Gastrointestinal: motility

Question 1

What is GI motility? (3)

Answer 1

• Movements of the wall of the GI tract
• Due to contractions of the muscular externa
• Function: to mix and propel

Question 2

What are the different types of electrical activity in the GI smooth muscle? (4)

Answer 2

Slow waves of depolarisation
Frequency of waves: basic electric rhythm
BER vary in different areas of GI tract
Height of BER affected by neural and hormonal input

Question 3

What are the parasympathetic and sympathetic roles in GI smooth muscle?

Answer 3

Parasympathetic: excitation
Sympathetic: inhibition

Question 4

What cells act as pacemaker cells for the GI muscle and where are they located?

Answer 4

• Interstitial cells of Cajal - instigate slow waves

- Sit at boundary of longitudinal and circular smooth muscle layers

Question 5

What is the relationship between electrical and mechanical activity in smooth stomach muscle? (2)

Answer 5

Larger depolarisations = stronger contractions

Action potentials = even stronger contractions

Question 6

What is the relationship between electrical and mechanical activity in smooth intestinal muscle? (2)

Answer 6

Action potentials required for force

Strength of contraction varies with frequency of action potentials

Question 7

What is peristalsis and segmentation? (3)

Answer 7

Peristalsis propels contents forwards
Segmentation mixes contents
Waves of contraction

Question 8

How does peristalsis occur? (3)

Answer 8

Circular and longitudinal muscle contractions

• Proximal segment - circular contracts, longitudinal relaxes, diameter decreases
• Distal segment - circular relaxes, longitudinal contracts, diameter increases

Question 9

How does segmentation occur? (3)

Answer 9

• Motility in the small intestine
• requires circular muscle
• mixes chyme

Question 10

How do we chew? (4)

Answer 10

Chewing reflex - cyclical reflex
Jaw muscles active - mouth closed
Food enters and inhibits jaw muscles
Jaw dropping relieves pressure of food

Question 11

What is saliva + chewed food called?

Answer 11

Bolus

Question 12

How do we swallow? (3)

Answer 12

• Tongue moves bolus to pharynx
• Initiates swallowing reflex
• Integration center - swallowing centre of medulla oblongata

Question 13

What are the steps of the swallowing reflex? (8)

Answer 13

1. Bolus descends into pharynx - presses epiglottis
2. Epiglottis covers glottis so food does not enter trachea
3. inspiration inhibited
4. bolus stretches oesophagus, triggering peristalsis
5. Peristalsis propels bolus to stomach (9s)
6. Bolus arrives at stomach
7. triggers relaxation of lower eosophagul sphincter
8. Bolus enters stomach

Question 14

What are the functions and mechanisms of gastric motility?

Answer 14

Functions: Mix chyme, regulate gastric emptying
Mechanism: peristalsis, enteric nervous system

Question 15

What are the patterns of gastric motility? (4)

Answer 15

1. Waves of peristalsis - increase closer to pylorus
2. Functions in mixing chyme - pyloric sphincter closed
3. Functions in gastric emptying - pyloric sphincter opens with stronger contractions
4. Emptying rate increases - vol. of chyme and strength of gastric peristalsis

Question 16

What regulates the increase force of contractions?

Answer 16

Gastrin

Question 17

What regulates the decrease in force of contractions? (3)

Answer 17

CCK
Secretin
GIP

Question 18

What are the 4 phases of regulation?

Answer 18

Cephalic phase - excitations (anger, aggression)
Cephalic phase - inhibitions (pain, fear, depression)
Gastric phase - excitatory stimulus (distension of the stomach)
Intestinal phase - inhibitory stimuli (distension of duodenum)

Question 19

How is vomiting stimulated? (3)

Answer 19

• Stimuli stimulate stretch receptors and chemoreceptors
• Afferent nervous impulses from GI lining sympathetic and vagal nerves to the brain
• Mediated through vomiting centre in medulla

Question 20

How is the vomiting centre activated? (4)

Answer 20

1. Triggers reverse peristalsis, pyloric sphincter relaxed
2. Powerful efferent nervous impulses cause:
   - contractions of diaphragm and abdominal muscles
   - relaxation of gastro-oesophageal sphincter
3. Gastric and intestinal contents forcefully expelled through the mouth
4. Glottis is closed temporarily

Question 21

What are the 4 other ways vomiting can be caused?

Answer 21

1. Activation of chemoreceptor trigger zone (drugs)
2. Disturbance of vestibular labyrinths by movement (motion)
3. Sensory stimuli - visual olfactory
4. Psychic stimuli - cerebral cortex

Question 22

What hormone stimulates motility?

Answer 22

Gastrin

Question 23

What are the 3 motility reflexes?

Answer 23

Intestino-intestinal reflex - injury or stress
Ileogastric reflex
Gastroileal reflex

Question 24

What is haustrations and where does it occur?

Answer 24

Mixing

Proximal colon

Question 25

How is colon motility regulated? (2)

Answer 25

Colonocolonic reflex - distension in one area causes relaxation in the other
Gastrocolic reflex - food in stomach increases motility

Question 26

What are the steps in defacation?

Answer 26

1. Distension of colon
2. Stretch receptors
3. Rectum and smooth muscle contracts
4. Increase pressure in the rectum
   =5. Both sphincters relax - defecation
   =5. Internal anal sphincter relaxes/external anal sphincter contracts