One important role of control systems in mammals is homeostasis. Explain what is meant by the term homeostasis.
Insulin contributes to homeostasis. It acts on muscle and liver cells to lower blood glucose concentration, especially after a meal. Insulin consists of two polypeptides that are produced in $\beta$ cells of the pancreas. State exactly where in $\beta$ cells polypeptide molecules are synthesised.
Name the process used to secrete insulin from $\beta$ cells.
Describe the way insulin affects muscle cells.
When stress or intense exercise occurs, extra glucose must be released into the blood. The hormone adrenaline is secreted and attaches to receptors on the cell surface membranes of liver cells. Describe how adrenaline’s effect on liver cells leads to an increase in blood glucose concentration.