GI tract secretion

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GI tract secretion
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Secretory function of the GI tract

• Digestion
• Movement of food materials
• Linear movement
• Mixing
• Digestion
• Mechanical
• Chemical
• Absorption

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• Secretion by the GI tract
• Aids movement
• Mucus
• Provides protection
• Digestion
• Enzymes
• Bile acids
• In response to the presence of foods in the tract

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Anatomical structures

• Single cell mucous gland
• Mucous cells/goblet cells
• Pits
• Submucosal glands
• Crypts of Lieberkun
• Tubular glands
• Oxyntic glands in stomach
• Complex gland
• Salivary
• Liver
• Pancreas

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• GI tract secretion
• Epithelial stimulation
• Direct contact with food
• Enteric nerve stimulation
• Tactile
• Chemical
• Distension
• Parasympathetic stimulation
• Increased secretion in the upper GI tract
• Sympathetic stimulation
• Increase in some area
• Reduced parasympathetic-induced secretion

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Mechanism of secretion

• Organic materials
• Exocytosis
• Water and electrolytes
• Increased ion uptake
• Inward movement of chlorine
• Movement of sodium ion
• Osmosis
• Release of fluids by opening of channels
• Hydrostatic pressure

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Mucus

• Chemical composition
• Different among different regions within the
  tract
• Adhesiveness
• Ability to coat the tract
• Low resistance against movement
• High resistance to digestion
• Buffering

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Saliva
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• Composition
• Serous
• Amylase
• Mucous
• Mucin
• Ions
• Bicarbonate
• Potassium
• Low sodium and chloride ion concentrations

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Salivary Glands
Type of of total Gland
saliva Secreted Parotid
Serous Submandibular Mucous /
Serous Sublingual Mucous
10 / Serous Buccal Mucous
lt1
90
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• Saliva and oral hygiene
• Removal of pathogens and food particles
• Bactericide activity
• Immunity

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• Nervous regulation of secretion
• Parasympathetic nervous system
• Tactile and taste stimulation of salivatory
  nuclei
• Higher CNS
• Regulation of salivatory nuclei
• Reflexes
• Lower GI tract

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Esophageal secretion

• Mucus
• Lubrication for swallowing
• Simple mucous cells
• Protection of the lower esophagus
• Compound glands located in the lower portion

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Gastric secretion

• Types of secretion
• Mucous cells
• Mucus
• Oxyntic glands
• Hydrochloric acid
• Pepsinogen
• Intrinsic factor
• Pyloric glands
• Mucus
• gastrin

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Phase of secretion
20
70
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• Oxyntic glands
• Cells
• Mucous neck cells
• Parietal cells
• HCL
• Intrinsic factor
• Peptic/chief cells
• Pepsinigen

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• HCL
• Formed at the villus-like structures inside of
  canaliculi

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• Pepsinogen
• Activated by HCL
• Secretion
• Acetylcholine
• Stomach acid
• Inhibition of gastric secretion
• Reverse enterogastric reflex
• Presence of chemicals within the intestine

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Pancreatic secretion

• Digestive enzymes
• Pancreatic acini
• Sodium bicarbonate
• Ducts

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• Secretion
• Presence of chyme
• Determines the composition of pancreatic
  secretion
• Stimulated by
• Acetylcholine
• Acinar secretion
• Cholecystokinin
• Acinar secretion
• Secretin
• Ductal secretion

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• Pancreatic enzymes
• Carbohydrate digestion
• Amylase
• Protein digestion
• Trypsin
• Chymotrypsin
• Carboxylpolypeptidase
• Lipid digestion
• Lipase
• Cholesterol esterase
• Phospholipase

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Phase of secretion
20 pancreatic secretion
5-10 Pancreatic secretion
Majority of secretion (secretin)
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Bile secretion

• Secretion
• Hepatocytes
• Initial secretion
• Drained into ducts
• Secretion to the SI
• Accumulation in the gallbladder
• Gallbladder
• Increased concentrations of bile salts
• Removal of sodium ions
• Absorption of chloride ions
• Osmosis of water

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• Emptying
• In response to fats in the chyme
• Secretion of cholecystokinin
• Contraction of gallbladder wall and relaxation of
  the sphincter of Oddi

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• Function
• Fat digestion and absorption
• Emulsification
• Detergent function
• Formation of micelles
• Bile is amphipathic in nature (cholesterol plus
  salt)
• Hydrophobic core/pocket for lipids
• Bile salts
• Recycled
• Enterohepatic circulation

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Secretion of the small intestine

• Compound mucous cells
• Brunners gland
• Site where pacreatic secretion and bile enter the
  intestine
• Alkaline mucus for protection
• Added effects with pacreatic bicarbonate ions and
  bile
• Secretion
• Tactile stimulation
• Irritation
• Vagus stimulation
• Secretin

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• Crypts of Liererkuhn
• Goblet cells
• Mucus
• Enterocytes
• Water and electrolytes
• Secretion
• Rapidly reasborbed by the villi

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• Secretion of the watery mucus
• Active secretion of chloride ions
• Active secretion of bicarbonate ions
• Passive/drag movement of sodium ions
• Results of these
• Osmosis

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• Digestive enzymes
• Peptidases
• Enzymes for disaccharide digestion
• Sucrase
• Maltase
• Lactase
• Isomaltase
• Lipase
• Secretion
• Regulated by the local stimuli
• Enteric nervous reflex

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Secretion by the large intestine

• No enzyme secretion
• Only mucus
• Bicarbonate ions
• Non-mucous cells
• Secretion
• Tactile stimulation
• Local nervous reflex to the cryts of Leiberkuhn
• Protection of the large intestine
• Acids from bacterial metabolism
• Adhesive for feces formation