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Dr.hassan al-awady
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5/8/2017
GASTROINTESTINAL PHYSIOLOGY
First Lecture
The digestive system is composed of a long muscular tube –
the gastrointestinal (GI) tract, or alimentary canal-and a set of
accessory organ.
The GIT consist of oral cavity, pharynx, esophagus, stomach,
small intestine, large intestine, rectum, and anal canal.
fliver, and gallbladder. There are four major functions of GIT:
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MOTILITY
SECRETION
DIGESTION
ABSORPTION
General structure of GIT:
Is a hallow tube composed of lumen of variable diameter
surrounded by a wall made up of four principle layers :
1-Mucosa:composed of epithelial lining and lamina properia of
loss connective tissue rich in blood and lymph vessels.
2-Submucosa: composed of loss connective tissue with many
blood and lymph vessels and nerve plexus caaed Miessner
plexus.
3-Muscularis externa :consist of inner layer of circular and
outer layer of longitudinal oriented smooth muscle fiber
Myenteric (Aurbach) nerve plexus lies between the tow
muscles sublayer.
4-Serosa: is a thin layer composed of loss connective tissue rich
in blood and lymph vessel and adipose tissue.
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Dr.hassan al-awady
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5/8/2017
Neural control of GIT:
Is provided by extrinsic and intrinsic(enteric) neuron:
1-Extrinsic nervous control comes from the parasympathetic and
sympathetic nervous system.
a. Parasympathetic innervation :
(1) Parasympathetic nerve fibers come from
(a) The vagus nerve, which innervates the striated
muscle of the esophagus, the stomach,, the small intestine, and
the ascending colon.
(b) The pelvic nerve, which innervates the lower portion
of the colon and the striated muscle of the external anal canal.
2- Parasympathetic nerve activity:
(a) Increase GI motility and secretion.
(b)Decrease the activity of sphincters.
b.Sympathetic innervation:
(1) Sympathetic fibers reach all level of the GIT from
the celiac, mesenteric and hypogastric ganglia
(2) Sympathetic nerve activity:
(a) Increase sphincter tone.
(b) Reduce blood flow to the GIT.
3. The intrinsic nervous system is composed of the myentric
and submucosal plexuses .
a. The extrinsic nerve fibers synapse on neurons within the
intrinsic nervous system.
(b) Intrinsic nervous activity can act independently of the
extrinsic nervous.
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Dr.hassan al-awady
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5/8/2017