Gastric Motility Flashcards
Function of stomach
-mix and store food and initiate protein and fat digestion
Anatomical regions of single compartment stomach
-fundus
-corpus (body)
-cardia
-antrum
-pyloric
Functional regions of stomach
-distal stomach
-proximal stomach
-pacemaker band
Fundic region ID in dog and cat
-difficult to define in cat or dog
-apparent only in well-fed state
What protects acid erosion in the stomach?
-mucus secretion
Gastric acidity
-humans: 1.7
-dogs: 6.8
-rats and mice: 3.9-4.0
Proximal region of stomach function
-for storage
Distal region of stomach function
-grinding and sieving
Proximal stomach motility
-weak continuous contractions, provide gentle propulsions of material into the distal stomach
>Adaptive relaxation- enlargement of stomach without increasing pressure
>minimal mixing
Distal stomach (antrum) wave activity
1.Waves of peristalsis begins at the junction of the proximal and distal areas moving towards the pylorus
2.as waves approach the pylorus, the pylorus constricts and some of the ingesta is pushed back
3.some finely ground and/or liquified material is pushed through the pylorus and allowed to enter the duodenum
4.between contractions, no gross movements
What stimulates stomach contractions?
-distention of fundus activates contraction
-Cajal cells within the fundus are stretched and they activate a smooth muscle contraction
Cajal activation
-activated by mechanosensitive (stretch) and modulated by parasympathetic nervous system
**Cl exit, Ca entry
Types of digestive contractions
1.mixing contractions
2. antral contractions
Mixing contraction
-the contraction wave does not proceed all the way through the antrum/distal stomach to the open pylorus
**results in turning over and mixing of contents
Antral contraction
-the contraction wave does proceed all the way through the antrum/distal stomach for a quick opening and closure of the pylorus
-results in turning over and mixing of contents, AND a small release of stomach content into duodenum
Stomach motility- regulation of emptying
-rate of food leaving the stomach “must match” the rate at which it can be digested and absorbed by the small intestine
Receptors regulating stomach emptying
-duodenal receptors
>respond to the physical composition of the meal AND volume, osmolarity, chemical composition and caloric density
Order of stomach content emptying
> > water leaves stomach almost immediately
digestible solids leave after being reduced to particles ~2-3mm
Gastric tunnel
-along the lesser curvature of stomach allowing shunting of water, bypassing solids
Inhibitor of gastric emptying
12-18 C (long chain) Lipids
Fats and amino acids in stomach
-enteroendocrine cells in upper duodenum release cholecystokinin (CCK) when they sense fats or amino acids
-inhibit gastric motility and cause pyloric sphincter to contract more tightly
**Fats and proteins remain in stomach and send satiety signals back to brain whereas carbohydrates do not stay in stomach
Stomach motility particle sizes
-larger particles stay in stomach for longer period
- liquid leaves the stomach at a faster rate than particulates
Filling stage in stomach
-volume of food can be accommodated without an increase in pressure
-no or minimal contractions
Motility stage in stomach
-phase of slow tonic contractions of the fundus and increased peristalsis to allow mixing
-tenderized food than propelled into pylorus by contractions that become forceful in the antrum/distal stomach
-pyloric contractions cause some food to be moved retrograde for more mixing and some enter the duodenum
Pressure pump
-fundus and proximal corpus
-tonic muscle type and tonic contractions
-cajal cells absent
-if inhibited, slow gastric emptying
Peristaltic pump
-distal corpus and proximal antrum
-phasic muscle and phasic and peristaltic contractions
-Cajal cells present
-when inhibited, impaired mixing and slow gastric emptying of solids
Grinder
-located in terminal antrum and pyloric sphincter, and pylorus
-both phasic and tonic muscle, and strong phasic nearly simultaneous contractions
-Cajal cells present
-when inhibited, impaired grinding and duodeno-gastric reflux
-when excited, outlet obstruction
Parasympathetic activity during digestive period
-immediately: increased inhibitory/reduced excitatory
