1.2 Regulation of the GIT: Motility Flashcards
Define gut motility
Stretching and contractions of the muscles under involuntary control in the gastrointestinal tract
- controlled movements that enable food to progress along the digestive tract & ensuring the absorption of important nutrients
What is peristalsis?
Series of involuntary wave-like muscle contractions that moves food to different processing stations in the digestive tract
Define mechanical digestion
Physical act of breaking down the food by non-chemical means
- begins in the mouth with mastication
Describe the function of the tunica muscularis
Contains smooth muscle fibres
- allowing the folds to move and the whole area of the stomach can process food mechanically
What is the Margo Plicatus?
Separates glandular and non-glandular parts of the stomach
- horses only
What are the stages of mechanical digestion in ruminants?
- Mastication & mixing
- Ingestion & foregut fermentation
- Regurgitation, re-mastication and eructation (liberation of gases from/through the foregut → oesophagus → mouth)
Which nerve innervates the rumen?
Vagus (CN X)
How is mechanical digestion in the rumen stimulated?
Distention (stretch receptors), ingesta consistency, VFA concentration
Describe primary movements of the rumen
Inside the rumen to mix bolus of food
- ingesta with microbiota
- promote separation of this fermentation into different phases
Describe secondary movement of the rume
Occurs outside of the rumen
- facilitate expulsion of gas from the rumen
What is intestinal motility controlled by?
Excitatory and inhibitory signals from enteric nervous system
What is intestinal motility modulated by?
Inputs from the central nervous system, and gastrointestinal hormones
What is segmentation?
Contractions chop, mix and roll the chyme
What is peristalsis?
Slowly propels it towards the large intestine
What is haustration?
Chop and mix the ingesta, presenting it to the mucosa where absorption occurs
- contractions form sacculations > hausta/haustrum
What are antiperistaltic contrations?
Propagate towards the ileum - retards the movement of ingesta through the colon - reabsorption of water & electrolytes
What are mass movements?
Very intense and prolonged peristaltic contraction which strips an area of large intestine clear of contents
What is the digestive phase of peristalsis?
Peristaltic contractions pass over short segments of the intestine
What is the interdigestive phase of peristalsis?
Peristaltic contractions pass over large segments of the intestine
What is the migrating motor complex?
Distinct pattern of electromechanical activity observed in gastrointestinal smooth muscle during the periods between meals
What are functions of the migrating motor complex?
Sweep residual undigested material through the digestive tube
Control bacterial population
What are the phases of the migrating motor complex?
- Smooth muscle quiescence. Rare action potentials and contractions
- Peristaltic contractions occur and progressively increase in frequency
- Rapid, evenly spaced peristaltic contractions occur
- Short period of transition between contractions in phase 3 and inactivity in phase 1
Describe the intrinsic control of GIT motility
Gut smooth muscle exhibits spontaneous “slow wave activity” = Basic Electric Rhythm of depolarisation and re-polarisation
- when the amplitude of BER reaches a threshold level an action potential occurs leading to contraction of smooth muscle cells
Describe the extrinsic control of GIT motility
Endocrine - hormones released in the bloodstream reach target
Paracrine - agents released for local diffusion to target on nearby cells
Nervous - intrinsic control from enteric nervous system + autonomic control from CNS (parasympathetic ‘rest and digest’)
What is the myenteric plexus?
Outside submucosal plexus, within muscularis internal and external
- controls digestive tract motility
What is the submucosal plexus?
Present on submucosal layer
- senses environment within lumen → regulates GI blood flow + controls epithelial cell function
What hormone decreases GIT activity in the sympathetic nervous system?
Noradrenaline
What hormone decreases GIT activity in the parasympathetic nervous system?
Acetylcholine
Describe the function of interneurons
Responsible for integrating information from sensory neuron + providing it for programming for interior motor neurons
What are the sensory nerve endings?
Neurons which capture stimuli from within GI tract, from mucosa + pass these onto a pre-vertebral ganglia
Describe the flow of information through the excitatory neurons
Ach → smooth muscle contraction, intestinal secretions, release of enteric hormones and dilation of blood vessels
Describe the flow of information through the extrinsic sympathetic neurons
Noradrenaline → opposite effects from Ach
