small intestine - tuesday

Question 1

What are the two types of contractions that the GI muscle exhibits

Answer 1

tonic and phasic

Question 2

what determines the type of contraction

Answer 2

the electrical properties of gut smooth muscle

Question 3

what type of wave is the tonic contraction

Answer 3

long lasting (sphincters/antrum)

Question 4

what type of wave is phasic contraction

Answer 4

slow waves

Question 5

what can phasic contractions be depending upon ENS/paracrine/endocrine signaling events

Answer 5

• propulsive (peristalsis)
• mixing (segmentation)

Question 6

what are the three autonomic innervations of the GI

Answer 6

1. parasympathetic
2. sympathetic
3. enteric

Question 7

what does parasympathetic innervation do to the GI

Answer 7

promotes passage of food through GI

rest and digest

Question 8

parasympathetic innervation to the upper GI is via which nerve

Answer 8

vagus nerve

Question 9

parasympathetic innervation to the lower GI is via which nerve

Answer 9

pelvic nerve

Question 10

what does sympathetic innervation do to the GI

Answer 10

inhibits passage of food through GI via:
*closing of sphincters
*inhibition of enteric motor neurons

Question 11

what nerves does sympathetic innervation to the GI arise from

Answer 11

splanchnic nerves

Question 12

what is the function of the the enteric nervous systen

Answer 12

control GI movements, secretions, regional blood flow, fluid flow, etc.

Question 13

what is the activity of the ENS modulated by

Answer 13

the sympathetic and parasympathetic nervous system, but the ENS is able to function without any external input

Question 14

what two plexuses does the ENS house along its length

Answer 14

• outer plexus: myenteric
• inner plexus: submucosal

Question 15

where does the myenteric plexus lie

Answer 15

between the inner circular and outer longitudinal layers of the muscularis externa

Question 16

what does the myenteric plexus control

Answer 16

controls the overall muscle tone of the gut as well as its rhythmic contractions

Question 17

what is peristalsis

Answer 17

• stimulated by distension of the gut
• inner circular layer of ME forms a contractile ring - squeezing, around the gut
• outer longitudinal layer contracts - pushing bolus caudally
• at same time, the distal gut relaxes allowing food to enter

Question 18

where does the submucosal plexus lie

Answer 18

within the submucosal layer

Question 19

what does the submucosal plexus oversee

Answer 19

localized secretions and absorptions of the epithelium in the lumen, regulation of blood flow, etc

Question 20

what is the submucosal plexus responsible for

Answer 20

localized contractions of the muscularis mucosae and the villi of the gut

Question 21

what are the interstitial cells of cajal the origin of

Answer 21

electrical slow waves: sweeping waves of partial membrane depolarization (due to calcium flux)

Question 22

what do the interstitial cells of cajal serve as

Answer 22

pacemaker cells

Question 23

what do interstitial cells of cajal form

Answer 23

a network surrounding smooth and longitudinal muscle

Question 24

how are interstitial cells of cajal coupled to smooth muscle cells

Answer 24

via gap junctions

Question 25

what are interstitial cells of cajal affected by

Answer 25

ENS

Question 26

slow waves initiated by interstitial cells of cajal are necessary but.....

Answer 26

not sufficient to induce muscle contraction

Question 27

what happens in the presence of norepinephrine to the slow wave

Answer 27

slow wave baseline is lowered, thus raising the threshold requisite for action potential

Question 28

what happens in the presence of acetylecholine to the slow wave

Answer 28

the slow wave baseline is raise, enabling the crest to reach the critical point of depolarization

Question 29

action potentials can trigger two major movements..

Answer 29

1. segmentation 2. peristalsis

Question 30

what is the principal motor pattern

Answer 30

segmentation

Question 31

what is segmentation/what does it do

Answer 31

* mix and circulates chyme * regional gradient in frequency

Question 32

what is the stimulus and what does it require

Answer 32

* distension * requires a preprogrammed ENS

Question 33

what is duration a function of

Answer 33

* nutrient content * caloric density of the meal

Question 34

what is short distances of movements

Answer 34

peristalsis

Question 35

what is GI emptying

Answer 35

* exit rate from stomach much match digestion rate in SI * liquids empty before solids

Question 36

what period foes undigestible food empty

Answer 36

interdigestive period NOT the digestive period

Question 37

coordination of stomach emptying with SI digestion occurs via the action of the ....

Answer 37

enterogastric reflex

Question 38

ingesta that cannot be broken down into small enough particles remains in the stomach throughout the digestive period. these items are cleared during the interdigestive period by the ....

Answer 38

interdigestive (migrating) motility complex | not interdigestive in ruminants, where it's related to feeding

Question 39

how is the migratory motility complex characterized

Answer 39

by stong peristaltic contractions (~ hourly) through the distal stomach while the pyloric sphincter is relaxed

Question 40

what will disrupt the activity of the interdigestive motility complex (in monogastrics)

Answer 40

feeding

Question 41

digestive period motility

Answer 41

* nonpropulsive segmentation * propulsive peristalsis over short distances

Question 42

interdigestive motility

Answer 42

* strong peristaltic waves over long distances (**migratory motility complex**) * may be involved in aboral localization of gut flora (bacterial conc. high in colon, low orally)

Question 43

bicarbonate secreted by digestive glands must be ____ to maintain pH balance

Answer 43

recovered

Question 44

K+ is primarily absorbed by ____ diffusion through a paracellular route

Answer 44

passive

Question 45

why is all intestinal H2O absorption passive

Answer 45

because the absorption of osmotically active solutes

Question 46

what are the 3 mechanisms of Na+ absorption

Answer 46

* co-transport (SI - jejunum) * coupled sodium-chloride absorption (ileum/colon) * diffusion

Question 47

what are the 4 steps in the coupled sodium-chloride absortion mechanism of Na+ absorption

Answer 47

1. HCO3 and H+ from H2CO3 via carbonic anhydrase go into lumen 2. hydrogen exchanged for sodium 3. accumulating bicarbonate exchnaged for Cl 4. pumped out by Na/K- ATPase pump

Question 48

what are 3 mechanisms of Cl- absorption

Answer 48

1. coupled sodium-chloride absorption (ileum/colon) 2. paracellular chloride absorption (SI) 3. chloride-bicarbonate exchange

Question 49

what happens during coupled sodium-chloride absorption | Cl- absorption

Answer 49

Cl accumulation from Cl/Na couple absorption diffuses out once favorable gradient is reached

Question 50

what happens during paracellular chloride absorption | Cl- absorption

Answer 50

Cl slips though tight junctions to achieve electrical neutrality after Na cotransport

Question 51

what happens during chloride-bicarbonate exchange | Cl- absorption

Answer 51

the Cl-/HCO3- exchanger (or antiporter) to neutralize acid in lumen (colon of ruminants post-fermentation)

Question 52

what is the purpose of bicarbonate recovery

Answer 52

to maintain body acid-base balance

Question 53

what are the 4 steps in bicarbonate recovery

Answer 53

1. H+ and HCO3 are formed inside the cell from water and CO2 2. H+ and Na+ are exchanged at apical membrane 3. luminal H+ neuralizes HCO3 4. intracellular HCO3 and Na+ are electrically balanced

Question 54

what is the net effect ofr bicarbonate recovery

Answer 54

absorption of sodium bicarbonate NaHCO3