Sex hormones in humans — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

Section 1 of 30Puberty and sex hormones

Puberty and sex hormones

Puberty

• Puberty the stage when children become adolescents and the reproductive system matures.

Testosterone

• Testosterone made in the testes; controls male secondary sexual characteristics.

Oestrogen

• Oestrogen made in the ovaries; controls female secondary sexual characteristics.

Primary sexual characteristics

• Primary sexual characteristics the reproductive organs themselves, present from development in the uterus.

Secondary sexual characteristics

• Secondary sexual characteristics changes during puberty controlled by hormones.

Section 2 of 30Secondary sexual characteristics

Boys (testosterone)	Girls (oestrogen)
Growth of pubic, underarm and facial hair	Growth of pubic and underarm hair
Voice becomes deeper	Breasts develop
Wider shoulders and muscle development	Hips widen
Penis and testes enlarge; sperm production starts	Ovaries release eggs; menstrual cycle begins

• Both sexes
  • growth of sexual organs, body hair and emotional changes such as mood swings and interest in sex.

Section 3 of 30The menstrual cycle

1Start and length

• Start and length begins in early adolescence at about age 12 and averages 28 days.

2Ovulation

• Ovulation release of an egg around day 14; the egg then travels down the oviduct.

3Menstruation

• Menstruation breakdown of the thickened uterus lining if the egg is not fertilised, lasting about 5 to 7 days.

4Rebuilding

• Rebuilding after menstruation the lining thickens again for possible implantation.

Section 4 of 30Hormones of the menstrual cycle

Hormone	Made in	Effect
FSH	Pituitary gland	Matures an egg in the ovary and stimulates oestrogen release
Oestrogen	Ovary follicle	Repairs and thickens the uterus lining; inhibits FSH; stimulates LH when high
LH	Pituitary gland	Causes ovulation and stimulates progesterone production
Progesterone	Corpus luteum	Maintains the uterus lining

Section 5 of 30Order of events

1

The pituitary releases FSH, which stimulates a follicle to develop in the ovary.

2

The follicle produces oestrogen, which thickens the uterus lining and inhibits FSH.

3

High oestrogen stimulates the pituitary to release LH.

4

LH causes ovulation around day 14.

5

The follicle becomes the corpus luteum and produces progesterone.

6

If the egg is not fertilised, the corpus luteum breaks down, progesterone falls and menstruation occurs.

Section 6 of 30Hormones in pregnancy

Corpus luteum

• Corpus luteum continues to make progesterone if pregnancy occurs, preventing the lining breaking down.

Placenta

• Placenta once developed, the placenta makes progesterone for the rest of pregnancy.

Contraceptive pill

• Contraceptive pill contains oestrogen and/or progesterone.

Section 7 of 30More from the specification

1

Steroid hormone synthesis by gonadal cells

• Steroid hormone synthesis by gonadal cells cholesterol derivatives are converted into active sex steroids by interstitial testicular and ovarian follicular cells.

2

Hormonal Control of the Menstrual Cycle

• Pituitary FSH stimulates follicle development in the ovary, developing follicles secrete oestrogen to regenerate the uterine endometrium,
  • and a surge in LH triggers ovulation on day 14.

3

Maintenance of the Uterine Lining by Progesterone

• Following ovulation, the collapsed ovarian follicle transforms into the corpus luteum, secreting progesterone to maintain a thick, glandular, vascularised uterine endometrium ready for embryo implantation.

4

Testosterone and Male Secondary Sexual Characteristics

• Elevated testosterone secretion during puberty promotes testicular growth, spermatogenesis, laryngeal enlargement,
  • and skeletal muscle mass development.
  • (deepening voice)

5

Variation

• Differences between individuals of the same species.

6

Germination

• The start of growth of a seed.

7

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

8

Genetically identical

• Having the same alleles

9

Genetic variation

• Differences in alleles within a population.

10

Structural adaptation

• An adaptation of body form.

11

Pollen

• Grains made by plants, each type with a different shape.

12

Fertilisation

• The fusion of the nuclei of a male and a female gamete.

13

Gamete

• A haploid sex cell.

