6.2. Motor functions of the gastrointestinal tract and their control Flashcards
I. Slow waves
1. What are the features of SMCs in the GI tract?
The SMCs in the GI-tract are single-unit SM that are electrically coupled together via gap junctions, that allow a spread of APs for coordination
I. Slow waves
2. What are the features of slow waves?
- The SMC of the GI-tract experience a characteristic fluctuation of depolarization and repolarization, known as slow waves
- Slow waves are not APs, but described as membrane potential that cyclically gets less negative and then more negative
- They can be considered the pacemaker cells of the GI smooth muscle and they drive the frequency in different areas of the GI
I. Slow waves
3. Origin of slow waves
- Slow waves originate from interstitial cells of Cajal in the myenteric plexus which have spontaneous, cyclic depolarizations/repolarizations that spread to adjacent cells
I. Slow waves
4. What are the 2 thresholds in SMC slow wave potential?
a) Threshold for contraction (w/o having an AP spike)
b) Electrical threshold (AP is generated)
I. Slow waves
5A. How are different types of contractions made?
Depending on the degree of depolarization, different types of contractions are made
I. Slow waves
5B. Depending on the degree of depolarization, What are the 2 types of contractions?
1) Depolarization does not peak beyond electrical threshold
=> tonic contraction (basal activity)
2) Depolarization reaches above electrical threshold
=> phasic contractions (↑AP
frequency => ↑ contraction force)
I. Slow waves
6. What are the 4 steps in development of SMC AP?
II. MECHANICAL FUNCTIONS OF GI MOTILITY
1A. What are the 5 mechanical functions of GI motility?
- Grinding
- Mixing
- Storage
- Propulsion
- Reflex inhibition
II. MECHANICAL FUNCTIONS OF GI MOTILITY
1B. One of mechanical functions is
“Grinding”
=> Explain this function
mechanical preparation, ↑surface area helps digestion (↑ contact with enzymes) and movement of food
II. MECHANICAL FUNCTIONS OF GI MOTILITY
1C. One of mechanical functions is
“Mixing”
=> Explain this function
Mixing: aids in digestion + ‘’renewal’’ of surface, since chyme/food near the walls of intestine is absorbed
=> new material can get close to wall and get absorbed
II. MECHANICAL FUNCTIONS OF GI MOTILITY
1D. One of mechanical functions is
“Storage”
=> Explain this function
- Storage: optimized digestion + absorption
II. MECHANICAL FUNCTIONS OF GI MOTILITY
1E. One of mechanical functions is
“Propulsion”
=> Explain this function
- Propulsion: in predefined portions as appropriate
II. MECHANICAL FUNCTIONS OF GI MOTILITY
1F. One of mechanical functions is
“Reflex inhibition”
=> Explain this function
Reflex inhibition: inhibits the food/chyme to move in the orad direction (except proximal colon)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
2. What are the components of GI-upper tract?
the oral cavity and oropharynx
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
3A. What are the 7 main functions of the oral cavity and oropharynx?
1) Immunological sampling of food for pathogens (Waldeyer’s lymphatic ring)
2) Lubricationoffood
3) Tasting of food (taste buds)
4) Teeth protection
5) Vocalization = not able to speak w/o saliva => dry mouth (xerostomia = loss of speech)
6) Mastication
7) Swallowing (3 phases)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
3B. One of the main functions of the oral cavity and oropharynx is
“Vocalization”
=> Explain
Vocalization = not able to speak w/o saliva
=> dry mouth (xerostomia = loss of speech)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
3C. One of the main functions of the oral cavity and oropharynx is
“Mastication”
=> Explain
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
3D1. One of the main functions of the oral cavity and oropharynx is
“Swallowing”
=> What are the 3 phases of swallowing?
- Oral phase (voluntary)
- Pharyngeal phase (involuntary)
- Esophageal phase (involuntary)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
3D2. One of the main functions of the oral cavity and oropharynx is
“Swallowing”
=> What happen in phase 1 - Oral phase (voluntary)?
When tongue forces bolus back toward the pharynx, which has many somatosensory receptors that initiate involuntary swallowing
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
3D3. One of the main functions of the oral cavity and oropharynx is
“Swallowing”
=> What happen in phase 2 - Pharyngeal phase (involuntary)?
- Soft palate pulled up so that food cannot go into the nasal cavity.
- UES relaxes, allowing food to move to esophagus and a peristaltic wave of contraction propels food through the open sphincter
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
3D4. One of the main functions of the oral cavity and oropharynx is
“Swallowing”
=> What happen in phase 3 - Esophageal phase (involuntary)?
- Food is propelled through esophagus by a primary peristaltic wave.
- If that wave is not enough, a secondary wave is initiated due to the distension of the esophagus
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
4. Describe the structure of esophagus?
Composed of UES (upper esophageal sphincter), corpus
(body), LES (lesser esophageal sphincter)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
5. What is the mechanism of operation of esophagus?
Composed of UES (upper esophageal sphincter), corpus
(body), LES (lesser esophageal sphincter)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of the upper GI-tract
6. What happens if vagal N (PARA-autonomous N) is cut?
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility
7. What are the main functions of the stomach
STORAGE + GRINDINIG/MIXING
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility
8. What is the main function of proximal stomach?
storage function
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility
9. What is the mechanism of proximal stomach?
- Membrane potential around this region is stable, therefore, no phasic contraction occurs
- Receptive relaxation occurs before receiving the food, and adaptive relaxation occurs when it is being filled with food => relaxation due to NO
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility
10. What are the main functions of distal stomach?
grinding, mixing and propulsive functions
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility
11A. What is the mechanism of distal stomach?
