4 - Insulin secretion and intermediary metabolism

Question 1

How to remember what insulin does?

Answer 1

The eating hormone - it is released after you’ve eaten

Question 2

What does insulin do in terms of blood [Glucose]?

Answer 2

DECREASES blood glucose concentration

Question 3

What 4 things increase the concentration of glucose in the blood?

Answer 3

• Glucagon
• Catecholamines (hormones produced by adrenal glands)
• Somatotrophin
• Cortisol

Question 4

Define Type 1 Diabetes Mellitus.

Answer 4

Elevated glucose, were insulin is required to prevent ketoacidosis

Question 5

Define Type 2 Diabetes Mellitus.

Answer 5

More common. It’s defined in terms of glucose but related to hypertension and dyslipidaemia.

Question 6

How can glucose be monitored?

Answer 6

Capillary glucose monitoring

Question 7

When does hypoglycaemia occur?

Answer 7

When there is an imbalance between diet, exercise and insulin

Question 8

What is hypoglycaemia?

Answer 8

Low blood sugar.
Below 4-5mM

Below 2mM: unconscious, coma, death

Question 9

What is the structure of the pancreas?

Answer 9

98% of the pancreas does exocrine secretions via a duct to the small intestine

2% of the pancreas are clumps of cells called Islets of Langerhans

Question 10

What are the 3 types of cell in the islets of Langerhans?

Answer 10

alpha cells
beta cells
delta cells

Question 11

What is the purpose of gap junctions between cells?

Answer 11

Allow small molecules to pass directly between cells

Question 12

What are the purpose of tight junctions between cells?

Answer 12

To form small intercellular spaces

Question 13

What do α-cells produce?

Answer 13

Glucagon

Question 14

What do β-cells produce?

Answer 14

Insulin

Question 15

What do δ-cells produce?

Answer 15

Somatostatin

Question 16

What does insulin stimulate?

Answer 16

Growth and development

Question 17

What does somatostatin inhibit?

Answer 17

Insulin and Glucagon

Question 18

What does glucagon increase?

Answer 18

Blood glucose

Question 19

How does insulin decrease blood glucose?

Answer 19

1. Increases glycogenesis (making glycogen from glucose)
2. Increased glycolysis (breakdown of glucose)
3. Increased transport of glucose into cells via GLUT4

= Decreased blood glucose

Question 20

How does insulin affect amino acids?

Answer 20

Insulin increases amino acid transport and increases protein synthesis

Question 21

How does insulin affect lipids?

Answer 21

Decreases lipolysis (breakdown of fats & lipids into fatty acids)

Increased lipogenesis (the metabolic formation of fat)

Question 22

What triggers make B-cells produce insulin?

Answer 22

1. Increased blood glucose
2. Glucagon from α cells.
3. Certain gastrointestinal hormones
4. Certain amino acids
5. Parasympathetic activity (β-receptors)

Question 23

What triggers stop B-cells from making insulin?

Answer 23

1. Somatostatin from δ-cells.

2. Sympathetic activity (α receptors)

Question 24

How does glucagon increase blood glucose?

Answer 24

1. Increased amino acid transport into the liver
2. Increased lipolysis
   1 & 2 = increased gluconeogenesis (making new glucose)
3. Increased hepatic glycogenolysis (breaking down glycogen into glucose in the liver)

= Increased blood glucose

Question 25

How does a β-islet cell know when to make insulin? | What is the process?

Answer 25

1. Glucose enters B-cell through GLUT2 2. Glucokinase enzyme turns glucose into glucose-6-phosphate. This is the rate limiting step 3. Metabolic pathways 4. Insulin synthesis and release

Question 26

What is glucokinase also known as?

Answer 26

Hexokinase IV | 'The glucose sensor'

Question 27

What is proinsulin?

Answer 27

The precursor to insulin

Question 28

What is C-peptide?

Answer 28

A polypeptide that connects the A-chain of insulin to the B-chain. It is removed before insulin is released.

Question 29

Slide 22

Answer 29

Look this up

Question 30

Which causes more insulin secretion, drinking glucose or giving it into a vein?

Answer 30

Drinking glucose causes more insulin secretion.

Question 31

What is the incretin effect?

Answer 31

Incretin is a hormone that stimulates insulin secretion in response to meals (food in the gastrointestinal tract)

Question 32

What is GLP-1? | What does it do?

Answer 32

Glucagon like peptide-1. - gut hormone - secreted in response to nutrients in gut - STIMULATES INSULIN - SUPPRESSES GLUCAGON - increases satiety (feeling of fullness)

Question 33

How do insulin receptors work? (Draw a picture)

Answer 33

It is a transmembrane receptor. 1. Insulin attaches to α-subunits, this recognises the insulin. 2. β-subunits span the membrane and are attached to the α-subunits. 3. β-subunits pass the message onto the cytoplasm. 4. Leads to phosphorylation of cell protein substrates.

Question 34

Which domains are found in the β-subunits?

Answer 34

Tyrosine kinase domains

Question 35

When glucose is metabolised into glucose-6-phosphate in the β-cells, ATP is produced, what does this ATP then do?

Answer 35

ATP blocks the ATP sensitive K+ channel. This causes calcium to rush into the cell through voltage gated calcium channels. Stored insulin is then released & new insulin production.