system, thats whats really running the show.

Question 12

Oropharyngeal phase

Answer 12

elevation of tongue, closure of nasopharynx, relaxation of UES, closure and protection of airway, pharyngeal peristalsis.

Primary peristalsis: wave form that essentially initiates the bolus being pushed down itself. Initiated by swallowing center.

Question 13

Esophageal phase

Answer 13

UES relaxes so food from pharynx can enter.
Primary peristalsis = wave-like contraction. Moves bolus downward.
LES relaxes allows bolus to enter fundus.

Secondary peristalsis: myenteric plexus signals this in response to enlarged esophagus from lodged bolus and by gastric acid entering lower esophagus.

Question 14

Functional regions of the stomach

LES / Cardia:
Proximal stomach:
Distal Stomach:

Answer 14

LES / Cardia: Prevention of reflux, entry of food site

Proximal stomach (Fundus and body): tonic contractions, receptive relaxation (vago- vagal reflex), temp storage of food. NO PACEMAKER CELLS IN PROX. STOMACH

Distal stomach (body and antrum): Phasic contractions (slow waves), mixing grinding, gastric emptying. ICC’s and pacemaker cells here, not in proximal stomach.

Question 15

Fasting motility in the small intestine

Answer 15

3 primary phases
phase 3 and motilin
contractions are synchronized with slow waves (phasic)

Most intense contractions linked with phase 3, preceded by a secretion of motilin.

Contractions on every slow wave. Fed state contractions not as strong.

Question 16

Migrating Motor complexes of Fasting

Why do we have these MMCs?

Answer 16

Housekeeping (there may be residual material left behind)

for example if u eat a large food particle, it wont digest until phase 3.

This prevents overgrowth of enteric bacteria.

Question 17

Interstitial Cells of Cajal

Answer 17

Cells in the gut that are part of the enteric nervous system

These are pacemakers

generate hypopolarization phases (like SA node of heart)

Responsible for the phasic contractions and contractions are going to be synchronized with the slow waves.

Question 18

Spike relationships

Answer 18

More spikes = more intensity of contractions.
Increase of magnitude of slow waves = increase in number of spikes

no action potentials = no contractions.

Contractions occur on hypopolarization part of slow wave, not hyperpolarization.

Question 19

What do these pacemaker cells have to do with gastrointestinal physiology?

Answer 19

2 kinds of contractional pattern: phasic / tonic.

Can we have slow waves without spikes? yes in both fasting / fed

These pacemaker cells are for the phasic contractions.