Intro to Gastroenterology Flashcards
What are the three main functions of the GI tract?
- Digestion
- Absorption
- Elimination
What are the mechanical processes of digestion?
- Chewing
- Gastric churning
- To/fro mixing
Which enzymes play the largest role in digestion?
Pancreatic Enzymes
What is the main function of proteases and peptidases?
Proteases and peptidases split proteins into amino acids.
What is the main function of lipases?
Lipases split fat into three fatty acids and glycerol.
What is the main function of carbohydrases?
Carbohydrases split CHO into simple sugars.
Name the salivary glands
- Parotid
- Submandibular
- Sublingual
What does saliva contain?
- Mucin
- Immunoglobulin A (IgA)
- Lingual lipase
- Salivary alpha-amylase
- Bicarbonate
What is the function of Mucin?
Lubricate, make saliva more viscous.
What is the function of IgA?
Helps prevent bacterial infection.
What is the function of lingual lipase?
Begins fat digestion.
What is the function of salivary alpha-amylase?
Breaks down complex carbohydrates to simple sugars.
What is the function of bicarbonate in saliva?
Maintains high pH (7.4), protectes tooth enamil, and neutralizes certain bacterial enzymes.
Upper Esophageal Sphincter
- Cricopharyngeal
- Prevents air from traveling into esophagus during respiration and food from traveling into trachea during swallowing.
- Voluntary control
Lower Esophageal Sphincter
- Cardiac
- Involuntary control
- If patient has GERD - this is not working correctly.
What are the main functions of the stomach?
- Store food
- Mix food with digestive juices
- Propel food into the duodenum
- Absorption of alcohol and ASA
What stimulates gastric motility and secretion?
- Stomach distention or vagal nerve stimulation.
- Enteric nerve stimulation.
What are the three phases of gastric secretion?
- Cephalic phase: see food, may begin to taste it, stimulates vagal nerve and acid production.
- Gastric phase: food enters the stomach.
- Intestinal phase: when chyme moves into the duodenum, negative feedback loop sends signal to turn off acid in stomach.
Parietal Cells
- Secrete HCL and Intrinsic Factor
- Have receptors for histamine, gastrin and ACH
- Have receptors for prostaglandins and somatostatin
Chief Cells
- Primarily in fundus of stomach
- Secrete pepsinogen
G Cells
- Secrete gastrin
- Stimulated by ingesting food/stomach distention
- Inhibited by gastric acid secretion
Enterochromaffin like cells (ECL)
- Secrete histamine
Enterochromaffin Cells
- Secrete serotonin
Gastrin
- Produced in response to stomach stretching & exposure to proteins.
- Stimulates the production of HCL acid and intrinsic factor.
- Promotes histamine secretion.
Mucus
- Protects lining of the stomach.
- Stimulated by prostaglandins and nitric oxide.
- Produced by goblet cells
- AKA Mucin
Hydrochloric Acid (HCL)
- Denatures proteins
- Destories any bacteria or virus that remains in the food
- Activates pepsinogen into pepsin
- pH about 2
Intrinsic Factor
- Binds vitamin B12 and creates a complex necessary for absorption
Pepsinogen
- Main gastric enzyme
- Breaks down protein into peptides
- Feedback: an acid pH stimulates somatostatin which inhibits gastrin release and acid secretion for the next phase
D Cells
- Found in endocrine cells of gastric mucosa and pancreas
- HCL stimulates them to secrete somatostatin
S Cells
- Localized in duodenum and stimulated by low duodenal pH
- Produce secretin
I Cells
- Located in duodenum and jejunum
- Synthesize and release cholecystokinin which is stimulated by fatty acids entering the duodenum.
What are the main functions of the small intestine?
- Primary site of digestion/absorption
- Convert food into usable energy
Where is iron primarily absorbed?
In the duodenum.
Where is calcium primarily absorbed?
In the ileum, but also throughout the small intestine.
Where is B12 primarily absorbed?
In the ileum.
What is produced in the duodenum?
- Motilin
- Secretin
- Cholecystokinin
Motilin
- Secreted in response to acid entering the duodenum.
- Increases gastrointestinal motility
Secretin
- secreted in response to acidity, gastric chyme
- decreases gastric motility
- decreases gastric secretion of HCl
- stimulates pancreatic alkaline secretion
- stimulates the liver to release bile
Cholecystokinin
- Secreted in response to fat
- Decreases gastric motlity
- Involved in contraction of the gallbladder to release bile
- Stimulates pancreatic alkaline secretion
What are the main functions of the large intestine?
- Formation, storage, and evacuation of feces.
Haustral Contraction
- Short segmental movements
- Function to increase contact time for absorption of water and sodium.
Mass Movement
- Different than peristalsis
- Function to propel intestinal contents
- Occurs several times per day, usually after meals
Gastrocolonic Reflex
- Occurs during or after a meal
- Initiates propulsion through the entire colon
Defecation Reflex
- Can be overridden by voluntary control
Anatomy of the biliary system
liver, pancreas and gallbladder
What are the main functions of the biliary system?
- Liver: produce bile
- Gallbladder: store and release bile
- Pancreas: secrete digestive enzymes
What are the main functions of the liver?
- Gluconeogenisis
- Bile production
- Produce albumin and coagulation proteins
- Absorb toxic materials
- Enterohepatic circulation
What are the main functions of the gallbladder?
- Stores, concentrates, and secretes bile
- Contraction is stimulated by cholecystokinin and motillin during meals
What are the main functions of the endocrine pancreas?
- Insulin is secreted in response to high blood sugar
- Glucagon is secreted in response to low blood sugar
What are the main functions of the exocrine pancreas?
- Trypsin and chymotrypsin break down protein
- Lipase breaks down triglycerides
- Amylase breaks down starch (carbohydrates)
- Bicarbonate neutralizes acid from the stomach
