General principles of gastrointestinal motility

Transcription

1 General principles of gastrointestinal motility

2 OBJECTIVES Physiological anatomy General Principles Circulation of blood through the GIT organs Control of all GIT functions by local, nervous, and hormonal systems Movement of food through alimentary tract Secretion of digestive juices Digestion of food Absorption of water, various electrolytes, and digested products

3 Functions of Alimentary tract Provides water, electrolytes, vitamins, and nutrients HOW? movement of food secretion of digestive juices absorption of water, various electrolytes, vitamins, and digestive products circulation of blood control.. by local, nervous, and hormonal systems

4

5 Digestive System Digestive Tract: Long tube from mouth to anus Accessory Organs: Teeth, Tongue, Salivary Glands, Liver, Gall bladder, Pancreas. Primary Organs: Mouth, pharynx, esophagus, stomach, small intestine, large intestine

6 Physiological anatomy From outer surface inward: the serosa a longitudinal smooth muscle layer, a circular smooth muscle layer the submucosa mucosa

7

8 Layers of the intestinal wall

9 Layers of the intestinal wall 1. Serosa (Peritoneum) 2. Longitudinal muscle (Muscularis Externa) 3. Circular muscle (Muscularis Interna) 4. Submucosa 5. Mucosa Myenteric Plexus/Auerbach Plexus Submucous Plexus/Meissner s Plexus i. Muscularis mucosa ii. Lamina propria iii. Epithelium

10 Typical cross section of the gut

11 Layers of the Intestinal Wall

12 Pharynx to Anus Similar structure Exception: No serosa on esophagus & distal rectum

13 GIT smooth muscle Structure Action potential

14 Smooth Muscles Generally Divided into Two Types 1.Multiunit smooth muscle. Composed of : discrete, Independent fibers innervated by separate single nerve ending e.g Iris Piloerector muscle

15 Unitary Smooth Muscle 2.Unitary: fibers contract as a unit.

16 GIT smooth muscle Each muscle fiber Length: micrometer Diameter: 2-10 micrometer Arranged in bundles of 1000 parallel fibers approx. Longitudinal ms layer Horizontal

17 Gastrointestinal Smooth Muscle Functions as a Syncytium Gap junctions Low resistance to movement of ions Rapid spread along length of bundle each muscle layer represents a branching latticework of smooth muscle bundles each muscle layer functions as a syncytium distance travelled depends on the excitability of the muscle

18 Electrical activity of GIT Smooth Muscle 1. Slow waves 2. Spike potentials

19 Slow waves (Basic Electrical Rhythm) (BER) GIT contractions occur rhythmically Not Action Potentials Slow, undulating changes in RMP Intensity: 5-15 mv Frequency: 3-12/min (3/min body of stomach, 12/min in duodenum,8-9/min in terminal ileum) Cause:? electrical pacemakers (interstitial cells of Cajal) Do not cause muscle contraction (except in stomach?) Excite the appearance of intermittent spike potential

20 Spike Potentials True Action Potentials When RMP >+ve than -40 mv ( RMP: -50 to -60 mv) Frequency: 1-10/sec Duration: ms (10-40 times of large nerve fibers) Calcium-sodium channels

21 Changes in voltage of RMP -56 mv ( mv) Depolarization Potential becomes less negative 1. Stretching of muscle 2. Acetylcholine 3. Parasympathetic stimulation 4. GIT Hormones

22 Changes in voltage of RMP -56 mv ( mv) Hyperpolarization Potential becomes more negative Catechloamines Sympathetic stimulation

23 Calcium Ions and Muscle Contraction Slow waves: Sodium ions only; no contraction Spike Potentials: Calcium ions; Contraction Ca ions act through Calmodulin control mechanism Actin/ moysin filaments

24 Tonic Contraction of some GIT Smooth muscle As well as or instead of rhythmical contractions Continuous Several minutes to hours Not associated with basic electrical rhythm of slow waves Caused by 1. Continuous repetitive spike potentials 2. Hormones---continuous partial depolarization not causing AP 3. Continuous entry of calcium ions into the cell but not associated with changes in membrane potential

25 Select true or false 1. Slow waves are true action potentials. T/F 2. Spike potentials occur when resting membrane potential become more positive than -40 mv. T/F 3. Depolarization causes smooth muscle of GIT more excitable. T/F 4. Hyperpolarization causes smooth muscle of GIT more excitable. T/F 5. Depolarization is caused by sympathetic stimulation. T/F 6. Depolarization is caused by parasympathetic stimulation T/F 7. Hyperpolarization is caused parasympathetic stimulation. T/F

26