Gastrointestinal Physiology Flashcards
What are the intrinsic innervation of the GI tract?
Meissner Plexus
(Submucosal Plexus)
Auerbach Plexus
(Myenteric Plexus)
What is the function of the Myenteric Plexus?
Motility
Meissner Plexus for secretion
What muscle is innervated by the Meissner Plexus?
Muscularis Mucosa
Located between submucosa and inner circular layer
What are the five official GI hormones?
Gastrin, CCK, Secretin, GIP, Motilin
What specific amino acids stimulate gastrin release?
Phenylalanine (F)
Tryptophan (W)
Methionine (M)
Where are G cells for gastrin secretion located?
G cells of the GASTRIC
ANTRUM (not in the cardia-fundus area!) duodenum, jejunum
What is the effect of CCK on bile secretion?
Gallbladder contraction,
Sphincter of Oddi relaxation
What GI hormone stimulates pancreatic enzyme AND pancreatic HCO3- secretion?
CCK
Secretin – does not affect pancreatic enzyme secretion
What is the main stimulus of GIP (Glucose-Dependent Insulinotropic Peptide)?
ORAL glucose
Stimulates insulin secretion
Which part of the GI tract does motilin affect?
Acts only on the stomach
and small intestines
By stimulating their motility (has no effect on the large intestines)
Activates inter digestive / migrating
myoelectric complex (MMC)
What are the three candidate GI hormones?
Pancreatic Polypeptide
Enteroglucagon Glucagon-Like Peptide 1
What is the incretin effect?
Occurs when ingested
glucose has a greater effect
on insulin secretion than
injected glucose – Mediated
by GIP and GLP-1
What GI paracrine is secreted by cells throughout the GI tract in response to H+ and inhibits the release of ALL GI hormones?
Somatostatin
What is the effect of VIP on the
lower esophageal sphincter?
Relaxes lower esophageal
sphincter
What stimulates gastrin release from G cells?
GRP (Bombesin)
What hypothalamic nuclei inhibit appetite?
Ventromedial Hypothalamus (Satiety Center)
Lateral Hypothalamic (Appetite Center)
What neurons release POMC to decrease appetite?
Anorexigenic Neurons
Orexigenic Neurons: Releases Neuropeptide Y to increase appetite
What secretion by fat cells stimulates Anorexigenic Neurons and inhibits
orexigenic Neurons?
Leptin
Insulin
GLP-1
What inhibits Ghrelin?
Peptide YY
Ghrelin: inhibits anorexigenic neurons, secreted by gastric cells
Contractile Tissue in the GI tract is made up of Unitary Smooth Muscles EXCEPT:
Pharynx
Upper 1/3 of Esophagus
External Anal Sphincter
What GI smooth muscle contraction is due to spike potentials?
Phasic Contractions
What GI smooth muscle contraction is due to subthreshold slow waves?
Tonic Contractions
What is the function of Phasic Contractions?
For mixing and propulsion
Seen in the esophagus, gastric antrum, small intestines
Depolarization of spike potentials is due to:
Calcium influx
True action potential
What GI electrical activity determines the pattern of contraction?
Slow Waves
How are slow waves described?
Slow, oscillating membrane potentials
Due to Cyclic opening of Ca2+ channels (depolarization) followed by opening of K+ channels (repolarization)
What is the most common stimulus for GI peristalsis?
Distention
Time to transfer material from pylorus to ileocecal valve:
3-5 Hours
Time to transfer material from the ileocecal valve to the colon:
8-15 Hours
Where is the swallowing center?
Medulla
What are the three phases of
swallowing?
Oral Phase:
triggers reflex when food is at the pharynx
Pharyngeal Phase:
soft palate pulled upward (closes
nasopharynx), glottis covered (prevents aspiration), Upper Esophageal Sphincter (UES) relaxes
Esophageal Phase:
UES closes, Primary and Secondary
Esophageal Peristalsis occurs
In the esophageal peristalsis, what creates the high pressure behind the bolus for food propelling?
Primary Peristaltic Contraction
What two hormones or substances cause relaxation of the lower esophageal sphincter?
