Animal Hormones Notes

Edexcel GCSE Biology: Revision notes

Key facts

  • Endocrine glands secrete hormones into the blood to act on target organs.
  • Adrenalin prepares the body for fight or flight.
  • Thyroxine is controlled by negative feedback.
  • FSH, oestrogen, LH and progesterone control the menstrual cycle.
  • Hormonal contraception inhibits FSH; Clomifene and IVF use FSH and LH to improve fertility.

Pituitary

  • Master gland: TSH, FSH, LH

Thyroid

  • Thyroxine

Pancreas

  • Insulin, glucagon

Endocrine glands

Endocrine glands release hormones directly into the blood, and each acts on a target organ.

Endocrine glands secrete hormones directly into the blood. Each hormone acts on a target organ that has the right receptors.

  1. 1

    Endocrine gland

    for example the pancreas or pituitary

  2. 2

    Hormone released into the blood

  3. 3

    Carried round the body

  4. 4

    Target organ

    has the right receptors, so it responds

How a hormone works.

Pituitary

  • Master gland
  • TSH, FSH, LH

Thyroid and pancreas

  • Thyroxine
  • Insulin and glucagon

Adrenal and reproductive

  • Adrenalin
  • Oestrogen, progesterone (ovaries)
  • Testosterone (testes)

Which gland produces insulin?

Adrenalin: fight or flight

Adrenalin from the adrenal glands prepares the body for fight or flight.

The adrenal glands release adrenalin. It increases heart rate and blood pressure, sends more blood to the muscles and raises blood sugar as the liver converts glycogen to glucose.

  1. 1

    Adrenalin released

    by the adrenal glands

  2. 2

    Heart rate and blood pressure rise

    more blood flow to muscles

  3. 3

    Blood sugar rises

    liver converts glycogen to glucose

Fight or flight

How does adrenalin raise blood sugar?

Thyroxine and negative feedback

Low thyroxine triggers TRH and TSH; normal levels switch them off by negative feedback.

Thyroxine controls metabolic rate. Negative feedback is a response that counteracts a change. When levels are normal, thyroxine inhibits TRH and TSH.

  1. 1

    Low thyroxine

    detected by the hypothalamus

  2. 2

    TRH

    hypothalamus releases TRH

  3. 3

    TSH

    pituitary releases TSH

  4. 4

    Thyroxine

    thyroid releases thyroxine

  5. 5

    Normal levels

    inhibit TRH and TSH release

Then back to step 1

Thyroxine control loop

What happens to TRH and TSH when thyroxine levels are normal?

The menstrual cycle

FSH, oestrogen, LH and progesterone each control one stage of the cycle.

FSH matures an egg and stimulates oestrogen. Oestrogen repairs the uterus lining and triggers the LH surge. LH triggers ovulation. Progesterone maintains the lining, and falling levels cause menstruation.

  1. 1

    FSH

    matures an egg, stimulates oestrogen

  2. 2

    Oestrogen

    repairs uterus lining, triggers LH surge

  3. 3

    LH

    triggers ovulation

  4. 4

    Progesterone

    maintains the lining

  5. 5

    Progesterone falls

    menstruation

Order of events in the cycle

Which hormone triggers ovulation?

Contraception and fertility treatment

Contraception prevents pregnancy; Clomifene and IVF use hormones to help it.

Hormonal contraception inhibits FSH, preventing egg maturation. Barrier methods block sperm physically and also prevent STIs. Clomifene stimulates FSH and LH to cause ovulation. In IVF, FSH and LH mature multiple eggs, which are fertilised outside the body before an embryo is inserted into the uterus.

Contraception

  • Hormonal: inhibits FSH
  • Barrier: blocks sperm, prevents STIs

Fertility treatment

  • Clomifene: stimulates FSH and LH
  • IVF: eggs fertilised outside the body
  1. 1

    Hormones

    FSH and LH mature multiple eggs

  2. 2

    Fertilisation

    eggs and sperm combined outside the body

  3. 3

    Embryo

    inserted into the uterus

IVF

Which method also protects against STIs?

Try an exam question

Describe the roles of FSH, oestrogen and LH in the menstrual cycle.

[4 marks]

That's the notes covered.

Carry on to the next subtopic.