•GI motility Flashcards Preview

GI > •GI motility > Flashcards

Flashcards in •GI motility Deck (56):
0

the migrating myoelectric complex begins ____ hours after you finish eating

3-4

1

the migrating myoelectric complex is active from the ____ through the _____

midstomach, terminal ileum

2

___ produces a series of serial contractions that sweep material into the colon. It lasts about ___ per cycle and is caused by secretion of the hormone ____

Phase III of MMC  

10 minutes

motilin

3

and entire MMC cycle lasts ____

75-120 minutes

4

motilin is secreted by ____

M cells of the duodenum (small intestine)

5

swallowing begins as a _____ but becomes _____ as the ____ and _____ nervous systems take over

voluntary action, involuntary, enteric, autonomic

6

primary vs. secondary esophageal peristalsis

primary: vagal, signals go back to the brain's swallowing center and medulla secondary: more local, enteric nerves help out, if something gets stuck

7

achalasia

a smooth muscle disorder in which the lower area of the esophagus and LES doesn't have enteric nerves

- LES cannot relax, food can't get into stomach

-  typically will have a dilated esophagus, and many develop anorexia. 

8

gastric accommodation is able to occur because of the ____

vagus nerve anticipation

9

the narrowed area at the bottom of the stomach:

antrum

10

organize the following by speed of gastric emptying: oleate meal (fat), saline meal, acid meal (protein)

saline, acid, oleate

11

hormones that regulate the rate of gastric emptying come from the ____

duodenum

12

the basic electrical rhythm of the GI tract is generated by:

ICC- interstitial cells of cajal

13

the basic electrical rhythm is associated with ____

metabolism

14

the ICC rate of stomach is:

3/min

15

the ICC rate of the small intestine is:

10-12/min

16

the ICC rate of the colon is:

variable

17

the action potentials at the top of resting membrane potential slow waves causes:

calcium to be released which binds to calmodulin and activates myosin to cause a contraction

18

what are things that can depolarize the slow waves?

stretch (presence of chyme), ACh/parasympathetics (vagus), gastrin, serotonin, tachykinin

19

what are things that can hyperpolarize the slow waves?

NE, sympathetics, VIP, NO

20

_____ helps mixing in addition to propulsion

segmentation

21

describe the release of bile after ingestion of food:

the vagus nerve stimulates bile production in anticipation. When chyme reaches the duodenum, it secretes CCK. CCK stimulates rhythmic contractions of the gallbladder which releases bile into the duodenum. The vagus also relaxes the sphincter of Oddi (where the common bile duct enters into the duodenum)

22

the majority of the time, it is ____ that is the dominant force of propulsion in the colon

segmental propulsion

23

segmental propulsion is achieved by bands of longitudinal muscle called ______

taneia coli

24

sacs formed by taneia coli for reabsorption:

haustrae

25

what are the two types of propulsions in the colon?

mass movements and segmental propulsion

26

gastrocolic reflex

food in the stomach causes colonic mass movement, due to vagus and gastrin

27

rectosphincteric reflex

rectal stretch stimulates a defecation response

28

Hirshsprung's disease

aka Megacolon: ENS / enternic nerves are absent from lower colon, rectum and internal anal sphincter. The normal defecation reflex does not occur: IAS remains constricted, and the colon becomes dilated.

- congenital disorder, usually diagnosed when child is several months old.

- Treatment: excision of lower colon and rectum, and reanastamosis with external sphincter. child is trained to defecate in a normal manner as a toddler.

29

Motilin and Gastrin are ______  hormones, and thus, are secreted into ____ 

Motilin and Gastrin are endocrine hormones, secreted into the blood

30

Where is Gastrin produced and when is it released? 

- produced from endocrine G cells located in the gastric glands of the antrum (stomach) and duodenum

- is secreted into the blood in response to stretch and the composition of the chyme (carbs, proteins, fats).

31

2 functions of gastrin

- Major action: enhances HCl secretion from the gastric parietal cells

- Early in feeding, when chyme is in stomach and duodenum, gastrin stimulates motility in ileum and colon (in conjunction with PNS) to make room in the colon and push out feces. 

32

Factors that depolarize slow waves include ___

  1. stretch
  2. substance P (tachykinin)
  3. ACh (PNS)
  4. serotonin

33

Factors that hyperpolarizeslow waves include ____

  1. NE (SNS)
  2. nitric oxide (NO)
  3. vasoactive intestinal peptide (VIP)

34

What generated the slow waves in the GIT?