VIP, NO
What is the purpose of the esophageal secondary peristaltic contraction?
clear esophagus of remaining food
What is the capacity of the stomach (L)?
1.5L
What is the effect of gastric volume on gastric emptying?
Increases gastric emptying
What is the effect of HCl in the duodenum on gastric emptying?
Decreases gastric emptying
This refers to the food that enters the small intestines (partially digested):
Chyme
This refers to the back-and forth movement in the SI with no net forward motion:
Segmentation Contraction
Mixes chyme with pancreatic enzymes
What is the function of the proximal colon versus the distal colon?
Proximal: absorption of water
Distal: storage of feces
How many times a day does mass movement in the LI occur?
occur 1-3x a day
to move colonic contents over long
distances
What GI secretion has high HCO3- AND is hypotonic?
Saliva
What are the factors that DECREASES salivary production
Sleep, dehydration, fear, anticholinergic drugs
What GI secretion has high HCO3- AND is isotonic?
Pancreatic Secretion
Initial saliva is high on what electrolytes?
Na+, Cl-
Final Saliva: high in HCO3-, K+
What gastric cell secretes HCl?
Parietal / Oxyntic Cells
What gastric cell secretes Serotonin?
Enterochromaffin / Kulchitsky Cells
What secretion is accompanied by HCl from the parietal cells?
Intrinsic Factor
Chronic use of PPI (Proton Pump Inhibitors) can lead to an increase of which GI hormone?
Gastrin
Attempts to promote acid secretion
What are the three factors that promote HCl secretion?
Histamine on H2 receptors
ACh on M3 receptors
Gastrin on CCK-B receptors
What are some factors that inhibit HCl secretion?
Low pH (<3.0)
Somatostatin
Prostaglandin
Drugs
Atropine on M3, Cimetidine on H2 and PPI (Omeprazole) on H+- K+-ATPase exchange pump
What are the three substances
that stimulate exocrine pancreatic secretion?
Secretin, CCK, ACh
What is the most common component of bile?
Water
What is the active component of bile?
Bile Salts
Bile salts are formed from Cholesterol
What are the components of bile other than water and bile salts?
Bilirubin, Cholesterol,
Phospholipids, Electrolytes
How many percent of bile salts are recirculated back to the liver?
94%
What is the transporter used in
the enterohepatic circulation
found in the terminal ileum?
Na-Bile salt cotransporter
Overall, gallbladder has low
concentrations of:
Cl- and HCO3-
HIGH: Na+, Ca2+, Bile Salts, Cholesterol, Lecithin
Where does digestion of carbohydrates begin?
Mouth via salivary amylase
What type of carbohydrates are absorbed?
Monosaccharides only
What is the competitive inhibitor of glucose in the SI?
Galactose
Luminal Side: SGLT-1 for glucose and galactose (secondary active transport)
What is the transporter used by fructose on the basolateral side?
GLUT-2 (facilitated diffusion): all types of monosaccharides
GLUT-5: Luminal side
What enzyme is required for
protein assimilation?
Enterokinase / Enteropeptidase
What enzyme degrades proteins from the edge (Cterminus)?
Exopeptidases
Endopeptidases: degrade proteins from interior peptide bonds
How are free amino acids absorbed from the luminal side?
Na-AA symport
Basolateral Membrane: facilitated diffusion
How are dipeptides and tripeptides absorbed from the luminal side?
H+-dipeptide/tripeptide symport
Basolateral Membrane: Facilitated diffusion of free A
Lipids enter intestinal cells via:
Micelles
Leave intestinal cells via: Chylomicrons
How are vitamins A-D-E-K absorbed?
Incorporated into micelles and absorbed with lipids
How are water-soluble vitamins absorbed?
Na+-dependent symport
What cell in the liver is responsible for liver fibrosis?
Stellate Cells of Ito
Found in the perisinusoidal space of Disse
What vitamin is stored by the liver Ito cells?
Vitamin A
What hepatic cells act as antigen-presenting cells?
Kupffer Cells