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility
11B. What is the role of Interstitial cells of Cajal in distal stomach?
Interstitial cells of Cajal (pacemaker cells) initiate slow waves
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility
11C. What cause the peristaltic constrictor waves in distal stomach?
- Slow waves eventually become stronger, causing peristaltic constrictor waves (mixing waves)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility
11D. How can constrictor rings mix the distal stomach?
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility - Regulation of stomach emptying
12A. What are 2 types of regulation of stomach emptying?
- Gastric factors that promote emptying (open pylorus)
- Duodenal factors that inhibit gastric emptying
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility - Regulation of stomach emptying
12B. How do gastric factors promote emptying?
Gastric factors that promote emptying (open pylorus):
- Increased food volume stretches stomach wall => stretch activates myenteric reflexes
- Gastrin released from G-cells of antral mucosa => stimulates motor functions in the body of the stomach
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility - Regulation of stomach emptying
12C1. What are the 2 main effects of Duodenal factors?
Duodenal factors that inhibit gastric emptying
1. Effects of enterogastric nervous reflexes
2. Hormonal feedback
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility - Regulation of stomach emptying
12C2. How can Duodenal factors lead to Effects of enterogastric nervous reflexes?
- When food enters the duodenum, nervous reflexes are initiated
- These reflexes pass back to stomach to slow down (stop gastric emptying if there is too much chyme in the duodenum)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility - Regulation of stomach emptying
12C3. How can Duodenal factors lead to Hormonal feedback?
- Fat stimulates inhibitory hormone release
- CCK blocks increased stomach motility
- Secretin and GIP decreases GI motility
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Gastric motility - Regulation of stomach emptying
12D. Make the schematic diagram of Regulation of stomach emptying
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines
13. What are the main functions of small intestine?
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - MOVEMENTS IN THE SMALL INTESTINE
14A. What are the 2 main movements in the small intestine?
- Segmentation
- Peristalsis
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - MOVEMENTS IN THE SMALL INTESTINE
14B. The first movement of small intestine is SEGMENTATION
=> Describe
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - MOVEMENTS IN THE SMALL INTESTINE
14C1. The second movement of small intestine is PERISTALSIS
=> Describe
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - MOVEMENTS IN THE SMALL INTESTINE
14C2. The second movement of small intestine is PERISTALSIS
=> What is Propulsive movement?
Propulsive movements (peristaltic waves 1cm/sec) which propel chyme through the intestine
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - MOVEMENTS IN THE SMALL INTESTINE
14C3. The second movement of small intestine is PERISTALSIS
=> How does Peristaltic contractions begin?
- Peristaltic contractions begin by contraction behind the bolus, while muscle in front relaxes
=> this propels the chyme forward
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - MOVEMENTS IN THE SMALL INTESTINE
14C4. The second movement of small intestine is PERISTALSIS
=> How is Peristalsis regulated?
Regulated by gastroenteric reflexes (myenteric plexus) and hormones:
- ↑ gastrin, CCK, insulin, serotonin
- ↓ secretin, glucagon
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - Law of intestine
15. State the law of intestine?
Peristalsis occurs when the enterochromaffin cells in the mucosa detect the bolus and release serotonin (5-hydroxytryptamine) which activates the peristaltic reflex.
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - Law of intestine
16. What happen in orad side?
Orad side: contraction
- Excitatory transmitters are released (ACh, substance P)
- Circular muscles contract, while longitudinal muscles relaxes
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of small intestines - Law of intestine
17. What happen in Caudad side?
Caudad side: receptive relaxation
- Inhibitory transmitters are released (NO, ATP, VIP)
- Circular muscles relax, while longitudinal muscles contract
=> Drugs for mood disorder usually effect serotonin, so one of the side effects can be constipation
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of large intestines
18. What are the main functions of large intestine?
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of large intestines
19. What are the functions of the ileocecal valve and sphincter?
- Valve is protruded into the lumen of the cecum, preventing backflow of content
- Gastroileal reflex and gastrin induce opening of the sphincter
- Distension/irritation of the cecum closes the sphincter
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of large intestines
20. What are the features of Motility of large intestines?
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Motility of large intestines
21. Describe Defecation reflex (stretch)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Special motility patterns
1. Explain Vomiting
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Special motility patterns
2. What is the neural mechanism of vomiting?
- Vagus N and SYM afferent fibers transmit signal to vomiting
center in the brainstem
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Special motility patterns
3. What happen in the early stages of vomiting?
- In the early stages of vomiting, the patient starts to feel nauseous and autonomic symptoms are seen (nausea, ↑HR, pale skin, sweating)
- Such events are followed by anti-peristalsis (backward peristalsis up the GI-tract)
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Special motility patterns
4. What does vomiting result from?
Vomiting results from a squeezing action of the abdominal muscles (inhalation with mouth + nostrils closed) associated with simultaneous gastric contraction and opening of the esophageal sphincters
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Special motility patterns
5. What is the purpose of vomiting?
- A way by which the upper GI-tracts get rid of its content when they become irritated, overdistended
II. MECHANICAL FUNCTIONS OF GI MOTILITY - Special motility patterns
6. Make a schematic diagram of diarrhea
