Gastric Motility and Pancreatic Function

Question 1

What controls gastric motility?

Answer 1

• peristaltic waves that move from the body of the stomach to the antrum

Question 2

Where does the mixing of boli take place in the stomach and why does it occur here?

Answer 2

• antrum

- it has a much thicker muscle and therefore produces a more powerful contraction

Question 3

What does contraction of the plyori sphincter cause?

Answer 3

• cycling in the bottom of the stomach

Question 4

State the two functions of cycling in the stomach.

Answer 4

• controls the release of chyme

- allows more time for mixing as it forces the left over chyme back into the body

Question 5

How are peristaltic waves generated and produced?

Answer 5

• peristaltic waves are generated by pacemaker cells

- produced as a combined action of the circular and longitudinal muscles.

Question 6

Where are the pacemaker cells of peristalsis located?

Answer 6

• in the longitudinal muscle layer

Question 7

In addition to peristaltic waves, which other type of wave is important in gastric secretion?

Answer 7

• slow waves

Question 8

How are slow waves generated?

Answer 8

• through spontaneous depolarisation and repolarisation

Question 9

Where are slow waves conducted?

Answer 9

• through gap junctions along the longitudinal muscle layer

Question 10

True or False?

Slow wave depolarisation reaches threshold.

Answer 10

False.
Slow wave depolarisation does not reach threshold, so further depolarisation is required to induce action potentials - and therefore contraction

Question 11

Name two other factors which increase gastric contraction.

Answer 11

• the release of gastrin

- distension of the stomach wall triggering long and short reflexes

Question 12

Name three things that when present in the duodenum stimulate an inhibition of motility.

Answer 12

• fats
• acids
• hypertonicity

Question 13

How is acid in the duodenum neutralised?

Answer 13

• by bicarbonate secretion brom Brunner’s gland duct cells

Question 14

What does any acid arriving in the duodenum trigger?

Answer 14

• long (vagal) and short (ENS) reflexes
• release of secretin from S cells in the duodenal mucosa
  These both lead to bicarbonate secretion

Question 15

From which three areas does secretin trigger bicarbonate release?

Answer 15

• duodenum
• pancreas
• liver

Question 16

Describe the negative feedback loop of secretin release.

Answer 16

• presence of acid triggers the release of secretin
• this triggers bicarbonate release
• acid neutralisation will take place
• this neutralisation inhibits secretin release

Question 17

Name the parts of the pancreas.

Answer 17

• head
• body
• tail
• endocrine portion
• exocrine portion
• lobules
• pancreatic duct
• accessory pancreatic duct

Question 18

Where in the pancreas is the endocrine portion contained?

Answer 18

• pancreatic islets

Question 19

Where in the pancreas is the exocrine portion contained?

Answer 19

• in acinar cells within lobules

Question 20

How are lobules of the pancreas connected?

Answer 20

• via intercalated ducts

Question 21

In what circumstances will the accessory pancreatic duct open?

Answer 21

• if the pancreatic duct is blocked

Question 22

Where would you find the digestive precursors of the pancreas?

Answer 22

• at the apical end of the acini

Question 23

What is responsible for the digestive function of the pancreas?

Answer 23

• the exocrine system

Question 24

What is the exocrine system of the pancreas responsible for?

Answer 24

• the secretion of bicarbonate by duct cells

- the secretion of digestive enzymes by acinar cells

Question 25

What type of cells are the duct cells of the pancreas?

Answer 25

• cuboidal epithelial cells

Question 26

True or False?

The sphincter of Oddi controls the flow of both bile and pancreatic juices.

Answer 26

True

Question 27

True or False?

No digestion takes place while travelling through the duct.

Answer 27

True

Question 28

What do acinar cells contain?

Answer 28

• digestive enzymes stored as inactive zymogen granules

Question 29

Why are digestive enzymes stored in their inactive form?

Answer 29

• prevents autodigestion of the pancreas

Question 30

Which enzyme converts trypsinogen to trypsin?

Answer 30

• enterokinase

Question 31

True or False?

Each digestive enzyme has a unique enzyme with converts it from its inactive form to its active form.

Answer 31

False.

Enterokinase actives trypsin, which then activates all other zymogens to active forms.

Question 32

Where is enterokinase bound and why?

Answer 32

• the apical membrane of the duodenum

- this ensures that zymogens can only be activated in the duodenum

Question 33

Name and briefly describe the six categories of pancreatic enzymes.

Answer 33

• proteases (cleave peptide bonds)
• nucleases (hydrolyse DNA/RNA)
• elastase (digests collagen)
• phospholipidases (digests phospholipids to fatty acids)
• Lipases (digests triglycerides to fatty acids and glycerol)
• alpha-amylase (digests starch to maltose and glucose)

Question 34

What stimulates zymogen secretion?

Answer 34

• cholecystokinin (CCK)

Question 35

What triggers neural control of pancreatic function?

Answer 35

• triggered by the arrival of organic nutrients in the duodenum.