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Animal HormonesEdexcel GCSE Biology: Revision notes

Section 1

Endocrine Glands

GlandHormone
PituitaryMaster gland, TSH/FSH/LH
ThyroidThyroxine
PancreasInsulin, glucagon
AdrenalAdrenalin
OvariesOestrogen, progesterone
TestesTestosterone
Key termsHormoneEndocrine glandTarget organ

Section 2

Adrenalin: Fight or Flight

Adrenal glands release adrenalin: increased heart rate, blood pressure, blood flow to muscles, raised blood sugar (liver converts glycogen to glucose).

Key termsAdrenalinGlycogen

Section 3

Thyroxine and Negative Feedback

Low thyroxine → hypothalamus releases TRH → pituitary releases TSH → thyroid releases thyroxine → normal levels inhibit TRH/TSH.

Key termsThyroxineNegative feedbackTRHTSH
Think of it like this

Like a thermostat: low level triggers response; normal level switches it off.

Section 4

The Menstrual Cycle

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

Key termsOestrogenProgesteroneFSHLHOvulationMenstruation

Section 5

Contraception and ART

Hormonal contraception inhibits FSH, preventing egg maturation. Barrier methods block sperm physically (also prevent STIs).

Clomifene: stimulates FSH/LH for ovulation. IVF: FSH/LH matures multiple eggs, fertilised outside body, embryo inserted into uterus.

Key termsHormonal contraceptionBarrier methodClomifeneIVF

Must Know

  • Hormones from endocrine glands act on target organs via blood.
  • Adrenalin: heart rate, BP, blood flow, blood glucose ↑.
  • Thyroxine negative feedback: TRH→TSH→thyroxine→inhibits TRH/TSH.
  • FSH matures egg/oestrogen; oestrogen→LH surge→ovulation; progesterone maintains lining.
  • Hormonal contraception inhibits FSH; Clomifene/IVF use FSH/LH for fertility.

That's the notes covered.

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