Electrical activity of gastrointestinal smooth muscle. Functional types of movements in the gastrointestinal tract – mixing and propulsive movements. Interdigestive myoelectric complex

Question 1

Electrical activity of gastrointestinal smooth muscle - 1

Answer 1

RESTING MEMBRANE POTENTIAL

• when the GI system is at rest
• range from -50mV to -70mV
• unequal distribution of ions across membrane
• selective permeability to these ions

Question 2

Electrical activity of gastrointestinal smooth muscle - 2

Answer 2

slow waves

• rhythmic oscillating changes in membrane potential
• generated by interstitial cells of cajal which act as pacemakers
• display basic electrical rhythm
• determines rhythm of peristalsis

stomach = 3 per min
small intestine = 15 per min
colon = 10 per min

Question 3

Electrical activity of gastrointestinal smooth muscle - 3

Answer 3

SPIKE POTENTIALS

when slow waves reach a peak value causes voltage gated calcium ion channels to - ca2+ influx
- causing muscle contraction

Question 4

Electrical activity of gastrointestinal smooth muscle - 4

Answer 4

PACEMAKER ACTIVITY

the pacemaker of the cells are interstitial cells of cajal

located in all parts of GI tract

function to
- generate slow waves
- communicate with all parts of GI tract

Question 5

Electrical activity of gastrointestinal smooth muscle - 5

Answer 5

ACTION POTENTIALS

when membrane potential of GI tract reaches a certain threshold = rapid depolarisation = AP formed

generated when slow waves peak

Question 6

Electrical activity of gastrointestinal smooth muscle - 6

Answer 6

INNERVATION

PNS
SNS
ENS

Question 7

Electrical activity of gastrointestinal smooth muscle - 7

Answer 7

NEUROTRANSMITTERS

excitatory = Ach/ substance P = stimulate electrical activity = contraction

inhibitory = NO/ vasoactive intestinal peptide = reduce electrical activity = relaxation

Question 8

Electrical activity of gastrointestinal smooth muscle - 8

Answer 8

HORMONES

Question 9

Functional types of movements in the gastrointestinal tract – mixing and propulsion

TYPE 1

Answer 9

PERISTALSIS

rhythmic contraction + relaxation of smooth muscles
functions to push chyme from stomach -> small intestine
- involuntary
- controlled by ENS
- wave-like propulsion

Question 10

Functional types of movements in the gastrointestinal tract – mixing and propulsion

TYPE 2

Answer 10

SEGMENTATION

localised contractions that targets specific regions of SI

• absorption of nutrients into walls
• digesting contents
• mixing food with gastric enzymes

Question 11

Functional types of movements in the gastrointestinal tract – mixing and propulsion

TYPE 3

Answer 11

MOTOR MIGRATING COMPLEX

= combination of electrical + muscular movements between meals
- clearance of undigested food to prevent bacteria from growing
-regulated by motilin which is released when stomach is empty

Question 12

Functional types of movements in the gastrointestinal tract – mixing and propulsive movements - propulsive

TYPE 4

Answer 12

PENDULAR MOVEMENTS

slow backward-forward movement of lower-mid part of small intestine

function to spread food around to help make contact with whole small intestine

happens 15 mins

Question 13

Functional types of movements in the gastrointestinal tract – mixing and propulsive movements - propulsive

TYPE 5

Answer 13

TONIC CONTRACTIONS

prolonged/ sustained contractions of circular muscle

generate enough pressure to push chyme along

Question 14

Functional types of movements in the gastrointestinal tract – mixing and propulsive movements - propulsive

TYPE 6

Answer 14

HAUSTRAL CONTRACTIONS

colon is divided into small pouches called haustra

haustra contract to keep food moving

local/ slow/ 25-30 minutes

Question 15

Functional types of movements in the gastrointestinal tract – mixing and propulsive movements - propulsive

TYPE 7

Answer 15

MASS MOVEMENTS

powerful contractions that happen many times a day

generate enough force to push fecal content to rectum (long distances)

= gastrocolic reflex

Question 16

Functional types of movements in the gastrointestinal tract – mixing and propulsive movements - propulsive

TYPE 8

Answer 16

wave like contractions
pushing food along colon

Question 17

interdigestive myoelectric complex - FUNCTION

Answer 17

ensuring food being sweeped from stomach to small intestine between meals

to ensure no food is left behind causing bacterial growth/ gut problems

preparing GI system for next meal

Question 18

interdigestive myoelectric complex - PHASE 1

Answer 18

= QUIESCENCE

minimal electrical activity = minimal contraction

45-60mins

Question 19

interdigestive myoelectric complex - PHASE 2

Answer 19

INTERMEDIATE PHASE

irregular electrical activity = low contraction

20-30 mins

Question 20

interdigestive myoelectric complex - PHASE 2

Answer 20

HOUSEKEEPING PHASE

high electrical activity = high contraction

10-20 mins

Question 21

interdigestive myoelectric complex - PHASE 3

Answer 21

TRANSITION CONTRACTIONS

= transition from from phase III to phase I

electrical activity lowers