GI (Quiz 1) Flashcards
What is the role of the GI tract?
-extract nutrients
-serve as a physiological barrier to microorganisms & foreign materials
What are the 4 concentric layers of the GI tract (innermost to outer)?
-mucosa
-submucosa
-muscularis externa
-adventitia/serosa
Which GI layer has direct contact with food?
Mucosa
What does the submucosa contain?
-large blood vessels
-lymphatics
-nerves branching into the mucosa and muscularis
What does the muscularis externa consist of? What does it do?
Circular inner layer and longitudinal outer muscular layer which are responsible for peristalsis
What does the adventitia/serosa consists of?
Several layers of epithelium
What are the Accessory Organs of the GI tract?
-pancreas
-liver
-gall bladder
How does the pancreas aid the GI tract?
Consists of:
-pancreatic digestive enzymes
-Bicarbonate
-cations (Na, K, Ca)
-anion (Cl)
What is synthesized by hepatocytes?
Bile (for fat digestion, emulsifies fat)
What is the function of the gall bladder?
Concentrates and stores bile
What is stimulated by CCK?
-gallbladder
-pancreatic digestive enzymes
Where is the stomach located?
Between the lower esophageal sphincter (LES) and the duodenum (pyloric sphincter)
What is the stomach volume at rest? Expanded?
Rest: ~50 mL (2oz)
Expanded: 1.5 L (~37-52oz)
How much gastric fluid can the stomach produce/secrete?
~2-3 liters per day
Where does chyme form?
The Stomach
Where are parietal and chief cells found?
Stomach
What do parietal cells secrete?
-hydrochloric acid (HCI)
-intrinsic factor
What do chief cells secrete?
Pepsinogen
What is the function of hydrochloric acid and pepsinogen?
Denatures ingested proteins
What is the function of intrinsic factor?
Aid in B12 absorption
What is secreted by mast cells ?
Histamine
What is secreted by g cells?
Gastrin
What is secreted by d cells?
Somatostatin
What is secreted by mucus cells?
Mucus and bicarbonate
What stimulates the production of gastric juice?
-hormones (gastrin)
-stomach distention
-thoughts/smell/sight of food
-histamine (binds to H2 receptors on parietal cells)
When does the production of gastric juice stop?
When the pH is ~2
Why is there a thick mucus layer in the stomach?
To prevent auto digestion
What are the functions of stomach acid (HCl)?
-destroys activity of protein
-lowers pH (to ~2)
-partially digests dietary protein
-converts pepsinogen to pepsin
-assists in Ca/Fe absorption by ionizing them
How is the mucosa of the SI different from the rest of the GI?
Structured to maximize surface area/absorb more nutrients
Surface area is ~300 m^2
What allows the SI to have an increased surface area?
-large folds of mucosa
-villi
-microvilli
What is glycocalyx?
-surface coat of microvilli
-most digestion occurs here
—> contains most of the enzymes produced by mucosal cells
Where are bicarbonate ions secreted from?
-pancreas
-Brunner’s glands in the proximal duodenum
How long does food stay in the SI?
3-10 hours (dependent on composition/amount)
Where are epithelial absorptive cells produced?
Crypts (valleys b/w villi)
—> continually undergo mitosis and mature as they move from the crypts to the tips of the villi
What happens to epithelial absorptive cells when they reach the tips of the villi?
They are degraded by digestive enzymes and excreted into feces
How often are epithelial absorptive cells replaced?
every 3-5 days
What happens to epithelial absorptive cells during nutrient deficiency?
They deteriorate
—> if more aren’t made then there will be GI issues
What do goblet cells secrete?
Mucus
What is Peristalsis?
Contraction of muscularis layer causing chyme to move ahead
-inner circular layer tightens tube
-longitudinal layer pushes chyme forward
What is segmentation?
Circular muscle contraction that causes chyme to be broken up/mixed with digestive enzymes
What is pendulum movement
Periodic contractions and relaxations of the longitudinal muscles of the intestinal wall
T/F: Segmentation and pendulum movements propel food
FALSE
What is a cardio spasm?
A sustained tight contraction of the muscle sphincter
What digestive enzyme is found in the mouth?
Salivary amylase
Which digestive enzymes are found in the stomach?
-pepsin
-lingual lipase (gastric lipase)
Which digestive enzymes are found in the pancreas?
(Literally so many)
-pancreatic amylase
-trypsin
-chymotrypsin
-carboxypeptidase
-elastase
-co-lipase
-pancreatic lipase
-phospholipase A2
-cholesterolesterase
What digestive enzymes are found in the SI?
-Aminopeptidase
-enterokinase
-disaccharidase
-> Maltase
-> sucrase
-> lactase
-> trehalase
-> isomaltase
Which enzymes digest carbs?
-salivary amylase
-pancreatic amylase
-all the disaccharidases
Which enzymes digest proteins
-pepsin
-trypsin
-chymotrypsin
-carboxypeptidases
-elastase
-enterokinase
-aminopeptidases
Which enzymes digest lipids?
-lingual/gastric lipase (only in babies)
-co-lipase
-pancreatic lipase
-phospholipase A2
-cholesterolesterase
What is bile composed of?
-mainly bile salts
-cholesterol
-phospholipids
-bile pigment (direct bilirubin)
-all dissolved in an alkaline solution
What are the two primary bile acids?
-chenodeoxycholic acid
-cholic acid
Where is bile synthesized?
