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Digestive System - Coggle Diagram

- - - - released when blood glucose levels are high and induces decrease in intake
    - - it is released by fat cells in propotion to how much lipid they contain
      - it is a satiety signal that acts to prevent overeating and resultant obesity
    - - it is released by stomach when it is empty
      - its levels rise before meals and fall after meals
- - - - absorbed nutrients go to the liver in the hepatic portal vein \
      - this large vein delivers the blood to small space called sinusoids between teh groups of liver cells
      - these cells absorc the nutrients and either convert them or store them
  - - - closes bile duct
      - as fat is digested, CCK is produced (CCK stimulates walls of gallbladder to contract rhythmically to squeeze out through the cystic duct to common bile duct)
      - , peristalsis moves the bile down the bile duct and the sphincter relaxes causing bile to enter the duodenal lumen
  - - - tract almost closes
      - forms lumpy bits
      - less segmentation the closer to the ileum
      - increased by gastroilleal reflex
    - - lesser activity and shorter waves
      - motilin is hormone involved
  - - - fatty acids and monoglycerides enter cell by diffusiona dn resynthesised to triglycerides in ER
      - triglycerides are packaged with cholesterol and phospholipids in chylomicrons
      - chylomicrons are encllosed in vesicles and leave the cell by exocytosis and enter lymphatic system
- - - - lingual lipase
      - 30% of triglycerides
    - - lingual lipase (still acive)
      - gastric lipase
    - - pancreatic lipase
    - - Bile emulsifies large lipid droplet (hydrophobic end sticks out to prevent aggregation)
      - forms micelles
    - - monoglycerides and fatty acids diffuse into the cell
      - triglycerides are synthesized in SER
      - combined with cholesterol, phospholipds and coated with with proteinto form chylomicron (water soluble)
      - exocytosis into lacteal
  - - - many humans stop producing lactase
      - lactose is a disaccharide that cannot be absorbed without being cleaved
      - unabsorbed lactose is metabolised by bacteria in large intesting causing gas, diarrhea adn abdominal cramps
- - - - lines the luminal surface
      - highly folded (microvilli to increase SA)
      - has three layers
        
        Mucous membrane
        
        protective layer
        
        modified for secretion and absorption
        
        contains exo and endocrine gland cells
        
        contains epithelial cells which secrete mucus (to lubricate and protect the walls of the gut), digestive enzymes and some hormones
        
        Lamina propria
        
        thin layer
        
        houses gut-associated lymphoid tissue (GALT)
        
        helps defend infection
        
        Mucularis mucosa
        
        smooth muscle
        
        The smooth muscle cells are in random orientation and its function is to move the mucosal epithelium to maximise its contact with gut content
    - - thick layer of connective tissue
      - provides distensibility
      - contains larger blood and lymph vessels
      - contains Meissner's plexus
    - - smooth muscle coat
      - has 2 layers
        
        circular- inner layer- contraction decreases lumen diameter
        
        longitudinal layer- outer layer- contraction shortens tube length
      - its contraction causes peristalsis
      - contains Auberbach's plexus between the 2 muscle layers
    - - secretes serous fluid which lubricates and prevents friction between organs
      - continuous with mesentry to allow relative fixation but also some movement
  - - - Auberbach's and Meissner's plexus
      - interconnected with neurones
      - nerve nets in submucosa and between smooth muscle layers, only exception are postganglionic cells of ANS and enteric system
    - - parasympathetic increases activity and smpathetic decreases activity
  - - - secretes water, salts, mucus and amylase
      - involved in lubrication and polysaccharide digestion
    - - secretes lingual lipase, IgA and lysozymes
    - - secretes mucus
      - involved in lubrication
    - - secretes HCl, pepsinogen bicarbonate
      - solubilses food, protein digestion and protection
    - - secretes lots of enzymes
      - digests fats, neutralises chime with bicarbonate
    - - secretes Bile salts and bicarbonate
      - helps in fat digestion
    - - secretes enzymes and mucus
      - involved in lubrication
    - - involved in defecation
- - - - motor nerves in skeletal muscle of mouth and jaw
      - voluntary
    - - the food bolus enters into oseophagus
      - Food is chewed and the tongue pushes the bolus to the back of the mouth
      - sensory nerves intiate the swallowing reflex
      - The soft palate is pulled up as vocal cords are pulled together to close the larynx
      - The larynx is pulled up and forward and is covered by the epiglottis, the esophageal sphincter relaxes
  - - - upper 1/3 has skeletal muscle, everywhere else is smooth
      - gives forward movement and mixing
        
        segmentation is the localised contractions of circular muscle which isolates small sections and mixes the contents
      - Secondary peristalsis
        
        does not require a second swallow
        
        afferent/efferent pathways
      - involves circular and longitudinal muscles
      - anticipatory wave of relaxation- when a region of smooth muscle contracts, the circular muscle just beyond relaxes causing the movement of food, and this is controlled by the enteric nervous system
      - Oesophageal sphincter
        
        It is found at the junction between oesophagus and stomach
        
        it is a ring of circular smooth muscle that is usually constricted, waves of peristalsis cause it to relax to let enough food pass
  - - - oxyntic mucosa and pyloric gland area are areas of gastric mucosa that secrete gastric juice
    - - secreted in inactive form and stimulated by nervous input
      - converted back to pepsin by HCl, autocatalytic and is positive feedback
      - pepsinogen converted into pepsin in low pH as sequence of amino acids are removed that cover active site (then follows positive feedback called autocatalysis)
      - Acid and the proteolytic enzyme pepsin could damage the stomach walls but the muscus secreting cells provide a protective coating for walls of gastric pits and stomach
    - - Fundus at top, body, Pyloric antrum at bottom
      - more muscle at bottom, which if shut encourages mixing
      - Cell type
        
        Parital- produces HCl
        
        Chief- pepsinogen
        
        Mucus- protects stomach and lubricates
    - - Caphalic phase- parasympathetic nerves stimulate parietal cells
      - gastric phase- neural reflexes and release gastrin
      - Intestinal phase- neural reflexes, release of secretin and CCK
      - Carbonic anhydrase
        
        this enzyme catalyses hydration of CO2 to H2CO3 which dissociates into H+ and HCO3-
        
        An antiporter transport protein exhanges bicarbonate for Cl- on the blood side of the gastric pits and an antiporter on gastric pot side exchnages H+ for K+
        
        The K+ leaks out of the parietal cells down its concentration gradient and so the inward K+ transport continues to move H+ out into stomach lumen
        
        Cl- also passively leaks out of gastric lumen side of parietal cells to maintain electrical neutrality