LEC 17: GI tract motility Flashcards
How do horses carry out food prehension?
Rip w/ teeth
– and–
Manipulate with lips
How do cattle carry out food prehension?
Rip w/ hard palate and lower teeth
– and –
Manipulate w/ tongue
How do carnivores carry out food prehension?
Cut w/ incisors
— and –
Rip w/ canines
What are the three stages of swallowing?
Voluntary - Pharyngeal - Esophageal
What happens in the voluntary phase of swallowing?
Bolus to back of oral cavity
What happens in the pharyngeal phase of swallowing?
Oral cavity to esophagus
What happens in the Esophageal phase of swallowing?
Food to stomach
What are the three types of motility?
Propulsive - Retentive - Mixing
How does propulsion increasing affect transit time?
Decreases
What is the stimulus for peristalsis?
Distension
What is happening behind the bolus of food?
Longitudinal muscles - relax
Circular muscles - contract
What is happening around the bolus of food?
Longitudinal muscles - contract
Circular muscles - relax
Where does the sensory from the GI tract transmit to?
Dorsal vagal complex
What does the dorsal vagal complex activate?
Somatic
– and –
Vagal
What do the cranial and caudal sphincters do?
Prevent food and air to enter the esophagus
What causes orad contraction?
ACh
What causes caudad distension?
NO
What do the vagal efferents act on?
Myenteric nerves
What does myastenia gravis cause?
Ab’s block/alter/destroy Ach receptors
What is the major characteristic of the LES?
Myogenic, tonic contraction – independent of neural input increases if stretched
What can increase LES contraction?
ACh - Gastrin - NOR
What can decrease LES contraction?
NO
What are the origin of electrical activity in the GI tract?
ICC
What do the gap junction btwn the SM and ICC allow for?
Contractions can occur together
What does the basal electric rhythm of ICC allow for?
Nothing; not strong enough to start AP; only set timing
What direction do ICC waves move in?
Aboral direction
What is the rate of an ICC wave in the SI of a dog?
~20/min
What induces the PM depolarization in ICC?
Cytosolic Ca2+ oscillators
What is the GI motility modulated by?
ANS
What is the direct effect of ENS on the ICC?
Contration –> via voltage change through gap junction
How do ICC waves become contractions?
Factors that cause depolarization or hyperpolarization
What are depolarizing factors of the ICC?
Stretching – ACh/Substance P – PNS - GI hormones
How is Gi contraction supressed?
SNS (via NOR)
– and–
VIP/NO
What is the frequency of the slow waves in the stomach?
3-5m
What is the frequency of the slow waves in the SI?
10-20m
What is the frequency of the slow waves in the colon?
6-8m
What is the function of the fundus?
Storage
What is the function of the antrum?
Grinding
– and –
Sieving
What is the adaptive reflex?
Reflexive response of proximal region to food entering stomach
What does vagal stimulation cause in the stomach?
Proximal region: Suppresses contraction
Distal region: Stimulates peristalsis
What is the motility like in the antrum?
Intense slow wave activty and contraction
What is the motility like in the body?
Strong waves of peristalsis from body to pylorus
What does gastrin do?
Stimulate motility
– and –
Gastric acid secretion
What is the limiting factor of motility in the stomach?
Digestion and absorption in the SI
What slows emptying in the stomach?
Low pH in duodenum
– and –
High fat in stomach
What is secreted in response to fat and low pH?
CCK
– and –
Secretin
What does CCK do?
Inhibits antrum motility
What stimulates CCK secretion?
Fat
What does Secretin do?
Inhibits antrum motility
What stimulates secretin secretion?
low pH
What does duodenal distension cause?
Inhibition of stomach motility
What is the interdigestive motility complex?
Relaxtion of pylorus w/ strong waves of peristalsis through stomach
What is the point of the interdigestive motility complex?
Force out anything in stomach
When do interdigestive motility complexes occur?
once an hour
What two major things are involved in vomiting?
Motility of the GI tract
– and –
Pressure regulation in abdomen and thorax
Where is the vomiting center?
Reticular formation in the medulla
What are the four things that input into the vomiting center?
Higher center - Vestibular app. - Vagal afferent - CRTZ
What does the high center sense?
Trauma - Intracranial pressure
What does the vestibular apparatus sense?
Motion sickness
What does the vagal afferent fibers sense?
Peritoneum - Bile ducts - Heart
What does the CRTZ sense?
blood borne - Drugs - Toxins
What are the two phases of the digestive period?
Nonpropulsive
– and –
Propulsive
What is the MMC?
Migrating motility complex
What doe the MMC do?
Strong contractions, entire SI
Forceful emptying of SI
What are the motility patterns of the large intestines?
Segmentation – Retropulsion – Propulsion
What does the colonic pacemaker do?
Antiperistaltic motility – shift site of pacemaker
What is the rectospincteric reflex?
Feces enters rectum - Internal sphincter relaxes - Rectal walls contraction
What voluntary structure can stop the rectosphincteric reflex?
External anal sphichter
Where does the PNS control of the sphincter originate?
Sacral spinal cord
What is the stimulus/response of the orthocolic reflec?
Stimulus: Standing up
Response: Increased colonic motility/mass movemetn
What occurs with the fear-stress induced defecation?
Fear - CRH - Activates PNS - Enhance colonic motility
What is the stimulus/response to the gastrocolic reflex?
Stimulus: Full stomach
Response: Increase colonic motility –> fills rectum
What is the stimulus/response enterogastric reflex?
Stimulus: Digesta in the duodenum
Response: inhibition of gastric emptying
What is the stimulus/response of the coloileal reflex?
Stimulus: Full colon
Response: Inhibition of ileum emptying
What is the stimulus/response of the ileogastric reflex?
Stimulus: Full ileum
Response: Inhibition of gastric emptying
