Lecture 24: Introduction and Motility Flashcards
What does the GI tract regulate?
Conditions in the intestinal lumen
What do receptors in the walls of the GI tract respond to?
2
- Stretch
- Strange in composition
What can change in composition within the lumen of the GI tract consist of?
(5)
- pH
- Osmolarity
- Amino acids
- Sugars
- Fats
What are effectors of the GI tract?
2
- Smooth muscle
- glands
What do reflexes stimulated by receptors cause in the GI tract?
(2)
- Smooth muscle contraction
- Gland secretion
What 2 types of regulation control the GI tract?
- Nervous regulation
- Hormonal regulation
What distance does the central nervous co-ordinate activity of the GI tract over?
Long distances
How does the parasympathetic nervous system influence the GI tract?
It stimulates motility and secretion
How does the sympathetic nervous system influence the GI tract?
It inhibits motility and secretion
What does the central nervous system modulate?
The activity of the enteric nervous system
What is the enteric nervous system comprised of?
2
- Submucosal plexus
- Myenteric plexus
What does the submucosal plexus regulate?
Secretion
What does the myenteric plexus regulate?
Motility
What local reflexes is the enteric nervous system involved in?
(2)
- Peristalsis
- Segmentation
The enteric nervous system is totally self what?
Contained
The GI tract is the largest what in the body?
Largest endocrine organ in the body
What type of functions does the GI tract express?
2
- Endocrine
- Paracrine
What are 4 critical hormones in the GI tract?
- Gastrin
- Gastric inhibitory peptide (GIP)
- Secretin
- Cholecystokinin (CCK)
What does movement through the GI tract at a controlled rate help with?
(3)
- Propulsion
- Storage
- Chemical digestion/absorption
What does mechanical digestion do?
Increases the surface area of foods
What is mechanical digestion essential for?
Chemical digestion
What does mixing in the GI tract aid in?
Chemical digestion
What does exposure to absorptive surfaces within the GI tract aid in?
Absorption
What is a property of smooth muscle?
It contracts spontaneously without external input
How often does the stomach contract?
3 times per minute
How often does the duodenum contract?
12 times per minute
How often does the ileum contract?
9 times per minute
What is the strength of contractions through the GI tract regulated by?
(2)
- Nervous input
- Hormonal input
What generalised motility pattern occurs in a fasting state?
Migratory motor complex
How often does the migratory motor complex occur?
4 hours after a meal, then every 2 hours until you eat again
During a feeding state where can storage of material occur?
2
- Stomach
- Colon
What does relaxation of smooth muscle in the stomach and colon allow for?
Volume to increase without a change in pressure
What type of movement causes propulsion throughout the GI tract?
Peristalsis
What type of movement causes mixing in the stomach?
Retropulsion
What type of movement causes mixing in the small and large intestine?
Segmentation
What does chewing do to food?
Reduces the size of food
What is mixed with food as a result of chewing?
Saliva (which is required for taste)
As chewing is voluntary what kind of muscle is used?
Skeletal muscle
Reflex controls what during chewing?
3
- Strength of chewing
- Frequency of chewing
- Side of mouth used to chew
What happens during swallowing?
Material is transferred rapidly from mouth to stomach
How is swallowing initiated and how does it proceed?
It is initiated at will, then proceeds reflexly
What part of the stomach is used for storage?
2
- Fundus
- Body
Where does mechanical digestion occur within the stomach?
Antrum
Where does mixing occur within the stomach?
Antrum
What controls the delivery of substance from the stomach to the duodenum?
The pyloric sphincter
What happens to the stomach during a fasted state?
It shrinks to about 50ml in volume
What happens during the first hour of the migratory motor complex?
Inactivity
How long does uncoordinated activity occur during the migratory motor complex?
50 minutes
How long does coordinated activity occur during the migratory motor complex?
10 minutes
What are the functions of the migratory motor complex?
House keeping of residual secretions/undigested material
During a feeding state what occurs to help allow storage?
- Receptive relaxation
- Gastric accomodation
What does nervous regulation through the vagus nerve cause the stomach to do during a feeding state?
Increase in volume with minimal change in pressure
Where is peristalsis initiated in the stomach and where does it spread to?
initiated on the greater curvature of the stomach and spreads to the antrum
What happens to activity in the stomach 60 mins after a meal?
There is gentle activity
What happens 60-300 mins after a meal?
There is more intense activity
What is retropulsion?
A combination of peristalsis and closure of the pyloric sphincter in the stomach causing mechanical breakdown
What does the rate of gastric emptying match?
The digestive capacity of the intestine
What is gastric emptying of the stomach regulated by?
Feedback from the duodenum
What factors effect the rate of gastric emptying?
2
- Size of a meal
- Composition of a meal
What does a larger meal do to the rate of gastric emptying?
Increase the rate of gastric emptying
What empties from the stomach faster fluids or solids?
Fluids
What do fats do to gastric emptying?
Slow gastric emptying
What does motility in the small intestine cause to be mixed with food?
(3)
- Pancreatic secretions
- Biliary system (liver/gallbladder) secretions
- Intestine secretions
What motility patterns occur between meals in the small intestine?
Migratory motor complex
What motility patterns occurs after meals in the small intestine?
Segmentation
What does segmentation in the small intestine allow for?
2
- Mixing
- Exposure to absorptive surfaces
What is stored in the colon/large intestines?
Feaces
What does the large intestine experience large periods of?
Inactivity
What does segmentation in the large intestine allow for?
2
- Exposure to absorptive surfaces
- Absorption of fluid and salts from faeces
How often does mass movement occur in the large intestine occur?
1-2 times a day following meals
What do peristaltic waves in the large intestine do?
2
- Drives faeces into the rectum
- Initiates defecation
