GI Basics Flashcards
What “chemicals” assist in the chemical breakdown of food?
Hydrochloric acid and pepsin
Hydrochloric acid is secreted by _____.
parietal cells
What are the functions of hydrochloric acid?
- solvent that dissolves food
- activates pepsin (to begin protein digestion)
- stimulates duodenal release of other digestive enzymes
- kills bacteria in food
What is the function of pepsin?
digests proteins
Pepsinogen is secreted by ____.
chief cells
Which 3 hormones stimulate the parietal cells to secrete hydrochloric acid?
- gastrin
- histamine
- acetylcholine
What is the function of gastrin?
stimulate stomach acid secretion and motility
____ cells secrete gastrin which causes _____ cells to secrete ________.
- G cells
- Enterochromaffin-like cells
- histamine
What is the function of histamine?
stimulate the parietal cells to secrete HCl in response to gastrin
What is the function of acetylcholine?
directly stimulate the parietal cells to secrete HCl
Parasympathetic system (primarily vagus nerve!)
What is the function of somatostatin?
act as negative feedback mechanism to inhibit secretion of gastrin, insulin, glucagon, pancreatic enzymes, and gallbladder contraction
Somatostatin is produced by _____ cells.
Delta (D cells)
What are the main functions of the large intestine?
- Absorb remaining water from undigested food
- Transport undigested food for removal via feces– contains Haustra
- Absorb certain vitamins produced by bacteria (vit. K, biotin)
The large intestine consists of the _____ and the _____.
cecum and colon
What is the function of the duodenum?
responsible for most of the chemical digestion of small intestine and regulates the rate of stomach emptying
Secretin is released by the _____.
Duodenum
What is the function of secretin?
causes the pancreas to release bicarbonate to buffer the acid from the chyme entering the duodenum from the stomach
What are the functions of cholecystokinin (CCK)?
- stimulate release of pancreatic enzymes (trypsin, amylase, lipase)
- increase bicarb release
- stimulate gall bladder contraction and bile release
What is the function of bile release?
help to emulsify fats to make lipase breakdown of fats more effective
Which substances are produced by the acinar cells of the pancreas?
- bicarb
- proteases
- amylase
- lipase
The exocrine gland of the pancreas contains the _____ cells.
acinar
The function of proteases (trypsinogen, chymotrypsinogen)
precursors to enzymes that break down proteins. Are released in an inactive form to prevent auto digestion
Function of amylase?
breaks down starches into simple sugars
Function of lipase?
breaks down fats into fatty acids (with help of bile salts which increase surface area)
The endocrine gland of the pancreas contains the _____.
islets of Langerhans
Insulin is produced by _____ cells and its function is _____
beta cells
decrease blood glucose levels
Glucagon is produced by _____ cells and its function is _____
alpha cells
increase blood glucose levels
What substances are produced by the islets of Langerhans of the pancreas?
- insulin
- glucagon
- somatostatin
Upper endoscopy is the diagnostic test of choice for what conditions?
- Mallory-Weiss tear
2. PUD
Barium enema is contraindicated if what is suspected?
Perforation! it is an irritant outside of the structures of the GI tract
Also in acute ulcerative colitis (can cause toxic mega colon)
An esophageal manometry (esophageal motility study) is the diagnostic test of choice for what conditions?
- achalasia
2. nutcracker esophagus
What is the function of the diagnostic test ERCP?
Is an upper GI endoscopy + X-rays to diagnose and treat disorders of the bile or pancreatic ducts
What is the function of the diagnostic test esophageal manometry?
used to monitor pressure changes especially of the lower and upper esophageal sphincter. Used for motility disorders, evaluate peristalsis and patients with difficulty swallowing
What are the 3 phases of bilirubin metabolism?
- Prehepatic phase
- Intrahepatic phase
- Post hepatic phase
Bilirubin is produced from ______.
heme metabolism
What happens in the pre hepatic phase of bilirubin metabolism?
Heme is degraded esp. in liver and spleen by macrophages.
Heme —> biliverdin (green) —> unconjugated bilirubin (red-orange) —> sent to liver for conjugation and excretion
______ bilirubin is NOT soluble in water.
Unconjugated (indirect)
Unconjugated bilirubin is conjugated via the enzyme _____.
glucuronosyltransferase (UGT)
What happens during the intrahepatic phase of bilirubin metabolism?
In hepatocytes, the unconjugated bilirubin is conjugated via UGT enzyme
______ bilirubin IS soluble in aqueous bile
Conjugated
What happens during the post hepatic phase of bilirubin metabolism?
Bilirubin is transported thru biliary and cystic ducts to be stored in gallbladder to enter the intestine —> then conjugated bilirubin converted to urobilinogen that can go thru 3 pathways
When conjugated bilirubin reaches the intestine it is then converted to ______.
urobilinogen
What are the 3 main pathways urobilinogen can go thru?
- is oxidized by intestinal bacteria to stercobilin (gives stool its brown color)
- is converted in kidney to urobilin and excreted (gives urine its color)
- is recycled back to the liver and bile for reuse
What gives stool its brown color?
stercobilin
What gives urine its color?
urobilin
Jaundice occurs when bilirubin levels are ______ mg/dL.
> 2.5
What etiologies can cause jaundice?
- increased bilirubin production (hemolysis)
- decreased bilirubin uptake
- impaired conjugation
- biliary obstruction
- hepatitis
If a pt has increased bilirubin without increased LFTs you should suspect —>
familial bilirubin discorders (Gilbert’s, Dubin-Johnsons) and hemolysis
