Physio Gi 7,8.


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Physio Gi 7,8.

  1. 1. Gastrointestinal physiology GIT Secretions (Cont). Dr.M.A.M.Shaikhani.
  2. 2. <ul><li>Pancreatic secretions: </li></ul><ul><li>Pancreas; complex gland ( similar to salivary glands) Except of having an Endocrine part(secreting insulin& glucagons) </li></ul><ul><li>     Digestive part which consist of acini secreting digestive enzymes : </li></ul><ul><li>1.Pancreatic lipase: for digesting fats. 2.pancreatic Amylase : for digesting carbohydrates. 3.Pancreatic Trypsin,chymotrypsin,carboxypolypeptidase,elastase & neuclease : for digesting proteins. </li></ul><ul><li>secreted in an inactive form in the acini : </li></ul><ul><li>(trypsinogen,chymptrypsinogen,procarboxypolypeptidase) to prevent autodigestion of pancreas & this inactivation is facilitated by a substance called trypsin inhibitor. </li></ul>
  3. 3. Pancreas <ul><li>Endocrine </li></ul><ul><ul><li>Insulin,glucagon </li></ul></ul><ul><li>Exocrine </li></ul><ul><ul><li>Enzymes (acini) </li></ul></ul><ul><ul><li>Bicarbonate (ducts) </li></ul></ul>
  4. 4. <ul><li>Pancreatic secretions: </li></ul><ul><li>when this trypsin inhibitor is overwhelmed by pancreatic duct obstruction or pancreatic diseases or damage the proteolytic inactive enzymes are activated inside pancreatic acini leading to acute pancreatitis causing death or pancreatic insufficiency. </li></ul><ul><li>Inactive panc enzymes are only activated when they reach the SI , by an enzyme released from SI enterokinase stimulated by the presence of chyme.1 st enzyme activated is trypsinogen to active trypsin & trypsin in turn activates the other enzymes: CTP&PCP. </li></ul><ul><li>Pancreatic ductioles & ducts secreting HCO3 important for neutralizing the acid of the chyme coming to the upper SI from stomach & for preparing the optimal alkaline medium essential for digestion in SI. </li></ul><ul><li>  Regulation of pancrearic secretion: </li></ul><ul><li>I by ACH, Cholycystokinin(CCK) & Secretin. </li></ul><ul><li>ACH, Cholycystokinin(CCK) :cause secretion of mainly digestive enzymes while Secretin causes mainly secretion of large amounts of HCO3.        </li></ul>
  5. 5. <ul><li>Phases of pancreatic secretion: The same for of gastric acid secretion: 1.cephalic phase. 2.gastric phase. 3.intestinal phase. </li></ul><ul><li>stimulated by vagi,secretin & CCK. secretin released from upper SI cells ( S cells) in the presence of acidic chyme causes secretion of large amounts of HCO3 from pancreatic ducts( for neutralization of acidic chyme coming from stomach resulting in formation of Nacl & water) </li></ul><ul><li>Secretion of pancreatic enzymes mainly under the control of CCK which is secreted by SI cells (I-cells) in response to the presence of food in upper SI specially protein digestion end products(peptones, proteoses & long chain fatty acids. ) </li></ul><ul><li>vagal stimulations helps both processes but the effects of Secretin & CCK are more pronounced. </li></ul>
  6. 7. Bile secretion: It helps : fat digestion by saponification & emulsification of fats. Essential for excretion of several important waste products from blood as billirubin & cholesterol. The amount is 1000ml./day.Composition of bile:about 50% are bile salts + billirubin,cholesterol,lecithin & plasma electrolytes. In the gall bladder water & large amounts of electrolytes except Ca++ are reabsorbed by gall bladder mucosa, but the other constituents bile salts,cholesterol & lecithin are not reabsorbed so become highly concentrated .
