Gastrointestinal Physiology I

Front 1

a. What are the 3 divisions of the intestinal mucosa?

Back 1

i. Epithelium
ii. Lamina propria
iii. Muscularis mucosa

Front 2

b. What are the characteristics of intestinal epithelium?

Back 2

i. Single layer of cells
ii. Epithelial function varies based on location in GI tract

Front 3

c. What are the characteristics of the lamina propria in the GI tract?

Back 3

i. Contains collagen and elastin

Front 4

d. What is the innermost layer of smooth muscle cells in the GI tract?

Back 4

i. Muscularis mucosa

Front 5

e. What are “fluctuations” in the muscularis mucosa?

Back 5

i. Contraction results in fluctuations of entire mucosal layer
ii. Increases exposure of epithelial cell to luminal contents

Front 6

a. What is the composition of the submucosa in the GI tract? What does it support?

Back 6

i. Collagen and elastin
ii. Supports blood vessels and larger nerve trunks in intestinal wall

Front 7

a. What are the two layers of the muscularis externa?

Back 7

i. Inner circular
ii. Outer longitudinal

Front 8

b. What is the purpose of contraction of the muscular layers of the muscularis externa?

Back 8

i. Mixing of luminal contents

Front 9

a. What is the serosa? What type of epithelium covers it?

Back 9

i. Outermost connective tissue layer
ii. Covered with squamous mesothelial cells

Front 10

a. Where is the submucosal plexus best developed? In what layer is it found?

Back 10

i. Small intestine
ii. Submucosa

Front 11

b. Where is the myenteric plexus located? Where is it found best developed?

Back 11

i. In between the circular and longitudinal smooth muscle layer
ii. Well developed throughout entire gut

Front 12

a. Over what does the ENS have control?

Back 12

i. Motility
ii. Exocrine
iii. Endocrine
iv. Microcirculation

Front 13

b. What is the purpose of extrinsic nerves from the ANS in the ENS?

Back 13

i. Coordination of GI functions
ii. Not necessary for functional characteristics of GI tract

Front 14

c. What neurons are responsible for local reflexes in the GI tract? How?

Back 14

i. Interneurons within the plexuses
ii. Connect afferent sensory fibers to efferent fibers innervating smooth muscle cells and secretory cells

Front 15

d. How are central reflexes in the GI tract coordinated?

Back 15

i. Afferent fibers from chemoreceptors and mechanoreceptors in the gut wall run to CNS
ii. Can also elicit local reflexes in ENS

Front 16

a. What nerves are responsible for supplying parasympathetic innervation to the GI tract?

Back 16

i. Vagus nerve
ii. Pelvic/sacral nerves

Front 17

b. To what level does the vagus nerve supply parasympathetic innervation to the GI tract?

Back 17

i. Transverse colon and above

Front 18

c. To what level do pelvic/sacral nerves supply parasympathetic innervation to the GI tract?

Back 18

i. Transverse colon and below

Front 19

d. What type of response is usually elicited following activation of parasympathetic nerves in the GI tract?

Back 19

i. Excitatory
ii. Increases motility and/or secretion

Front 20

e. What neurotransmitters, when released from postganglionic neurons, incite contraction in the GI tract?

Back 20

i. ACh
ii. SubP

Front 21

f. What neurotransmitters, when released from postganglionic neurons, inhibit contraction of GI smooth muscle?

Back 21

i. VIP
ii. NO

Front 22

a. From where do postganglionic sympathetic fibers arise to innervate the GI tract?

Back 22

i. Sympathetic chain
ii. Celiac ganglion
iii. Superior mesenteric ganglion
iv. Inferior mesenteric ganglion

Front 23

b. What does activation of sympathetic nerves cause in the GI tract?

Back 23

i. Inhibition of motor secretory activity

Front 24

c. How do sympathetic fibers inhibit acetylcholine secretion?

Back 24

i. NE is released, activating α2 presynaptic receptors

Front 25

d. What type of pathway influences the muscularis externa?

Back 25

i. Inhibitory

Front 26

e. What type of pathway influences the muscularis mucosae?

Back 26

i. Stimulating

Front 27

f. What receptor mediates sympathetic innervation of blood vessels in the GI tract? What is the physiologic response?

Back 27

i. α1
ii. Leads to vasoconstriction

Front 28

a. What type of smooth muscle is found in the GI tract (unit)?

Back 28

i. Single unit

Front 29

b. What is a major determinant of how far the electrical signal is transmitted in the GI tract?

Back 29

i. Excitability of adjacent cells in muscle bundles

Front 30

c. What is BER?

Back 30

i. Slow wave or Basic Electrical Rhythm
ii. Rate at which slow waves occur in smooth muscle of GI tract

Front 31

d. What is the span of resting membrane potential in smooth muscle of the GI tract?

Back 31

i. -40 to -80 mV

Front 32

e. What are slow waves?

Back 32

i. Oscillations in the resting membrane potential

Front 33

f. What is the normal BER frequency in the stomach?

Back 33

i. 3/min.

Front 34

g. What is the normal BER frequency in the duodenum?

Back 34

i. 12/min.

Front 35

h. What does the BER frequency do from the duodenum to the ilium?

Back 35

i. It slows down

Front 36

i. What structure sets the BER for each intestinal segment?

Back 36

i. Pacemakers

Front 37

j. What modulates the amplitude of the slow waves in GI smooth muscle?

Back 37

i. Intrinsic and extrinsic neural input
ii. Sympathetic→ decreases amplitude
iii. Parasympathetic→ increases amplitude

Front 38

k. How are action potentials created in GI smooth muscle?

Back 38

i. Slow wave amplitude exceeds threshold

Front 39

l. What is primarily responsible for the initial rising phase of the action potential?

Back 39

i. Ca2+ entry into the cell

Front 40

m. What causes the intestine to contract?

Back 40

i. Action potentials

Front 41

n. What GI structure can contract in the absence of action potentials?

Back 41

i. Stomach