3 Gastrointestinal Physiology

Question 1

4 main topics we discuss

Answer 1

motility
secretion
digestion
absorption

Question 2

organs of the GI tract

Answer 2

oral cavity
pharynx
esophagus
stomach
small intestine
large intestine

Question 3

what are the two GI muscular layers?

Answer 3

• outer, longitudinal layer (shortens tract)

* inner, circular layer (constricts tract)

Question 4

what muscular layer is close to lumen?

Answer 4

circular

Question 5

sphincters are located between?

Answer 5

major compartments

Question 6

what is similar between cardiac and smooth muscle innervation?

Answer 6

NOT every cell is innervated. They form functional syncytium with gap junctions and ephhaptic conduction
**opposite for skeletal

Question 7

organelles found in smooth muscle are?

Answer 7

• poorly developed SR
• less organized contractile units
• **lack troponin (use calmodulin instead)

Question 8

most Ca for smooth muscle comes from? binds to?

Answer 8

comes from ECF

*bins to calmodulin bc smooth muscle lacks troponin

Question 9

two types of electrical waves?

Answer 9

slow waves

spikes

Question 10

slow waves are also called?

Answer 10

basal electrical rhythms (BERs)

Question 11

what are slow waves?

Answer 11

spontaneous oscillations of membrane potential= non-propagated (local) potentials

Question 12

are slow waves or spikes non-propagated or propagated?

Answer 12

slow waves= NON-propagated

spikes= propagated

Question 13

slow waves do not result in muscle contraction because?

Answer 13

they don’t usually reach the muscles cell’s threshold for excitation

Question 14

do slow wave frequency vary? Exs?

Answer 14

YES

• stomach= 3/min
• duodenum= 12/min

Question 15

spikes are also called?

Answer 15

action potentials

Question 16

when do action potentials occur?

Answer 16

when threshold is reached= propagated potentials

Question 17

what are “additional signals” for spikes?

Answer 17

nervous, mechanical, hormonal

Question 18

what are additional signals for spikes required for? (explain process)

Answer 18

for slow waves to become spikes
(additional signals > BERs reach threshold > AP > contraction > travels down GI in wave-like fashion = propagated potentials

Question 19

what are the two contraction types?

Answer 19

1) tonic= common in sphincters

2) phasic= more coordinated, but not as rhythmic as cardiac

Question 20

describe tonic contractions. last how long? purpose? Exs?

Answer 20

• sustained contractions
• last min-hrs
• purpose to prevent forward flow until ready
• sphincters and upper stomach (fundus)

Question 21

describe phasic contractions. last how long? purpose? Exs?

Answer 21

• rapid contractions -contract and relax FAST
• last seconds
• purpose to mix and move
• esophagus, small intestine, lower stomach (antrum)

Question 22

what are 4 factors regulating GI muscle contraction?

Answer 22

1) entertic nervous system
2) extrinsic NS
3) stretch
4) hormones

Question 23

what are the enteric nervous system plexuses? location?

Answer 23

1) myenteric plexus
- – b/w inner long and outer circle muscles
2) sunmucosal plexus
- – closer to absorptive surfaces in Submucosa

Question 24

myenteric plexus controls?

Answer 24

movement: controls and coordinates motility of the gut

Question 25

submucosal plexus controls?

Answer 25

secretions of the gut

Question 26

Myenteric and submuscoal plexuses are also known as?

Answer 26

* myenteric= Auerbach's plexus | * submucosal= meissner's plexus

Question 27

are efferent or afferent fibers found in the plexuses?

Answer 27

both

Question 28

does the enteric nervous system (myenteric or submucosal plexuses) function dependently or independently of extrinsic NS?

Answer 28

BOTH | *independent OR function in conjunction with autonomic extrinsic NS

Question 29

for the enteric NS, afferent fibers carry what information?

Answer 29

sensory * myenteric= pressure * submucosal= chemical

Question 30

how do enteric NS fibers communicate?

Answer 30

* interconnect/communicate to activate or inhibit each other * interconnect/communicate with EXTRINSIC (autonomic) NS * over 20 neurotransmitters have been identified

Question 31

what does extrinsic NS mean?

Answer 31

OUTSIDE of the gut * autonomic * sym and para

Question 32

where do the sym and para fibers originate for extrinsic NS?

Answer 32

* Sym= thoracolumbar spinal cord (T5-L2) | * para= originate in vagus and pelvic splanchnic nerves (S2-4)`

Question 33

How does para and sym affect the GI compared to cardio?

Answer 33

* Sym= slows, inhibits, diminishes GI - --decreases motility and secretions * Para= activated, speeds up GI - -- increases motility and secretions * ***opposite is true for cardiac

Question 34

what is the affect of stretch on the gut?

Answer 34

increases motility, contractility and secretions

Question 35

the gut has a 'reflex arc', this means?

Answer 35

that the plexuses have afferent and efferent fibers to the gut

Question 36

what are 4 major hormones that affect gut motility?

Answer 36

1) gastrin 2) GIP 3) CCK 4) secretin

Question 37

gastric mucosa secrets?

Answer 37

gastrin

Question 38

gastrin is secreted into?

Answer 38

CIRCULATION** not the lumen

Question 39

duodenal mucosa secrets what hormones?

Answer 39

GIP CCK secretin

Question 40

GIP stands for?

Answer 40

glucose-dependent insulinotrophic peptide (GIP)

Question 41

CCK stands for?

Answer 41

cholecystokinin

Question 42

gastrins affect on GI motility?

Answer 42

increase

Question 43

GIP, CCK, and secretin on GI motility? | stimulate release of what?

Answer 43

decrease (inhibits stomach) | **release of enzymatic carbonate

Question 44

protein, stretch, and vagus stimuli cause the release of what hormone?

Answer 44

gastrin

Question 45

CHO and fat stimuli in SI cause the release of what hormone?

Answer 45

GIP from pancreas

Question 46

Fat and protein stimuli in SI cause the release of what hormone?

Answer 46

CCK from pancreas

Question 47

acid stimuli in SI cause the release of what hormone?

Answer 47

secretin

Question 48

what are the two major functions of the release of duodenal hormones?

Answer 48

1) decrease motility and slows emptying of the stomach into the intestine 2) causes release of particular pancreatic enzymes to break down food