1. Gastrointestinal system
Xiang-Yao LI, PhD
Department of Physiology
Zhejiang University School of Medicine

2. Accessory Digestive Organs
Alimentary Canal
Continuous, muscular digestive tube winding throughout the body
Digests and absorbs food particles
Contains the following organs:
Mouth,
Pharynx,
Esophagus,
Stomach,
Small Intestine
Large Intestine
Accessory Digestive Organs
Teeth,
Tongue,
Salivary Glands
Liver,
Gallbladder,
Pancreas

3. General properties of gastrointestinal smooth muscle
Low excitability
High distensibility
Tonic contraction
Autorhythmicity
High sensitivity to temperature, stretch and chemical stimulation

4. Electrophysiological properties of gastrointestinal smooth muscle
Resting membrane potential
-40~-80 mV
Ionic basis
Em (selective membrane permeability to K+, Na+, Cl- and Ca2+)
Electrogenic Na+-K+ pump

6. Slow wave (basic electrical rhythm)
The spontaneous rhythmic, subthreshold depolarizations of the cell membrane (slow wave) of the gastrointestinal tract that characterizes the underlying electrical activity of the bowel
Initiated in the interstitial cells of Cajal (ICC) (pacemaker cell)

7. Santiago Ramon Y Cajal
He and Camillo Golgi received the Nobel Prize in 1906 for introduction of the silver-chromate stain

8. Slow wave (basic electrical rhythm)
Intensity: 10~15 mV
Frequency: 3~12 cpm
Ionic mechanism
spontaneous rhythmic changes in Na+-K+ pump activity

10. Normal BER frequencies in the gastrointestinal system

11. Spike potential (Action potential)
Duration: 10~20 ms
Ionic mechanism:
Depolarization: Ca2+ influx
Repolarization: K+ efflux

13. The digestion and absorption
Carbohydrate
About g/day:
Plant polysaccharides starch (2/3), Disaccharides: sucrose, lactose (1/3)
Mouth(5%) + Small intestine (95%)
Amylase
Brush border enzymes
Cellulose (fiber)
Large intestine
Bacteria

15. Proteins

16. Proteins

17. Fat

18. Fat

20. Neural control of gastrointestinal function
Enteric nervous system (intrinsic)
Autonomic nervous system (extrinsic)

23. Enteric (Intrinsic) nervous system
Myenteric plexus (Auerbach’s plexus)
Submucosal plexus (Meissner’s plexus)
Neurotransmitters secreted by enteric neurons
Ach, NE, ATP, serotonin, dopamine, cholecystokinin, substance P, vasoactive intestinal polypeptide, somatostatin, leu-enkephalin, met-enkephalin, bombesin, etc.

26. Autonomic nervous system
Parasympathetic nerve
Mainly ACh
Stimulatory (+)
Sympathetic nerve NE
Inhibitory (-)

27. Afferent sensory nerve fiber from the gut
Sensory fibers with their cell bodies in the ENS terminate in the ENS
Sensory fibers with their cell bodies in the ENS send axons upward through the ANS to terminate in the prevertebral sympathetic ganglia
Sensory fibers with their cell bodies in the dorsal root ganglia or in the cranial nerve ganglia send axons to multiple area of the spinal cord or brain stem

29. Gastrointestinal reflexes
Three types
Reflexes that are integrated entirely within the enteric nervous system
Reflexes from the gut to the prevertebral sympathetic ganglia and then back to the gastrointestinal tract
Reflexes from the gut to the spinal cord or brain stem and then back to the gastrointestinal tract

30. Gastrointestinal hormones
The hormones synthesized by a large number of endocrine cells within the gastrointestinal tract
Physiological functions
Control of the digestive function
Control of the release of other hormones
Trophic action

31. Gastrointestinal hormones
Four main types
Gastrin
Secretin
Cholecystokinin (CCK)
Gastric inhibitory peptide (GIP)

34. Digestion in the stomach

35. Difficult to see food bolus (raw liver
Difficult to see food bolus (raw liver?)– can a brighter color be used (blueberry yogurt)?
The swallowing reflex is coordinated by the medulla oblongata, which stimulates the appropriate sequence of contraction and relaxation in the participating skeletal muscle, sphincters, and smooth muscle groups.

36. The coordinated sequence of contraction and relaxation in the upper esophageal sphincter, the esophagus, and the lower esophageal sphincter is necessary to deliver swallowed food to the stomach.

37. End.