Human reproduction

3rd Topic

What is testosterone?

• Main male reproductive hormone

• Produced by testes

• Stimulates sperm production

Describe the role of FSH in the menstrual cycle

• Secreted by the pituitary gland

• Causes eggs to mature in their follicles in the ovaries

• Stimulates ovaries to produce oestrogen

Describe the role of oestrogen in the menstrual cycle

• Main female reproductive hormone

• Produced and secreted by the ovaries

• Stimulates uterus lining to grow again/thicken after menstruation

• Stops FSH being produced (so only 1 egg matures per cycle)

• Stimulates pituitary gland to release LH

Describe the role of LH in the menstrual cycle

• Produced by pituitary gland

• Triggers ovulation

Describe the role of progesterone in the menstrual cycle

• Secreted by empty egg follicle (corpus luteum) in ovary after ovulation

• Maintains lining of the uterus during second half of menstrual cycle and during pregnancy

• Stops release of FSH and LH

What is ovulation?

• The release of an egg from the ovary approximately every 28 days

• Happens 1 days from the end of the menstrual cycle

How do oral contraceptives work + pros and cons?

• Contains oestrogen and progesterone or only progesterone

• They inhibit the production of FSH

• Therefore, no eggs will mature in the ovaries, preventing pregnancy

Pros - 99% effective, easy to use (take a pill every day for 21 days and then stop for 21 days)

Cons - Increased blood pressure, thrombosis (blood clots), breast cancer, need to take regularly

How do contraceptive implants work + pros and cons?

• Tiny tube under skin slowly releases progesterone to inhibit maturation and release of eggs, thicken mucus of cervix and thin uterus lining (so egg can’t implant)

Pros - lasts up to 3 years, can be removed at any time, natural fertility will return very quickly, 99.95% effective

Cons - May be bruising/tenderness/swelling around implant at first, can’t take it out yourself, periods may stop/become irregular, some medications make it less effective

How do contraceptive patches work + pros and cons?

• Delivers oestrogen and progesterone into your body through your skin

• Prevents ovulation, thickens cervical mucus, thins womb lining

Pros - more than 99% effective. may protect against ovarian, womb and colon cancer, easy to use

Cons - need to replace patch every 7 days, may increase blood pressure, headaches, wear for 3 weeks then 1 week without

How do contraceptive injections work + pros and cons?

• Use progesterone to inhibit maturation and release of eggs

Pros - lasts 12 weeks, 99% effective

Cons - in some women it stops ovulation

What are some advantages of hormonal contraception?

• Over 99% effective

• Easily reversible

What are some disadvantages of hormonal contraception?

• Have to remember to take hormones

• Periods may stop/become irregular

• May increase blood pressure

• Don’t protect against STDs

What are spermicidal agents?

• Chemical substances in the forms of creams, gels or tablets

• They kill or disable sperm

• Usually are paired with barrier methods

• They are readily available

How do male condoms work?

• Male condoms: thin latex sheath placed over p(e)nis during intercourse to collect semen and prevent egg and sperm from meeting

Pros and cons of male condoms

• No side effects

• No medical advice needed/easy to use

• Offer some protection against STDs

• Very effective, >98%

• Can get damaged and let sperm through

How do female condoms work?

• Female condoms: thin, soft plastic worn in v(a)gina to prevent semen getting to the egg

Pros and cons of female condoms

• No side effects

• No medical advice needed/easy to use

• Offer some protection against STDs

• Very effective, >95%

• Can get damaged and let sperm through

How does a diaphragm work?

• Diaphragm/cap: thin, rubber dome placed over cervix before intercourse to prevent the entry of sperm (generally used with spermicidal agents and must be left in place at least 6 hours after intercourse)

Pros and cons of a diaphragm

• No side effects

• Has to be fitted by a doctor initially

• If cap is not positioned correctly sperm may get past and reach the egg

• Must be left for 6 hours after intercourse

How do intrauterine devices work?

• A small structure inserted into uterus by doctor

• Contains either copper which prevents implantation of an embryo or is made of plastic and releases progesterone which thickens the cervical mucus, thins the womb lining and stops ovulation

Pros and cons of intrauterine devices

• Last 3-5 years

• Can be removed at any time

• Effective

• Once in place you don’t have to think about contraception at all until it is removed

• It may cause period problems or infections

• Has to be inserted by a doctor

• Ethical objections as it involves the death of a fertilised egg

What are the two surgical methods?

• Male sterilisation (vasectomy)

• Female sterilisation

Both are permanent

How does male sterilisation work?

• The sperm ducts are cut and tied. This prevents sperm from reaching semen.

• If there is no sperm in the semen that is released, the egg can’t be fertilised.

Pros and cons of vasectomy

• Very effective

• Once done you never have to think about contraception

• May experience pain in testes

• Difficult to reverse the operation

• Slight risk of infection in surgery

How are women surgically sterilised?

• Fallopian tubes (oviducts) are cut or tied which prevents eggs from reaching the uterus

• Eggs will still be released from ovaries once a month but are just absorbed naturally into the body

Pros and cons of female sterilisation

• Permanent

• Very effective

• Doesn’t interfere with the hormonal cycle (menstruation happens but no egg is released)

• Can be done at any time

• Need to go under general anaesthesia

• Risk of infection during surgery

• Difficult to reverse the operation

What is abstinence/the rhythm method?

• Not having intercourse around ovulation or when egg is in the oviduct

• So no egg for sperm to fertilise so no pregnancy

Pros and cons of abstinence

• Good for religious groups who don’t accept artificial contraception

• It’s an unreliable method

What are some common causes of infertility?

• Age

• Damage to fallopian tubes/sperm duct

• Lack of FSH/other female hormones/sperm in semen

• Obesity

• Eating disorders

How are fertility drugs used to help women get pregnant in the normal way?

• Used when women don’t produce enough FSH to stimulate the maturation of eggs in ovaries

• Artificial FSH stimulates eggs in ovary to mature and triggers oestrogen production

• Artificial form of LH then used to trigger ovulation

When is IVF used?

Any of:

• Oviducts are damaged or blocked by infection

• Donor egg has to be used

• No obvious cause of long-term infertility

What happens in IVF?

• Mother is given FSH and LH to stimulate the maturation of several eggs

• A thin needle is used to collect mature eggs from ovary (under an anaesthetic)

• The eggs are placed in a Petri dish with semen that contains sperm

• Fertilisation occurs (after roughly 48 hours)

• Within 8 hours of fertilisation happening, cell division will start

• The egg can be checked if it is fertilised by seeing if there is more than one cell (from cell division) rather than just one egg

• Once they are tiny balls of cells, 1 or 2 embryos are inserted into the mother’s uterus (womb) after injecting the mother with oestrogen and progesterone to allow uterus lining to thicken

Advantages of IVF and fertility drugs

• Major scientific breakthrough

• Gives women and men who would otherwise be infertile the chance to have a baby of their own

Disadvantages of IVF and fertility drugs

• Expensive

• Success rates are not high

• Can lead to multiple births which is a risk to both the babies and the mother

• Stored eggs raise ethical issues if the woman dies, relationship breaks up, or one parent no longer wants the eggs or embryos

What is adrenaline?

• Produced by adrenal glands in times of fear or stress

• Increases heart rate

• Boosts delivery of oxygen and glucose to brain and muscles

• Prepares body for ‘fight or flight’

What is the target organ for adrenaline?

Most tissues

What is thyroxine?

• From thyroid gland

• Stimulates basal metabolic rate

• Plays important role in growth and development

• Levels are controlled by negative feedback

What is the target organ for thyroxine?

Most tissues