2.3 Reproduction, Fertility and Contraception 🐣

Function of male reproductive system

make sperm and deliver it to female reproductive system

Urethra

Tube through which sperm and urine leave penis

Prostate gland

Secretes fluid to nourish the sperm

Penis

Organ that releases sperm into vagina

Scrotum

Sac that holds and protects testes, slightly lower than body temperature

Sperm ducts

Carries sperm from testis to urethra

Testis

Produces sperm

Sperm

haploid male gametes formed by meiosis

Adaptations of sperm

• flagellum allowing it to swim through the female reproductive system

• haploid nucleus containing half normal number of chromosomes

• many mitochondria to produce energy

Function of female reproductive system

make and release eggs/ ova, protecting and nourishing the foetus until birth

Ovaries

Produce ova (eggs)

Cervix

Opening of the uterus which widens during birth

Vagina

Where sperms is released and travels from

Oviducts

Carries ova from ovaries to the uterus and is where fertilisation takes place

Uterus

Will nourish developing foetus if pregnancy results

Fertilisation

fusion of haploid sperm nucleus and haploid egg nucleus to form diploid zygote, in the oviducts

Zygote

First cell of new individual

What happens after fertilisation

• Zygote travels down the oviduct and divides by mitosis to form ball of cells (embryo)

• Implantation when embryo reaches uterus, attaching to its thick lining to receive nourishment

• Placenta, umbilical cord, amnion and amniotic fluid form.

• Embryo differentiates to produce variety of tissues and organs

• Referred to as foetus when all organs start to form

Placenta

allows useful substances to diffuse from mother’s blood to foetus and waste from foetus to mother’s blood

Adaptations of the placenta

• large surface area for exchange between uterus wall

• finger like projections that extend into uterus wall, called villi, further increasing surface area

• good blood supply

Umbilical cord

attaches placenta to the foetus, contains umbilical artery and vein

Umbilical artery

Carries urea and carbon dioxide from foetus to mother’s blood

Umbilical vein

Carries oxygen and nutrients from mother’s blood to foetus

Maternal and foetal blood systems

Close together but not joined, thin membranes separate and allow for diffusion

Amnion

Protective membrane that forms around the embryo and contains amniotic fluid

Amniotic fluid

Surrounds and cushions developing embryo

Male sex hormone

Testosterone, produced in testes

Female sex hormone

Oestrogen, produced by ovaries

Secondary sexual characteristics in males

• Testes enlarge

• Body becomes more muscular

• Voice deepens

Secondary sexual characteristics in females

• Sexual organs enlarge, breasts develop

• Pelvis and hips widen

• Menstruation begins

Secondary sexual characteristics in males and females

• Body and pubic hair grow

• Sexual awareness and drive increase

Menstrual cycle

28 days cycle (on average) that prepares for pregnancy

Menstruation

breakdown and removal of blood rich uterine lining through the vagina, at end of each cycle

Days 1-5

Menstruation occurs, both progesterone and oestrogen levels are low

Days 6-13

Oestrogen increases, repairing uterus lining and its initial buildup

Day 14

Ovulation, oestrogen levels peak and cause egg to be released

Days 15-28

Progesterone levels peak after ovulation to maintain thick lining

Day 28

If no pregnancy occurs hormone levels decrease and cycle restarts

When is fertilisation most likely

Few days before or after ovulation, sperm left in vagina still lives for a few days

Oestrogen

stimulates ovulation and starts buildup/ repair of uterine wall

Progesterone

Continues and maintains buildup of uterine lining

Causes of male infertility

• Not enough sperm produced

• Non-healthy sperm (can be smoking or drinking)

• Impotence

Causes of female infertility

• Ovaries don’t produce eggs

• Blocked/ twisted oviducts

• Complication from previous STI

• Uterus lining not developing enough for implantation

• Vagina too hostile to sperm e.g too acidic

Treatment for infertility

• Fertility drugs

• IVF

Fertility drugs

Hormones given to woman which increase egg production

IVF - in vitro fertilisation

1. Fertility drugs given to increase egg production

2. Eggs surgically collected from ovaries and sperm collected

3. Sperm and egg cells are mixed in a lab

4. Woman is given hormones to ensure the uterus lining is thick.

5. Embryos are placed into the uterus

6. If successful embryo implants into uterus lining

Why several embryos are used in IVF

Higher chance of success, risk of multiple births

Ethical issues of IVF

can be used to screen for abnormalities or selecting characteristics like gender

Contraceptives

Methods used to prevent pregnancy

Mechanical contraception

Male and female condoms

Condoms

• Barrier that prevents sperm entering or passing up

• Easily obtained and protects against STIs

• Unreliable if not used properly

Chemical contraceptives

Contraceptive pill or implant

Contraceptive pill

• Taken regularly to prevent ovulation by changing hormone levels

• Very reliable

• Need to remember and has side effects, doesn’t protect against STIs

Side effects of contraceptive pills

Weight gain, mood swings or increased risk of blood clots

Contraceptive implant

• Small tube under skin of upper arm, releasing hormones slowly over time to prevent ovulation

• Very reliable, can last up to 3 years

• Doesn’t prevent against STIs and can prevent menstruation

Surgical contraceptives

Vasectomy or female sterilisation

Vasectomy

• Sperm tubes are cut, preventing sperm entering penis

• Virtually 100% reliable

• Difficult or impossible to revert

Female sterilisation

Oviducts are cut, preventing fertilisation

• Virtually 100% reliable

• Difficult or impossible to revert

Natural contrceptives

Rhythm method

Rhythm method

• Intercourse is avoided around ovulation

• No chemicals used, chosen by those who appose contraceptives for religious or ethical reasons

• Not very reliable, especially if cycle is irregular