14

Pollination

• Transfer of pollen from an anther to a stigma.

Section 8 of 30Puberty

Puberty

• Puberty the stage, usually between ages 10 and 15, when the reproductive system matures.

Trigger

• Trigger the pituitary gland increases secretion of hormones that stimulate the sex organs to make sex hormones.

Testes

• Testes make testosterone in males.

Ovaries

• Ovaries make oestrogen in females.

Both sexes

• Both sexes also make small amounts of the other hormone.

Section 9 of 30Primary and secondary characteristics

Primary and secondary characteristics

Primary sexual characteristics

• Primary sexual characteristics the reproductive organs, present from before birth.

Secondary sexual characteristics

• Secondary sexual characteristics features that appear at puberty and distinguish males from females.

They are not directly involved in gamete production.

Section 10 of 30Secondary sexual characteristics

Male (testosterone)	Female (oestrogen)
Growth of pubic, underarm and facial hair	Growth of pubic and underarm hair
Voice becomes deeper	Breasts develop
Wider shoulders and muscle development	Hips widen
Penis and testes enlarge; sperm production starts	Ovaries start to release eggs; menstrual cycle begins
Growth spurt	Growth spurt; fat deposited on hips and thighs

Section 11 of 30Control of puberty

1

The hypothalamus and pituitary increase release of FSH and LH.

2

FSH and LH stimulate the testes or ovaries.

3

The gonads release testosterone or oestrogen into the blood.

4

Target tissues respond and the secondary characteristics develop.

• Feedback
  • as the sex hormone level rises it influences the pituitary and hypothalamus, keeping levels regulated.

Section 12 of 30Timing and growth

Age

• Age puberty varies between individuals and is affected by genes, nutrition, health and body fat.

Growth spurt

• Growth spurt earlier in girls than in boys (about 12 to 14 years).
  • (about 10 to 12 years)

Skin

• Skin oilier because of more active sebaceous glands, which can cause acne.

Emotions

• Emotions mood and behaviour may change as hormone levels fluctuate.

Sex hormones

• Sex hormones steroid hormones carried in the blood to many target tissues, so changes affect the whole body.

Section 13 of 30Anabolic steroids

Anabolic steroids

• Anabolic steroids synthetic drugs similar to testosterone that increase muscle mass.

Harmful effects

• Harmful effects infertility, mood changes and heart damage.

Section 14 of 30More from the specification

1

Endocrine Leydig and granulosa cells

• Endocrine Leydig and granulosa cells specialized gonadal endocrine cells secrete testosterone, oestrogen,
  • and progesterone regulating human sexual maturation.

2

Male and female sex hormones

• Testosterone produced by the testes promotes male secondary sexual characteristics and spermatogenesis;
  • oestrogen and progesterone regulate the female menstrual cycle.

3

Menstrual cycle regulation

• Pituitary hormones (FSH and LH) stimulate ovarian follicle maturation and ovulation;
  • subsequent oestrogen and progesterone secretion rebuilds and vascularises the uterine endometrium.

4

Fertilisation and placenta function

• Fusion of sperm and egg nuclei in the fallopian tube forms a zygote;
  • upon uterine implantation, the placenta facilitates gas, nutrient,
• and waste exchange with maternal blood.

5

Oestrogen and progesterone roles

• Oestrogen and progesterone roles ovarian hormones stimulate thickening of the uterus endometrium, maintaining tissue integrity during pregnancy.

6

Placental barrier and diffusion

• Placental barrier and diffusion placenta allows exchange of respiratory gases and nutrients between maternal blood and developing foetus tissues.

7

Human fertilisation

• Human fertilisation haploid sperm cell fuses with haploid ovum in the fallopian tube to form a diploid zygote.

8

Variation

• Differences between individuals of the same species.

9

Germination

• The start of growth of a seed.

10

Progesterone

• A hormone that maintains the uterus lining.

11

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

12

Genetically identical

• Having the same alleles

13

Genetic variation

• Differences in alleles within a population.

14

Structural adaptation

• An adaptation of body form.

15

Pollen

• Grains made by plants, each type with a different shape.

