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Smooth Muscle. Smooth muscle surrounds the major hollow organs - including: blood vessels, bronchi, gut, uterus, bladder. Diverse Functions. Responsive to a variety of stimuli: neural input (autonomic and enteric nervous systems) broad array of hormones and drugs metabolites. - PowerPoint PPT Presentation
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Smooth muscle surrounds the majorhollow organs - including: blood vessels,bronchi, gut, uterus, bladder.
Responsive to a variety of stimuli:neural input (autonomic and enteric
nervous systems)broad array of hormones and drugsmetabolites
Diverse Functions
Smooth Muscle
Smooth Muscle – Non-Striated
Arteries – blood vessels
Lines Hollow Organs
- Uterus
- Alimentary Canal
Lines Ducts of Secretory Glands – e.g. Salivary
- Maintain Tension for long periods
- Rhythmically Contract to Propel Contents
- Speed of Contraction 10X less than striated muscle
* Coupled into a syncitium by gap junctions
Rhythmic Changes in Smooth MuscleMembrane Potential
Inhibitory Input from Myenteric Inter-neurons Limits the Level of Depolarization
Interstitial Cells of Cajal (ICC): Pacemaker Cells with Ion Channel Characteristics Similar to SA node cells
Slow Waves
membranepotential
mV
Force (gms)
tetrodotoxinslow waves spikes
Slow Waves Exhibited in Duodenal Visceral Smooth Muscle Cells
• Digestive Inter-digestive
• Patterns of Contractility
Patterns of Motor Activity
• Digestive Inter-digestive
• Patterns of Contractility
Tonic PhasicForce (gms)
Patterns of Motor Activity
Peristalsis: Propulsive Movements- Central Coordination
Rhythmic Segmentation:
Mixing and Slow Propulsion- Local Control
Paced by Slow Wave Frequency
Patterns of Motor Activity
• Reservoir: Colon, Proximal Stomach
• Mixing: Distal Stomach, Small and Large Intestine
• Propulsion: Distal Stomach through Colon, Esophagus
3 Functions of Motility
• Proximal Stomach- Reservoir: Receptive Relaxation
• Distal Stomach- Mixing and Grinding- Regulation of Emptying
DistalEsophagus
LES
ProximalStomach
mmHg
Intraluminalpressure
mmHg
Swallow
BasalTone Relaxation
BasalTone
Seconds
0
0
0
mmHg
Minutes
Fra
ctio
n in
Sto
mac
h
Solid
Liquid
1.0
0.8
0.6
0.4
0
0.2
0 30 60 90 120 150 180
Distal Stomach
VolumeRemaining in Stomach
%
Minutes
pH 2.0
pH 4.0
pH 7.0
100
50
0
0 10 20
Gastric Emptying
Peristalsis: Propulsive Movements- Central Coordination
Rhythmic Segmentation:
Mixing and Slow Propulsion- Local Control
Paced by Slow Wave Frequency
Patterns of Motor Activity
cycles/min
Duodenum
Pylorus IleocecalJunction
Jejunum Ileum
12
11
10
9
8
: Mixing and Movement
SLOW WAVE FREQUENCY
Haustrations: Proximal Colon- Mixing
Mass Movements: Propulsive Contractions
:: Rectosphincteric Reflex
Motility within the Large Intestine
Lower Esophageal: Retard Gastric (LES) Retropulsion
Pyloric: Retard Gastric Emptying
Ileocecal: Retard Colonic Retropulsion
Internal Anal: Regulate Emptying Into the Rectum
External Anal: Regulate Defecation
Primary Role of Individual Sphincters
Esophagus: Seconds
Stomach: 1-3 Hours
Small Intestine: 3-5 Hours
Colon: 1-3 Days
Transit Times During Digestion/Absorption of a Meal
I45 - 60
0
II30 - 45
50
III5 - 10100
MMC PhaseDuration (min)% Slow Waves
with Spikes
MyoelectricActivity
ContractionAmplitude
mm Hg
mV
Time
Inter-Digestive Period: Temporal Patterns of Motility
Phase III
MINUTES
Phase III
Inter-Digestive Period: Migrating Motor Complex.
EndogenousMotilin
MMCsDuodenum
Prox. Jejunum
Mid Jejunum
Intravenous Motilin
Phase I Phase II Phase III
hours
• Exogenous motilin stimulates both MMCs and endogenous motilin release
Inter-Digestive Period: Migrating Motor Complex
