Lecture 45 - Control of Digestion Flashcards
What are the major functions of the gut?
- digestion
- absorption
- removal of waste products
- fermentation: breakdown of cellulose
- epithelial barrier to pathogens
How does fermentation occur in the gut?
Gut Microbiome / probiotics digest cellulose to deliver us with short chain fatty acids
Which is the largest immune system in the body?
The gut
Why is the epithelial barrier in the gut important?
- protect us from invaders in food
* protect us from our own microbiome
Which is the largest endocrine system in the body?
The gut
Describe the gut as a chemical refinery
- Mechanical crushing
- Mixing vats
- Solvents and catalysts
- product separation
- conveyor belt
- waste disposal
- control systems
What are the control systems of the gut?
- CNS
- ENS
- hormones
- muscle
Why is the pylorus important?
Separates with acid contents of the stomach and the base contents of the duodenum.
Controls the flow into the duodenum
How long is the gut in total?
7 metres
What are the basic elements of neural control of the GIT?
Local: ENS
Central: vagus and sympathetic pathways
• Cephalic phase
How is the smooth muscle of the gut controlled?
Pacemakers
which control:
• propulsion
• mixing
What is the longer distance, slow control of the GIT?
Endocrine
Controls:
• appetite (satiety, hunger)
• coordination
Describe the ENS
Network of neurons within the intestinal wall
Describe how the ENS changes along the length of the gut
Doesn’t change
What are the layers / plexuses of the ENS?
- Submucous plexus
* Myenteric plexus
Where does the submucous plexus lie?
Between the mucosa and the circular muscle
Where does the myenteric plexus lie?
Between longitudinal and circular muscle layers
What happens when a part of the gut is cut out and out in a dish?
Can still produce many of the basic functions
The pacemakers and sensory neurons are still present
What does the CNS do in the GIT ?
- Modulates
- Initiates
… the activity of ENS
What are the three basic functions of the ENS?
- motility of gut
- absorption of salt and water
- release of enzymes and hormones
Describe the motility pattern after a meal
Fed state: • stomach relaxation -- for storage • segmentation • peristalsis (• retropulsion)
What is segmentation?
Localised constrictions to mix up the contents
No propulsion
How does vomiting occur?
Anesis / Retropulsion
Describe the motility of the stomach when fasting
MMC: migrating motor complex
Describe MMC
Slowly propagating constrictions through the intestines; ‘housekeeping’
Get rid of debris:
• epithelial cells
• bacteria
Describe the motor patterns in the colon
Mass movement contraction
Defecation
Why don’t we swim after a meal?
Exercise: blood flow to muscles
Not enough blood for digestion –> cramps
Where are the pacemakers
Antrum of stomach : special cells
Also, the whole way along the stomach
Why is it called slow wave?
Slow compared to what is seen in the rest of the nervous system
What are ICC?
Interstitial cells of Cajal
Modified smooth muscle cells
What is the catch mechanism?
Once the smooth muscle in GIT contracts, it remains contracted.
It need inhibitory stimulation to relax
What are the stimuli of the ENS?
Products of digestion
(pH
Stretch
Osmolarity)
What detects stimuli in the GIT
ENS sensory neurons
What other stimuli affect the GIT?
How is this different from the others?
Sight
Smell
Memory of food
This is different, because they are sensed by the brain, not the ENS
Describe the long reflexes that control digestion
CNS is involved
• Stimulus: products of digestion / extrinsic factors
• Receptor: sensory neurons of ENS
• Integration: Cephalic brain
• Efferent: para- and sympathetic neurons
• Effectors: smooth muscle and secretory cells
Describe the short reflexes that control digestion
Within the ENS
• Stimulus: products of digestion
• Receptor: sensory neurons of ENS
• Integration: within ENS, sensory neurons
• Efferents: neurons of submucous and myenteric plexuses
• Effectors: smooth muscle and secretory cells of GIT
What are some of the feed forward reflexes involved with digestion?
Describe them
Cephalic reflex
• Sight, smell etc. of food stimulates the cephalic phase (salivation, distension of stomach)
Gastro-colonic reflex
• ingestion of food stimulates defecation
What are some of the feed back reflexes involved with digestion?
Acid in stomach stimulates release of:
• secretin
Protein in stomach stimulates release of:
• CCK
CCK and secretin feedback to reduce stomach motility and gastric acid secretion
