2. Dr. Alzoghaibi 2
Gastrointestinal physiology:
A branch of human physiology
that addresses the physical function of
the gastrointestinal (GI) system.
3. .
Gastrointestinal system:
1-The GITâ a series of hollow organs:
Mouth
Esophagus
stomach
small intestine
large intestineâ rectum and anus.
2- Solid accessory organs:
Liver
Pancreas
Gallbladder 3
4.
5. Primary Functions of Digestive System
1. Ingestion - getting food into the GI tract (eating)
2.Propulsion - moving food along the tract by swallowing and peristalsis
(wave-like motion)
3.Mechanical Digestion - the physical grinding and churning of foodstuffs to
breakdown and expose to enzymes and the surface of the GI tract
4.Chemical Digestion - breakdown of larger molecules into absorbable parts
by enzymatic action
5.Absorption - transport of digested molecules, vitamins, minerals, water, into
blood
6. Excretion - elimination of unused foodstuff, heavy metals, toxins,
alkaloids.(feces).
7. Helps Erythropoises by secreting intrinsic factor needed for Vitamin B12
absorption 5
9. The Musculature of the Digestive
Tract
ī Two Main Muscle Layers:
ī Longitudinal muscle layer
ī Circular muscle layer
ī§ Oblique muscle layer (stomach only)
9
10. The Musculature of the Digestive Tract
Longitudinal Muscle:
ī§ Contraction shortens the segment of the intestine and
expands the lumen
ī§ Innervated by ENS, mainly by excitatory motor neuron
ī§ Ca influx from out side is important.
Circular muscle:
ī§ Thicker and more powerful than longitudinal.
ī§ Contraction reduces the diameter of the lumen and
increases its length .
ī§ Innervated by ENS, both excitatory and inhibitory motor
neurons.
ī§ More gap junctions than in longitudinal muscle.
ī§ Intracellular release of Ca is more important
10
11. SMOOTH MUSCLE OF G.I.T
1.Unitary type,visceral or syncytial
smooth muscle.
2.Multiunit type smooth muscle.
11
12. SMOOTH MUSCLE OF G.I.T
Unitary type,visceral or syncytial smooth
muscle.
īContract spontaneously in response to
stretch in the absence of neural or hormonal
influence (such as in stomach and intestine)
īCells are electrically coupled via gap junctions
so each muscle layer functions as a
syncytium.
12
13. SMOOTH MUSCLE OF G.I.T
Multiunit type smooth muscle.
īContract in response to neural input but
not to stretch (such as in esophagus &
gall bladder).
īComposed of discrete independently
working smooth muscle fibers ,each of
which is innervated by single nerve
ending.
13
16. Slow waves
They are not action potential but are slow undulating changes
in membrane potential(-56mv)
īFrequency of slow waves determines rhythm of gastrointestinal
movements.
īThey do not cause Ca++ to enter the smooth muscles so by
themselves cause no muscle contraction.They mainly excite
the appearance of intermittent spike potentials.
īOccur at different frequency
stomach (3/min)
small intestine (duodenum, 12/min)
ileum & colon (8-9/min).
16
17. .
17
īCaused by complex interactions among smooth muscle
cells and specialized cells called Interstitial Cells Of
Cajal (Electrical Pacemaker).
īThese interstitial cells form a network with each
other and are interposed between the smooth muscle
layers, with synaptic-like contacts to smooth muscle
cells.
īThe interstitial cells of Cajal undergo cyclic changes in
membrane potential due to unique ion channels that
periodically open and produce inward (pacemaker)
currents that may generate slow wave activity.
19. Spike Potentials
ī The spike potentials are true action potentials.
īThey occur automatically when the resting membrane
potential of the gastrointestinal smooth muscle becomes more
positive than about â40 millivolts (the normal resting
membrane potential((â50 â60 ml.volts).
īSpike potentials appear on the peaks of slow waves.
īThe higher the slow wave potential rises, the greater the
frequency of the spike potentials, usually ranging between 1
and 10 spikes per second.
īThe spike potentials last 10 to 40 times as long in
gastrointestinal muscle as the action potentials in large nerve
fibers, with each gastrointestinal spike lasting as long as 10 to
20 milliseconds.
19
21. Figure 62-3; Guyton & Hall
Each time the peaks of the
slow waves temporarily
become more positive
than -40 millivolts, spike
potentials appear on these
peaks
The higher the
slow wave
potential rises, the
greater the
frequency of the
spike potentials,
usually ranging
between 1 and 10
spikes per second.
22. .
ī§ Factors that depolarize the membrane:
ī Stretching of the muscle
ī Ach
ī Parasympathetic stimulation
ī Hormonal stimulation
ī§ Factors that hyperpolarize the membrane:
ī Norepinephrine
ī Sympathetic stimulation
22
23. Contractions in Gastrointestinal Smooth Muscles
ī Phasic contractions
īPeriodic contractions followed by relaxation; such as in gastric
antrum, small intestine and esophagus
ī Tonic contractions
ī Maintained contraction without relaxation; such as in orad
region of the stomach, lower esoghageal, ileocecal and
internal anal sphincter
ī Not associated with slow waves .
- Caused by:
âĸ Continuous repetitive spike potential
âĸ Hormonal effects
âĸ Continuous entery of Ca ions.
23