Lecture 4: Motility of the GI Tract

Question 1

what are the basic layers of the GI tract

Answer 1

• mucosa
• submucosa
• muscularis externa
• serosa

Question 2

what is motility of the GI tract governed by

Answer 2

• involuntary contraction of smooth muscle with pacemaker interstitial cells of Cajal
• except for upper oesophagus and external anal sphincter

Question 3

what is motility of the upper oesophagus and external anal sphincter governed by

Answer 3

voluntary striated skeletal muscle

Question 4

what controls GI motility and secretion intrinsically

Answer 4

enteric nervous system

Question 5

what makes up the enteric nervous system

Answer 5

• myenteric plexus for motility

- submucosal plexus for secretion and local blood flow

Question 6

what are endocrine hormones secreted by

Answer 6

entero-endocrine cells in the epithelial layer of GI mucosa

Question 7

where is cholecystokinin secreted and what does it do

Answer 7

• secreted by I cells of small intestine

- inhibits gastric emptying

Question 8

where is motilin secreted and what does it do

Answer 8

• secreted by M cells of duodenum and jejunum

- stimulates GI motility

Question 9

what stimulates depolarisation

Answer 9

• stretch
• hormones eg motilin
• acetylcholine release

Question 10

what causes hyperpolarisation

Answer 10

• inhibitory enteric nervous system
• noradrenaline
• hormones eg secretin

Question 11

what happens in Hirchsprung’s disease

Answer 11

• rare congenital absence of myenteric plexus, usually in distal portion of colon
• leads to lack of peristalsis, leading to obstruction and severe constipation

Question 12

what are the 3 stages of deglutition

Answer 12

1) oral
2) pharyngeal
3) oesophageal

Question 13

what are the sections of the pharynx

Answer 13

• nasopharynx
• oropharynx
• laryngopharynx

Question 14

where is the swallowing centre in the brain

Answer 14

• medulla oblongata

- pons in brain stem

Question 15

what happens in achalasia

Answer 15

• lower oesophageal sphincter fails to relax causing food to remain in oesophagus
• could be due to vagal or myenteric defect
• causes distension, inflammation, infection and ulceration

Question 16

what happens in gastro-oesophageal reflux

Answer 16

• lower oesophageal sphincter loses its tone, leading to flow of acidic gastric contents into oesophagus
• could cause hiatus hernia
• causes inflammation and ulceration

Question 17

what allows the stomach to store food

Answer 17

• vagovagal reflex
• mediates receptive relaxation
• reduces muscle tone and allows reservoir function

Question 18

how is emptying of the stomach regulated

Answer 18

excitatory:
- ENS/ANS stimulation
- motilin
inhbitory:
- ANS regulation
- duodenal enterogastric reflexes
- secretin
- cholecystokinin

Question 19

what effect does gastric chyme have on the contents of the small intestine

Answer 19

• makes it more acidic
• makes it hyper/hypo-tonic
• increases fat digestion products

Question 20

which hormones cause decreased gastric emptying

Answer 20

• secretin
• gastric inhibitory peptides
• cholecystokinin

Question 21

what is dumping syndrome

Answer 21

• rapid emptying of gastric contents into small intestine
• occurs following a big meal after gastrectomy
• causes nausea, pallor, sweating, cramps, vertigo and sometimes fainting

Question 22

what is gastroparesis

Answer 22

• stomach fails to empty
• causes bloating and nausea
• may be caused by gastric cancer or peptic ulcers
• occasionally observed in severely diabetic patients

Question 23

what give the small intestine a large surface area

Answer 23

• plicae circulares
• villi projections of mucosa
• brush border microvilli on epithelial cell surface

Question 24

which hormones are involved in peristalsis of the small intestine

Answer 24

excitation:
- gastrin
- cholecystokinin
- insulin
- motilin
- serotonin
inhibition:
- secretin
- glucagon

Question 25

what are the muscle specialisations in the large intestine

Answer 25

• longitudnal muscle is thickened to form three bands
• taeniae coli
• which tonically contract
• to form haustral bulges