14.3 Hormones

Hormones as chemical messengers — substances produced by endocrine glands, carried in the blood, that alter the activity of one or more specific target organs. Identify the four Cambridge gland-hormone pairs (adrenal→adrenaline, pancreas→insulin, testes→testosterone, ovaries→oestrogen). Adrenaline as the fight-or-flight hormone with three named effects (increased heart rate, breathing rate, pupil diameter). Comparison of nervous vs hormonal control on speed of action and duration of effect. HL extension: glucagon secreted by the pancreas (opposite of insulin), and the role of adrenaline in metabolic activity (increasing blood glucose concentration and increasing heart rate).