Lecture 24 Flashcards
How are conditions of the intestinal lumen regulated by receptors?
Receptors in the wall of GI tract respond to stretch and change in composition
What are the effectors in the G tract
Smooth muscle and glands
What do reflexes stimulated by receptors stimulate?
Smooth muscle contraction and gland secretion
How are the conditions of the intestinal lumen in the GI tract regulated?
Receptors
Effectors
Nervous and hormonal regulation
How does the CNS regulate GI function?
Co-ordinates activity over long distances.
Parasympathetic nervous system stimulates motility and secretion.
Sympathetics Nervous system inhibits motility and secretion.
Modulates activity of ENS.
How does the ENS regulate GI function?
Enteric nervous system (ENS) Submucosal plexus – regulation of secretion Myenteric plexus – regulation of motility Involved in local reflexes Peristalsis and segmentation Totally self contained
How is GI function regulated by hormones?
Endocrine and paracrine function.
Critical hormones such as gastrin, GIP, secretin, CCK.
What are the function of motility in the GI trqact?
Movement at a controlled rate.
Mechanical digestion.
Mixing.
Exposure to absorptive surfaces.
What are the properties if smooth muscle that assist with GI motility?
Spontaneously active.
Frequency of contraction property of region.
Strength of contraction regulated by nervous and hormonal input.
What are generalised motility patterns?
fasting and feeding
What is the fating motility pattern?
Migrating Motor Complex: `
4 hours after a mal
Repeats every 2 hour until eat again.
Housekeeping.
Functions of the Feeding motility pattern?
Storage
Propulsion
Mixing
Where does storage occur?
Fundus and body of stomach and colon
Where and how does propulsion happen?
Esophagus, stomach, small intestine and large intestine.
By peristalsis
Where does mixing occur?
Stomach - retropulsion
Small and Large intestine - segmentation
Purpose of chewing?
Reduce size of food
allows ingestion
taste
where does mechanical digestion and Mixing occur?
Antrum
What structure allows controlled delivery to duodenum?
Pyloric sphincter.
What does the fasting gastric motility state consist of?
1 hour of inactivity
50 minutes of uncoordinated activity
10 minutes of coordinated activity
Functions of fasting state?
Residual secretions
Undigested material
Features of peristalsis?
Initiated on greater curvature & spreads to antrum
3 contractions per min
First 60 min following meal gentle
60 - 300 min more intense activity
Features of storage?
Nervous regulation - vagus nerve
Increase in volume with minimal change in pressure
Fundus and body
Features of mechanical breakdown?
Retropulsion
Combination of peristalsis and closure or the pyloric sphincter
Mechanical breakdown
What regulates gastric emptying?
Feedback from duodenum
How is the rate of gastric emptying determined?
Rate matches digestive capacity of intestine
What factors affect gastric emptying?
Size of meal
composition of meal
How do different macronutrients affect gastric emptying?
Fats slow gastric emptying because they are more difficult to gest.
fluids faster tha solids.
What is the function of small intestine motlity?
Mixing with secretions from pancreas, biliary system (liver/gallbladder) and intestine Controlled movement
Exposure of products of digestion to absorptive surfaces
What Motility patterns occur in the small intestine ?
Between meals - Migrating motor complex
After meal - Segmentation for mixing and exposure to absorptive surfaces
Limited peristalsis (in humans) for movement
What is the function of the large intestine colon?
Storage of feces
What motility patterns occur in the large intestine?
Large periods of inactivity
Segmentation
Mass movement
What is mass movement>?
1-2 time a day following meals
Peristaltic wave
Drives faeces into rectum
initiates defecation
