Final Exam

Three phases of the digestive process
neurogenic phase, gastric phase and intestinal phase
neurogenic phase
initiated by stimulation of the cerebral cortex resulting in the secretion of pepsinogen, HCl and gastrin.
gastric phase
resulting from distention of the stomach or neutralization of gastric pH by foodstuffs.
intestinal phase
which begins when the weakly acidic digestive products enter the duodenum.
parietal cells
secrete HCl and intrinisic factor.
chief cells
secrete pepsinogen
enterochromaffin cells
secrete serotonin.
epithelial cells
secrete mucus
Gastrin
Is produced and stored in the G cells, of the antral mucosa.
Luminal stimuli of Gastrin include
Alcohol
Caffeine
Insulin-induced hypoglycemia
Vagal stimulation initiated by foodstuff.
Amino-acid products of protein digestion
Gastrin stimulates the secretion of
Gastric acid by the fundal parietal cells,
Gastric pepsinogen and intrinsic factor by the gastric mucosa
Release of secretin by the small intestinal mucosa
Pancreatic HCO3 and enzymes
Hepatic bile.
Cholecystokinin
intestinal hormone activating gallbladder contraction and stimulates secretion of pancreatic enzymes
Cholecystokinin formation
synthesised by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum.
Cholecystokinin role
digestion of fat and protein
Secretin
peptide hormone produced in the S cells of the duodenum in the crypts of Lieberkuhn.
Secretin primary effect
regulate the pH of the duodenal contents via the control of gastric acid secretion and buffering with pancreatic bicarbonate.
Secretin stimulates the secretion of
Bile from the liver.
Increases bicarbonate from pancreatic duct epithelium.
increases bicarbonate secretion from duodenal Brunner’s gland
enhances the effects of cholecystokinin to induce the secretion of digestive enzymes and bile
How does secretin reduce acid secretion from the stomach
by inhibiting gastrin release from G cells
What activates pepsinogen
HCl
Pepsin
digest up to 20% of ingested carbon bonds by cleaving preferentially after the N-terminal of aromatic amino acids (phenylalanine, tryptophan, and tyrosine)
Amylase
enzymes that breaks starch down into sugar. Amylase is present in human saliva, where it begins the chemical process of digestion.
Pancreatic alpha-Amylase
randomly cleaves the ?(1-4) glycosidic linkages of amylose to yield dextrin, maltose or maltotriose. Because it can act anywhere on the substrate, ?-amylase tends to be faster-acting than ?-amylase. In animals, it is a major digestive enzyme and its optimum pH is 6.7-7.0.
Lipase
main enzyme to break down fats in the human digestive system, converts triglyceride substrates found in ingested oil to monoglycerides and free fatty acids.
Trypsin
serine protease found in the digestive system where it breaks down proteins
enteropeptidase
activates trypsinogen to trypsin by proteolytic cleavage.
Very high Trypsin
acute pancreatitis
Gastrin tests to diagnose
gastrin-producing tumors called gastrinomas, Zollinger-Ellison (ZE) syndrome, and hyperplasia of G-cells. (produce gastrin)
Zollinger-Ellison Syndrome
The syndrome consists of fulminant peptic ulcers, massive gastric hypersecretion, and non-? islet cell tumors of the pancreas.
Secretin Challenge Test
Test may be ordered if a gastrin result is not significantly elevated, but there remains suspicion that the patient’s symptoms are due to a gastrinoma.
Gastric Analysis
The gastric analysis test involves draining the stomach secretions to determine basal unstimulated acid production.
Gastric Analysis parameters
acidity, mucus, blood, food
D-Xylose absorption test
useful screening test for generalized malabsorption
Steatorrhea
The clinical syndrome caused by the malabsorp- tion of dietary fat.
Steatorrhea produced in
Zollinger-Ellison Syndrome
Increased duodenal acid
Abnormal bile output
Pancreatic insufficiencies
Mucosal impairments
Celiac Disease
Patients have an abnormal immunological response to the presence of gluten in the diet. 90% have circulating antibodies to gluten
Lactose Intolerance
Those lacking lactase fail to split lactose properly
The unabsorbed sugar creates and osmotic force pulling fluid into the intestinal lumen. Results in cramps, bloating, diarrhea.
D-Xylose Absorption Test procedure
Where urine collection is questionable blood may be collected at 1 and 2 hours. Most patient will demonstrate plasma level of greater than 300mg/L. In chldren values above 100mg/dl are acceptable.