  7. 8. The Gallbladder Figure 24.21a, b
  8. 9. Figure 24.21a, b Bile Salts and Emulsification fat globule Water (polar) bile salts fat droplets bile salt phospholipids triglycerides Increases surface area for attack by lipases. polar coating
  9. 10. <ul><li>Emptying of gall bladder: </li></ul><ul><li>Needs: </li></ul><ul><li>contraction of gall bladder wall & relaxation of sphincter of oddi(SOO) </li></ul><ul><li>CCK plays an important role in contraction of gall bladder wall & to less degree relaxation of (SOO) </li></ul><ul><li>Relaxation of (SOO) mainly in response to movement of the wall of upper SI. </li></ul>
  10. 12. <ul><li>Bile salts & their functions: </li></ul><ul><li>0.6gms. is secreted /day. </li></ul><ul><li>Synthesized from cholesterol which is converted to cholic acid & chenodeoxycholic acid & both combine with glycin or taurin to form glyco or tauro conjugated bile acids. </li></ul><ul><li>Functions: </li></ul><ul><li>The main functions is : </li></ul><ul><li>1.Emulsificatin of fats to form micelles to facilitate Fat absorption . </li></ul><ul><li>2.Secretion of some important waste products as billirubin and cholesterol. </li></ul><ul><li>The enterohepatic circulation of bile salts from the SI is through the terminal ileum TI to the liver then to SI again ,so in TI disease or removal, this enterohepatic circulation of bile salts is interupted causing bile salts deficiency and so fat malabsorption. </li></ul><ul><li>The hormone Secretin causes secretion of HCO3 & not bile acids from the bile ductioles for neutralization of excess acid coming from stomach in cooperation with the pancreatic HCO3. </li></ul>
  11. 13. Gall bladder Cholesterol Large intestine Ileum Duodenum Liver Bile salts Stomach Bile salts Bile salts Bile salts Bile salts Bile salts Sphincter of Oddi Portal circulation These salts are reabsorbed in the ileum and returned to the liver where they are once again secreted into bile  only 3-4 g of bile salts in body, thus highly recycled = active transport
  12. 14. <ul><li>Gall stones formation: </li></ul><ul><li>Is mainly due to imbalance between bile salts & cholesterol content of bile ,either more cholesterol or less bile salts so excess cholesterol will precipitate to form cholesterol gall stones. </li></ul><ul><li>Causes of gall stones: </li></ul><ul><li>1.Too much absorption of water to form concentrated bile easy to precipitate. </li></ul><ul><li>2.Too much absorption of bile acids. </li></ul><ul><li>3.Too much secretion of cholesterol into the bile mainly from diet. </li></ul><ul><li>4.Inflamation of gall bladder epithelium. </li></ul><ul><li>Medical therapy of gall stones: </li></ul><ul><li>Although the mainstay of gall stones therapy is surgery,sometimes the patient is given bile salts in form of ursodeoxycholic acid or chenodeoxycholic acid for at least 1 year, which help in redissolution of cholesterol gall stones by increasing the ratio of bile salts in relation of cholesterol. </li></ul>
  13. 15. <ul><li>Secretions of SI: </li></ul><ul><li>Of 3 types: </li></ul><ul><li>1.Brunner glands for mucose secretion. </li></ul><ul><li>2.crypts of Liberkhan for secretion of pure extracellular fluid to aid absorption of intestinal contents by active secretion of HCO3 & Cl- into the crypts these cause osmotic movement of water. </li></ul><ul><li>3.SI enzymes present on villi brush border consisting of; </li></ul><ul><li>Several different peptidases for splitting peptides into amino acids. </li></ul><ul><li>Several disaccharidases as sucrase,maltase,isomaltase and lactase. </li></ul><ul><li>Small amounts of intestinal lipase for splitting neutral fats into glycerol & fatty acids. </li></ul><ul><li>The regulation of SI secretions is by local enteric stimuli through local enteric reflexes and hormonal secretions specially Secretin & CCK. </li></ul>
  14. 16. <ul><li>Large intestinal secretions: </li></ul><ul><li>Are: </li></ul><ul><li>1.Mucose secreted by mucose cells in colonic wall . </li></ul><ul><li>The mucose protects the colonic wall from excoriation & bacterial activity and provides an adherent medium for holding feces together. </li></ul><ul><li>2.HCO3 by crypts of Liberkhan ,stimulated by tactile stimuli & pelvic PS nerves. </li></ul><ul><li>The HCO3 protects the colonic wall from acids formed deep in the feces by intestinal flora. </li></ul>