2. Motility processes at each stage of the alimentary system

Question 1

What are the 3 purposes of mastication?

Answer 1

Reduce particle size of food bolus
Mixes food with saliva - lubrication and enzymes
Increases surface area of food particles

Question 2

Describe the control of swallowing.

Answer 2

Is both voluntary (striated muscle) and involuntary (smooth muscle)
Starts off as voluntary and then becomes involuntary (mostly involuntary)
‘Swallowing centre’ within the reticular formation of the brainstem

Question 3

Describe the function of the oesophagus

Answer 3

Acts as a conduit (tube) to propel the bolus from the pharynx to the stomach via peristalsis

Question 4

Describe the innervation of the oesophagus

Answer 4

Receives both sympathetic and parasympathetic control from the vagus nerve
Also receives innervation from the myenteric plexus

Question 5

Describe the functions of the stomach

Answer 5

Reservoir of large quantities of indigested food
Initiates digestion
Acid secretion
Releases contents in controlled fashion into duodenum

Question 6

What cranial nerve innervates the stomach?

Answer 6

Vagus nerve

Question 7

Describe how contractions of the upper stomach are involved in gut motility to maintain a constant pressure.

Answer 7

The upper stomach, composed of the fundus and upper body, shows low frequency, sustained contractions that are responsible for generating a basal pressure within the stomach. Importantly, these tonic contractions also generate a pressure gradient from the stomach to small intestine and are thus responsible for gastric emptrying. Interestingly, swallowing of food and consequent gastric distention inhibits contraction of this region of the stomach, allowing it to balloon out and form a large reservoir without a significant increase in pressure.

Question 8

Describe how the contractions of the lower stomach are involved in gut motility to grind gastric contents.

Answer 8

The lower stomach, composed of the lower body and antrum, develops strong peristaltic waves of contraction that increase in amplitude as they propagate toward the pylorus. These powerful contractions constitute a very effective gastric grinder; they occur about 3 times per minute in humans. Gastric distention strongly stimulates this type of contraction, accelerating liquefaction and hence, gastric emptying. The pylorus is functionally part of this region of the stomach - when the peristaltic contraction reaches the pylorus, its lumen is effectively obliterated - chyme is thus delivered to the small intestine in spurts.

Question 9

What are the 3 functions of the small intestine?

Answer 9

1. Mix foodstuffs and digestive secretions
2. Circulate digested contents to facilitate contact with mucosa
3. Propulsion of contents towards terminal ileum

Question 10

How long does propagation to the ileum take?

Answer 10

Over 2-3 hours

Question 11

What is the name used to describe the contractions of smooth muscle in the GI tract between meals?

Answer 11

Migrating motility complex - every 90(-120) minutes

Question 12

Name and describe the 4 types of movements in the small intestine along with their purpose.

Answer 12

1. Segmentation contractions (non synchronised) - circular smooth muscle - mix chyme
2. Pendular contraction - longitudinal muscle - mix chyme
3. Villous movements - brought about by muscularis mucosae
4. Peristaltic waves - arise from duodenal bulb and propel food towards terminal ileum