Physiology of GIT:Gastro intestinal wall including many layers :- Serosa-Longtudinal muscle layer& Circular m. layer- Submucosa- Mucosa , a layer of smooth muscle lies in the deeper layer of

mucosa called (muscularis mucoasa).The motor function of the gut performed by different layer of

smooth muscle..The smooth muscle fibers arranged in bundles , they extends longitudinally down the intestinal tract in the longitudinal m. layer, & arranged around the gut in the circular m. layer .Within each bundle the muscle fiber electrically connected with one another through large number of gab junction that allow low resistance movements of ions from one cell to the next. therefore electrical signals can travel readily from one fiber to the next within each bundle but more rapidly along the length of the bundle than sideways.

Each bundle of smooth separated from the next by loose connective tissue but the bundle fuse With one another at many points , therefore each muscle layer function as syncytium , that is when an action potential is elicited anywhere within the muscle mass , it generally travels in all directions in the muscle.the distance that it travels depends on the excitability.

Autonomic control of GIT:Autonomic control of GIT: The parasympathetic supply of GIT is divided into cranial The parasympathetic supply of GIT is divided into cranial

& sacral divisions, except for few parasympathetic fibers & sacral divisions, except for few parasympathetic fibers to the mouth & pharangeal regions , the cranial to the mouth & pharangeal regions , the cranial parasympathetic transmitted almost entirely in the vagus parasympathetic transmitted almost entirely in the vagus nerve, these fibers provide innervation to the nerve, these fibers provide innervation to the esophagus ,stomach pancreas & somewhat less to the esophagus ,stomach pancreas & somewhat less to the intestine down through the 1intestine down through the 1stst half of large intestine half of large intestine

,the sacral parasympathetic originate in the S2, S3 &S4 ,the sacral parasympathetic originate in the S2, S3 &S4 segment of spinal cord .segment of spinal cord .

The parasympathetic neurone of parasympathetic The parasympathetic neurone of parasympathetic system located in the myenteric &submucosal plexuse, system located in the myenteric &submucosal plexuse, stimulation of parasympathetic nerve generally cause stimulation of parasympathetic nerve generally cause increase in activity of enteric nervouse system.increase in activity of enteric nervouse system.

The sympathetic fiber of the of the GIT originate from The sympathetic fiber of the of the GIT originate from segment T-5 & L-2 of spinall cord .segment T-5 & L-2 of spinall cord .

Hormonal control of GIT motility:Hormonal control of GIT motility:

1- cholecystokiniin:(cck): secreted by the mucosa of 1- cholecystokiniin:(cck): secreted by the mucosa of duodenum& jejunum in response to the presence duodenum& jejunum in response to the presence of some substances in the intestinal contents. it of some substances in the intestinal contents. it has a potent effect in increasing the contractility has a potent effect in increasing the contractility of GB, also it inhibit the stomach motility.of GB, also it inhibit the stomach motility.

2- secretin secreted by S cell in the mucosa of 2- secretin secreted by S cell in the mucosa of duodenum in response to gastric acid juice , it has duodenum in response to gastric acid juice , it has inhibitory effect on most of GIT.inhibitory effect on most of GIT.

3- gastric inhibitory peptide:secreted by the mucosa 3- gastric inhibitory peptide:secreted by the mucosa of upper S.I. ,it has mild effect in decreasing motor of upper S.I. ,it has mild effect in decreasing motor activity of stomach .activity of stomach .

Transport & mixing of food in the GIT:Transport & mixing of food in the GIT:

Mastication (chewing):Mastication (chewing):

The teeth are designed for chewing , the The teeth are designed for chewing , the anterior (incisors) provide strong cutting anterior (incisors) provide strong cutting action & the posterior (molars)provide action & the posterior (molars)provide granding action . Most of chewing process granding action . Most of chewing process caused by caused by chewing reflex chewing reflex which can be which can be explained as that : the presence of bolus of explained as that : the presence of bolus of food in the mouth initiates reflex inhibition to food in the mouth initiates reflex inhibition to the muscle of mastication which allow the the muscle of mastication which allow the lower jaw to drop, the drop in turn initiates a lower jaw to drop, the drop in turn initiates a stretch reflex of the jaw muscle that leads to stretch reflex of the jaw muscle that leads to rebound contraction & , this automatically rebound contraction & , this automatically

raises the jaw to cause closure of the teeth, raises the jaw to cause closure of the teeth, but it also compress the bolus again but it also compress the bolus again against the lining of the mouth, which against the lining of the mouth, which inhibit the jaw muscle once again inhibit the jaw muscle once again allowing the jaw to drop &rebound again allowing the jaw to drop &rebound again

Chewing is important for digestion of all foodChewing is important for digestion of all foodbut it especially important for most fruit ,raw but it especially important for most fruit ,raw vegetables because these have undigested vegetables because these have undigested cellulose membrane around their nutrient cellulose membrane around their nutrient portions that must be broken before the foodportions that must be broken before the foodcan be used , the digestive enzyme act only can be used , the digestive enzyme act only on the surface of food particles,the rate of on the surface of food particles,the rate of digestion is highly depenndent on the total digestion is highly depenndent on the total surface area exposed to the intestinal surface area exposed to the intestinal secretion .secretion .

Swallowing (deglutition):Swallowing (deglutition):

1- voluntary stage1- voluntary stage

When the food is ready for swallowing it isWhen the food is ready for swallowing it is

voluntary squeezed or rolled posteriorly involuntary squeezed or rolled posteriorly in

to the pharynx by pressure of tongue to the pharynx by pressure of tongue

upward & bachward against the palate.upward & bachward against the palate.

2- pharangeal stage of swallowing (involuntary)2- pharangeal stage of swallowing (involuntary)

When the bolus of food enter the pharynx it When the bolus of food enter the pharynx it stimulate the swallowing receptors arround stimulate the swallowing receptors arround the opening of pharynx & send signals to the the opening of pharynx & send signals to the brain stem to initiate swallowing brain stem to initiate swallowing

3- pharangeal stage of swallowing .3- pharangeal stage of swallowing .

Function of lower esophageal sphincterFunction of lower esophageal sphincter((gasrtoesophageal sphincter GOS)gasrtoesophageal sphincter GOS)::at the lower 2 -5 cm of esophagus above its at the lower 2 -5 cm of esophagus above its

junction with stomach , the circular muscle junction with stomach , the circular muscle function as sphincter , this sphincter function as sphincter , this sphincter remain tonically consrticted in contrast to remain tonically consrticted in contrast to the mid part of esophagus which remain the mid part of esophagus which remain relaxed .relaxed .

when peristaltic wave pass down the when peristaltic wave pass down the esophagus ,receptive relaxation relax the esophagus ,receptive relaxation relax the LOS ,& allow propulsion of swallowed food LOS ,& allow propulsion of swallowed food to the stommach.if LOS faild to relax result to the stommach.if LOS faild to relax result in condition known as in condition known as achalassiaachalassia..