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Extrinsic NS
- autonomic CNS
- P- long preganglionic fibers: vagus & pelvic nerves synapse w/i intrinsic NS
- S- postganglionic, directly on smooth m fibers, endocrine glands, bv's
- In GENERAL: P- inc GI motor and secretory
- S- inhib
- EXCEPTION: salivary secretion-both (P- long-lasting hi V, protein-poor; S- transient lo V, protein-rich)
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Motility:
1. Propulsion
2. Mixing
3. Reservoir
4. Sphincter
- 1. Propulsion- aboral direction via perstalsis
- 2. Mixing- segmentation, size reduction, mixing fooed with secretions & dig NZs
- 3. Reservoir- Storage, relax to accomodate more
- 4. Sphincter- separation, tonic contraction, controlled passage of food
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Lumen is mostly relaxed...
- relaxed (physiological ileus) "default"- active ("on") enteric inhibitory neuron
- But at contractions and default tonic contractions (sphincters)- inactivate ("off") enteric inhibitory neurons --so sphicters become active when food needs to pass
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Salvia composition and tonicity
- High rates of secretion: less hypotonic (near isotonic)
- Low rates of secretion: more hypotonic
- Acinus- isotonic
- Duct- becomes hyptonic
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Achalasia
"nutcracker esophagus", failure of LES to relax while swallowing
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Diffuse spasm
temporaly uncoordnated contractions
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GERD
"heart burn" like problems, etc. ?
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Stimulation of acid secretion
1. Ach
2. Gastrin
3. Histamine
- 1. Ach- neurocrine, release from intrisic motor neurons
- 2. Gastrin- endocrine, released from G cells- stim gastrn R and releases HISTAMINE from ECL cells 3. Histamine- paracrine, released from ECL cells
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Acid secretion
1. Cephalic phase
2. Gastric phase
3. Intestinal phase
- 1. Cephalic phase- b4 eating, vagal activation on intrinsic neurons
- 2. Gastric phase- food in stomach, responds to distention and peptides & aa, mechonoR and vago-vagal reflex
- 3. Intestinal phase- in intestine, Enterooxyntin released in response to aa & peptides, and distention
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Pepsin
secreted in response to Ach in cephalic and gastric phases
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Mucus
- Soluble- mucus neck cells, Ach from vagal stim, lubricate bolus
- Insoluble- surface mucus cells, protective epithelial linin of stomach (irritant, alcohol, spicy food)
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Stomach receptive relaxation
- vago-vagal reflex from mechanoR, activation of inhibitory intrinsic neurons, NO & VIP.
- therefore, no inc in P
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Gastric emgptyin
- Rate of gastric emptying is controlled neg fb that balances amt of chyme entering duodenum with ability od duodenum to process chyme
- Dec emptying: DEC rate/force of gastric gontraction & INC force of contracion of pyloric sphincter
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Pancreas
bicarb-rich soln for neutralization of stomach acid, hydrolytic NZ for dig
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Liver/GB
- bile for dig & absorption
- waste products (bilirubin & chol)
- BA transport is primary driver of everything else
- constititively: BA-dep-bile flow
- during meal: BA-indep-bile flow (secretin)
- Bile secreted to canalicus is isotonic.. the gets to bile duct: adds bicarb and H20 (like with pancreatic duct)
- GB secretion- contraction by Ach via vagus & CCK relaxes SOO and contract GB
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Digestive NZ
- membrane-bound: intrinsic membrane ptoteins
- luminal NZ: secreted by pancreas act in lumen
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