Topic 6.2 Flashcards
What are the 5 main functions of GI motility?
- Grinding
- Mixing
- Storage
- Propulsion
- Reflux inhibition
What is the role of grinding? (3)
Mechanical preparation,
increase surface,
eased propulsion
What is the role of mixing? (2)
Renewal of surface
Only nutrients near the wall are absorbed so mix
Why do we need storage in GI?
colon stomach : store for optimized digestion, absorption
Where do we have reflux inhibition in the GI tract?
In the proximal colon, which shows anti peristalsis
Which cells generate the slow waves of GI?
the interstitial cells / cajal cells in the GI wall
What is the average slow wave rythm?
3-10 cycles per minute : slow / basal rythm
What are the 6 main functions of the oral cavity and oropharynx?
- mastication
- swallowing
- immunological sampling of food for pathogens (Waldeyer lymph ring)
- Lubrication + tasting of food
- Vocalization
- Protection of teeth
What is xerostomia?
Dry mouth (can be due to drugs)
What are the 3 main parts of the esophagus?
- UES
- Body
- LES / cardia
What is the average travel speed down the esophagus?
5cm/s (depends on viscosity)
What are the 3 steps of swallowing?
- drop in neural tone of UES
- Inhibition of contraction in SM due to NO (relaxation of LES)
- Rebound contraction to push food downwards
What is akalesia?
condition where SM is not relaxing
How much food can the stomach store?
up to 1.5L
Volume of empty stomach
50mL
What is the size of the pylorus opening?
1mm
8 roles of the stomach
- Storage of ingested food
- Grinding and mixing with the secretion
- slow and controlled emptying of chyme in duodenum
- digestion of lipids and proteins
- limited absorption of lipids
- regulation of food intake by ghrelin
- VB12 uptake
- Chemical barrier for pathogens
What are the 3 functional parts of the stomach?
- proximal part
- pacemaker zone
- distal part
What is the pacemaker zone of the stomach?
the origin of the contractions which then go down
What are the roles of the proximal part of the stomach? (2)
- Storage function
- receptive and adaptative relaxation (steady mb pot)
What are the roles of the distal part of the stomach? (2)
- Grinding / mixing
- Propulsion
What is retropulsion?
Only done by stomach, pushes contents towards closed pylorus so that it flows backwards and causes grinding
Which factors regulate stomach emptying and how?
- gastric factors : promote emptying
2. duodenal factors : inhibit / limit emptying
What is the enterogastric reflex?
stretch receptors in the duodenum sense presence of chyme, and send a signal to the CNS, which will decrease peristalsis using vagus n.
What are the 2 gastric factors for regulation of gastric emptying?
- food volume
- release of gastrin from antral mucosa
What are the 4 duodenal factors for regulation of gastric emptying?
- Acid : release of secretin
- Nutrients, fat sensed by chemoreceptors : release of CCK, GIP
- Hypertonicity
- Enterogastric reflex
6 main functions of the small intestines
- Mixing, propulsion
- Digestion and absorption of nutrients
- Regulation of iron levels
- Reabsorption of molecules like bile acids
- Immune functions
- Symbiosis with bacteria
What is segmentation?
renewal of the parts close to the enterocytes for better absorption
What regulates segmentation?
enteric nervous system
How fast are peristaltic waves?
1cm/sec but really 1cm/min since there’s a bunch of other processes
What regulates peristalsis?
Gastroenteric reflexes (myenteric plexus) + hormones
Which hormones promote peristalsis? (4)
Gastrin, CCK, Insulin, serotonin
Which hormones inhibit peristalsis? (2)
Secretin, glucagon
What is the law of intestine?
If there is a bolus in the small intestine, there will be contraction in the oral direction and relaxation in the caudal direction
Which molecules cause contraction in the oral direction? (2)
Acetylcholine, substance P
Which molecules cause relaxation in the caudal direction? (4)
NO, ATP, VIP, PACAP
Which drugs can have an impact on serotonin reuptake?
SSRIs : selective serotonin reuptake inhibitor -often for mood disorders)
5 main functions of large intestines
- Propulsion of contents
- Regulation of H20 and electrolyte balance
- Storage of fecal matter
- Immune functions
- Symbiosis with bacteria
Speed of propulsion in large intestines
5-10cm/hour
Which kind of movement can we find in the proximal colon?
retropulsive / antiperistalsis
Which type of movements can we find in the distal colon?
propulsive movements (mass movements)
Which part of the colon does the mixing / segmentation movements?
teniae coli (circular + longitudinal)
What regulates the iliocecal valve and sphincter?
Mechano receptors, chemoreceptors, hormones
What opens the iliocecal valve? (3)
- distention / irritation of the ileum
- gastrin
- gastroileal reflex
What closes the iliocecal valve?
Distention / irritation of the colon
What is the defecation reflex?
stretch of the rectum is reported to S2-S4 spinal chord, leading to relaxation of the internal anal sphincter (SM) thanks to parasympathetic nerve fibers
How can the defecation reflex be controlled?
External anal sphincter : SK muscle, can increase tone
What is the migrating myoelectric complex?
Motility pattern of stomach and small intestines in bw meals, during which the pylorus is completely open
What regulates MMC?
Motilin, which is produced in the duodenum
How often does MMC happen?
Roughly every 90 minutes
What type of afferents does the vomiting center have?
sympathetic afferents
Which process loads the esophagus with content?
The Müller maneuver
