GI Part II Flashcards
Dr. Chad Touchberry (UMKC)
What is the purpose of the phasic portion of GI contractions?
Basically the circular muscles contract in the stomach, SI, and LI to aid in mixing the food, this is called segmented contraction
What are tonic contractions driven by, and what is there job?
Mainly by sphincters, to seperate sections of the GI tract by contracting and releasing. Tonic contraction is typically always contracted and job is seperation
What is the job of the peristaltic contractions (phasic), and where are they mostly located?
Contraction of the smooth muscle propels further and further along to propel food forward. Occurs in the esophagus, stomach, SI and LI
What principally drives SMC contraction throughout the GI system?
Driven by the basal electral rhythm (BER) generated by the SMC under control of the interstitial cells of cahal (ICC) that are the pacemakers of the GI system
What are the main phases of Chewing (mastication) & swallowing (deglutition)…?
Phase 1 Oral - Chew: (voluntary) Chewing (mastication) that breaks down the cells and increase the surface area as well as lubricate food, goal is to form a bolus. Stretch reflexes help to form rebound contractions to aid in chewing.
Phase 1 Oral - Propulsion: (voluntary) oral propulsion phase. You can’t swallow if mouth is dry. Superior constrictor muscles cause an upward movement of the soft palate to block food into the nasopharynx
Phase 2 Pharyngeal - (involuntary) food goes down esophagus and 1. Epiglottis covers the glottis shutting off respiration/protecting the airway and 2. Vocal cords are adducted to protect the airway and 3. Upper esophageal sphincter opens and allows food to enter the digestive system
Phase 3 Esophageal - (involuntary) peristalsis helps push food down to lower esophageal sphincter. Upper third of esophagus is skeletal muscle, but they are involuntary still
How is swallowing controlled?
- Vagal afferents provide sensory info about food applying pressure to walls of esophagus (Swallowing center).
- Efferent outflow to upper esophageal sphincter tells it to contract or relax by releasing or stopping Ach release
- Bottom 2/3 is smooth muscle (efferent ANS) and enteric neurons of GI cause peristalsis
- LES is under tonic contraction (from NE) and myogenic tone (diaphragm) can be relaxed through Ach. Purpose is prevent reflex (newborns don’t have a tonic sphincter until about age 2 or so)
What are the two different forms of peristalsis of the esophagus?
Primary peristalsis is controlled by the dorsal vagal complex that innervates the upper esophageal sphincter and lower esophageal sphincter through long reflexes. Vagal afferent send sensory info to DVC and vagal efferents 1. release Ach (contraction of esophagus) and 2. vagal efferent release NO/BIP to dilate downstream and relax
Secondary peristalsis the LES opens/UES closes and the enteric nervous system (short reflex) is activated by distension where interneurons (sensory ENS) are activated that cause contraction upstream of distension and relax downstream. This is not vagally innervated so a vagotomy would not inhibit this
What is a vagotomy?
The vagus nerve is cut prior to all branches that go to the GI system, this would prevent primary peristalsis
What is GERD?
GERD the LES is too relaxed and can lead to asthma. A chronic sinus infection opens and closes the UES and cause a reflex back into the esophagus.
Main thing we are worried about is Barrett’s esophagus, where the tissue is severly irritated from acid exposure leading to dysplasic (precancerous) tissue. If it is caught soon enough it can be prevented.
Treatment: Antacids/proton inhibitors and diet modifications
What is achalasia?
LES is too constricted and have very bad breath and belching, coordination of opening the UES is inhibited leading to dysphagia. People eat less or liquid diets.
Threat is megaesophagus (complete rupture)
Treatment: 1. Antispasmotic drugs (pneumatic dilator) and a stiff balloon to expand or 2. Surgical myotomy where they cut some of the LES to help
Increasing spike potential frequency
GI function would be better in a spinal cord injury patient who would lose ANS innervation and pelvic and vagus innervation. If ENS is preserved, you would have better gut function.
What is the migrating motor complex (MMC)?
Only in phase 3, M cells release motiliin that induce the phase 3 MMC. Contractions last about 5 minutes that propagate the whole GI system every 90 minutes or so.
Once we eat a meal, vagus nerve output increase contractions and inhibit motilin induced contractions
What is ghrelin?
Hunger hormone released by the stomach when it is empty, it goes to the brain and acts on the hypothalamus that increases vagus nerve activity to increase MMC.
How does stomach distension allow stretching and the ability to hold more food?
How much intragastric pressure (cmH20) is needed before someone feels full/discomfort? What is the window or pressure?
How does the stomach propel food forward through the SI?
What is the enterogastric reflex?
The duodenum of the SI is regulated by factors to slow gastric emptying through short and long reflexes as well as release of enterogastric hormones (CCK, secretin)
When you don’t have this reflex you end up with dumping syndrome causing hypertonic hypovolemia and delayed emptying
What are the rules of gastric emptying, what foods increase satiety the most?
What increases gastric emptying?
What decreases gastric emptying?
What is the function of the SI?
What is starlings law of the small intestine?
Instestino-Intestinal reflex inhibits the contraction of the small intestine that relieves thier pain before seeking medical attention
What is the BER along the SI?
How does food stuff move from the SI to LI?