16

Fertilisation

• The fusion of the nuclei of a male and a female gamete.

17

Uterus

• The organ in which the foetus develops.

18

Placenta

• The organ where substances are exchanged between mother and foetus.

19

Pollination

• Transfer of pollen from an anther to a stigma.

Section 15 of 30Overview of the cycle

1Menstrual cycle

• Menstrual cycle a monthly series of changes in the ovary and uterus lasting about 28 days.

2Purpose

• Purpose an egg is released and the uterus lining is built up to receive an embryo.

3If the egg is not fertilised

• If the egg is not fertilised the lining is lost.

Section 16 of 30Stages of the cycle

Days	Event	Hormone action
1 to 5	Menstruation: lining breaks down and leaves through the vagina	Progesterone has fallen
6 to 13	Lining repairs and thickens; follicle matures	FSH stimulates the follicle; the follicle releases oestrogen
14	Ovulation: egg released from the ovary	LH surge triggers it
15 to 28	Lining is maintained and rich in blood vessels	Progesterone from the corpus luteum

Section 17 of 30Hormones in control

FSH

• FSH from the pituitary; makes a follicle develop and stimulates oestrogen release.

Oestrogen

• Oestrogen from the ovary; repairs the uterus lining, inhibits FSH, and stimulates LH release when high.

LH

• LH from the pituitary; triggers ovulation.

Progesterone

• Progesterone from the corpus luteum; maintains the lining and inhibits FSH and LH.

Section 18 of 30Hormone levels across the cycle

Oestrogen

• Oestrogen rises in the first half, peaks just before ovulation, then falls and rises a little again.

Progesterone

• Progesterone low until after ovulation, rises through the second half, then falls before menstruation.

FSH

• FSH highest early in the cycle.

LH

• LH a sharp surge just before ovulation around day 13 to 14.

Lining thickness

• Lining thickness lowest on days 1 to 5, then increases and reaches a maximum around day 21 to 28.

Section 19 of 30If fertilisation occurs

Fertilisation

• Fertilisation sperm fertilise the egg in the oviduct.

Implantation

• Implantation the embryo implants in the thick uterus lining.

Progesterone

• Progesterone the corpus luteum keeps secreting it and later the placenta takes over.

Result

• Result the lining is kept, so menstruation does not occur.

Section 20 of 30Feedback and fertile period

Negative feedback

• Negative feedback high oestrogen and progesterone inhibit FSH and LH, so a new follicle does not develop while the lining is maintained.

Positive feedback

• Positive feedback the high oestrogen level before ovulation stimulates the LH surge.

Egg survival

• Egg survival the egg survives about a day after ovulation.

Sperm survival

• Sperm survival sperm survive several days in the reproductive tract, so the fertile window spans several days around ovulation.

Section 21 of 30More from the specification

1

Sexual reproduction and gametes in humans

• Human sexual reproduction involves the fusion of haploid gametes (sperm and ovum) to produce a diploid zygote that develops into an embryo and subsequent foetus.

2

Female sex hormones and pregnancy support

• Oestrogen and progesterone regulate the female menstrual cycle and maintain the uterine endometrium to nourish the developing foetus following implantation.

3

Comparison with sexual reproduction in flowers

• In flowering plants, male gametes are contained inside pollen grains produced by anthers,
• which are transferred to the female stigma when flowers are pollinated by wind or insects.

4

Specialised reproductive cells in plants and animals

• Motile sperm cells and sessile ova in humans correspond functionally to the microscopic pollen grains and female ovules in insect- or wind-pollinated flowers.

5

Sexual reproduction and gametes in humans

• Human sexual reproduction involves the fusion of haploid gametes (sperm and ovum) to produce a diploid zygote that develops into an embryo and subsequent foetus.

6

Female sex hormones and pregnancy support

• Oestrogen and progesterone regulate the female menstrual cycle and maintain the uterine endometrium to nourish the developing foetus following implantation.

7

Comparison with sexual reproduction in flowers

• In flowering plants, male gametes are contained inside pollen grains produced by anthers,
• which are transferred to the female stigma when flowers are pollinated by wind or insects.

