Homeostasis and responses

• Endocrine system

  Composed of glands that secrete chemicals called hormones into the bloodstream
• Hormones

  Chemicals secreted by glands that are carried in the blood to target organs where they produce an effect
• Pituitary gland

  • Located in the brain, known as 'master gland' as it secretes several hormones into the blood
• Pituitary gland hormones

  Act on other glands to stimulate the release of other hormones, and bring about effects
• Negative feedback

  Systems that work to maintain a steady state, e.g. blood glucose, water, and thyroxine levels
• Adrenaline

  • Produced by adrenal glands in times of fear or stress, increases heart rate, boosts delivery of oxygen and glucose, prepares body for 'fight or flight' response, does not involve negative feedback
• Thyroxine

  • Produced by the thyroid gland, regulates how quickly the body uses energy and makes proteins (metabolic rate), important for growth and development, levels controlled by negative feedback
• There are lots of different hormones, for each you need to know where they come from, where they act, what they do, and how long they stay around for
• Blood glucose

  Monitored and controlled by the pancreas through the hormones insulin and glucagon
• Diabetes is a non-communicable disease where the body either cannot produce or cannot respond to insulin, leading to uncontrolled blood glucose concentrations
• Type 1 diabetes

  • Pancreas stops producing sufficient insulin, commonly treated through insulin injections, also diet control and exercise
• Type 2 diabetes

  • Usually later onset, obesity is a risk factor, body doesn't respond to the insulin produced, commonly treated through a carbohydrate-controlled diet and exercise
• Oestrogen

  • Main female reproductive hormone, produced in the ovary, at puberty eggs begin to mature and one is released every 28 days
• Testosterone

  • Main male reproductive hormone, produced by the testes, stimulates sperm production
• Hormones involved in the menstrual cycle

  • Follicle stimulating hormone (FSH)
  • Luteinising hormone (LH)
  • Oestrogen
  • Progesterone
• Follicle stimulating hormone (FSH)

  Causes eggs to mature in the ovaries, stimulates the ovaries to produce oestrogen
• Luteinising hormone (LH)

  Triggers the release of mature eggs from the ovaries (ovulation)
• Oestrogen

  Causes the lining of the uterus to thicken
• Progesterone

  Inhibits the release of FSH and LH, maintains the thickened uterus lining
• Hormones are used in modern reproductive technologies to treat infertility, such as IVF
• IVF treatment


  1. Mother given FSH and LH to stimulate egg maturation

  2. Eggs collected and fertilised in a lab

  3. Fertilised eggs develop into embryos

  4. One or two embryos inserted into mother's uterus
• Fertility treatment has disadvantages: it is emotionally and physically stressful, has a low success rate, and can lead to multiple births
• Hormonal contraception methods

  • Oral contraceptives
  • Injection
  • Implant
  • Skin patch
  • Rings
• Hormonal contraception

  Contains hormones to inhibit FSH production so no eggs mature
• Non-hormonal contraception methods

  • Barrier methods (e.g. condoms, diaphragms)
  • Copper IUD
  • Surgical sterilisation
  • Spermicidal agents
  • Abstinence