Gastrointestinal Physiology

Question 1

What are the intrinsic innervation of the GI tract?

Answer 1

Meissner Plexus
(Submucosal Plexus)
Auerbach Plexus
(Myenteric Plexus)

Question 2

What is the function of the Myenteric Plexus?

Answer 2

Motility

Meissner Plexus for secretion

Question 3

What muscle is innervated by the Meissner Plexus?

Answer 3

Muscularis Mucosa

Located between submucosa and inner circular layer

Question 4

What are the five official GI hormones?

Answer 4

Gastrin, CCK, Secretin, GIP, Motilin

Question 5

What specific amino acids stimulate gastrin release?

Answer 5

Phenylalanine (F)
Tryptophan (W)
Methionine (M)

Question 6

Where are G cells for gastrin secretion located?

Answer 6

G cells of the GASTRIC
ANTRUM (not in the cardia-fundus area!) duodenum, jejunum

Question 7

What is the effect of CCK on bile secretion?

Answer 7

Gallbladder contraction,
Sphincter of Oddi relaxation

Question 8

What GI hormone stimulates pancreatic enzyme AND pancreatic HCO3- secretion?

Answer 8

CCK

Secretin – does not affect pancreatic enzyme secretion

Question 9

What is the main stimulus of GIP (Glucose-Dependent Insulinotropic Peptide)?

Answer 9

ORAL glucose
Stimulates insulin secretion

Question 10

Which part of the GI tract does motilin affect?

Answer 10

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)

Question 11

What are the three candidate GI hormones?

Answer 11

Pancreatic Polypeptide
Enteroglucagon Glucagon-Like Peptide 1

Question 12

What is the incretin effect?

Answer 12

Occurs when ingested
glucose has a greater effect
on insulin secretion than
injected glucose – Mediated
by GIP and GLP-1

Question 13

What GI paracrine is secreted by cells throughout the GI tract in response to H+ and inhibits the release of ALL GI hormones?

Answer 13

Somatostatin

Question 14

What is the effect of VIP on the
lower esophageal sphincter?

Answer 14

Relaxes lower esophageal
sphincter

Question 15

What stimulates gastrin release from G cells?

Answer 15

GRP (Bombesin)

Question 16

What hypothalamic nuclei inhibit appetite?

Answer 16

Ventromedial Hypothalamus (Satiety Center)

Lateral Hypothalamic (Appetite Center)

Question 17

What neurons release POMC to decrease appetite?

Answer 17

Anorexigenic Neurons

Orexigenic Neurons: Releases Neuropeptide Y to increase appetite

Question 18

What secretion by fat cells stimulates Anorexigenic Neurons and inhibits
orexigenic Neurons?

Answer 18

Leptin
Insulin
GLP-1

Question 19

What inhibits Ghrelin?

Answer 19

Peptide YY

Ghrelin: inhibits anorexigenic neurons, secreted by gastric cells

Question 20

Contractile Tissue in the GI tract is made up of Unitary Smooth Muscles EXCEPT:

Answer 20

Pharynx
Upper 1/3 of Esophagus
External Anal Sphincter

Question 21

What GI smooth muscle contraction is due to spike potentials?

Answer 21

Phasic Contractions

Question 22

What GI smooth muscle contraction is due to subthreshold slow waves?

Answer 22

Tonic Contractions

Question 23

What is the function of Phasic Contractions?

Answer 23

For mixing and propulsion
Seen in the esophagus, gastric antrum, small intestines

Question 24

Depolarization of spike potentials is due to:

Answer 24

Calcium influx
True action potential

Question 25

What GI electrical activity determines the pattern of contraction?

Answer 25

Slow Waves

Question 26

How are slow waves described?

Answer 26

Slow, oscillating membrane potentials Due to Cyclic opening of Ca2+ channels (depolarization) followed by opening of K+ channels (repolarization)

Question 27

What is the most common stimulus for GI peristalsis?

Answer 27

Distention

Question 28

Time to transfer material from pylorus to ileocecal valve:

Answer 28

3-5 Hours

Question 29

Time to transfer material from the ileocecal valve to the colon:

Answer 29

8-15 Hours

Question 30

Where is the swallowing center?

Answer 30

Medulla

Question 31

What are the three phases of swallowing?

Answer 31

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

Question 32

In the esophageal peristalsis, what creates the high pressure behind the bolus for food propelling?

Answer 32

Primary Peristaltic Contraction

Question 33

What two hormones or substances cause relaxation of the lower esophageal sphincter?

Answer 33

VIP, NO

Question 34

What is the purpose of the esophageal secondary peristaltic contraction?

Answer 34

clear esophagus of remaining food

Question 35

What is the capacity of the stomach (L)?

Answer 35

1.5L

Question 36

What is the effect of gastric volume on gastric emptying?

