2.3 Biology Of Controlling Fertility
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Females have cyclical fertility
Fertile for 1-2 days following ovulation
Males have continuous fertility
Negative feedback control maintains a fairly high level of FSH & ICSH which allows testosterone to always secrete sperm
How can a woman calculate her fertile period?
Temp rise of 0.1-0.2 degrees Celsius Thinner & watery vaginal mucus
Why may a woman fail to ovulate?
Failure to secrete FSH & LH
How can ovulation be stimulated if a woman fails to ovulate
Drugs which mimic actions of FSH & LH
What is artificial insemination?
The insertion of sperm into female tract using a syringe
When is artificial insemination useful
When a mans sperm count is low If a partner is sterile a donors sperm can be used
When is IVF ( in vitro fertilisation) used
When infertility is caused by a blockage of oviducts
The stages of IVF
Women given hormone treatment to stimulate multiple ovulation Several Eggs are removed from ovary using syringe Eggs mixed with sperm in culture dish containing nutrient medium to allow fertilisation to take place
When is ICSI ( intracytoplasmic sperm injection ) employed
When a mans sperm count is low Sperm are dead
Stages of ICSI are
Women given hormone treatment to stimulate multiple ovulation Several Eggs are removed from ovary using syringe Sperm are injected into an egg using a syringe in a culture dish Eggs are incubated in nutrient medium for 1-3 days Some are tested for genetic abnormalities
What is PGS ( pre-implantation genetic screening )
PGS is a non specific approach which checks the embryo for genetic disorders & chromosomal abnormalities
What is PGD ( pre implantation genetic diagnosis )
PGD is a specific approach used to check for a known chromosomal or gene defect
What is meant by contraception
Initial prevention of conception or pregnancy by natural or artificial means
Physical contraception methods include
• Barrier methods eg condom, diaphragm, cervical cap • intra-uterine devices • sterilisation procedures • tubal ligation
What is intra uterine devices ?
T shaped structure fitted into uterus for months/ years to prevent implantation of embryo into endometrium
A sterilisation procedure is a vasectomy which is
Cutting & tying two sperm ducts to prevent sperm being released
What happens to sperm produced after a vasectomy?
Undergo phagocytosis & are destroyed
What is a tubal ligation
Cutting & tying two oviducts to prevent eggs meeting sperm & is normally irreversible
Chemical methods involve
Contraceptive pills
What does the pill do to stop fertilisation?
Inhibits secretion of FSH & LH by pituitary gland which causes follicle maturation to remain inhibited - is taken for 3 weeks from final day of menstration
How does morning after pill work?
Took up to 72 hours after sex, contains high doses of progesterone & oestrogen to prevent ovulation/ implantation from occurring
How does the mini pill work?
Progesterone only pill, causes thickening of cervical mucus which reduces viability of sperm and access to uterus