1. Digestive system I

2. Alimentary tract Continuous provision Achieved by Water Electrolytes
Nutrients
Achieved by
Movement of food
Digestion
Mechanical and chemical
Absorption
Transport

3. Anatomical structures

4. Smooth muscles within the GI tract
Layers
Longitudinal
Length-wise
Circular
Formation of syncitium
Each fiber within respective layer
Connected via gap junctions
Ion movement

5. Contraction of GI smooth muscles
Continual, slow intrinsic electrical activity
Slow waves
Not action potentials
Too low
Generated by the interaction of interstitial cells of Cajal
Periodic openings of channels
Do not usually cause muscle contraction

6. Contraction of GI smooth muscles
Continual, slow intrinsic electrical activity
Spike potentials
Action potentials
Generated when the resting potential goes over -40 mV
Greater the rise in resting potential, greater the frequency
Lasts longer than normal action potential (10-20 mSec)
Generated by the movement of calcium ions
Slower channels

7. Changes in resting potentials
Depolarization
Stretching of muscle
Acetylcholine
Stimulation of parasympathetic nerves
GI hormones
Hyperpolarization
Epinephrine and norepinephrine
Stimulation of sympathetic nerves

8. Role of calcium ions Tonic Entrance to cells
Slow waves
No muscle contraction
Spike potentials
Tonic
Continuous but not associated with slow waves
Continuous repetitive spike potentials
Hormones and other factors
Continuous entry of calcium ions
Not associated with changes in membrane potential

9. Enteric nervous system
Regulation
GI tract movement
GI tract secretion

10. Movement
Afferent
Fibers
(local and other reflexes)
Secretion
Local
Blood flow

11. Myenteric plexus Mostly linear chain
Extends entire length of the GI tract
Controls muscle activity along the length of the GI tract
Tonic contraction/tone of the wall
Intensity
Rhythm (slight)

12. Myenteric plexus Movement of peristalic wave Inhibitory neurons
Increased conduction velocity of excitatory wave
Inhibitory neurons
Secretion of inhibitory peptide
Inhibition of sphincters
Inhibits food movement

13. Submucosal plexus
Local functions
Absorption
Secretion
Contraction

14. Role of ANS Parasympathetic Cranial Sacral Excitation Vagus
Esophagus, stomach, and pancreas
Sacral
Large intestine and anus
Defecation reflex
Excitation
Increased activity

15. Sympathetic T5 and L2 of spinal cord Celiac and mesenteric ganglia
Essentially innervates entire GI tract
Excitation
Inhibition of activity
Smooth muscle
Neurons of enteric nervous system T5 L2

16. Neurotransmitters Aceylcholine Norepinephrine/epinephrine Excitation
Inhibition

17. Afferent sensory nerve fibers
Activation
Irritation of mucosa
Distention
Chemicals
Inhibition or activation
Transmission of information to the CNS
Afferent vagus nerves (80 %)

18. Role of enteric nervous system
Generation of reflexes
Integrated within the enteric nervous system
Local reflex
Loop between the prevertebral sympathetic ganglia and GI tract
Signals from lower portion of the GI tract to regulate activity of the upper GI tract or vise versa

19. Loop between the spinal cord/brain stem and the GI tract
Vagus nerves from the stomach to the brainstem
Pain reflex (inhibitory)
Defecation reflex

20. Movement within the GI tract
Propulsive movement
Peristalsis
Generated in response to GI tract distension
Requires active myenteric plexus
Formation of the contractile rings
Receptive relaxation
Polarized movement
Move in one direction

21. Mixing movement Inhibition of peristalisis forward movement
Sphincter
Churning of the content within the segment
Local intermittent constrictive contractions

22. Splanchnic circulation
Flow of blood
Afferent flow
The GI tract
Pancreas
Spleen
Enters liver via the portal vein
Flow through liver sinusoids
Exits liver via hepatic veins
Vena cava

23. Absorption of nutrients
Water soluble molecules
75 % temporally stored in liver
Fats
Intestinal lymphatics
Enters circulation via thoracic duct

24. Arterial supply to the GI tract
Mesenteric arteries (superior and inferior)
Intestines
Celiac artery
Stomach
Branches of arteries
Muscle bundles
Intestinal villi
Submucosal vessels

25. Rate of flow Proportional to activity levels Increased flow
Active absorption increases flow by max. 8 X
Increased flow
Vasodilators
Decreased tissue oxygen concentrations

26. Counter-current exchange of oxygen
Diffusion of oxygen from arterioles to venules without going through circulation
Bypassed oxygen is not available for tissue metabolism

27. Neural regulation Parasympathietic stimulation Sympathetic stimulation
Increased flow
Increased glandular secretions
Cause of increased flow
Sympathetic stimulation
Decreased flow
Vasoconstriction
Overcome by local vasodilators
Local ischemia
Allows re-direction of blood