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Digestive Physiology

Digestive Physiology. By: M.H.Dashti . Lecture 4. Physiological functions of pancrease & large intestine . Digestion & Absorption of Fat products in Small Intestine. Final Digestion & Absorption in Of Carbohydrates in Small Intestine.

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Digestive Physiology

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  1. Digestive Physiology By: M.H.Dashti Lecture 4 Physiological functions of pancrease & large intestine

  2. Digestion & Absorption of Fat products in Small Intestine

  3. Final Digestion & Absorption in Of Carbohydrates in Small Intestine Monosaccharides leave the basolateral Membrane via GLUT-2

  4. Final Digestion & Absorption of Protein products in Small Intestine

  5. Chemical Digestion in Small Intestine:Nucleic Acids • Pancreatic juice convert RNA & DNA to Nucleotides by Ribonuclease & Deoxyribonuclease • brush border enzymes (nucleosidease and phosphatase) converts Nucleotides to pentose, phosphate & nitrogenous bases

  6. Absorption of vitamin B12

  7. absorption of Fe2+ in small intestine iron transporter DMT1, heme transporter (HT), heme oxidase (HO) , ferroportin (FP) ,hephaestin (Hp), transferrin (TF)

  8. absorption of Ca2+ in small intestine is controlled by vitamin D3

  9. Sodium absorption in ileum is coupled to choloride absorption Sodium absorption in jejunum is coupled to glucose , amino acid & bicarbonate absorption

  10. Absorption of Water • 9 liters of fluid dumped into GI tract each day • Small intestine reabsorbs 8 liters • Large intestine reabsorbs 90% of that last liter • Absorption is by osmosis through cell walls into vascular capillaries inside villi

  11. Where will the absorbed nutrients go?

  12. Ileocecal sphincter • Controlled by pressure differences • Neural events • Ileo -colic & colono-ileal reflexes • Ileo- gastricic & gastro-ileal reflexes • Ileal break • Oxyntomodulin & neurotensin

  13. Anatomy of Large Intestine • 5 feet long by 2½ inches in diameter • Ascending & descending colon are retroperitoneal • Cecum & appendix • Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx • Anal canal = last 1 inch of GI tract • internal sphincter----smooth muscle & involuntary • external sphincter----skeletal muscle & voluntary control

  14. Digestion in Large Intestine • No enzymes are secreted only mucous • Bacteria ferment • undigested carbohydrates into carbon dioxide & methane gas • undigested proteins into simpler substances (indoles)----odor • turn bilirubin into simpler substances that produce color • Bacteria produce vitamin K and B in colon

  15. Absorption & Feces absorption in the Large Intestine • Some electrolytes---Na+ and Cl- • After 3 to 10 hours, 90% of H2O has been removed from chyme • Feces = dead epithelial cells, undigested food such as cellulose, bacteria (live & dead)

  16. Presence of food in the stomach Stomach Presence of chyme in the duodenum Gostric stimulation (activates gastrocolic reflexes) Colon Duodenocolic stimulation (activates Duodenocolic reflexes) Moss movements Stimulation of local defecation reflexes Feces Stimulation parasympathetic controlled defecation reflexes Rectum Large intestine motility • Haustral churning • BER (3 to 18/min) • haustral shuttling • Multihustral contraction in ascending colon • Mass movement • Mainly starts in the pacemaker site at the beginning of transverse colon • Affected by gastrocolic reflex • Defecation reflex • Local & central

  17. Defecation • Gastrocolic reflex moves feces into rectum • Stretch receptors signal sacral spinal cord • Parasympathetic nerves contract muscles of rectum & relax internal anal sphincter • External sphincter is voluntarily controlled

  18. Pressures in the Rectum

  19. Neural pathways of defecation reflex

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