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Published byJourney Atwell Modified over 10 years ago
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Smooth muscle surrounds the major hollow 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 drugs metabolites Diverse Functions Smooth Muscle
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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
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Rhythmic Changes in Smooth Muscle Membrane 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
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membrane potential mV Force (gms) tetrodotoxin slow waves spikes Slow Waves Exhibited in Duodenal Visceral Smooth Muscle Cells
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Digestive Inter-digestive Patterns of Contractility Patterns of Motor Activity
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Digestive Inter-digestive Patterns of Contractility Tonic Phasic Force (gms) Patterns of Motor Activity
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Peristalsis: Propulsive Movements- Central Coordination Rhythmic Segmentation: Mixing and Slow Propulsion- Local Control Paced by Slow Wave Frequency Patterns of Motor Activity
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Reservoir: Colon, Proximal Stomach Mixing: Distal Stomach, Small and Large Intestine Propulsion: Distal Stomach through Colon, Esophagus 3 Functions of Motility
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Proximal Stomach -Reservoir: Receptive Relaxation Distal Stomach -Mixing and Grinding -Regulation of Emptying
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Distal Esophagus LES Proximal Stomach mm Hg Intraluminal pressure mm Hg Swallow Basal Tone Relaxation Basal Tone Seconds 0 0 0 mm Hg
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Minutes Fraction in Stomach Solid Liquid 1.0 0.8 0.6 0.4 0 0.2 0 3060 90 120 150180 Distal Stomach
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Volume Remaining in Stomach % Minutes pH 2.0 pH 4.0 pH 7.0 100 50 0 0 1020 Gastric Emptying
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Peristalsis: Propulsive Movements- Central Coordination Rhythmic Segmentation: Mixing and Slow Propulsion- Local Control Paced by Slow Wave Frequency Patterns of Motor Activity
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cycles /min Duodenum Pylorus Ileocecal Junction Jejunum Ileum 12 11 10 9 8 : Mixing and Movement SLOW WAVE FREQUENCY
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Haustrations: Proximal Colon- Mixing Mass Movements: Propulsive Contractions :: Rectosphincteric Reflex Motility within the Large Intestine
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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
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Esophagus: Seconds Stomach: 1-3 Hours Small Intestine: 3-5 Hours Colon: 1-3 Days Transit Times During Digestion/Absorption of a Meal
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I 45 - 60 0 II 30 - 45 50 III 5 - 10 100 MMC Phase Duration (min) % Slow Waves with Spikes Myoelectric Activity Contraction Amplitude mm Hg mV Time Inter-Digestive Period: Temporal Patterns of Motility
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Phase III MINUTES Phase III Inter-Digestive Period: Migrating Motor Complex.
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Endogenous Motilin MMCs Duodenum Prox. Jejunum Mid Jejunum Intravenous Motilin Phase IPhase IIPhase III hours Exogenous motilin stimulates both MMCs and endogenous motilin release Inter-Digestive Period: Migrating Motor Complex
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