Gastric Motility & Pancreatic Function

Question 1

How do gastric contents move through the stomach?

Answer 1

By peristaltic waves

Question 2

In what section of the stomach does most mixing occur and why?

Answer 2

The antrum as it has a thick powerful muscle
The muscle around the body of the stomach is much weaker and so does little more than move the contents along

Question 3

How does the pyloric sphincter control movement of gastric contents?

Answer 3

Once a small amount of gastric contents hits the duodenum the pyloric sphincter closes forces most of the contents back up towards the body to be mixed again

Question 4

How fast is the gastric peristaltic rhythm?

Answer 4

~3 waves/min

Question 5

What regulates the peristaltic rhythm?

Answer 5

Spontaneous depolarisation in pacemaker cells in the longitudinal muscle layer

Question 6

What do we call the basic electrical rhythm of the gastric muscle?

Answer 6

Slow Wave Rhythm

Question 7

What parts of the GI tract are slow waves conducted to and how?

Answer 7

The stomach, and intestines.
The longitudinal muscle is connected by gap junctions all the way down

Question 8

The slow wave depolarisation happens constantly, why isnt your stomach contracting even when empty?

Answer 8

The slow wave depolarisation is sub threshold and requires further depolarisation from another source to trigger an action potential

Question 9

What other sources of depolarisation add to the slow wave depolarisation?

Answer 9

Gastrin -> Increases Contraction

Distension of stomach wall -> Vagal and ENS reflexes (long & Short) -> Increased Contraction

Question 10

What factors reduce gastric motility?

Answer 10

Acid in duodenum -> More Secretin from S cells -> Reduce gastric motility

Fat/amino acids/hypertonicity in duodenum -> Cholecystokinin -> reduce gastric motility

Question 11

What chemical neutralises stomach acid upon reaching the duodenum? and where is it produced?

Answer 11

Bicarbonate (HCO3-)

Made in ductal cells (pancreatic duct) and brunners glands (duodenal submucosa)

Question 12

How is HCO3- secretion regulateD?

Answer 12

Acid is detected in the duodenum:
1) Long vagal & short ENS reflexes
2) Secretin released from S cells
- triggers HCO3- secretion in ductal cells
- acid neutralisation then inhibits secretin release

Question 13

Describe the endocrine portions of the pancreas?

Answer 13

Islets of langerhans
They secrete:
- insulin & glucagon.
- Somatostatin (controls insulin/glucagon release)

Question 14

Describe the exocrine portion of the pancreas and the passage to the duodenum

Answer 14

Acinar cells forms lobules
-> Lobules connected by intercalated ducts
-> Join into intralobular ducts
-> Join into interlobular ducts
-> Combine into pancreatic duct
-> Joins common bile duct at hepatopancreatic ampulla
-> Passes through sphincter of Oddi
-> Exits into duodenum at the major duodenal papilla

Question 15

How do we compensate for a blocked pancreatic duct?

Answer 15

WE have a smaller accessory pancreatic duct that can open if needed

Question 16

What type of epithelium lines the pancreatic duct and what do they produce?

Answer 16

Cuboidal epithelium makes up the ductal cells.

They produce bicarbonate

Question 17

What does the exocrine portion of the pancreas secrete?

Answer 17

Acinar cells -> Digestive enzymes
Ductal cells -> Bicarbonate

Question 18

Why do acinar cels store their secretions as zymogens?

Answer 18

So they dont self digest

Question 19

How are the zymogens of digestive enzymes activated upon hitting the duodenum?

Answer 19

Enterokinase is bound to the brush border of duodenal enterocytes
-> It activates trypsinogen to trypsin
-> Trypsin then converts the rest of the zymogens to active forms

Question 20

Name the 6 types of pancreatic enzymes and what they do:

Answer 20

Proteases - cleave peptide bonds
Nucleases - Hydrolyse DNA/RNA
Elastases - Digest collagen
Phospholipidases - break down phospholipids to fatty acids
Lipases - break TAG to fatty acids + glycerol
Alpha-amylase - Breaks starch to maltose & glucose

Question 21

Summarize the control of pancreatic secretions

Answer 21

Bicarbonate:
- Secretin controlled
- Released in response to acid in the duodenum

Zymogens:
- Controlled by Cholecystokinin (CCK)
- Released in response to fats & amino acids in the duodenum

Neural control through long vagal and short ENS reflexes also trigger bicarbonate and zymogen release in response to organic nutrients in the duodenum.