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Physiology Lectures 27-29

Wannie Chisala Physiology Degree Englisch 48 Karten

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  1. 1Motility- Mechanical breakdown
    - Controlled movement along the gut
  2. 2Excretion- Addition of enzymes, electrolytes
  3. 3Digestion- Chemical breakdown
  4. 4- Absorption- Transport proteins
  5. 5Excretion- Excretion of metabolic waste products and xenobiotics
    - Elimination of faeces
  6. 6Mouth- Chewing
    - Saliva (salivary amylase)
    - No salivary lipase because no lipid digestion, only carbohydrates
  7. 7Stomach- Mixing
    - Parietal cells produce HCL, pepsinogen and gastric lipase,
    - Surface mucosal cells produce mucus
    - Gastrin and histamine also produced
    - Digestion of proteins and fats
    - Lipid soluble substances e.g. alcahol and asprin absorbed
  8. 8Intestines- Mixing, enzymes secreted by pancreas and bile from liver
    - Mucus produced by goblet cells, also lots of hormones involved
    - Digestion of fats, carbohydrates, polypeptides and nucleic acids
    - Peptides absorbed by active transport, fats by diffusion, water = osmosis, ions and vitamins = active transport
  9. 9Large intestine- Mixing
    - Mucus from goblet cells
    - No digestion except bacteria
    - Absorbtion of ions water and minerals (some vitamins produced by bacteria)
  10. 10Regulation of gut function- Neural (autonomic nervous system, vagus nerves, enteric nervous system)
    - Hormaonal (endocrine - dispersed entero-endocrine cells)
    - Local (paracrine) e.g. histamine
  11. 11Stages of regulation- Cephalic - responds to senses of food
    - Gastric - gastric acid secretion
    - Intestinal
  12. 12Functions of saliva- Lubrication (fluid and mucus)
    - Digestion (amylase and Rproteins - vitamin B12)
    - Solution, moistness and protection:
    - Fluid and bicarbonate to regulate pH
    - Lysozymes and immunoglobulins for antibacterial
  13. 13Composition of salivary glands- 3 pairs of glands making 90% of saliva
    - Parotid glands = sereous (watery) and amylase
    - Sublingual and submandibular glands = mixed secretions (serous and mucous)
    - 10% from minor glands = musous and mucins
    - Total secretion of 1.5L per day
  14. 14Saliva formation- Acinus = where primary secretions are produced, contains Na+, Cl-, K+ and HCO3- (plasma like and isotonic)
    - Duct = where modifications take place (low H2O permeability) Na+ leave and Cl- leave
    - Final saliva = hypotonic and HCO3- rich, K+ and HCO3- enter
  15. 15Control of salivation- In cephalic phase - sight, smell, taste and thought of food
    - Parasympathetic (cholinergic) = cranial nerves VII and IX (NOT VAGUS). Produces large volumes
    - Sympathetic (noradrenergic) = smaller volumes produced but rich in enyzmes (e.g. amylase) and mucus
  16. 16Gastric functions- Resevoir
    - Mixing food with gastric secretions
    - Digestion (mechanical, chemical = proteins)
    - Controlled gastric emptying - moves food to duodenum
    - Protection (bactericidal and mucus, bicarbonate)
  17. 17Composition of gastric juice- HCL produced by parietal cells (140mM)
    - Pepsinogen produced by chief cells, converted to pepsin
    - Mucus and bi carbonate produced by mucus neck and surface epithelial cells
    - Intrinsic factor by parietal cells
    - Around 2 liters a day
  18. 18How does the stomach stop autodigestion- Gastric mucosal protection
    - Mucos layer is a physical barrier from stomach acid in lumen (pH2)
    - Bicarbonate is a chemical barrier that neutralises acid (pH 7)
    - Bicarbonate diffuses through the mucus and buffers acid close to epethelium
    - pH gradient across mucus layer
  19. 19Control of parietal cell function- Direct and indirect chemical regulators
    - Histamine from ECL cells
    - Somatostatin from D cells
    - Gastrin from G cells
    - Acetylcholine from vagus and enteric neurons
