14.3 Hormones

2026 Syllabus Objectives

  1. Describe a hormone as a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
  2. Identify in diagrams and images specific endocrine glands and state the hormones they secrete, limited to:
    • (a) adrenal glands and adrenaline
    • (b) pancreas and insulin
    • (c) testes and testosterone
    • (d) ovaries and oestrogen
  3. Describe adrenaline as the hormone secreted in 'fight or flight' situations and its effects, limited to:
    • (a) increased breathing rate
    • (b) increased heart rate
    • (c) increased pupil diameter
  4. Compare nervous and hormonal control, limited to speed of action and duration of effect
  5. State that glucagon is secreted by the pancreas
  6. Describe the role of adrenaline in the control of metabolic activity, limited to:
    • (a) increasing the blood glucose concentration
    • (b) increasing heart rate

What Are Hormones? 🔑

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Animals use two main systems for coordination and communication within the body: the nervous system (using electrical impulses) and the endocrine system (using chemical messengers called hormones).

Key Definitions

Hormones are chemicals that are produced by a gland and carried in the blood, which alter the activities of their specific target organs.

Endocrine glands are glands that secrete hormones directly into the bloodstream.

Target organs are organs whose activity is altered by a hormone.

How Hormones Work

Hormones are produced in specialized endocrine glands and then:

  1. Pass from the gland into the blood
  2. Are carried around the body in the blood plasma
  3. Each hormone affects particular target organs
  4. The hormone alters the activity of these target organs

Hormones travel throughout the entire body in the bloodstream, but only affect specific target organs that have receptors for that particular hormone.

The Endocrine System 📌

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Major Endocrine Glands and Their Hormones

The human body contains several important endocrine glands, each producing specific hormones:

GlandHormone SecretedFunction of Hormone
Adrenal glandAdrenalinePrepares body for vigorous action
PancreasInsulinReduces the concentration of glucose in the blood
PancreasGlucagonIncreases the concentration of glucose in the blood
TestisTestosteroneCauses the development of male secondary sexual characteristics
OvaryOestrogenCauses the development of female secondary sexual characteristics, and helps in the control of the menstrual cycle

Location of Endocrine Glands

The endocrine glands are distributed throughout the body:

  • Adrenal glands: Located one above each kidney (two glands in total)
  • Pancreas: Located in the abdomen, near the stomach
  • Testes (in males): Located in the scrotum
  • Ovaries (in females): Located a little higher in the abdomen

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