GIT Secretion Regulation
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Transcript of GIT Secretion Regulation
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Gastrointestinal function
secretion, regulation
Daniel HodycDepartment of Physiology
Pictures and schemes – L. R. Johnson – Essential Medical Physiology, Elsevier, 2003
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1. Salivary secretion
2. Gastric secretion
3. Pancreatic secretion
GIT secretion
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Salivary
secretion
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Anatomy, Inervation
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Functions of saliva Digestion
- ptyalin (α-amylase) - identical to pancreatic amylase
- cleaves α-1,4-glycosidic bonds of carbohydrates - 75 % of starch, pH optimum 7- functionally replaceable by pancreatic enzyme
- lingual lipase- triglycerides- lower acidic optimum – remains active throughout the stomach and into the proximal duodenum
- dissolves dietary constituents
- increases the sensitivity of taste buds
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Functions of saliva Lubrication
- mucus content- facilitates swallowing- necessary for speech
Protection
- dilution and buffering of harmful substances- salivation before vomiting- xerostomia chronic infections- lysozym, IgA binding protein, lactoferin- take-up of Ca and phosphate - concentration
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Composition of saliva
Major characteristics of saliva:
- relatively large volume
- high potassium concentration
- low osmolarity
- two stages in secretion acini x salivary duct
- specialized organic materials
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Composition of saliva
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Composition of saliva
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Composition of saliva
Organic composition:
- ptyalin, lipase
- lysozym, IgA binding protein, lactoferin
α-globulin bradykinin
kallikrein
vasodilation
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Neural regulation of secretion
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Gastric
secretion
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Gastric secretionGastric juice
- hydrochloric acid- conversion of pepsinogen to pepsine- bacteriostatic effect
- pepsin- protein digestion- replaceable by pancreatic enzymes
- mucus- protective coating, lubricant- part of gastric mucosal barrier
- intrinsic factor- binds B12 vitamin, absorption in the ileum- the only indispensable substance in gastric juice
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Gastric secretion
Secretory regions
Oxyntic gland
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Gastric juice electrolytes
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Hydrochloric acid secretion
alkaline tide
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Stimulation of acid secretion
Parasympathetics (Ach)
Gastrin
Histamine
Potentiation of agents
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Hydrochloric acid secretion – perietal cell
Nonsecreting cell Secreting cell
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Stimulation of acid secretion – cephalic
phase blocked by vagotomy
sham feeding
hypoglycemia
role of GRP(bombesin)
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Gastric phase
60 % of acid response
distension
peptides
calcium alcohol caffeine
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Stimulation of gastric acid secretion
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Regulation of gastrin release
Gastrin Cell Somatostatin Cell
Acetylcholine
-
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Intragastric pH after a meal
Stomach – somatostatinDuodenum – secretin, hyperosmotic chyme fatty acids
Inhibition of acid secretion
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Production of Pepsin
Ach H+
Pepsinogen
Pepsin
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Pancreatic
secretion
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Secretion of water and electrolytes
Na, K – the same as in plasma
Bicarbonate concentration – up to 5 times higher than in plasma
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Mechanism of water and electrolytes secretion
Na-K-ATPase
Bicarbonatein plasma
High extracellular Cl- concentration
Carbonic anhydrase
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Mechanism of enzymes secretion
Proteolytic enzymes – secreted as inactive precursors
trypsinogen trypsinenterokinase
chymotrypsinogenprokarboxypeptidase
chymotrypsinkarboxypeptidase
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Mechanism of enzymes secretion
Inhibition of pancreatic autodigestion
trypsinogen trypsinenterokinase
chymotrypsinogenprokarboxypeptidase
chymotrypsinkarboxypeptidase
Trypsin inhibitor
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Mechanism of enzymes secretion
Inhibition of pancreatic autodigestion
trypsinogen trypsinenterokinase
chymotrypsinogenprokarboxypeptidase
chymotrypsinkarboxypeptidase
Trypsin inhibitor
Failure PANCREATITIS
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Mechanism of enzymes secretion
Glycolytic enzymes- secreted as active enzymes- pancreatic α-amylase- cleaves starch and glycogen into di- and
trisacharides
Lypolytic enzymes - secreted as active enzymes - pancreatic lipase - glycerol + fatty acids
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Regulation of pancreatic secretionCephalic and gastric phase
Acetylcholine
CCK
Secretin
waterbicarbonate
enzymes
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Regulation of pancreatic secretionIntestinal phase
Acetylcholine
CCK
Secretin
waterbicarbonate
enzymes
Fat
H+
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Response to a meal
neutralization- pancreatic
bicarbonate
changes in diet
changes in enzyme
secretion
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The effect of potentiation of enzyme secretion in pancreas
Phenylalanin + Secretin (CCK)
Secretin 1unit / kg.hr
Phenylalanin (CCK)