Transcript 1 GIT general

Gastro-intestinal
Physiology
General
Prof. K. Sivapalan.
Why Eat?
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Hunger.
Taste and satisfaction.
Passing time
Energy.
Growth.
Socialization.
Health.
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Functions of GIT
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Tranquility [oral activity]
Ingestion.
Digestion.
Absorption
Excretion.
Protection- immunity
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Gastro-Intestinal Tract
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General Organization of GIT
Dorsum
Mesentery
Glands:
Mucosa
Sub mucosa
Goblet
cells
Sub mucus muscle
Mucosal
Sub mucosal
mucus [Meissner’s] plexus
Sub
Circular muscle
Glands
outside.
Myenteric [Auerbach’s] plexus
Longitudinal muscle.
Serosa.
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Smooth muscle in GIT
• Smooth muscles in intestine form a syncytium with
tight junctions and gap junctions.
• Membrane potential shows slow waves. More in
pace makers. (Basic electrical rhythm (BER) of
gastrointestinal smooth muscle)
• When the waves reach threshold level, spike
potentials occur.
• Muscle tension increases or decreases depending
on the number of spikes.
• Acetylcholine increases and adrenaline reduces
tension.
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Innervation
• Sub mucus [Meissner’s] plexus is mainly
sensory - stimulated by, irritation, distention
or chemicals.
• Autonomic afferents from tissues [vagal (80
%) and sympathetic] and Meissner’s plexus
go centrally.
• Myenteric [Auerbach’s] plexus is motor.
• Parasympathetic
[Vagus] end on cells of
Sensory
neurons
Myenteric
plexus.
• Sympathetic fibers end on Myenteric plexus,
muscles and glands.
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Gut Reflexes
• Coltroll within the gut- secretions,
peristalsis, mixing, local inhibitions etc.
• Coordinated in para vertibral sympathetic
ganglia- enterogastric reflex, colonoilial
reflex
• Coordinated in brain stem- stomach to
stomach: motor and secretary, pain
inhibiting entire GIT function, defecation
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Peristalsis.
• Coordinated by myenteric
plexus
• Contraction of circular
muscles proximal to the
stimulus and relaxation
distally.
• Longitudinal muscles
contract and pull over the
contents.
• The relaxed circular
muscles contract.
• The sequence is
propagated in oral to
caudal direction.
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Migrating Motor Complex
• Cycles of motor activity, initiated by
motilin, migrate from the stomach to the
distal ileum during fasting at 90 minute
intervals at 5 cm/min
• Clear the stomach and small intestine of
luminal contents in preparation for the next
meal
• Quiescent period (phase I), irregular
electrical and mechanical activity (phase
II), burst of regular activity (phase III)
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Voluntary and Involuntary
Aspects
• Searching, cooking, serving, placing in the
mouth, mastication- voluntary.
• Swallowing- begins as voluntary and ends as
involuntary.
• Gastric functions- involuntary but affected by
moods.
• Small intestinal functions- fully involuntary.
• Storage of feces- involuntary.
• Defecation- starts as involuntary and ends as
voluntary.
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Regulation of the functions
• Voluntary actions are generally conditioned
reflex.
• Intrinsic plexus coordinates local reflexes.
• Sympathetics inhibit [stimulate sphincters].
– Nerve endings on muscles and glands
• Parasympathetic- stimulate [inhibit sphincters].
– Nerve endings on Myenteric plexus [preganglionic]
• Pace makers in GIT.
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