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Lecture

BIOD60H3 Lecture Notes - Enteric Nervous System, Osmoreceptor, Submucosa


Department
Biological Sciences
Course Code
BIOD60H3
Professor
Daman Bawa

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Lecture 24: Nervous and Hormonal Regulation of Digestion
Gut motility and secretes of substances are controlled by two nerve plexes
Submuscosal nerve plexis innervates the sub-mucosa layer and the myenteric nerve plexis innervates the smooth muscle
Submuscosal nerve plexis influences secretory activity while myenteric plexis innervates smooth muscle activity
Receptors in the wall of the stomach are connect to nerve plexis via sensory afferent (connected to interneuron which connects to
motor or enteric neuron which then sends nervous signals to gut muscles or secretory cells
Three types of receptors in the gut
oMechanoreceptors: sense distension or stretching of the gut
oChemoreceptors that sense changes in pH, sugars, amino acids, and fatty acids
oOsmoreceptors: sense changes in osmotic pressure, as food gets smaller and smaller osmotic pressure of stomach chyme
increases
Osmoreceptors are stretch inhibited, as osmotic pressure increases around cells, water is drawn out of the osmoreceptors and into
stomach lumen, receptor cells shrink, open up stretch sensitive ion channels and finally depolarize which send signal to either motor
neurons or to the enteric neurons
Mechanoreceptors are stretch activated, distention causes ion channels to open leading to depolarization and receptor activation
Gut reflexes are either intrinsic or extrinsic
oIntrinsic: reflexes contained within the wall of the gut
oExtrinsic: relexes involve sensory neuron sendin an afferent process to the spinal cord or brainstem (former is short
extrinsic, mostly sympathetic activities, latter is long, consist of parasympathetic)
Sympathetic nerves innervate the gut cause a decrease in gastrointestinal muscle activity and fluid secretion, parasympathetic
innervate the large intestine and vagus nerves innervates everything else cause and increase in gastrointestinal muscle activity and
fluid secretion
Changes in the balance of gastrin and somatostatin regulate Hcl secretion and this is achieved by nervous innervation of the G and D
cells
Many vagal efferent fibers from CN innervate stomach
oEnteric neurons innervate G, D, mast and parietal cells (for last 3, acetylcholine is released to affect release of hormone)
Acetylcholine stimulates Hcl and histamine production, inhbits stomatostatin
G-cells gastin-releasing peptide stimulates gastrin production
Three phases of gastrointestinal control
oCephalic phase occurs in response to sight, smell or taste of food and chewing and swallowing, this increases
parasympathetic activity, releasing gastrin and thus acid from parietal cells
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