Please enable JavaScript.

Coggle requires JavaScript to display documents.

DIGESTIVE SYSTEM 1 (Physiology), Overview of GI Hormone, Bile salts,…

- - - - Intrinsic nerve plexuses
        
        Submucosal plexus
        
        Myenteric Plexus
      - Autonomous smooth
        muscle function
        Self excitable
      - Extrinsic autonomic
        nerves
        
        E.g Vagus nerve
      - GI hormones
- - - - Functions
        
        Breaks food into smaller pieces
        
        Facilitate swallowing
        
        Increases surface area of food particles
        
        Mixes food with saliva
        
        Expose food to taste buds
        
        Increases secretions to prepare for the arrival of food
    - - Functions
        
        Initiates digestion of dietary starch by salivary amylase
        
        Initiates digestion of some lipids by lingual lipase
        
        Some antibacterial effect (lysozyme and salivary IgA)
        
        Dissolving molecules (taste buds)
        
        Helps in swallowing, speech and oral health
  - - - Oropharyngeal stage
        
        Initiated by tongue voluntarily pushing bolus of food to pharynx
        
        Note functions of uvula, tongue, glottis and epiglottis
      - Esophageal stage
        Primary peristaltic wave sweeps from the beginning to end of the esophagus, forcing the bolus ahead of it toward the stomach
- - - - The contraction becomes more vigorous as it reaches the thick-muscled antrum (just before the pyloric sphincter).
        
        The strong antral peristaltic contraction propels the chyme forward.
        
        A small portion of chyme is pushed through the partially open sphincter into the duodenum. The stronger the antral contraction, the more chyme is emptied with each contractile wave.
        
        When the peristaltic contraction reaches the pyloric sphincter, the sphincter is tightly closed and no further emptying takes place.
        
        When chyme that was being propelled forward hits the closed sphincter, it is tossed back into the antrum. Mixing of chyme is accomplished as chyme is propelled forward and tossed back into the antrum with each peristaltic contraction, a process called retropulsion.
    - - Stomach
        
        Volume of chyme
        
        Distension has a direct effect on gastric smooth muscle excitability, as well as acting through the intrinsic plexuses, the vagus nerve, and gastrin
        
        Increased volume stimulates motility and
        emptying
        
        Degree of fluidity
        
        Direct effect; contents must be in a fluid form to
        be evacuated
        
        Increased fluidity allows more rapid emptying
      - Duodenum
        
        Presence of fat, acid,
        hypertonicity, or distension
        
        Initiates the enterogastric reflex or triggers the
        release of enterogastrones (secretin, cholecystokinin)
        
        These factors in the duodenum inhibit further gastric motility and emptying until the duodenum has coped with factors already present
      - Outside the digestive system
        
        Emotion
        
        Alters autonomic balance
        
        Stimulates or inhibits motility and emptying
        
        Intense pain
        
        Increases sympathetic activity
        
        Inhibits motility and emptying
  - - - Exocrine Cells
        
        Chief Cells
        
        Pepsinogen
        
        ACh, gastrin
        
        When activated, begins
        protein digestion
        
        Parietal cells
        
        Hydrochloric acid
        
        ACh, gastrin,
        histamine
        
        Activates pepsinogen, breaks down connective tissue, denatures proteins, kills microorganisms
        
        Facilitates absorption
        of vitamin B12
        
        Intrinsic factor
        
        Gastric Acid Secretion
        
        Luminal membrane on one end
        
        Basal lateral membrane on the other end
        
        CO2 +H20 <-> HCO3- + H+ happening within the parietal cell, catalysed by carbonic anhydrase (ca)
        
        H+-K+ ATPase pump moves H+ across luminal membrane, against concentration gradient
        
        Luminal K+ channel allow K+ to passively leak back
        
        There is an accumulation of HCO3-, hence driving the Cl- - HCO3- antiporter and out via the basal lateral membrane.
        
        Cl- is also brought into the cell. It then diffuses out of the cell and through the luminal membrane via the Cl- channel
        
        HCL is then produced
        
        Functions of HCL
        
        Formation of pepsin
        
        Pepsinogen to Pepsin
        
        Breakdown of connective tissue and muscle fibers
        
        So that it's easier for pepsin to break down proteins
        
        Denaturation of protein
        
        Killing of microorganisms
        
        Mucous cells
        
        Alkaline mucus
        
        Mechanical stimulation by contents
        
        Protects mucosa against mechanical, pepsin, and acid injury
    - - Endocrine/Paracrine Cells
        
        D cells
        
        Somatostatin
        
        Acid
        
        Inhibits parietal, G,
        and ECL cells
        
        Enterochromaffinlike
        (ECL) cells
        
        Histamine
        
        ACh, gastrin
        
        Stimulates parietal cells
        
        G cells
        
        Gastrin
        
        Protein products,
        ACh
        
        Stimulates parietal,
        chief, and ECL cells. Increases gastric motility
    - - Cephalic Phase
        Prepare stomach for arrival of food
        
        Prepare stomach for arrival of food
        
        Short phase (minutes)
        
        Directed by CNS via vagus nerve and submucosal plexus
        
        Increased production of gastric juice (mucous, Chief and parietal cells) and release of gastrin (G cells)
      - Gastric Phase
        
        Increased secretion started in previous phase
        
        Initiates digestion of proteins
        
        Increased secretion of gastric juice
        
        Long phase (3 – 4hr)
        
        Stimulation of stretch and chemoreceptors
        
        Submucosal and myenteric plexus
        
        Mucous
        
        Chief
        
        Parietal
        
        G Cells
        
        Effects of gastrin
        (↑ HCl, pepsinogen, gastric motility)
        
        Release of histamine and its local effect
        
        Sustained increased production of gastric juice and increased motility (mixing)
      - Intestinal Phase
        
        Control rate of gastric emptying
        
        Control rate of gastric emptying
        
        Long duration
        
        Distension of duodenum trigger enterogastric reflex (inhibits gastric motility)
        
        ↓ gastric contraction
        
        ↓ gastrin production
        
        Stimulation of CCK,GIP and secretin release, due to presence of lipids and carbohydrates, and the reduction of pH
        
        Inhibits Chief and parietal cells
        
        ↓ Gastric motility and secretion
        
        Feedback inhibition of pepsinogen and HCl production and gastric motility
- - - - Enterohepatic
        circulation
        
        Bile salts travel from
        
        Liver
        
        Common bile duct
        
        Duodenum, via sphincter of Oddi
        
        Terminal ileum, where 95% of bile salts are reabsorbed
        
        5% lost in faeces
        
        Hepatic portal vein
        
        Liver
        This is the enterohepatic circulation
- - - - Acid in duodenal lumen
        
        ↑ Secretin release from duodenal mucosa
        
        Activate Pancreatic duct cells
        
        ↑ Secretion of aqueous NaHCO3 solution into duodenal lumen
    - - Fat (especially) and protein products in duodenal lumen
        
        ↑ CCK release from duodenal mucosa
        
        Activate Pancreatic acinar
        cells
        
        Secretion of pancreatic digestive enzymes into duodenal lumen
- - - - Converts pepsinogen to pepsin to break down proteins