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

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 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

membrane potential mV Force (gms) tetrodotoxin slow 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 Phasic Force (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

Distal Esophagus LES Proximal Stomach mm Hg Intraluminal pressure mm Hg Swallow Basal Tone Relaxation Basal Tone Seconds mm Hg

Minutes Fraction in Stomach Solid Liquid Distal Stomach

Volume Remaining in Stomach % Minutes pH 2.0 pH 4.0 pH 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 Ileocecal Junction Jejunum Ileum : 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

I II III MMC Phase Duration (min) % Slow Waves with Spikes Myoelectric Activity Contraction Amplitude mm Hg mV Time Inter-Digestive Period: Temporal Patterns of Motility

Phase III MINUTES Phase III Inter-Digestive Period: Migrating Motor Complex.

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