Answer 36

Increases gastric emptying

Question 37

What is the effect of HCl in the duodenum on gastric emptying?

Answer 37

Decreases gastric emptying

Question 38

This refers to the food that enters the small intestines (partially digested):

Answer 38

Chyme

Question 39

This refers to the back-and forth movement in the SI with no net forward motion:

Answer 39

Segmentation Contraction Mixes chyme with pancreatic enzymes

Question 40

What is the function of the proximal colon versus the distal colon?

Answer 40

Proximal: absorption of water Distal: storage of feces

Question 41

How many times a day does mass movement in the LI occur?

Answer 41

occur 1-3x a day to move colonic contents over long distances

Question 42

What GI secretion has high HCO3- AND is hypotonic?

Answer 42

Saliva

Question 43

What are the factors that DECREASES salivary production

Answer 43

Sleep, dehydration, fear, anticholinergic drugs

Question 44

What GI secretion has high HCO3- AND is isotonic?

Answer 44

Pancreatic Secretion

Question 45

Initial saliva is high on what electrolytes?

Answer 45

Na+, Cl- Final Saliva: high in HCO3-, K+

Question 46

What gastric cell secretes HCl?

Answer 46

Parietal / Oxyntic Cells

Question 47

What gastric cell secretes Serotonin?

Answer 47

Enterochromaffin / Kulchitsky Cells

Question 48

What secretion is accompanied by HCl from the parietal cells?

Answer 48

Intrinsic Factor

Question 49

Chronic use of PPI (Proton Pump Inhibitors) can lead to an increase of which GI hormone?

Answer 49

Gastrin Attempts to promote acid secretion

Question 50

What are the three factors that promote HCl secretion?

Answer 50

Histamine on H2 receptors ACh on M3 receptors Gastrin on CCK-B receptors

Question 51

What are some factors that inhibit HCl secretion?

Answer 51

Low pH (<3.0) Somatostatin Prostaglandin Drugs Atropine on M3, Cimetidine on H2 and PPI (Omeprazole) on H+- K+-ATPase exchange pump

Question 52

What are the three substances that stimulate exocrine pancreatic secretion?

Answer 52

Secretin, CCK, ACh

Question 53

What is the most common component of bile?

Answer 53

Water

Question 54

What is the active component of bile?

Answer 54

Bile Salts Bile salts are formed from Cholesterol

Question 55

What are the components of bile other than water and bile salts?

Answer 55

Bilirubin, Cholesterol, Phospholipids, Electrolytes

Question 56

How many percent of bile salts are recirculated back to the liver?

Answer 56

94%

Question 57

What is the transporter used in the enterohepatic circulation found in the terminal ileum?

Answer 57

Na-Bile salt cotransporter

Question 58

Overall, gallbladder has low concentrations of:

Answer 58

Cl- and HCO3- HIGH: Na+, Ca2+, Bile Salts, Cholesterol, Lecithin

Question 59

Where does digestion of carbohydrates begin?

Answer 59

Mouth via salivary amylase

Question 60

What type of carbohydrates are absorbed?

Answer 60

Monosaccharides only

Question 61

What is the competitive inhibitor of glucose in the SI?

Answer 61

Galactose Luminal Side: SGLT-1 for glucose and galactose (secondary active transport)

Question 62

What is the transporter used by fructose on the basolateral side?

Answer 62

GLUT-2 (facilitated diffusion): all types of monosaccharides GLUT-5: Luminal side

Question 63

What enzyme is required for protein assimilation?

Answer 63

Enterokinase / Enteropeptidase

Question 64

What enzyme degrades proteins from the edge (Cterminus)?

Answer 64

Exopeptidases Endopeptidases: degrade proteins from interior peptide bonds

Question 65

How are free amino acids absorbed from the luminal side?

Answer 65

Na-AA symport Basolateral Membrane: facilitated diffusion

Question 66

How are dipeptides and tripeptides absorbed from the luminal side?

Answer 66

H+-dipeptide/tripeptide symport Basolateral Membrane: Facilitated diffusion of free A

Question 67

Lipids enter intestinal cells via:

Answer 67

Micelles Leave intestinal cells via: Chylomicrons

Question 68

How are vitamins A-D-E-K absorbed?

Answer 68

Incorporated into micelles and absorbed with lipids

Question 69

How are water-soluble vitamins absorbed?

Answer 69

Na+-dependent symport

Question 70

What cell in the liver is responsible for liver fibrosis?

Answer 70

Stellate Cells of Ito Found in the perisinusoidal space of Disse

Question 71

What vitamin is stored by the liver Ito cells?

Answer 71

Vitamin A

Question 72

What hepatic cells act as antigen-presenting cells?

Answer 72

Kupffer Cells