1. GI Control & Coordination Flashcards
Name the functions of the digestive system
Ingestion Movement of food Digestion Absorption Defacation
Briefly describe regulation of the GUT
Continuous processing by the duodenum despite irregular food intake.
There is a low duodenal pH which prevents injury:
– decreased antrum contraction (stops emptying)
– increased motility of duodenum (clearance)
What are the two major movements of the Small Intestine?
Peristalsis
Segmentation
o Dominant activity of SI
o Circular muscle mixes chime
What stimulates and Inhibits Peristalsis?
o Slow movement – want to move gut contents around so that it allcomes into contact with the brush border.
o Pressure gradient proximal -> distal
o Stimulated by gastrin, CCK, insulin
o Inhibited by SNS (danger/stress)
What are the main functions of the LARGE INTESTINE?
- Water and ion absorption (400-1000ml/day, reclaimed from digestive secretion)
- Storage of unwanted food remnants (typically 16-20 hours; up to 30% can remain for a week)
- Mixing is more difficult because contents become dehydrated and more solid.
Name the mediators of GI control
Voluntary Skeletal Muscle
Local Reflexes and secreted factors
Autonomic Regulation
Describe the control & co-ordinators of the GUT!
Neural Mechanisms
Endocrine Factors
Paracrine Factors
Describe some of the Neural Mechanisms of CONTROL of the GIT
• Somatic nerves (both ends) • Sympathetic NS • Parasympathetic NS o Vagus nerve (CNX) o Pelvic Splanchnics (S2/3/4) • Enteric NS • Self regulation: pacemakers, long reflexes, short reflexes
Describe Endocrine Factors & Paracrine Factors of Control and Coordination
Endocrine Factors • Mostly peptide hormones Paracrine Factors • Local intercellular secretion • Histamine, prostaglandins, somatostatin
Describe the GIT innervation (Efferents)
Parasympathetic & Sympathetic
Parasympathetic- secretomotor • Upper: vagus (CNX) • Lower: S2/3/4 → pelvic splanchnic nerves Sympathetic: vasomotor; shuts valves • Greater splanchnic (T5-T9) • Lesser splanchnic (T9, 10) • Least splanchnic (T12) • Lumbar splanchnic (L1-2)
Describe GI muscle potentiation
Parasympathetic effectors stimulate gut motility
• Ach, via muscarinic M2 and M3 receptors, triggers Ca++ cascade from stores and ECF to increase cystolic Ca++ (Ca++ turns rhythmic depolarisation into actual contraction- reaches threshold)
• Smooth muscle contraction is potentiated as a result
• The actual contractile rhythm is intrinsic to the smooth muscle network, clocked by pacemakers.
What are the three Intramural plexuses found in the GIT?
Myenteric Plexus (Auerbach's plexus) Submucosal plexus (Meissner's plexus)
Where are myenteric or Auerbach Plexus’ located?
Between longitudinal and circular muscle
Innervates the muscularis
Controls motility
Where are Meissner’s plexus’ located?
Submucosally, innervates mucosa and submucosa, has control of secretions and some sensory functions
Describe the Motor part of the Enteric Nervous System
Motor neurons are both excitatory and inhibitory (potentiate or reduce SMC activity)
Excitatory Motor Neurons:
• ACh release onto muscarinic receptors
• Axons project locally and extend orally
Inhibitory Motor neurons:
• VIP and NO; mechanisms not quite clear
• Axons project locally and extend anally.
