AQA GCSE Biology Year 10: Human Reproduction and negative feedback

What is testosterone?

. main male reproductive hormone

. produced by testes

. stimulates sperm production

Describe the role of FSH in the menstrual cycle

. Secreted by 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 ovaries

. Stimulates uterus lining to grow again / thicken after menstruation

. Stops FSH being produced (so only 1 egg matures in a 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 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 14 days from the end of the menstrual cycle

How do oral contraceptives work?

. contain hormones to inhibit FSH production so no eggs mature

. mixed pill contains oestrogen and progesterone

. some pills only contain progesterone

How do contraceptive implants work?

. Tiny tube under skin slowly releases progesterone to inhibit maturation and release of eggs

. Lasts up to 3 years

How do contraceptive injections work?

. Progesterone injected to inhibit maturation and release of eggs

. Lasts about 12 weeks

How do contraceptive patches work?

. Stick patch containing oestrogen and progesterone to inhibit maturation and release of eggs to skin

. Hormones are absorbed directly into bloodstream

. Has to be replaced every 7 days

What are some advantages of hormonal contraception?

. Over 99% effective

. Easily reversible (except implant)

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

How do spermicidal agents work?

. kill or disable sperm

. readily available

. usually paired with barrier methods

How do condoms work?

. Thin latex sheath placed over penis during intercourse

. Collects semen and prevents egg and sperm meeting

Pros and cons of condoms

. No side effects

. No medical advice needed / easy to use

. Offer some protection against STDs

. Can get damaged and let sperm through

How do diaphragms (contraception) work?

. Thin rubber diaphragm placed over cervix before sex to prevent entry of sperm

. Generally used with spermicidal agents

Pros and cons of diaphragms (contraception)

. No side effects

. Has to be fitted by a doctor initially

. If cap not positioned correctly sperm may get past and reach egg

. Must be left for 6 hours after sex

How do intrauterine devices work?

. small structure inserted into uterus by doctor

. contain either copper which prevents implantation of an embryo or progesterone

Pros and cons of intrauterine devices

. Last 3-5 years

. Can be removed at any time

. May cause period problems or infections

. Have to be inserted by doctor

What is abstinence / the rhythm method?

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

. So no sperm to fertilise the egg so no pregnancy

Pros and cons of abstinence

. Good for religious groups who don't accept artificial contraception

. Rhythm method is very unreliable

How does a vasectomy work?

Sperm ducts are cut and tied preventing sperm from getting into the semen

Pros and cons of a vasectomy

. Very effective

. Permanent so never have to think about it again

. May experience pain in testes

. Difficult to reverse operation

How are women surgically sterilised?

Oviducts are cut or tied to prevent egg reaching uterus

Pros and cons of female surgical sterilisation

. Permanent

. Very effective

. Need to go under general anaesthesia

. Risk of infection

. Very hard to reverse / irreversible

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

. Eggs are collected from mother and fertilised in the lab by sperm collected from father

. Fertilised eggs develop into embryos

. When they are tiny balls of cells, 1 or 2 embryos are inserted into the mother's uterus (womb)

Disadvantages of fertility treatments

. Very emotionally and physically stressful

. Success rates are not high

. Can lead to multiple births which are a risk to both babies and mother

What are some social and ethical issues of IVF?

. Expensive for individuals and society (if funded by NHS)

. Stored eggs raise ethical issues if 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