Gastrointestinal
Physiology
Tanveer Raza MD MS MBBS
r[email protected]
Cross Section of Intestinal wall
 Resting

membrane potential
Voltage can change to different levels
less negative
-56mv
Depolarization
At rest
more negative
Hyperpolarization
Tanveer Raza MD MS MBBS
[email protected]
GI Smooth Muscle:
Electrical Activity
Tanveer Raza MD MS MBBS
[email protected]
GI Smooth Muscle:
•
Slow waves
•
•
Electrical Activity
Not action potential
Spikes
•
True action potential
Tanveer Raza MD MS MBBS
[email protected]
GI Smooth Muscle:

Electrical activity
Slow waves




Not action potentials
Slow changes in resting membrane potentials
Rhythmic
 Intensity and rhythm varies
Cause
 Complex interaction between smooth muscle
cells and Interstitial cells of Cajal
 Interstitial cells of Cajal
 Electrical pacemaker for smooth muscle
cells
Tanveer Raza MD MS MBBS
[email protected]
GI Smooth Muscle:
Electrical activity
Slow wave
Spike potential
Not Action potential Action potential
Does not cause
calcium ions to
enter (only sodium
channels)
Calcium ions enter
Does not cause
muscle contraction
Causes muscle
contraction
Tanveer Raza MD MS MBBS
[email protected]
GI Smooth Muscle:
Electrical activity
Spike potential of GI
smooth muscle
Action potential of
large nerve fiber
Caused by CalciumSodium channels
Caused by Sodium
only
Slower to open and
close
Faster
Longer duration (1040 times)
Shorter
Tanveer Raza MD MS MBBS
[email protected]
GI Smooth Muscle:

Electrical activity
Calcium-Sodium Channels
Cause action potentials
 Acts through Calmodulin
 Large number of Ca++ enter along with
smaller number of Na+
 Ca++ is required for contraction

Tanveer Raza MD MS MBBS
[email protected]
GI Smooth Muscle:
 Tonic



Electrical activity
contraction
Some smooth muscles exhibit tonic
contraction
Continuous contraction
 Lasting several minutes to hours
Cause
1. Continuous repetitive spike potentials
2. Hormones or other factors
3. Continuous entry of Ca++
Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT
 Propulsive

Moves food forward along GIT at an
appropriate rate for digestion and
absorption
 Mixing

movements or Peristalsis
movements
Keeps intestinal contents thoroughly
mixed at all times
Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT
Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT: Peristalsis

A contractile ring appears around the
gut and then moves forward

Stimulation at any point in the gut can
cause a contractile ring to appear in
the circular muscle, and this ring then
spreads along the gut tube
Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT: Peristalsis

Stimulus for intestinal peristalsis
Distention of the gut
 Other stimuli
 Irritation
 Chemical or Physical
 Parasympathetic nervous signals

Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT: Peristalsis

Requires active myenteric plexus


Peristalsis is depressed or absent
 Congenital absence of myenteric
plexus
 Atropine (paralyzes cholinergic nerve
endings)
Directional movement toward Anus

Can occur in either direction but normally
occurs towards anus
Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT: Peristalsis

Law of the Gut

Peristaltic reflex plus anal direction of
movement of peristalsis is called "law of
the gut”
 Contractile
ring normally begins on orad side
of distended segment
 The gut sometimes relaxes several
centimeters downstream toward the anus,
called "receptive relaxation," thus allowing
food to be propelled easily anally
Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT: Peristalsis

Peristalsis also occurs in
Bile ducts
 Glandular ducts
 Ureters
 Many other smooth muscle tubes of the
body

Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT: Mixing Movement
 Differ
in different parts
Peristaltic contractions causing
mixing
 Occurs
when forward progression is
blocked by sphincter. Peristaltic wave
can then only churn the contents, rather
than propelling them
Local
intermittent constrictive
contractions
Tanveer Raza MD MS MBBS
[email protected]
Movement in GIT: Mixing Movement
 Differ
in different parts
 Peristaltic
contractions causing mixing
 Local intermittent constrictive
contractions

Occurs every few centimeters in gut wall.
These constrictions usually last only 5-30
seconds; then new constrictions occur at other
points, "chopping" & "shearing" the contents
first here and then there
Tanveer Raza MD MS MBBS
[email protected]
Thank You
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Gastrointestinal Physiology Tanveer Raza MD MS