IN-DEPTH GI Tract Motility

Question 1

Describe the function of mastication

Answer 1

• Mixes food with saliva (mucin acts as a lubricant),
• Reduces size of food particles,
• Mixes food components with digestive enzymes

Question 2

What does Deglutition consist of?

Answer 2

• Voluntary stage (initiates the swallowing process),
• A pharyngeal stage (Involuntary passage of food through the pharynx into oesophagus),
• Oesophageal stage (involuntary transport of food from the pharynx to the stomach)

Question 3

Describe features of the oral/voluntary phase

Answer 3

1) Food voluntarily moved posterior into the pharynx by the tongue.
2) The trachea is closed, oesophagus open and a fast peristaltic wave initiated by the nervous system

Question 4

Describe the pharyngeal phase

Answer 4

• Reflex act which is initiated by voluntary movement of food into the back of the mouth.
• Excitation of involuntary pharyngeal sensory receptors to elicit the swallowing reflex. The next stages are automatically initiated by neuronal areas of the medulla and lower pons.

Question 5

Describe the effects of pharyngeal stage on respiration

Answer 5

The swallowing centre specifically inhibits the respiratory centre of the medulla during this time. Respiration arrested very briefly

Question 6

Describe the oesophageal phase and peristalsis

Answer 6

Primary peristalsis - Continuation of peristaltic wave that began in the pharynx.

Secondary peristalsis - Results from distention of the oesophagus by retained food and the waves continue until all food has emptied into the stomach. It is initiated by intrinsic neural circuits in myenteric NS and reflexes that

Question 7

Describe the neurological control of the different muscle types of the oesophagus

Answer 7

Upper 1/3rd - Controlled by glossopharyngeal and vagus nerves.

Lower 2/3rd - Controlled by vagus and acts through connections with the oesophageal myenteric nervous plexus

Question 8

Describe the receptive relaxation of the stomach and lower oesophageal sphincter

Answer 8

• Relaxation wave occurs before peristalsis which is transmitted via myenteric inhibitory neurons. This means the stomach becomes relaxed in preparation for food arrival. This also allows for the sphincter to relax and easy propulsion of food into the stomach

Question 9

Describe the storage function of the stomach

Answer 9

Food stretches the stomach resulting in a vagovagal reflex. This decreases tone in muscular wall, it causes the wall to bulge out and greater quantities of food to come in.

Question 10

Describe the mixing function of the stomach

Answer 10

Mixing waves begin in the mid/upper stomach wall, initiated by ICC which create weak peristaltic constrictor waves. The waves then become more intense which plays an important role mixing the stomach contents and creates an upstream squeezing action.

Question 11

Describe the emptying function of the stomach

Answer 11

There is slow emptying of the chyme from the stomach into the small intestine. This is regulated by gastric and duodenal factors, eg, increased stomach volume = increase emptying and the enterogastric inhibitory reflex. Hormonal factors

Question 12

Explain what promotes and opposes stomach emptying

Answer 12

Promoted by intense peristaltic contractions in stomach antrum.

Opposed by pylorus constriction under the influence of nervous, hormonal signals from stomach and duodenum

Question 13

Describe the movements of the small intestine

Answer 13

• Chyme induced extension of GI wall leads to stretch and localised concentric contractions and segmentation.
• Slow peristalsis

Question 14

The frequency of segmentation is determined of what?

Answer 14

The frequency of slow waves. The slow waves cause the segmentation contractions.

Question 15

What is the ileocecal valce?

Answer 15

A sphincter (thickened circular muscle) from the small intestine into the cecum.

Question 16

What is the function of the gastroileal reflex?

Answer 16

Immediately after a meal it causes intensifying of peristalsis which empty’s the contents of the ilium into the cecum. It is mediated via myenteric plexus and extrinsic autonomic nerves

Question 17

Describe the mixing movements in the colon

Answer 17

Bowel contents are mixed in haustrations which are bag-like sacs that appear due to combines contraction of circular and longitudinal smooth muscle

Question 18

Describe the propulsive movements in the colon

Answer 18

Modified peristalsis - Constrictive ring occurs in response to distention and 20cm of colon distal to this ring lose their haustrations and contract as a unit. Allowing for mass faecal movement

Question 19

What is the function of the Gastrocolic and Duodenocolic reflexes?

Answer 19

They facilitate mass movements after meals and occur due to distention of the stomach and duodenum.

Question 20

What can irritation of the colon cause?

Answer 20

It can initiate intense mass movement. eg, can occur with ulcerative colitis

Question 21

Describe the process of defecation

Answer 21

Gas or faeces in the rectum stimulates stretch receptors in its wall stimulating the rectosphincter reflex

Question 22

Describe the rectosphincter reflex

Answer 22

It is the reflex relaxation of smooth muscle of the internal anal sphincter and contraction of the striated muscle of the external anal sphincter