Gastrointestinal and digestion

Gastrointestinal and digestion

1. GI Tract

   • Digest
     • Absorb
       • Metabolism
         • Excretion
           • Secretion

2. Liver

   • 1.Processing of nutrients
     • Lipid break down
       • Triglycerides + cholestorel
       • Lypoproteins
   • Carb breakdown, glycogenisis
     • Eat, high levels of insulin (From pancreas) Low levels of Glucagon
   • Stores Glycogen
     • Turns to glucose
   • Protein breakdown
     • Gut breaks down protein to Amino acids
       • Liver puts them back to either functional proteins or pre-hormone proteins
   • 2. Synthetic function of liver
     • Albumin
     • Coagulation Factors
       • Fibrinogen
         • Vit K dependent factors 7, 9 + 10 and prothrombin
     • Transport and binding proteins
       • eg Transferrin for Iron
     • Immunologic proteins
       • Complement proteins CD4 etc
     • Bile Salts
   • Stores Vitamins/minerals
   • 3. Protection and clearence
     • Portal Vein collects crap from Intestine/colon
     • Protection from Bacteria
     • Sinusoids, lined with Kuppfer cells(macrophages)
     • Breakdown of toxins
       • By oxidisation or cleaving proteins
       • Breaksdown Amino acids into Urea
     • Produces anti-oxidants to stop too much breakdown by oxidisation

3. Pancreas

   • Drains into Dueodenum
     • Secretes Bicarb to increase pH
       • Produces pancreatic enzymes
   • Pancreas
     • Drains via the pancreatic duct into Duodenum
       • Acini Cells, secrete pancreatic juices
         • Islet of Langerhan cells
           • Endocrine part
         • Contains Zymogin granules
         • Contains Bicarb, higher than plasma (150)
           • pH 8.4
             • Which increase pH in duodenum from the high pH of stomach (7.4)
         • Acini cells contain Lipase (breaks lipids), Amalyse (Cleves starch), Pro-Proprotease(inacctive protein breaking enzyme)
         • Makes Tripsinogen
           • Acctivated by brush boarder enzymes in duodenum
             • Turns into Tripsin
               • Turns Pro-Proprotease into Protease
                 • Only happens in Duodenum

4. Mouth

   • Oesophagus
     • Stomach
       • Dueodenum
         • Jejunum
           • Illium
             • Colon

5. Gallbladder

   • Produces bile acids
     • Secretes bile salts into Dueodenum to break down fat
       • Drains via the common bile duct, with the pancreatic duct

6. Peristalsis

   • Cajal Cells (pacemaker cells of the gut)
     • Produce action potentials
       • Causes muscle cells to move
       • Baseline Rhythm
   • Myenteric plexus
     • Afferent sensory nerves
       • Above muscle layer
         • decending efferent nerves, stimulate spike wave/ action potential
           • Stimulated by
             • Reflexive (stretch/chemo recptors) Enteric system
             • Parasympathetic system Acetycholin
             • Inhibited by sympathetic system
               • Epinephrin/norepinephrin
                 • Fight or flight
       • Stretch receptors + chemoreceptors
     • Enteric nervous system Gut's own nerves
       • doesn't go to spinal cord

7. Bilirubin Pathway

   • RBC breakdown
     • Macrophage 'eats RBC
       • Globin
         • Gets recycled
       • Haem
         • Iron gets reused to make RBC
           • Leaves a Porphryin Ring
             • Ring gets broken into chain, (Bilirubin)
               • Bright yellow
               • Toxic, can't break down easily in water
                 • Attaches to Albumin molecule
                   • Goes to Liver
                     • Glucoroltransferase
                       • Makes Bilirubin more water soluble
                         • Turns into conrgigated billirubin
                           • Drains into intestine
                             • Through oxidation, turns to Steribolinogen
                               • Gets excreted
                               • Urobilinogen gets back in blood
                                 • Filtered in kidneys
                                   • Oxidises to Urobilin
                                     • Colour of Urine

8. Breakdown of Fats

   • Begins in the stomach
     • Catalised by Lipase
       • Lingual and Gastro Lipases
         • Gastro- Stomach epitelial cell secretion
           • Cholecystokinin, secreted in Duodenum (small intestine) By endocrine cells
             • Cholecystokinin Release pancreatic enzymes
               • Cholecystokinin also releases bile salts from gall bladder
                 • Stops stomach mortility, to give time for fatty acid digestion
                   • Secretin, release Bicard into duodenum to raise pH
                 • By contrating the gall bladder and squeezing it out
   • Triacylgycerol
     • Colesterol
       • Free fatty acids
         • Short and Medium chained fatty acids
     • Breaks down into
   • Emulsification
     • Bile salts make fat partly water soluble
       • Breaks down into 2 fatty acids +monoglycerides, vit A or K etc
         • 80% of bile salts recycled back to liver
         • Micelles
   • no breakdown will result in no absorbtion of fat, calcium, vit D, K etc
     • Can happen from pancreas probs-no lipase, no bicarb to change pH. From liver- no bile salts (from hepatocytes)

9. Absorbtion

   • Bicarb in the Jigunum
   • Iron in the duodenum
   • Illlium
     • B12 absorbtion+ bile salts
   • Colon excretes no digestion
     • K+, excreted
     • Sodium/water uptake
       • Aldosterone helps this (lower blood preesure trigger)
     • Enter text here

10. Acid secretion

    • Phase 1
      • Sight, smell, thought
        • Cerebral cortex
          • Stimulates a condition responce
            • In Hypothalamus, the Medula Obongata
              • Stimulates Vagus
                • Which stimulate Acetycholine
                • Parasympathetic
      • Cephalic phase
    • Phase 2, gastric
      • Physical stretching of Bolus
        • stimulate vasovagus, which stimulates Medula Obongata
        • Local reflex
          • Stimulates Acetycholin
      • Chemical receptors
        • H+ buffers released from food, carbs etc, increase pH
          • Activate G cells
            • Secrete Gastria
          • Inhibits D cells
            • Secrete Somatistat
              • Higher than pH2 will activate
    • Phase 3, intestinal
      • Gastrin secretion from epithelial mucosa
        • secretes Interagastrin
          • Histamine is also produced
          • All act on PARIETAL Cells to produce acid