Mainly in hepatocytes from cholesterol
Where is bile secreted into?
the small intestine via common bile duct
What does 7 alpha-hydroxylase do?
Convert Cholesterol into 7-hydroxycholesterol (adds another OH group to cholesterol)
—> using NADPH + H+
ITS ALSO THE RLE!
What is the rate limiting enzyme for bile synthesis?
7 alpha-hydroxylase
How many hydroxyl groups are in cholic acid? Where are they?
3 @ C3, 7, 12
How many hydroxyl groups are in chenodeoxycholic acid? Where are they?
2 @ C3, 7
What is the affect of adding hydroxyl groups to bile salts?
More OH = more hydrophilic
—> increases emulsification
What is a byproduct of bile acid synthesis?
Propionyl-CoA
What are the two amino acids that can make conjugated bile acids?
Glycine and Taurine
What happens when you conjugate a bile acid?
Results in improved ionization & ability to form micelles
What % of bile acids are conjugated with glycine?
75%
The other 25% is taurine:)
What are the two conjugated bile acids made by glycine?
-Glycoholic acid
-Glycochenodeoxycholic acid
What are the two conjugated bile acids made with taurine?
-taurocholic acid
-taurochenodeoxycholic acid
What makes up a mixed micelle?
-bile salts
-triacylglycerol
-pancreatic lipase
When is bile sent from the liver to the gallbladder?
the inter-digestive period
What happens when conjugated bile acids get to the large intestine?
Bacteria act —> deconjugation and dihydroxylation
What is the secondary bile acid of Cholic acid?
Deoxycholic acid
The secondary bile acid of chenodeoxycholic acid?
Lithocholic acid
What is the difference between primary and secondary bile acids?
Secondary has no -OH @ C7
T/F: 95% of bile acids are reabsorbed by active transport in the ileum and delivered back to the liver
TRUE!
Delivered via the portal circulation
What is the clinical significance of bile?
- *** only significant mechanism for eliminating excess cholesterol
- Facilitate digesting of triglycerides
- Eliminate bilirubin
- Facilitate absorption of fat-soluble vitamins/substances
- Makes cholesterol soluble in the gallbladder (basically same as 1 but she has both listed)
How do gallstones form?
when bile becomes supersaturated with cholesterol
—> chol precipitates out —> deposition of Ca, bilirubin, PL to form stone
What happens to the gallstones after they form?
- Resident silently in the gallbladder
- Cause cholecystitis (inflammation of gallbladder)
- Block the common bile duct
What happens at the large intestine?
-absorption of 85-90% of water
-Absorption of some minerals/vitamins
-formation of feces
What are two examples of facilitated diffusion?
-GLUT 5 —> fructose
-GLUT 2 —> glucose + fructose
What type of absorption is involved with Na/K
Primary active transport
What is an example of secondary active transport
SGLT —> glucose and Na
What are the three main types of absorption
-passive
-active
-endocytosis
Where does portal circulation occur? What does it carry?
-portal vein —> liver
-water-soluble nutrients
Where does lymphatic circulation drain? What does it drain?
-into left subclavian vein
-fat-soluble nutrients + large particles
What is the pathway of bile circulation?
Liver—>gallbladder —> SI —> portal vein —> liver
What are the regulatory peptides?
(A lot tbh)
-gastrin
-cck
-secretin
-gastric inhibitory peptide (GIP)
-glucagon-like peptide (GLP)
-somatostatin
-motilin
What stimulates gastrin secretion?
-thoughts of food
-food
-distension of the antrum
-peptides and amino acids
-vagus nerve
What is the function of gastrin?
-stimulates the release of HCl
-stimulates gastric and intestinal motility
What inhibits gastrin?
-pH less than 1.5
-somatostatin
Where is GIP released from?
The k cells from duodenum and jejunum
What stimulates GIP secretion ?
The presence of glucose and fat
What is the function of GIP
-inhibits gastrin-stimulated gastric acid secretion/motility
Incretin hormone:
-controls blood glucose after a meal
-stimulates insulin secretion
Where is cck secreted from?
I cells in the duodenum and jejunum
What stimulates cck secretion?
The presence of fat, peptides, amino acids, HCl
What is the function of cck?
-stimulates secretion of pancreatic juice/enzymes
-stimulates gallbladder contraction —> release of bile
-inhibits gastrin emptying
-augments the action of secretin
What stimulates secretin secretion?
The presence of acidic chyme entering the duodenum
What is the function of secretin?
increase the pH of the duodenum
-increases bicarbonate and water
-decrease gastric acid secretion
Where is motilin released?
By cells of the proximal SI
What stimulates motilin secretion?
The presence of bile and pancreatic secretions into the duodenum
What is the function of motilin?
-increase rate of gastric emptying
-stimulates intestinal motility
-enhances contraction of the smooth muscles
Where is GLP released from?
Ileal L cells
What stimulates GLP?
The presences of nutrients in the lumen
What is the function of GLP?
incretin hormone
-delays CHO absorption
-increase glucose-dependent insulin secretion
-increase pancreatic beta-cell mass
-decrease glucagon secretion
-promotes insulin sensitivity
-inhibits gastric secretion/motility
What stimulates the secretion of somatostatin?
-Acidic chyme
-products of protein and fat digestion
What is the function of somatostatin?
-general: inhibitory and anti secretory
—> inhibits gastrin/gip/secretin/motilin
—> inhibits gall bladder contraction
