1 Motility of the GI Tract Flashcards
What do parietal cells secrete
HCl and IF
What do chief cells secrete
Pepsinogen
What are the pacemaker cells of the GI
Interstitial cells of Cajal
What type of muscle cell transmission do the ICC follow
SM (Na —> Ca —> K)
What is the spike rate in the stomach
3/min
What is the spike rate in the duodenum
12/min
What stimulates spikes in electrical activity in the gut
- stretch
- ACh
- parasympathetics
What stimulates hyperpolarization of the gut
- NE
- sympathetics
What is the resting membrane potential in the gut
-56
The contractions of SM are due to what ion
Ca (but it doesn’t propagate the rxn)
What effects does Ca entry have
- responsible for rising phase of AP
- triggers contraction
What is responsible for the falling phase of SM
K
Why is the proximal stomach in tonic contraction
To keep contents away from the LES
Why does the distal stomach have phasic contractions
Mechanical digestion to aid in chemical digestion
Half of our _______ and 90 percent of our _______ come from bacteria in our gut
Dopamine; serotonin
What is the myenteric plexus responsible for
Inhibitory and excitatory nerves control the function of the circular and longitudinal mm
What does the submucosal plexus do
Secretomotor neurons promote vasodilation, regulate the secretion of fluid and electrolytes, and contractions of the muscularis mucosa
What occurs in the mouth
- mastication
- buffers neutralize acids
- antibacterial agents kill some bacteria in food
What is deglutition
Swallowing
What is in saliva
Water, electrolytes, mucin, IgA ab, lysozyme, salivary amylase
Chewing muscles are innervated by what n
Fifth cranial
What is the function of chewing
- reduce size
- mix food and saliva
- increases SA
The oral portion of swallowing is under __________ control while pharyngeal is under __________ control
Voluntary; involuntary
Sensory signals pass through what nerves to the swallowing center in the medulla (during pharyngeal phase)
Glossopharyngeal
Vagus
Trigeminal
What are the three phases of swallowing
Oral
Pharyngeal
Esophageal
What is the end of the oral phase
Tongue moving food back to oropharnyx
What is the end of the pharyngeal phase
Forcing food through the UES
Where does the esophageal phase end
With food passing through the LES
What is primary peristalsis
First contraction wave pushing food through LES
What initiates secondary peristalsis
Distention of the esophagus
What is primary peristalsis regulated by
Medulla
What regulates secondary peristalsis
Medulla and myenteric NS
If the vagus is cut, what peristalsis continues
Secondary
What helps move food down
Contractions proximal to the food and negative pressure for transient relaxation
What is the process called in which a vagovagal reflex causes the stomach to relax to receive food
Receptive relaxation
What does receptive relaxation allow
Stomach to expand w/o increasing intragastric pressure
What do the myenteric neurons release to get the sphincters to relax
NO and VIP
What is the makeup of the UES
Striated circular m
What is the makeup of the LES
SM
What causes an increase in LES tone
- ACh
- increased intraabdominal and intragastric pressure
- gastrin
- motilin
- protein-rich foods
What causes a decrease in LES tone
- NO
- VIP
- CCK
- GIP
- β receptor agonists
- secretin
- progesterone
- prostaglandin E
- fat-rich food
What are some causes of GERD
- loss of LES tone
- increase ν of transient relaxations
- loss of 2o peristalsis
- increase stomach V or P
- increased production of H+
What is achalasia
LES doesn’t open fully and food becomes stuck in esophagus
What causes achalasia
-degeneration of the neurons in myenteric plexuses (inhibitory)
What enzyme is at fault in achalasia
NO synthase and decrease in VIP
What are the symptoms of achalasia
- regurg of food
- chest pain
- difficulty swallowing
- cough
- weight loss
Gastric motility is divided into what 2 zones
Orad (Fundus, cardia, and upper portion of body)
Caudad (lower body and antrum)
What are the muscle layers of the stomach
Circular, longitudinal, oblique
What is the primary purpose of the orad region
Accommodating new food
What is the musculature of the orad region llike
Thin
What signal functions to decrease contractions and gastric distensibility
CCK
What is a major function of the caudad region
Retropulsion back into the stomach
What functions to increase contractions
Vagus nerve
Gastrin
Motilin
What decreases contractions of GI
Sympathetics
Secretin
GIP
What increases gastric emptying
- decrease in distensibility of the orad stomach
- increased force in caudad stomach
- increase in the diameter and inhibition of segmenting contractions of the duodenum
Inhibition of stomach emptying depends on
- relaxation of the orad region
- decrease in force and number of contractions in the caudad region
- contraction of the pylorus
- increase in segmenting contractions of duodenum
What are some duodenal factors that slow emptying
- secretin release (increases pyloric tone)
- lipid digestion stimulating CCK and GIP which reduces motility
- products of protein digestion
- hypertonicity of fluid in duodenum
What is the housekeeper of the stomach
MMC (migrating motor complex)
When is the MMC active
During fasting it contracts every 90 to 120 mins
What does the MMC do
Removes:
- mucus
- sloughed cells
- bacteria
What is gastroparesis
Gastric emptying being delayed despite obstruction
What are the symptoms of gastroparesis
Early satiety, nausea, vomiting, bloating, and upper abdominal discomfort
Gastroparesis can result from systemic diseases involving neuromuscular function such as
Diabetes and scleroderma
Gastroparesis can also occur with damage to
Vagus
What is the main function of the SI
Breakdown into simple molecules
What are the types of movement in the SI
Peristalsis and segementation contractions
What is the myenteric reflex
Distention causing peristalsis
What is released during distention of the GI? What is activated in response
Serotonin; IPANs
What enhances intestinal motility
- gastrin
- CCK
- 5HT
- thyroxine
- insulin
What decreases intestinal motility
Secretin and glucagon
What causes vomitting
High positive thoracic pressure
What types of muscle is the IAS? EAS?
SM; striated
What is the innervation of the LI
Vagus to splenic flexure then pelvis splanchnic
What is the sympathetic innervation of the LI
T5-L2 or the thoracolumbar outflow
What can LI movements be initiated by
- gastrocolic or duodenocolic reflexes
- intense stimulation of parasympathetics
- overdistention of colon
The parasympathetic system causes what in the rectum? IAS? EAS?
Contract; relax; relax
What does sympathetic cause in rectum? IAS? EAS?
Relax; contract; contract
When does the urge to defecate begin
18 mm Hg
When does involuntary defecation begin
55 mm Hg
What reflexes are self contained in the GI
Ileogastric
Enterogastric
Gastrocolic
Colonoileal reflex
What the long reflexes of the GI
Vomiting
Pain
Vagovagal
Defectation