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Digestive system I.

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Presentation on theme: "Digestive system I."— Presentation transcript:

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

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

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