Gastrointestinal function secretion, regulation

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Gastrointestinal function secretion, regulation
Daniel Hodyc Department of Physiology
Pictures and schemes L. R. Johnson Essential
Medical Physiology, Elsevier, 2003
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1. Salivary secretion2. Gastric secretion3.
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 (a-amylase) - identical
to pancreatic amylase - cleaves
a-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
kallikrein
a-globulin
bradykinin
vasodilation
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Neural regulation of secretion
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Gastric secretion
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Gastric secretion
Gastric 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
Oxyntic gland
Secretory regions
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Gastric juice electrolytes
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Hydrochloric acid secretion
alkaline tide
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Stimulation of acid secretion
Potentiation of agents
Parasympathetics (Ach)
Gastrin
Histamine
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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
Acetylcholine
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Somatostatin Cell
Gastrin Cell
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Intragastric pH after a meal
Stomach somatostatin Duodenum secretin,
hyperosmotic chyme fatty acids
Inhibition of acid secretion
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Production of Pepsin
Pepsinogen
Ach
H
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
? Bicarbonate in plasma
? High extracellular Cl- concentration
? Carbonic anhydrase
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Mechanism of enzymes secretion
Proteolytic enzymes secreted as inactive
precursors
chymotrypsinogen prokarboxypeptidase
enterokinase
trypsinogen
trypsin
chymotrypsin karboxypeptidase
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Mechanism of enzymes secretion
Inhibition of pancreatic autodigestion
chymotrypsinogen prokarboxypeptidase
enterokinase
trypsinogen
trypsin
chymotrypsin karboxypeptidase
Trypsin inhibitor
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Mechanism of enzymes secretion
Inhibition of pancreatic autodigestion
chymotrypsinogen prokarboxypeptidase
enterokinase
trypsinogen
trypsin
chymotrypsin karboxypeptidase
Trypsin inhibitor
Failure
PANCREATITIS
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Mechanism of enzymes secretion
Glycolytic enzymes - secreted as active
enzymes - pancreatic a-amylase - cleaves starch
and glycogen into di- and trisacharides Lypolyti
c enzymes - secreted as active enzymes -
pancreatic lipase - glycerol fatty acids
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Regulation of pancreatic secretion
Cephalic and gastric phase
Acetylcholine
CCK
enzymes
Secretin
water bicarbonate
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Regulation of pancreatic secretion
Intestinal phase
Acetylcholine
CCK
Fat
enzymes
H
Secretin
water bicarbonate
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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)
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Regulation of secretion
- autonomic nervous system control - in
contrast to other glands (gastric, pancreatic) -
Aldosterone and ADH modulate ionis content, not
the flow