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Lecture 62

Physiology 3120 Lecture 62: Lec 62 - Regulations of GI


Department
Physiology
Course Code
PHYSIO 3120
Professor
Tom Stavraky
Lecture
62

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Lecture 62 Regulation of GI Tract
- For all our organs to work together, there is coordination of hormones and neural control
for digestion and absorption
- Body cannot control absorption but it can control what is secreted and how fast things are
moving
Regulation of GI secretions and motility
CEPHALIC PHASE
- The thought process of food and initiation of the digestive tract
- TRIGGER
o Thought, sight, smell or taste of food
- INITIATION OF RESPONSE
o Medulla oblongata regions activated (ie. nucleus tractus solitarii) by cerebral cortex
and/or feeding centre in hypothalamus
Cerebral cortex and feeding center feed onto NTS in medulla oblongata
From there neural pathways are activated
o Facial & Glossopharyngeal nerves stimulated
Salivary glands are activated
Facial: activate sublingual and submandibular glands
Glossopharyngeal: activate parotid glands = salivate
If food gets into mouth, get more glosspharyngeal nerve stimulation because
parotid gland is the one that secretes a highly enzymatic secretion which is
optimal for digesting carbohydrates
o Vagus nerve activated
Contains afferents and efferents that go to the digestive tract
PSYN activation
- RESPONSES
o Salivary glands secrete more saliva
If food involved, more parotid gland activation (salivary amylase and lingual
lipase produced in our saliva)
o Stomach secretions and motility increased
Vagus nerve causes some acid to be produced and released
Stomach moves around and upper part relaxes in preparation for food
Small amount of acid is secreted by the
stomach in preparation
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GASTRIC PHASE
- TRIGGER
o Presence of food in the stomach
o Bolus must reach the stomach
- INITIATION OF RESPONSE
o Stretch receptors - detect distension (stomach stretches to accommodate meal)
o Chemoreceptors detect pH increase
pH increases when food enters stomach because it buffers acid
Peptides buffers acid in stomach more strongly
o G cells release gastrin
Presence of peptide or single amino acids
Feeds back on parietal cells (neural, histamine, gastrin) = maximal amount
of acid secreted
This is more acid secretion than the cephalic phase cephalice only has
neural control but need gastrin + histamine to get highest level of secretion
- RESPONSES
o Increased gastric juice secretions including HCl from parietal cells
Acid, intrinsic factor, pepsinogen, etc. are all released
o Increased gastric motility
Grinding action triggered by enteric nervous system
ENS triggers myenteric plexus neurons which activates muscles in stomach
to move in certain patterns to grind and propel the food through the
stomach
o Enhanced gastric emptying - relaxation of pyloric sphincter (gastrin)
In the fed state when food is in stomach, the pyloric sphincter is first closed
As the gastric phase progresses, there is increased opening of the pyloric
sphincter
Gastrin triggers pyloric sphinchter to open = empty stomach
Gastric emptying can be delayed or inhibited by intestinal phase
DOES NOT HAPPEN RIGHT AWAY THERE IS A LAG PERIOD
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