Feedback Control of Plasma Glucose

Question 1

What is fuel metabolism?

Answer 1

Reactions involving catabolism, anabolism and transformation of protein, carb (CHO) and fat

Question 2

What 5 hormones influence glucose?

Answer 2

Insulin, Glucagon, Growth hormone, Adrenaline and Cortisol

Question 3

What hormones control the absorptive and post absorptive state?

Answer 3

insulin and glucagon

Question 4

What hormones control plasma glucose in emergencies?

Answer 4

adrenaline

Question 5

What hormones are control plasma glucose during starvation?

Answer 5

cortisol (made in adrenal) and growth hormones (pituitary)

Question 6

What is the role of the endocrine pancreas in the control of blood glucose?

Answer 6

Islets of langerhans, containing 4 secretory cells.

Question 7

What are the 4 secretory cells of the islets of langerhans and what does each produce?

Answer 7

Alpha - glucagon
Beta - insulin, proinsulin, C peptide and amylin
Delta - somatostatin
F cells - pancreatic polypeptide

Question 8

Describe the function of insulin?

Answer 8

Favours anabolism. Stimulates conversion of glucose to glycogen, fatty acids into triglycerides and amino acids into proteins

Question 9

Describe the function of glucagon?

Answer 9

Favours catabolism. Stimulations the conversion of glycogen to glucose, triglycerides to fatty acids

Question 10

What does insulin do during the feeding state?

Answer 10

B cells secrete more insulin
catabolism of endogenous fuel stores is inhibited
CHO, AA and lipid uptake is stimulated
insulin directs the tissues to replenish their fuel reserves that were used during the period of fasting

Question 11

What does insulin do during fasting?

Answer 11

B cells secrete less insulin
lipids and amino acids are mobilised from tissues\
they provide fuel for oxidation and act as precursors for ketogenesis and gluconeogensis (production of glucose from non-carbs)

Question 12

What does sympathetic and parasympathetic stimulation in the islets of langerhans do?

Answer 12

sympathetic stimulation - INHIBITS insulin secretion

parasympathetic stimulation - STIMULATES insulin secretion

Question 13

What does exercise do to insulin

Answer 13

It surpasses insulin secretion to help prevent excessive glucose uptake by muscles

Question 14

Which tissues are insulin sensitive?

Answer 14

Liver, Skeletal muscle, adipose tissue (cardiac muscle also)

Question 15

What is glycogen an important storage form of?

Answer 15

CHO in both liver and skeletal muscle

Question 16

How does insulin lower [glucose]p?

Answer 16

Liver - activates enzymes in liver and skeletal muscle which convert glucose into glycogen
Promotes storage of fats as triglycerides

Skeletal muscle - Stimulating uptake of glucose from the blood into skeletal muscle and fat cells (GLUT4)
increases glucose breakdown

Question 17

Describe GLUT4?

Answer 17

insulin sensitive glucose transporter
insulin stimulates glucose uptake by adipose and skeletal muscle, leading to a reduction in blood glucose levels
insulin causes the GLUT4 to be inserted onto the plasma membrane from intracellular stores.

Question 18

Describe type 1 diabetes? (IDDM)

Answer 18

Childhood onset
Little/no insulin secretion

Affects 10-20% diabetics
Defect in -cell function
Ketosis develops (if untreated)
Insulin injections for treatment
Symptoms develop rapidly

Question 19

Describe type 2 diabetes? (NIDDM)

Answer 19

Adult onset (until recently)
Insulin secretion may be normal (or exceed normal)
Affects 80-90% diabetics
Defect in insulin sensitivity
Ketosis rare

Diet/exercise and oral drugs for treatment
Symptoms develop slowly

Question 20

What are the effects of severe DM?

Answer 20

Plasma glucose will be very high after meals
Glucose appears in urine - leading to thirst, dehydration
There is an inability of cells to utilise glucose which causes compensatory increase in lipolysis to generate fatty acids as an energy source
Metabolism of fatty acids generates acetyl CoA - liver is unable to process extra acetyl CoA… ketone bodies formed
These lower the blood pH, leading to metabolic acidosis and compensatory hyperventilation

Question 21

What is glucagon principle target tissue?

Answer 21

Liver

Question 22

Explain the role of adrenaline in the release of glucose in emergencies?

Answer 22

Released from the adrenal gland in response to stress. 
 Raises [glucose]p 
 Stimulates glycogenolysis
 Stimulates gluconeogenesis
 Released during short-term emegencies

Question 23

Explain the role of growth hormone in providing glucose during prolonged fasting.

Answer 23

From anterior lobe of pituitary gland
Decreases glucose uptake by muscle – “glucose sparing” action
Mobilises glucose from liver
also promotes lipolysis in fat cells

Question 24

Explain the role of cortisol in providing glucose during prolonged fasting.

Answer 24

Released from adrenal gland in response to stress.
Raises [glucose]p
Stimulates protein catabolism
Stimulates gluconeogenesis
Also stimulates lipolysis
NOT important for rapid mobilisation of fuel

Question 25

Describe stimulation of glucagon release in the post absorptive phase?

Answer 25

Decreased blood glucose (direct effect on -cells)
Amino acids (raises [glucose]p after protein meal)
Sympathetic nerve activity (e.g. exercise)

Question 26

Describe inhibition of glucagon release in the post absorptive phase?

Answer 26

Raised blood glucose

Insulin