Interstitial cells of Cajal (ICC) between the longitudinal and circular smooth muscle layers.

35

What is the SIP syncytium?

- coupling of the smooth muscle in the GIT to the ICC and a PDGFR-α+ cell, forms a SIP syncytium.

smooth muscle +  Interstitial Cells of Cajal + PDGFR-α+ cell

36

The undulations in the slow waves reflect changes in the RMP caused by ........

coupling of the smooth muscles to the ICC and a PDGFR-α+ cell, forming a SIP syncytium

37

The SIP syncytium is regulated by ___

primarily pottasium (K+) ion channels and receptor-mediated processes

38

What is the BER?

- Slow waves are termed Basic Electrical Rhythm or BER

- because they are ALWAYS present, but their frequency (waves/min) is set by pacemaker cells, which change down the tract. 

39

What sets the BER? 

Different pacemaker cells throughout the GIT. 

40

What is the BER/frequency of slow waves in the stomach and the small intestine? 

slower in stomach (3 waves/min)

faster in small intestine (10-12 waves/min)

41

 when the resting potential is <40 mV, _____ 

- there are essentially no contractions. 

- spike potentials (AP) are generated on the peaks of the slow waves when RMP is depolarized above -40 mV. 

42

Depolarization above -40 mV by ____ will stimulate APs, and the greater the depolarization, _____

- by stretch or parasymp stimulation 

- the more APs, and the greater the contractions

43

The number of action potentials generated on a slow wave are directly related to ____

the force of contractions. 

44

_____ will stop APs and contraction.  

hyperpolarization (ie by sympathetic tone) will stop APs and contraction of GIT smooth muscle

45

Kinds of propulsion that takes palce in the Small intestine

Peristalsis and Segmentation

46

Describe difference between the 2 kinds of propulsion seen in the small intestine. 

Peristalsis:  contraction of circular smooth muscle "behind" the bolus, relaxation of the muscle distal/in front of to the bolus, moves bolus along the tract. Accomplished through stimulatory and inhibitory interneurons, may have more extrinstic (PNS) input.

Segmentation: mixes and propels, circular muscle contracts on either side of the bolus. Due more to local factors (eg stretch). 

47

What are the two types of propulsion seen in the colon (large intestine)?

Segmental propulsion

Mass movements

48

Segmental propulsion

- occurs in the colon/large intestine

- caused by the contraction of longitudinal bands of tanea coli, form pockets of chyme called haustra. - These pockets remain for long periods, allow additional reabsorption of sodium and water (colonic salvage), producing feces.

49

what are haustra? tani coli? 

  1. tani coli - longitudinal muscles on the colon
  2. haustra - when the tanai coli contract they cause chyme in the colon to form pockets called haustra

50

Mass movements

- occur in the colon, are more peristaltic in nature, occur 3-4 times/day coincident with feeding (gastrocolic reflex).

51

When a mass movement is stimulated, _____ relax, and peristaltic contractions in _______ move chyme and feces distally, towards rectum.

the haustra relax !

contractions in ascending and transverse colon

52

Gastrocolic reflex:

chyme in the stomach (gastro), stimulates colonic mass movements (colic) --> Moves chyme and feces out of lower GIT to prepare for more food

53

Describe nerves/hormones involved in Gastrocolic reflex. 

- involves stimulation of Parasympathetic NS:

  • vagus nerves-- through the transverse colon
  • pelvic nerve -- from transverse to descending colon 
  • gastrin-- (hormone from antrum and duodenum, both of which are stimulated very early in feeding)

- vagus and gastrin both stimulate depolarization of slow waves lower in the GI tract (ileum, ascending and T colon), initiating peristaltic-type movements. 

54

Ileogastric reflex:

- chyme in the ileum (ileo-) slows gastric emptying into duodenum (gastric). Buys more time to clear the lower GIT

- When motility in ilium increases via gastrocolic reflex, this signals pylorus to increase sphincter tone, and reduce the amount of chyme leaving stomach. 

55

Rectosphincteric reflex

Defecation reflex: Feces in the rectum relaxes the internal anal sphincter and we feel the urge to defecate.

- dependent on enteric nerves, which respond to mechanoreceptors in the rectum (stretch!) by relaxing IAS and send a reflex to the brain stimulating the urge to defecate. We then constrict the external anal sphincter until ready to go!