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Gastrointestinal function
secretion, regulation
Daniel HodycDepartment of Physiology
Pictures and schemes – L. R. Johnson – Essential Medical Physiology, Elsevier, 2003
1. Salivary secretion
2. Gastric secretion
3. Pancreatic secretion
GIT secretion
Salivary
secretion
Anatomy, Inervation
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
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
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
Composition of saliva
Composition of saliva
Composition of saliva
Organic composition:
- ptyalin, lipase
- lysozym, IgA binding protein, lactoferin
α-globulin bradykinin
kallikrein
vasodilation
Neural regulation of secretion
Gastric
secretion
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
Gastric secretion
Secretory regions
Oxyntic gland
Gastric juice electrolytes
Hydrochloric acid secretion
alkaline tide
Stimulation of acid secretion
Parasympathetics (Ach)
Gastrin
Histamine
Potentiation of agents
Hydrochloric acid secretion – perietal cell
Nonsecreting cell Secreting cell
Stimulation of acid secretion – cephalic
phase blocked by vagotomy
sham feeding
hypoglycemia
role of GRP(bombesin)
Gastric phase
60 % of acid response
distension
peptides
calcium alcohol caffeine
Stimulation of gastric acid secretion
Regulation of gastrin release
Gastrin Cell Somatostatin Cell
Acetylcholine
-
Intragastric pH after a meal
Stomach – somatostatinDuodenum – secretin, hyperosmotic chyme fatty acids
Inhibition of acid secretion
Production of Pepsin
Ach H+
Pepsinogen
Pepsin
Pancreatic
secretion
Secretion of water and electrolytes
Na, K – the same as in plasma
Bicarbonate concentration – up to 5 times higher than in plasma
Mechanism of water and electrolytes secretion
Na-K-ATPase
Bicarbonatein plasma
High extracellular Cl- concentration
Carbonic anhydrase
Mechanism of enzymes secretion
Proteolytic enzymes – secreted as inactive precursors
trypsinogen trypsinenterokinase
chymotrypsinogenprokarboxypeptidase
chymotrypsinkarboxypeptidase
Mechanism of enzymes secretion
Inhibition of pancreatic autodigestion
trypsinogen trypsinenterokinase
chymotrypsinogenprokarboxypeptidase
chymotrypsinkarboxypeptidase
Trypsin inhibitor
Mechanism of enzymes secretion
Inhibition of pancreatic autodigestion
trypsinogen trypsinenterokinase
chymotrypsinogenprokarboxypeptidase
chymotrypsinkarboxypeptidase
Trypsin inhibitor
Failure PANCREATITIS
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
Regulation of pancreatic secretionCephalic and gastric phase
Acetylcholine
CCK
Secretin
waterbicarbonate
enzymes
Regulation of pancreatic secretionIntestinal phase
Acetylcholine
CCK
Secretin
waterbicarbonate
enzymes
Fat
H+
Response to a meal
neutralization- pancreatic
bicarbonate
changes in diet
changes in enzyme
secretion
The effect of potentiation of enzyme secretion in pancreas
Phenylalanin + Secretin (CCK)
Secretin 1unit / kg.hr
Phenylalanin (CCK)