8

Specialised reproductive cells in plants and animals

• Motile sperm cells and sessile ova in humans correspond functionally to the microscopic pollen grains and female ovules in insect- or wind-pollinated flowers.

9

Structural adaptation

• An adaptation of body form.

10

Variation

• Differences between individuals of the same species.

11

Nucleus

• The part of the cell that controls its activities.

12

Germination

• The start of growth of a seed.

13

Sexual reproduction

• Reproduction involving fusion of two gamete nuclei, giving varied offspring.

14

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

15

Genetically identical

• Having the same alleles

16

Pituitary gland

• The master gland whose hormones control other glands.

17

Genetic variation

• Differences in alleles within a population.

18

Pollen

• Grains made by plants, each type with a different shape.

19

Gamete

• A haploid sex cell.

20

Pollination

• Transfer of pollen from an anther to a stigma.

Section 22 of 30Hormones in pregnancy

After implantation

• After implantation the embryo and later the placenta release hormones.

Progesterone

• Progesterone the placenta secretes it, maintaining the lining and preventing ovulation and menstruation.

Oestrogen

• Oestrogen levels also rise.

Birth

• Birth progesterone falls and contractions begin, helped by oxytocin.

Section 23 of 30Hormonal contraception

Contraceptive pill

• Contraceptive pill contains oestrogen and/or progesterone and keeps hormone levels steady.
• FSH release is inhibited, so no follicle develops.
• No egg is released, so ovulation is prevented.
• Cervical mucus thickens, making it harder for sperm to pass.

Other hormonal methods

• Other hormonal methods implants under the skin, injections and patches.

STIs

• STIs hormonal methods do not protect against them.

Section 24 of 30Contraception methods compared

Method	How it works	Protects against STIs
Pill, implant, injection	Hormones stop ovulation	No
Condom	Barrier stops sperm	Yes
Diaphragm or cap	Barrier over the cervix with spermicide	No
IUD (coil)	Prevents implantation or kills sperm	No
Sterilisation	Tubes cut or tied; permanent	No
Natural methods	Avoid sex near ovulation; less reliable	No

Section 25 of 30Fertility treatment

Fertility treatment

FSH

• FSH given as a fertility drug to women who do not ovulate, stimulating follicle growth and egg release.

IVF (in vitro fertilisation)

• IVF (in vitro fertilisation) eggs are collected after hormone treatment and fertilised with sperm in a dish.
• Embryos are placed in the uterus.

Issues

• Issues cost, the chance of multiple births, low success rates and the fate of unused embryos.

Section 26 of 30Issues with hormonal treatments

Argument for	Argument against
Lets couples plan family size	Some religious views oppose it
Fertility treatment helps those who cannot conceive	Cost, low success rates, health risks
Hormonal methods are highly effective	No protection against STIs; side effects

Pill side effects

• Pill side effects headaches, mood changes and a small increased risk of blood clots.

Regular use

• Regular use the pill must be taken regularly to be effective.

Section 27 of 30Placenta and care in pregnancy

Placenta

• Placenta exchanges oxygen, nutrients, carbon dioxide and urea by diffusion without the bloods mixing, and acts as an endocrine organ.

Amniotic fluid

• Amniotic fluid protects the foetus from shock.

Diet

• Diet the mother needs enough iron, calcium and folic acid.

Substances to avoid

• Substances to avoid smoking and alcohol cross the placenta and can harm the foetus.

Duration

• Duration pregnancy lasts about 40 weeks from the last menstrual period.

Breast milk

• Breast milk contains antibodies and is the ideal food for babies, with oxytocin helping milk release.

Section 28 of 30More from the specification

1

Gonadal steroidogenesis in endocrine cells

• Gonadal steroidogenesis in endocrine cells testosterone and oestrogen secreted by specialised gonadal cells stimulate secondary sexual characteristic development in adolescents.

2

Sexual Reproduction in Flowering Plants

• Sexual reproduction in plants involves the production of haploid gametes within flower structures;
  • anthers produce male pollen grains while the ovary contains female ovules.