  20. 20Overview of control mechanisms- Cephalic phase (sight, smell, taste and thought of food)
    - Also in cephalic phase = Vagal efferent nerves which have a direct effect, histamine release and gastrin release
    - Gastric phase = food in the stomach (stetch and chemical nature), gastrin release and negative feedback inhibition by acid (somatostatin release)
  21. 21Gall bladder- Common entry of bile duct and pancreatic duct into the duodenum (through ampulla of vater)
    - Common bile duct is mixture of secretions from gall bladder and from common hepatic duct
  22. 22Pancreatic juice- Fluid and electrolyte (HCO3-)
    - Wash out enzymes
    - Alkaline (pH8) to neutralise gastric acid secretion in duodenum (pH optimum for intestinal digestion)
    - Primary secretion from acinar cells
    - Modified to HCO3- rich juice by duct cells
    - 1.5L per day
  23. 23Pancreatic enzymes- Amylolytic (carbohydrate digestion) e.g. amylase
    - Proteolytic (protein digestion) e.g. trypsin and elastase
    - Lipolytic (fat digestion) e.g. lipase and phospholipase
    - Nucleolytic (nucleic acid digestion) DNAse/ RNAase
    - Mostly inactive precursors (zymogens) so they don't digest the pancrease
  24. 24Zymogens- Secretions of pancreatic proteases into duodenum as precursors (inactive). Activation by enterokinase in intestine
    - Trypsin can auto-activate
    - Inhibited by trypsin inhibitor
  25. 25Types of proteases- Exoproteases (cleaving form ends of protein)
    - Endoproteases (cleaving from middle of protein)
    - Amino acid specificity
    - Protein digestion completed by intestinal peptidases (brush-border membrane and cytosolic)
  26. 26Cystic fibrosis- Absence of CFTR channels
    - Lack of fluid secreton
    - Lack of washout of enzymes
    - Damage to pancreas
    - Poor nutrition
  27. 27Pancreatic secretion control- Secretin: Duodenal S cells, stimulated by acid, increases HCO3- rich secretion
    - Cholecystokinin-Pancreozymin (CCK): Duodenal I cells, release stimulated by fat and protein, stimulates gall bladder contraction and pancreatic enzyme secretion
    - Neuronal: Vagus, stimulates both acinar cells and duct cells
  28. 28Bile functions- Elimination of waste products (cholestrol, bile pigments, minerals, lipophillic drugs and metabolites, heavy metals)
    - Promotion of lipid digestion and absorption
  29. 29Bile flow- Hepatocytes secrete bile into canaliculi
    - Bile ducts secrete HCO3- rich fluid (like pancreas)
    - Bile enters duodenum by common bile duct
    - Between meals approximately 50% bile stored and concentrated in gall bladder
  30. 30Composition of bileBiliary lipids:
    - Bile acids 67%
    - Phospholipids 22% (lecthins)
    - cholesterol (4%)
    Bile pigments
    - Bilirubin (0.3%), higher in jaundice
    - BILE ACIDS KEEP CHOLESTEROL IN SOLUTION
  31. 31Types of bile acids1) Primary, synthesised from cholesterol e.g. cholic acid
    2) Secondary, modification by intestnal bacteria e.g. deoxycholate
    3) Conjugation, to amino acids e.g. glycine or taurine, increases solubility e.g. taurocholate. These type of bile acids are reabsorbed
  32. 32Enterohepatic recirculation- Synthesis of primary bile acids in liver (conjugated)
    - Secretion into duodenum in bile
    - Involved in lipid digeston/ absorption
    - Reabsorption in terminal ileum (some lost in faeces)
    - Recirculation through hepatic portal vein to liver
    - Taken up by liver and secreted into bile (can be recycles up to 12 times a day)
  33. 33Bile action on cholesterol- Bile acids coat lipids to make emulsions
    - Also phospholipids and cholesterol
    - They are amphipathic, hydrophillic side associates with water, hydrophobic side with cholesterol
    - Emulsion of dietary lipids increases the surface are exposed to lipases and therefore promotes digestion
  34. 34Function of gall bladder- Concentrates bile
    - Absorbes electrolytes
    - Isotonic
