L-8 Intro to GI

Question 1

what are the layers of the gut tract wall?

Answer 1

outer to inner

1) serosa
2) longitudinal smooth muscle layer
3) myenteric plexus (of auerbach)
4) circular smooth muscle layer
5) meissner’s plexus (submucosal plexus)
6) submucosa
7) mucosa

Question 2

describe the serosa

Answer 2

• outer layer of CT and simple squamous epithelium
• continuous with mesentery (pathway for blood vessels to gut tube)
• missing in some parts (i.e. esophagus) replaced w adventitia connecting to abdominal wall

Question 3

describe the submucosa

Answer 3

• incorporates blood vessels and submucosal plexus

Question 4

describe the mucosa

Answer 4

• forms a continuous sheet lining entire G.I. tract
• loose CT w sensory nerves, blood vessels and some glands
• includes muscularis mucosa: thin layer of smooth muscle.

Question 5

what are propulsive movements?

Answer 5

• stimulation at any point in the gut can cause a contractile ring to occur
• contractile ring moves forward after it appears

Question 6

what is the usual stimulus?

Answer 6

distension

Question 7

how else may it occur?

Answer 7

due to chemical or physical irritation or strong parasympathetic signals

Question 8

what does it require?

Answer 8

the presence of functional myenteric plexus

Question 9

what direction does it go?

Answer 9

any direction but usually dies out when heading towards the oral end

Question 10

describe mixing movements

Answer 10

• may be caused by peristaltic contractions themselves

- at other times local intermittent constrictive contractions occur every few centimeters in the gut wall

Question 11

what are slow waves?

Answer 11

• complex interactions among the smooth muscle cells and the interstitial cells of Cajal

Question 12

what are cells of Cajal?

Answer 12

smooth muscle cell electrical pacemakers

Question 13

further describe slow waves

Answer 13

• slow, oscillating potentials inherent to the smooth muscle itself in some parts of the digestive tract and spread through gap junctions
• slow waves are not action potentials

Question 14

what do slow waves set the baseline for?

Answer 14

for intermittent spike potentials

Question 15

T/F: slow waves occur spontaneously

Answer 15

true

Question 16

where do slow waves originate?

Answer 16

in interstitial cells of Cajal (pacemakers)

Question 17

the intensity varies btwn:

Answer 17

5 and 15 mv

Question 18

what about the frequency ranges?

Answer 18

from 3 to 12 per minute (increases fomr stomach to duodenum)

*slow waves set the max frequency of contraction of each part of the GI tract

Question 19

Describe spike potentials

Answer 19

• action potentials
• they excite muscle contractions
• occur automatically when resting membrane potential of GI smooth muscle becomes more positive than -40 mv

Question 20

what happens when the slow wave potential gets higher?

Answer 20

the higher the slow wave potential, the greater the frequency of the spike potential

Question 21

how long does it last?

Answer 21

10-40 times as long as a typical action potential in a large nerve fiber (10-20 ms)

Question 22

what are spike potentials responsible for?

Answer 22

for opening calcium-sodium channels in GI smooth muscle cells

channels open and close slowly

Question 23

what are some factors that cause depolarization?

Answer 23

• stretching of muscle
• stimulation by acetylcholine (parasympathetic)/ lack of sympathetic stimulation
• stimulation by specific GI hormones

Question 24

what are some factors that cause hyperpolarization

Answer 24

• norepinephrine and epinephrine (sympathetic)

Question 25

what are some causes of tonic contractions

Answer 25

- continuous repetitive spike potentials - hormones - continuous entry of calcium ions

Question 26

pattern of motility

Answer 26

- local stimulus like stretch from bolus - opens sodium channels - slow waves pass locally thru gap junctions - spikes occur causing action potentials