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Smooth Muscle

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.

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Smooth Muscle

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  1. 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

  2. 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

  3. Slow Waves Rhythmic Changes in Smooth Muscle Membrane Potential Interstitial Cells of Cajal (ICC): Pacemaker Cells with Ion Channel Characteristics Similar to SA node cells Inhibitory Input from Myenteric Inter-neurons Limits the Level of Depolarization

  4. Slow Waves Exhibited in Duodenal Visceral Smooth Muscle Cells tetrodotoxin spikes membrane potential slow waves mV Force (gms)

  5. Patterns of Motor Activity DigestiveInter-digestive Patterns of Contractility

  6. Patterns of Motor Activity DigestiveInter-digestive Patterns of Contractility Phasic Tonic Force (gms)

  7. Patterns of Motor Activity Peristalsis: Propulsive Movements- Central Coordination Rhythmic Segmentation: Mixing and Slow Propulsion- Local Control Paced by Slow Wave Frequency

  8. 3 Functions of Motility Reservoir: Colon, Proximal Stomach Mixing: Distal Stomach, Small and Large Intestine Propulsion: Distal Stomach through Colon, Esophagus

  9. Proximal Stomach Reservoir: Receptive Relaxation Distal Stomach Mixing and Grinding Regulation of Emptying

  10. Intraluminal pressure Swallow Distal Esophagus mm Hg 0 mm Hg LES 0 Basal Tone Basal Tone Relaxation Proximal Stomach mm Hg 0 Seconds

  11. Distal Stomach 1.0 0.8 Solid 0.6 Fraction in Stomach 0.4 Liquid 0.2 0 0 90 150 180 30 60 120 Minutes

  12. Gastric Emptying 100 pH 2.0 Volume Remaining in Stomach % 50 pH 4.0 pH 7.0 0 0 10 20 Minutes

  13. Patterns of Motor Activity Peristalsis: Propulsive Movements- Central Coordination Rhythmic Segmentation: Mixing and Slow Propulsion- Local Control Paced by Slow Wave Frequency

  14. : Mixing and Movement SLOW WAVE FREQUENCY 12 11 cycles /min 10 9 8 Ileum Duodenum Jejunum Ileocecal Junction Pylorus

  15. Motility within the Large Intestine Haustrations: Proximal Colon- Mixing Mass Movements: Propulsive Contractions :: Rectosphincteric Reflex

  16. Primary Role of Individual Sphincters 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

  17. Transit Times During Digestion/Absorption of a Meal Esophagus: Seconds Stomach: 1-3 Hours Small Intestine: 3-5 Hours Colon: 1-3 Days

  18. MMC Phase Duration (min) Inter-Digestive Period: Temporal Patterns of Motility I 45 -60 0 II 30 -45 50 III 5 -10 100 % Slow Waves with Spikes Myoelectric Activity mV Contraction Amplitude mm Hg Time

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

  20. Inter-Digestive Period: Migrating Motor Complex Intravenous Motilin Endogenous Motilin MMCs Duodenum Prox. Jejunum Mid Jejunum hours Phase I Phase II Phase III • Exogenous motilin stimulates both MMCs and endogenous motilin release

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