GASTROINTESTINAL PHYSIOLOGYDr. Meg-angela Christi Amores

Functional anatomy The gastrointestinal

wall(from outer to inner)1. Serosa2. Longitudinal muscle3. Circular muscle4. Submucosa5. Mucosa6. Mucosal muscle

Functional anatomy motor functions of the gut are performed

by the different layers of smooth muscle In the longitudinal muscle layer, the

bundles extend longitudinally down the intestinal tract;

in the circular muscle layer, they extend around the gut

each muscle layer functions as a syncytium

Neural control – ENTERIC nervous system

a nervous system all its own lies entirely in the wall of the gut especially important in controlling

gastrointestinal movements and secretion two plexuses:

myenteric plexus or Auerbach's plexus controls mainly the gastrointestinal movements

submucosal plexus or Meissner's plexus controls mainly gastrointestinal secretion and local

blood flow

Assignment Describe the differences between the

Myenteric plexus and the submucosal plexus

Hormonal control Gastrin

secreted by the "G" cells of the antrum of the stomach

stimulation of gastric acid secretion and stimulation of growth of the gastric mucosa

Cholecystokinin secreted by "I" cells in the mucosa of the

duodenum and jejunum in response to digestive products of fat, fatty acids, and monoglycerides

strongly contracts the gallbladder, expelling bile into the small intestine

Hormonal Control Secretin

secreted by the "S" cells in the mucosa of the duodenum in response to acidic gastric juice emptying into the duodenum

acts to promote pancreatic secretion of bicarbonate to neutralize the acid in the small intestine

Gastric inhibitory peptide secreted by the mucosa of the upper small

intestine decreasing motor activity of the stomach and

therefore slows emptying of gastric contents

Secretory functions 2 types of secretion

Digestive enzymes Mucus

are formed only in response to the presence of food in the alimentary tract

SECRETIONS Saliva Esophageal secretions Gastric secretions Pancreatic secretions Bile (liver) Secretions of the small intestine Secretions of the large intestine

Average daily volume of secretionsmL pH

Saliva 1000 6.0-7.0Gastric secretion 1500 1.0-3.5Pancreatic secretion 1000 8.0-8.3Bile 1000 7.8Small intestine secretion

1800 7.5-8.0

Brunner's gland secretion

200 8.0-8.9

Large intestinal secretion

200 7.5-8.0

Total 6700

Salivary secretions principal glands of salivation are the

parotid, submandibular, and sublingual glands

two major types of protein secretion: (1) a serous secretion that contains ptyalin

(an α-amylase), which is an enzyme for digesting starches

(2) mucus secretion that contains mucin for lubricating and for surface protective purposes

Saliva 0.5 milliliter of saliva, is secreted each

minute Becomes very little during SLEEP secretion plays an exceedingly important

role for maintaining healthy oral tissues flow of saliva itself helps wash away

pathogenic bacteria contains several factors that destroy bacteria contains significant amounts of protein

antibodies that can destroy oral bacteria

Gastric secretions oxyntic glands (also called gastric glands)

hydrochloric acid, pepsinogen, intrinsic factor, and mucus

body and fundus (proximal 80 per cent of stomach)

pyloric glands mucus for protection of the pyloric mucosa from

the stomach acid Gastrin antral portion of the stomach (distal 20%)

Gastric secretion parietal cell (also

called oxyntic cell), demonstrating that it contains large branching intracellular canaliculi

where HCl is produced

Gastric secretion Pepsinogen

has no digestive activity when first secreted as soon as it comes in contact with

hydrochloric acid, it is activated to form active pepsin

for protein digestion in the stomach Intrinsic factor

essential for absorption of vitamin B12 in the ileum

Gastric Secretion Pyloric glands

almost no parietal cells contain mostly mucous cells Secrete mucus Secrete gastrin in G cells

Act on histamine to stimulate gastric hydrochloric acid secretion

Pancreatic Secretions Secretes DIGESTIVE enzymes, bicarbonates secreted most abundantly in response to the

presence of chyme in the upper portions of the small intestine

digesting proteins : trypsin, chymotrypsin, and carboxypolypeptidase

digesting carbohydrates: pancreatic amylase fat digestion: pancreatic lipase, cholesterol

esterase, phospholipase

Liver secretions - BILE Functions:

fat digestion and absorption 1) they help to emulsify the large fat particles

of the food into many minute particles, the surface of which can then be attacked by lipase enzymes secreted in pancreatic juice

(2) they aid in absorption of the digested fat end products through the intestinal mucosal membrane

serves as a means for excretion of several important waste products from the blood

Liver secretions - BILE Bile is secreted continually by the liver

cells, but most of it is normally stored in the gallbladder

maximum volume that the gallbladder can hold is only 30 to 60 milliliters

When food begins to be digested in the upper gastrointestinal tract, the gallbladder begins to empty

the most potent stimulus for causing the gallbladder contractions is the hormone cholecystokinin

Small Intestinal Secretions Duodenum: Brunner’s Glands – secrete

mucus Small intestine – crypts of Leiberkuhn –

enzymes: Peptidase (small peptides to amino acids) Sucrase, maltase, isomaltase, lactase

(splitting disaccharides to monosaccharides)

Intestinal lipase – neutral fats to glycerol and fatty acids

Large Intestinal Secretions Crypts of Leiberkuhn – mucus protects the intestinal wall against

excoriation provides an adherent medium for

holding fecal matter together protects the intestinal wall from the

great amount of bacterial activity mucus plus the alkalinity of the secretion

SO HOW is FOOD DIGESTED? Bread: starch Mouth: Esophagus: Stomach: Pancreas/Liver: Small intestine: Large Intestine

Digestion and Absorption To be continued......