-Later: reduced inhibitory/increased excitatory
Hormonal activity during digestive period
-release of leptin, cholecystokinin (CCK), and GLP-1
Fundus during digestive period
-immediately: increased compliance
-Later: decreased compliance
Antrum during digestive period
-immediately: reduced phasic contractions
-later: increased phasic contractions
Pylorus during digestive period
-immediately: contraction
-later: relaxation
Interdigestive period
-during digestion, large food particles are often retained and never digested to the point that they can escape the stomach during normal contractions
-Special mechanism=Migrating Myoelectric complex (MMC) OR interdigestive motility complex used to empty fasting contents and/or larger particles from the stomach to the distal small intestine
**pyloric sphincter also relaxes as a strong wave of peristalsis occurs in antrum forcing the less digestible material into duodenum
Migrating Myoelectric Complex (MMC) phases
-Phase I- only slow waves, no spikes
-Phase II- intermittent spikes and some smooth muscle contraction
-Phase III- the big sweep; intense burst of spikes with each slow wave= strong contractions moving all solids and liquids into duodenum and quickly into the large intestine
-Phase IV- inhibition of contractile activity that merges with the next phase of digestive period activity
MMC patterns in carnivores, omnivores, and herbivores
-carnivores: MMC stopped during feeding, feed pattern like phase II
-herbivores: cyclic pattern uninterrupted during feeding
-omnivores: cycle is dependent on the diet
Control of MMC
-relatively unknown
-does require neural and endocrine inputs
Other name for MMC
-interdigestive motility complex
Interdigestive phase I
-increased inhibitory parasympathetic
-no pressure in fundus
-reduced phasic contractions in antrum
Interdigestive phase II
-reduced inhibitory parasympathetic
-ghrelin release
-increased tonic pressure in fundus
-increased phasic contractions in antrum
-relaxation of pylorus
Interdigestive phase III
-non vagal, peripheral neuro-hormonal
-motilin released
-increased tonic pressure in fundus
-migrating motor complex in antrum
-relaxation in pylorus
Interdigestive phase IV
-increased inhibitory parasympathetic
-increased compliance in fundus
-reduced phasic contractions in antrum
-contraction in pylorus
Inhibition of gastric emptying
-enterogastric reflux (neural mechanism)- depending on chemical composition of digesta
-enterogastrone (hormonal) mechanism- responds to fat and amino acids in the duodenum (via CCK)
**mechanisms can inhibit emptying when there are irritating, acidic or hypertonic contents in duodenum
Neural control of gastric motility
-autonomic nerves regulate gastric motility (vagus parasympathetic nerve with inhibitory and excitatory effects)
>sympathetic nerves do not have an important role in physiological regulation of gastric motility
Inhibitory vagal motor circuit
-consists of preganglionic cholinergic neurons and postganglionic inhibitory neurons in the myenteric plexus
>neurons released nitric oxide, ATP and peptide vasoactive intestinal peptide. Connected to anorexigenic neural pathways
Excitatory vagal motor circuits
-distinct gastric excitatory preganglionic cholinergic neurons in the dorsal nucleus of the vagus nerve ion the medulla AND postganglionic excitatory cholinergic neurons in the myenteric plexus
>smooth muscle is final target
>connected to orexigenic neural pathways
Tonic contraction locations
-smooth muscle of the pressure pump, fundus, and proximal corpus
Phasic contraction locations
-muscles of the peristaltic pump, distal corpus and the proximal antrum
*paired with interstitial cells of cajal
Interstitial cells of cajal slow wave rate
3-5 per min
CCK release
-released from neuroendocrine cells of duodenum by stimuli such as HCl, amino acids and fatty acids
-works on multiple pathways including GLP-1
GLP-1 release
-released from intestines stimulates vagal afferents
- multiple actions accounting for a strong inhibitory effect of GLP-1 on gastric motility
Gastric leptin
-released from chief cells along with pepsin
-effect takes hours
-inhibition of feeding
Ghrelin and motilin
-accelerate gastric emptying
-released during inter-digestive (fasting) period
