5.4.3: The pancreas and release of insulin

Question 1

What is the pancreas and why is it unusual?

Answer 1

• A small organ lying below the stomach.

- It is unusual in that it has both exocrine and endocrine functions.

Question 2

What are the two main secretions of the pancreas?

Answer 2

• The pancreatic juices containing enzymes which are secreted into the small intestine.
• Hormones which are secreted from the islets of Langerhans into the blood.

Question 3

What do exocrine glands secrete substances into?

Answer 3

Exocrine glands secrete substances into a duct.

Question 4

What is the exocrine function of the pancreas?

Answer 4

Most cells in the pancreas synthesise and release digestive enzymes.

Question 5

How are the exocrine cells arranged?

Answer 5

• The exocrine cells are in small groups surrounding tiny tubules.
• Each group of cells is called an acinus (plural acini). The acini are grouped together into small lobules separated into connective tissues.

Question 6

How do the enzymes secreted get to the small intestine from the acini?

Answer 6

• The cells of the acini secrete the enzymes they synthesise into the tubule at the centre of the group.
• The tubules from the acini join to form intralobular ducts that eventually combine to make up the pancreatic duct.
• The pancreatic duct carries the fluid containing the enzymes into the first part of the small intestine (duodenum)

Question 7

Which enzymes does the fluid from the pancreatic duct contain?

Answer 7

• Pancreatic amylase.
• Trypsinogen
• Lipase

Question 8

What is pancreatic amylase?

Answer 8

A carbohydrase which digests amylose to maltose.

Question 9

What is trypsinogen?

Answer 9

An inactive protease which will be converted to the active form trypsin when it enters the duodenum.

Question 10

What is lipase?

Answer 10

Enzyme that digests lipid molecules

Question 11

What does the fluid from the pancreatic fluid also contain?

Answer 11

• Sodium hydrogencarbonate, which makes it alkaline.
• This helps it to neutralise the contents of the digestive system that have just left the acid environment of the stomach.

Question 12

Where are the islets of Langerhans?

Answer 12

Dispersed in small patches along the lobules of acini.

Question 13

What do the islets of Langerhans contain?

Answer 13

-Alpha cells and beta cells that make up the endocrine tissue in the pancreas.

Question 14

What do the alpha cells secrete?

Answer 14

Glucagon

Question 15

What do the beta cells secrete?

Answer 15

Insulin

Question 16

When insulin is secreted from the beta cells in the islets of Langerhans, what effects does it have?

Answer 16

A reduction in blood glucose concentrations.

Question 17

If the blood glucose concentration is too high then it is important that insulin is released from beta cells. But, what must happen if blood glucose concentration drops too low?

Answer 17

It is important that insulin secretion stops.

Question 18

The secretion of insulin from bets cells is an 8 step process.
Step 1:

Answer 18

The cells membranes of the beta cells contain both calcium ion channels and potassium ion channels.

Question 19

The secretion of insulin from bets cells is an 8 step process.
Step 1: The cells membranes of the beta cells contain both calcium ion channels and potassium ion channels.

Step 2:

Answer 19

• The potassium ion channels are normally open and the calcium ion channels are normally closed.
• Potassium ions diffuse out of the cell making the inside of the cell more negative.
• The resting potential difference across the membrane is about -70mV

Question 20

The secretion of insulin from bets cells is an 8 step process.
Step 2: The potassium ion channels are normally open and the calcium ion channels are normally closed.
-Potassium ions diffuse out of the cell making the inside of the cell more negative.

Step 3:

Answer 20

When glucose concentrations outside the cell are high, glucose molecules move into the cell.

Question 21

The secretion of insulin from bets cells is an 8 step process.
Step 3: When glucose concentrations outside the cell are high, glucose molecules move into the cell.

Step 4:

Answer 21

• The glucose is quickly used in metabolism to produce ATP.

- This involves the enzyme glucokinase.

Question 22

The secretion of insulin from bets cells is an 8 step process.
Step 4: The glucose is quickly used in metabolism to produce ATP. This involves the enzyme glucokinase.

Step 5:

Answer 22

-The extra ATP causes potassium channels to close.

Question 23

The secretion of insulin from bets cells is an 8 step process.
Step 5: The extra ATP causes potassium channels to close.

Step 6:

Answer 23

• The potassium can no longer diffuse out and this alters the potential difference across the cell membrane.
• It becomes less negative inside.

Question 24

The secretion of insulin from bets cells is an 8 step process.
Step 6: The potassium can no longer diffuse out and this alters the potential difference across the cell membrane. It becomes less negative inside.

Step 7:

Answer 24

This change in potential difference opens the calcium ion channels.

Question 25

The secretion of insulin from bets cells is an 8 step process.
Step 7: This change in potential difference opens the calcium ion channels.

Step 8:

Answer 25

• Calcium ions enter the cell and…
• cause the secretion of insulin by making the vesicles containing insulin move to the cell surface membrane…
• and fuse with it, releasing insulin by exocytosis.