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)