Gastrointestinal function secretion, regulation Daniel Hodyc Department of Physiology Pictures and schemes – L. R. Johnson – Essential Medical Physiology, Elsevier, 2003

1. Salivary secretion 2. Gastric secretion 3. Pancreatic secretion 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 Protection - 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 acid response alcohol caffeine  60 % of  distension  peptides  calcium alcohol caffeine

Stimulation of gastric acid secretion

Regulation of gastrin release Acetylcholine - Somatostatin Cell Gastrin 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 enterokinase trypsinogen trypsin chymotrypsin karboxypeptidase

Mechanism of enzymes secretion Inhibition of pancreatic autodigestion chymotrypsinogen prokarboxypeptidase enterokinase trypsinogen trypsin Trypsin inhibitor chymotrypsin karboxypeptidase

Mechanism of enzymes secretion Inhibition of pancreatic autodigestion chymotrypsinogen prokarboxypeptidase enterokinase trypsinogen trypsin Trypsin inhibitor chymotrypsin karboxypeptidase 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 - 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 - pancreatic bicarbonate changes in diet changes in 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)