Human Reproductive Hormones

Section 1 of 8Hormones at puberty

Testosterone

• Testosterone Made by the testes, it triggers male secondary sexual characteristics and stimulates sperm production.

Oestrogen

• Oestrogen Made by the ovaries, it brings about female changes such as breast development and plays a major part in the menstrual cycle.

Target organs

• Target organs Hormones are carried in the blood to all parts of the body but only affect the target organs that have matching receptors.

Section 2 of 8The menstrual cycle in outline

1

The cycle lasts about 28 days and begins at puberty.

2

The uterus lining is lost during menstruation, the 'period'.

3

The lining then rebuilds while an egg matures in an ovary.

4

Around day 14 an egg is released in ovulation.

5

The lining stays thick to receive a fertilised egg; if none arrives it breaks down and the cycle repeats.

Section 3 of 8The four hormones (HT only)

Hormone	Made by	Main job
FSH	Pituitary gland	Makes a follicle develop in the ovary and stimulates oestrogen production
Oestrogen	Ovary (follicle)	Repairs and thickens the uterus lining; at a high level triggers LH release; inhibits FSH
LH	Pituitary gland	Causes ovulation
Progesterone	Corpus luteum, then placenta in pregnancy	Keeps the uterus lining thick

Section 4 of 8Hormone control in order (HT only)

1FSH rises

• FSH rises A follicle grows and an egg matures inside it.

2Oestrogen rises

• Oestrogen rises The lining thickens and FSH is switched down.

3LH surge

• LH surge High oestrogen prompts the pituitary to release LH, so ovulation follows.

4Progesterone

• Progesterone The empty follicle becomes a corpus luteum and releases progesterone to maintain the lining.

5Fertilisation or not

• Fertilisation or not No fertilisation: the corpus luteum breaks down, progesterone falls and the period starts.
  • With a pregnancy, progesterone production continues.

Section 5 of 8Negative feedback and the cycle (HT only)

Oestrogen inhibits FSH

• Oestrogen inhibits FSH As oestrogen rises it switches FSH production down, so only one follicle normally matures fully each cycle.
  • This is negative feedback.

Oestrogen stimulates LH

• Oestrogen stimulates LH Once oestrogen reaches a high level it has the opposite effect and stimulates the pituitary gland to release a surge of LH.
  • This is positive feedback.

Progesterone maintains

• Progesterone maintains High progesterone keeps the uterus lining thick and also inhibits FSH and LH,
  • which prevents new eggs maturing during pregnancy.

Section 6 of 8Timeline of a 28-day cycle

Days	Event in the ovary	Event in the uterus
1-5	A new follicle begins to develop under the influence of FSH	Lining breaks down and is lost during menstruation
6-13	Follicle matures and secretes increasing oestrogen	Lining is repaired and thickens
14	LH surge causes ovulation	Lining is thick and well supplied with blood
15-28	Empty follicle forms the corpus luteum, which releases progesterone	Lining is maintained; if no embryo arrives it breaks down at the end

Section 7 of 8Key terms

Term	Meaning
Puberty	The stage when reproductive hormones cause the body to become sexually mature.
Ovulation	Release of a mature egg from an ovary.
Follicle	A fluid-filled structure in the ovary in which an egg matures.
Corpus luteum	The structure left after ovulation that secretes progesterone.
Target organ	An organ that responds to a particular hormone.
Pituitary gland	The master gland at the base of the brain that releases FSH and LH.

Section 8 of 8Exam technique

1

Saying testosterone is made in the pituitary gland. It is produced in the testes.

2

Thinking ovulation happens at the start of the period. It occurs around day 14.

3

Confusing FSH and LHFSH matures the egg, LH triggers its release.

4

Forgetting that progesterone falling causes menstruation.

5

Describing menstruation as the start of ovulation instead of the loss of the uterus lining.