Transcript Prezentace aplikace PowerPoint

Gastrointestinal function
secretion, regulation
Daniel Hodyc
Department of Physiology
Pictures and schemes – L. R. Johnson – Essential Medical Physiology, Elsevier, 2003
GIT secretion
1. Salivary secretion
2. Gastric secretion
3. Pancreatic 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
kallikrein
α-globulin
bradykinin
vasodilation
Neural regulation of secretion
Gastric
secretion
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
Gastric secretion
Oxyntic gland
Secretory regions
Gastric juice electrolytes
Hydrochloric acid secretion
alkaline tide
Stimulation of acid secretion
Potentiation of agents
Parasympathetics
(Ach)
Gastrin
Histamine
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
Acetylcholine
Gastrin Cell
Somatostatin
Cell
Intragastric pH after a meal
Stomach – somatostatin
Duodenum – secretin, hyperosmotic chyme
fatty acids
Inhibition of
acid secretion
Production of Pepsin
Pepsinogen
Ach
H+
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
 Bicarbonate
in plasma
 High extracellular
Cl- concentration
 Carbonic anhydrase
Mechanism of enzymes secretion
Proteolytic enzymes – secreted as inactive precursors
chymotrypsinogen
prokarboxypeptidase
trypsinogen
enterokinase
trypsin
chymotrypsin
karboxypeptidase
Mechanism of enzymes secretion
Inhibition of pancreatic autodigestion
chymotrypsinogen
prokarboxypeptidase
trypsinogen
enterokinase
trypsin
Trypsin inhibitor
chymotrypsin
karboxypeptidase
Mechanism of enzymes secretion
Inhibition of pancreatic autodigestion
chymotrypsinogen
prokarboxypeptidase
trypsinogen
enterokinase
trypsin
Trypsin inhibitor
Failure
chymotrypsin
karboxypeptidase
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 secretion
Cephalic and gastric phase
Acetylcholine
CCK
enzymes
Secretin
water
bicarbonate
Regulation of pancreatic secretion
Intestinal phase
Acetylcholine
CCK
Fat
enzymes
H+
Secretin
water
bicarbonate
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)