1.2 Regulation of the GIT: Motility

Question 1

Define gut motility

Answer 1

Stretching and contractions of the muscles under involuntary control in the gastrointestinal tract
- controlled movements that enable food to progress along the digestive tract & ensuring the absorption of important nutrients

Question 2

What is peristalsis?

Answer 2

Series of involuntary wave-like muscle contractions that moves food to different processing stations in the digestive tract

Question 3

Define mechanical digestion

Answer 3

Physical act of breaking down the food by non-chemical means
- begins in the mouth with mastication

Question 4

Describe the function of the tunica muscularis

Answer 4

Contains smooth muscle fibres

- allowing the folds to move and the whole area of the stomach can process food mechanically

Question 5

What is the Margo Plicatus?

Answer 5

Separates glandular and non-glandular parts of the stomach

- horses only

Question 6

What are the stages of mechanical digestion in ruminants?

Answer 6

1. Mastication & mixing
2. Ingestion & foregut fermentation
3. Regurgitation, re-mastication and eructation (liberation of gases from/through the foregut → oesophagus → mouth)

Question 7

Which nerve innervates the rumen?

Answer 7

Vagus (CN X)

Question 8

How is mechanical digestion in the rumen stimulated?

Answer 8

Distention (stretch receptors), ingesta consistency, VFA concentration

Question 9

Describe primary movements of the rumen

Answer 9

Inside the rumen to mix bolus of food

• ingesta with microbiota
• promote separation of this fermentation into different phases

Question 10

Describe secondary movement of the rume

Answer 10

Occurs outside of the rumen

- facilitate expulsion of gas from the rumen

Question 11

What is intestinal motility controlled by?

Answer 11

Excitatory and inhibitory signals from enteric nervous system

Question 12

What is intestinal motility modulated by?

Answer 12

Inputs from the central nervous system, and gastrointestinal hormones

Question 13

What is segmentation?

Answer 13

Contractions chop, mix and roll the chyme

Question 14

What is peristalsis?

Answer 14

Slowly propels it towards the large intestine

Question 15

What is haustration?

Answer 15

Chop and mix the ingesta, presenting it to the mucosa where absorption occurs
- contractions form sacculations > hausta/haustrum

Question 16

What are antiperistaltic contrations?

Answer 16

Propagate towards the ileum - retards the movement of ingesta through the colon - reabsorption of water & electrolytes

Question 17

What are mass movements?

Answer 17

Very intense and prolonged peristaltic contraction which strips an area of large intestine clear of contents

Question 18

What is the digestive phase of peristalsis?

Answer 18

Peristaltic contractions pass over short segments of the intestine

Question 19

What is the interdigestive phase of peristalsis?

Answer 19

Peristaltic contractions pass over large segments of the intestine

Question 20

What is the migrating motor complex?

Answer 20

Distinct pattern of electromechanical activity observed in gastrointestinal smooth muscle during the periods between meals

Question 21

What are functions of the migrating motor complex?

Answer 21

Sweep residual undigested material through the digestive tube
Control bacterial population

Question 22

What are the phases of the migrating motor complex?

Answer 22

1. Smooth muscle quiescence. Rare action potentials and contractions
2. Peristaltic contractions occur and progressively increase in frequency
3. Rapid, evenly spaced peristaltic contractions occur
4. Short period of transition between contractions in phase 3 and inactivity in phase 1

Question 23

Describe the intrinsic control of GIT motility

Answer 23

Gut smooth muscle exhibits spontaneous “slow wave activity” = Basic Electric Rhythm of depolarisation and re-polarisation
- when the amplitude of BER reaches a threshold level an action potential occurs leading to contraction of smooth muscle cells

Question 24

Describe the extrinsic control of GIT motility

Answer 24

Endocrine - hormones released in the bloodstream reach target
Paracrine - agents released for local diffusion to target on nearby cells
Nervous - intrinsic control from enteric nervous system + autonomic control from CNS (parasympathetic ‘rest and digest’)

Question 25

What is the myenteric plexus?

Answer 25

Outside submucosal plexus, within muscularis internal and external
- controls digestive tract motility

Question 26

What is the submucosal plexus?

Answer 26

Present on submucosal layer

- senses environment within lumen → regulates GI blood flow + controls epithelial cell function

Question 27

What hormone decreases GIT activity in the sympathetic nervous system?

Answer 27

Noradrenaline

Question 28

What hormone decreases GIT activity in the parasympathetic nervous system?

Answer 28

Acetylcholine

Question 29

Describe the function of interneurons

Answer 29

Responsible for integrating information from sensory neuron + providing it for programming for interior motor neurons

Question 30

What are the sensory nerve endings?

Answer 30

Neurons which capture stimuli from within GI tract, from mucosa + pass these onto a pre-vertebral ganglia

Question 31

Describe the flow of information through the excitatory neurons

Answer 31

Ach → smooth muscle contraction, intestinal secretions, release of enteric hormones and dilation of blood vessels

Question 32

Describe the flow of information through the extrinsic sympathetic neurons

Answer 32

Noradrenaline → opposite effects from Ach