3

Insect-Pollinated vs Wind-Pollinated Flowers

• Insect-pollinated flowers have large, brightly coloured petals, scent,
• and sticky pollen grains,
• whereas wind-pollinated flowers produce abundant, lightweight, smooth pollen grains with dangling anthers exposed to the wind.

4

Fertilisation and Zygote Formation

• Following pollination, a pollen tube grows down through the style to deliver male gamete nuclei into the female embryo sac,
• where fertilisation of the egg cell forms a diploid zygote that develops into a seed.

5

Structural adaptation

• An adaptation of body form.

6

Variation

• Differences between individuals of the same species.

7

Nucleus

• The part of the cell that controls its activities.

8

Germination

• The start of growth of a seed.

9

Sexual reproduction

• Reproduction involving fusion of two gamete nuclei, giving varied offspring.

10

Asexual reproduction

• Reproduction from one parent giving genetically identical offspring.

11

Menstrual cycle

• A monthly series of changes in the female reproductive system controlled by hormones.

12

Genetically identical

• Having the same alleles

13

Pituitary gland

• The master gland whose hormones control other glands.

14

Pollen

• Grains made by plants, each type with a different shape.

15

Reproduction

• The processes that make more of the same kind of organism.

16

Gamete

• A haploid sex cell.

17

Pollination

• Transfer of pollen from an anther to a stigma.

Section 29 of 30Key terms

Term	Meaning
Puberty	The stage of sexual maturation controlled by sex hormones.
Testosterone	The male sex hormone made in the testes.
Oestrogen	A female sex hormone made in the ovaries.
Progesterone	A hormone that maintains the uterus lining.
FSH	Pituitary hormone that matures an egg.
LH	Pituitary hormone that triggers ovulation.
Ovulation	Release of an egg from the ovary.
Menstruation	Loss of the uterus lining through the vagina.

Term	Meaning
Puberty	The stage when the reproductive system matures.
Secondary sexual characteristic	A feature that develops at puberty under hormone control.
Testosterone	The male sex hormone from the testes.
Oestrogen	The female sex hormone from the ovaries.
Gonadotrophins	FSH and LH from the pituitary that stimulate the gonads.
Anabolic steroid	A synthetic hormone similar to testosterone.

Term	Meaning
Ovulation	Release of an egg from the ovary.
Menstruation	Breakdown and loss of the uterus lining.
Follicle	A structure in the ovary in which an egg develops.
Corpus luteum	The structure formed from the follicle that makes progesterone.
FSH	Hormone that makes a follicle develop.
LH	Hormone that triggers ovulation.

Term	Meaning
Contraceptive pill	A pill with oestrogen and/or progesterone that prevents ovulation.
IVF	Fertilisation of eggs with sperm outside the body.
Placenta	The organ that exchanges substances between mother and foetus and secretes hormones.
Oxytocin	A hormone that helps contractions at birth.
Fertility drug	A hormone, such as FSH, used to stimulate egg production.

Section 30 of 30Exam technique

1

Saying testes are secondary sexual characteristics — they are primary; secondary ones appear at puberty.

2

Saying ovulation happens on day 1 — it happens around day 14.

3

Mixing up FSH and LH — FSH matures the egg and LH triggers ovulation.

4

Saying progesterone is made in the pituitary — it is made in the corpus luteum and placenta.

1

Saying testosterone is produced only by the adrenal glands — the testes make it.

2

Saying girls have no testosterone — both sexes make small amounts of both hormones.

3

Calling the testes secondary sexual characteristics — they are primary.

4

Saying puberty starts at the same age in everyone — timing varies.

1

Saying ovulation happens on day 1 — it happens around day 14.

2

Mixing up FSH and LH — FSH causes follicle growth and LH causes ovulation.

3

Saying progesterone is made in the pituitary — it is made in the corpus luteum.

4

Saying menstruation is loss of an egg only — it is mainly the uterus lining and blood.

1

Saying the pill stops sperm production — it prevents ovulation in the woman.

2

Saying hormonal contraception prevents STIs — only condoms do.

3

Saying IVF takes place in the uterus — fertilisation occurs in a dish.

4

Forgetting that the placenta produces hormones — it secretes progesterone.