1. α cells in the islets of Langerhans - produce glucagon
2. β cells in the islets of Langerhans - produce insulin

The liver carries out the following to increase or decrease blood glucose concentration:

1. Glycogenesis - the conversion of glucose into glycogen when blood glucose concentration is high
2. Glycogenolysis - the breakdown of glycogen to glucose when blood glucose concentration is low
3. Gluconeogenesis - the production of glucose from sources other than carbohydrates like fats and amino acids

1. Glucose is needed for respiration
2. If blood glucose is too low or high it can cause osmotic problems in cells and even cell death

Insulin lowers blood glucose concentration when it is too high by:

1. Increasing the rate of glucose absorption into cells, especially muscle cells
2. Increasing the rate of respiration
3. Promoting glycogenesis
4. Activating enzymes that convert glucose to glycogen and fat
5. Decreasing gluconeogenesis
6. Inhibiting the secretion of glucagon from α cells via negative feedback

Glucagon increases blood glucose concentration when it is too low by:

1. Activating enzymes in liver cells that break down glycogen to glucose (glycogenolysis)
2. Activating enzymes in liver cells that promote gluconeogenesis
3. Inhibiting the secretion of insulin from β cells via negative feedback

Adrenaline also increases blood glucose concentration when it is too low by:

1. Activating enzymes in liver cells that break down glycogen to glucose (glycogenolysis)

Adrenaline can also activate enzymes in muscle cells that break down glycogen to glucose.