4.7: Glucose homeostasis

Question 1

What kind of substrate is glucose

Answer 1

Energy substrate

Question 2

What are normal blood glucose concentration levels

Answer 2

4-5mmol/L

Question 3

What occurs when blood glucose concentration falls below normal levels (hypoglycaemia)

Answer 3

Cerebral function is increasingly impaired

Question 4

What happens if blood glucose concentration falls below 2mmol/L

Answer 4

Unconsciousness
Coma
Ultimately death

Question 5

Glucose regulation

Answer 5

Closely regulated
Feedback system required for regulation
High blood glucose releases insulin, blood glucose decreases and glucagon cortisol GH and catecholamines secreted to increase it

Question 6

Persistent hyperglycaemia results in

Answer 6

Diabetes mellitus

Question 7

What % of people are affected with diabetes mellitus in the UK?

Answer 7

7%

Question 8

What is the % risk increase risk of a person with diabetes mellitus dying relative to aged-matched control without diabetes?

Answer 8

34%

Question 9

What is the most prevalent form of diabetes

Answer 9

Type 2 diabetes mellitus

Question 10

What structure does the pancreas gland have

Answer 10

Retroperitonael structure

Question 11

What cells are present in the pancreas

Answer 11

Islets of Langerhans

Question 12

98% of the pancreas generates

Answer 12

Exocrine secretions via duct to small intestine

Question 13

What proportion of pancreatic blood supply is delivered to the islets of Langerhans

Answer 13

10-15%

Question 14

3 types of islet cells and what they secrete

Answer 14

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

Question 15

Communication between islet cells is called

Answer 15

Paracrine communication

Question 16

Gap junctions between islet cells allow for

Answer 16

Small molecules to pass directly between cells

Question 17

Function of Tight junctions in islet cells

Answer 17

Create small intercellular spaces

Question 18

Broad function of insulin

Answer 18

Stimulates growth and development and reduces blood glucose
Growth and development in utero

Question 19

Broad function of glucagon

Answer 19

Increases blood glucose

Question 20

Function of somatostatin

Answer 20

Negative feedback effect on both insulin and glucagon

Question 21

Increase in blood glucose results in :

Answer 21

Stimulation of B-cells
Increased insulin secretion
Somatostatin inhibits glucagon
A-cells secrete glucagon to control insulin concentrations to ensure hyperglycaemia

Question 22

During high blood glucose insulin causes (3 main, 2 independent of glucose)

Answer 22

Build up of glycogen stores
Break down glucose
Increased glucose uptake

Increase protein synthesis
Reduction in breakdown of fat (glycolysis)

Question 23

As blood glucose decreases :

Answer 23

A-cells stimulated to produce glucagon
Somatostatin regulates insulin (stops secretion completely)
Some amino acids, GI hormones, SNS activity and PNS activity all regulate blood glucose

Question 24

Function of glucagon during low blood glucose levels

Answer 24

Increases lipolysis,
Increases amino acid transport in liver
Increases gluconeogenesis and hepatic glycogenolysis which increases blood glucose

Question 25

GLUT2 transporter sensitivity for insulin

Answer 25

Not insulin sensitive Has a high capacity but not affinity for glucose

Question 26

Glucokinase is

Answer 26

The main glucose sensor (aka hexokinase IV)

Question 27

What happens as glucose binds to GLUT-2 receptor

Answer 27

Glucose enters cell, glucokinase converts glucose into Glucose-6-phosphate which produces ATP which inhibits K+ transporter, leading to influx of K+ and membrane depolarisation . Ca channels open, causing influx of Ca2+ which causes mobilisation of insulin

Question 28

Effects of high glucose on c-peptide in healthy individuals

Answer 28

C-peptide increases

Question 29

Effects of high glucose on c-peptide in a person with type 1 diabetes, why?

Answer 29

Low C-peptide Not enough insulin to immobilise into c-peptide

Question 30

How is c-peptide formed

Answer 30

Insulin is cleaved into c-peptide Can be used much easier for testing

Question 31

Where is glucokinase (hexokinase IV) found in the body (4)?

Answer 31

Liver Pancreas Small intestine Hypothalamus

Question 32

Main difference between actions of hexokinase I and hexokinase IV

Answer 32

Hexokinase IV is not subjective to -ve feedback from glucose-6-P

Question 33

What is the gastrointestinal “incretin” effect

Answer 33

Increased stimulation of insulin secretion elicited by oral as compared with intravenous administration of glucose under similar plasma glucose levels

Question 34

What is glucagon like peptide-1 (GLP-1) and what is it secreted in response to?

Answer 34

Gut hormone Secreted in response to nutrients in gut

Question 35

What effects does GLP-1 have on the hormones secreted by the islets of langerhans?

Answer 35

Stimulates insulin Suppresses glucagon

Question 36

What effect does GLP-1 have on satiety?

Answer 36

Increases satiety (feeling of fullness) Delays gastric emptying

Question 37

Why does GLO-1 have a short half-life?

Answer 37

Rapid degradation from enzyme dipeptidyl peptidase-4 (DPPG-4 inhibitor)

Question 38

Which subunit does insulin bind to on the insulin receptors?

Answer 38

Alpha subunit

Question 39

What happens to the tyrosine kinase domains of beta subunits of the insulin receptors after insulin is bound to the receptor?

Answer 39

They undergo conformational change