Gastric Motility and Pancreatic Function

Question 1

Describe mixing of gastric contents via smooth muscle contraction

Answer 1

Peristaltic contractions by the stomach body move food to the antrum, weak - no mixing
Once contents in the antrum pyloric sphincter contracts and strong contraction of the antrum wall induces mixing

Question 2

Do gastric contents leak into the duodenum during mixing?

Answer 2

A small amount of chyme leaks into the duodenum but for the most part leaking is stopped due to pyloric sphincter contraction
Stops dumping syndrome from occurring

Question 3

What cells are responsible for setting gastric peristaltic rhythm?

Answer 3

Pacemaker cells in the longitudinal muscle - about 3 contractions/min

Question 4

What is slow wave rhythm?

Answer 4

Slow wave rhythm is the base rhythm at which pacemaker cells depolarize. It is called the basic electrical rhythm (BER)
It is not frequent enough for depolarization to threshold which induces peristalsis

Question 5

What causes pacemakers to depolarize at above BER?

Answer 5

Gastrin / Distension of stomach wall
The presence of hormones/neural signalling - gastrin induces motility, distension of the stomach causes vagus and enteric stimulation

Question 6

What inhibits gastric peristalsis?

Answer 6

Excess nutrients in the stomach/SI - avoid dumping syndrome

High acid/tonicity inhibits motility

Question 7

What determines force of motility contractions?

Answer 7

Frequency of AP’s fired from pacemaker cells in longitudinal muscle

Question 8

Which cells secrete bicarbonate? (HCO3) In which layer are they?

Answer 8

Brunner’s gland cells

In the submucosa of the duodenum

Question 9

What stimulus triggers secretion of bicarbonate by the duodenum?
Mechanism?

Answer 9

Acid in the duodenum
Causes vagal and short ENS reflexes
Causes release of secretin
Both stimulate Brunner’s glands

Question 10

What cells does secretin stimulate for the release of bicarbonate? What inhibits secretin release?

Answer 10

Stimulates Brunner’s gland cells
Stimulates HCO3 release from the pancreas and liver into the duodenum
Acid neutralization inhibits secretin (neg. feedback)

Question 11

Three parts of pancreas?

Answer 11

Head (within curve of duodenum)
Body
Tail (extends to spleen)

Question 12

Two portions of the pancreas?

Answer 12

Endocrine portion (islets) 
Exocrine portion (acinar cells - lobules)

Question 13

Function of the endocrine portion of the pancreas?

Answer 13

Islets of Langerhans produce insulin, glucagon and somatostatin (controls release of insulin and glucagon)
Secretes these into the blood to control blood glucose

Question 14

Pathway of pancreatic juices to duodenum?

Answer 14

Produced by acinar cells, acinar cells form lobules, lobules are connected by intercalated ducts, these lead into intralobular ducts, which lead into interlobular ducts - to main pancreatic duct - common bile duct
Common bile duct goes through the sphincter of oddi which controls secretion of pancreatic juice

Question 15

Function of acinar cells and duct cells in exocrine portion of pancreas?

Answer 15

Acinar cells - produce digestive zymogens

Duct cells - secrete bicarbonate

Question 16

What cells make up the islets of Langerhans and what do they secrete?

Answer 16

Alpha cells - secrete glucagon
Beta cells - secrete insulin
Delta cells - somatostatin

Question 17

Where are the duct cells of the pancreas located?

Answer 17

In the ducts leading away from the islets to the common bile duct (intra/interlobular ducts)

Question 18

How does the pancreas store digestive enzymes? What happens to them when they’re secreted into the duodenum?

Answer 18

Stores them as inactive zymogens
Trypsinogen is one of these zymogens, when pancreatic juice enters the duodenum it encounters enterokinase on the surface of gut enterocytes - converts it to active trypsin - it converts all other zymogens to active form

Question 19

Classes of pancreatic enzymes? Functions?

Answer 19

Proteases - cleave peptide bonds
Nucleases - Hydrolyse DNA/RNA
Elastases - Collagen digestion
Phospholipases - phospholipids to FA’s
Lipases - Triglycerides to FA’s and glycerol
Alpha amylase - Starch to maltose and glucose

Question 20

What stimulates zymogen secretion?

Answer 20

Fats/Amino Acids in the duodenum cause the release of CCK, CCK causes release of zymogens

(also under neural control, triggered by organic nutrients in duodenum)