    - Na+ with bile salts
    - 0.9l bile secreted by liver but only 0.5 added to duodenum (mixture of dilute and concentrated bile)
  35. 35Control of biliary acid secretion- Bile acid-dependent
    - Ductal (secretin increases secretion)
    - Gall bladder contraction (CCK, vagal nerves Ach, integrated with pancreatic enzyme secretion)
  36. 36Functions of the small intestines- Digestion (luminal, membrane and cytosolic)
    - Nutrient absorption (carbs, proteins, fats, vitamins, iron)
    - Electrolyte absorption (NaCl)
    - Water absorption
    - Secretion (fluid and NaCl) in crypts
  37. 37Carbohydrate digestion- Carbs digested as monosaccharides
    - Luminal digestion of starch-type polysaccharides (amylases produced by pancreas)
    - Membrane digestion by disaccharidases (maltase, sucrase-isomaltase, lactase)
    - Absorption of monosaccharides in the small intestines
  38. 38What type of enzyme is amylase- An endo-enzyme which can only break internal bonds so cannot produce monosaccharides
  39. 39Carbohydrate absorption/ transport- Only monosaccharides absorbed
    - Apical membrane: SGLT1 (glucose, galactose) which is an Na+ coupled, secondary active transport. Also GLUT5 (fructose) facilitated diffusion
    - Basolateral membrane GLUT2 facilitated diffusion, also has the Na+/K+ pump
  40. 40Key points in protein digestion and absorption- Luminal digestion by gastric and pancreatic proteases
    - Membrane digestion by brush-border peptidases
    - Cytosolic digestion within epithelium of small peptides
    - Absorption can be of amino acids, peptides and intact proteins (especially in neonates but nutritionally unimportant)
  41. 41Enzymes that digest proteins- Gastric pepsin (10-20% of digestion), endopeptidase
    - Pancreatic peptidases e.g. trypsin. Endo and exopeptidases
    - Membrane and cytosolic peptidases. Endo, exo or dipeptidases
  42. 42Amino acid absorption- Numerous types of amino acid transporters with overlapping specificity
    - Apical membrane (mainly coupled to ion uptake, Na+, secondary active transport)
    - Basolateral membrane, facilitated diffusion
  43. 43Key points in fat (lipid) digestion and absorption- Low water solubility
    - Solubalised by bile salts
    - Digestion by pancreatic lipase
    - Absorption is passive
    - Resterificationof fatty acids = maintains gradient for absorption
  44. 44Dietary lipids- Triglycerides (triesters of glycerol and long chain fatty acids)
    - Phospholipids (substitute one fatty acid chain with phopho-ester)
    - Short chain fatty acids (minor and dairy)
  45. 45Steps of lipid digestion1) detergent emulsification in lumen
    2) Digestion by lipases (break down fats to monoglycdes and stored in micelles) produces micelles in lumen
    3) Diffusion into epithelial cell (monoglycerides come out of micelles and enter cell)
    4) Rysynthesis of triglycerides (fatty acids combine with cholestrol and proteins to form chylomicrons)
    5) Chylomicrons released into lymphatic or blood system
  46. 46Stage 1 = emulsification- Begins with chewing, grinding and mixing of food
    - Fat droplets of 1micrometer
    - Increased oil-water interface area
    - Stabilised by bile salts and phospholipids
  47. 47Stage 2 = digestion- Pancreatic and gastric (15%) lipases, work at oil-water interface
    - Co-lipase prevents inhibition of lipase by bile acids
    - Triglycerides to fatty acids and a monoglyceride
  48. 48Stage 3 = Lipid absorption- Diffusion down gradient
    - Driven by re-esterification of fatty acids to triglycerides within epithelial cells (stage 4)
    - Released across basolateral membrane as chylomicrons (stage 5)
    - Fat soluble vitamins follow same rout of absorption

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Degree Physiology Karteikarten am Physiology Lectures 27-29, erstellt von Wannie Chisala am 26/05/2016.
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