GLOSSARY

Insulin is a peptide hormone secreted by the beta cells of the islets of Langerhans and is the body’s only major glucose-lowering hormone. It can be seen as the main anabolic hormone of the fed state.

Structure and Synthesis

Insulin consists of an A chain (21 amino acids) and a B chain (30 amino acids) joined by disulphide bonds. It is first made as proinsulin, which becomes active insulin when the C-peptide is removed; measuring C-peptide shows how much endogenous insulin the body is making.

Main Effects

• Muscle and fat: increased glucose uptake by moving GLUT4 to the cell membrane.
• Liver: increased glycogen synthesis and inhibition of gluconeogenesis and glycogenolysis.
• Adipose tissue: increased fat storage and strong inhibition of lipolysis.
• Protein: reduced muscle protein breakdown and help with amino acid uptake.
• Potassium: moves potassium into cells.

Scientific Note

Insulin