Physiology 3120 Lecture 62: Lec 62 - Regulations of GI
15 May 2018
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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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find more resources at oneclass.com
Document Summary
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. The thought process of food and initiation of the digestive tract. Trigger: thought, sight, smell or taste of food. Responses: salivary glands secrete more saliva. Trigger: presence of food in the stomach, bolus must reach the stomach, stretch receptors - detect distension (stomach stretches to accommodate meal) Increased gastric juice secretions including hcl from parietal cells: acid, intrinsic factor, pepsinogen, etc. are all released. Initiation of response: presence of chyme in the duodenum after gastric emptying, stretch receptors detect distension and filling of duodenum, chemoreceptors detect partially digested proteins and lipids (cck released) and acid (secretin released, glucose stimulates gip. Increased closure of pyloric sphincter (cck) how frequently it closes: pancreatic ductal cell secretions increased (secretin, ductal cells of liver increase bicarbonate secretion (secretin)
