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......