Coordination & Control – the Endocrine System (OCR GCSE Combined Science A (Gateway): Biology): Flashcards

False.

They are carried in the blood. Only nervous impulses travel along nerves.

The thyroid gland, in the neck.

It controls the body's metabolic rate — the rate at which the chemical reactions in cells take place.

A rise in thyroxine inhibits its own release, so the level falls again.

A fall in thyroxine removes that inhibition, so more is released. The level is kept steady.

The adrenal glands, above the kidneys.

It prepares the body for 'fight or flight' in a frightening or stressful situation.

It raises the heart rate and the blood glucose concentration.

More oxygen and glucose reach the muscles, so they can respire faster and release more energy.

Thyroxine controls the metabolic rate of the body.

False.

Adrenaline is released in response to fear or stress. It is thyroxine that is controlled by negative feedback.

Testosterone.

In the testes.

It stimulates sperm production.

It causes secondary sex characteristics such as body hair growth and a deeper voice.

Oestrogen.

In the ovaries.

It starts the menstrual cycle.

It causes secondary sex characteristics such as breast development and widening of the hips.

It maintains the lining of the uterus.

Follicle stimulating hormone.

It stimulates an egg to mature in the ovary.

Luteinising hormone.

It stimulates ovulation — the release of the mature egg.

The release of a mature egg from the ovary.

The physical changes, other than the reproductive organs themselves, that develop at puberty.

Oestrogen and progesterone.

Testosterone stimulates sperm production in males.

The hormone that causes an egg to mature in the ovary is FSH.

False.

Oestrogen builds the lining up; progesterone maintains it.

False.

Both are produced by the pituitary gland in the brain.

FSH, LH, oestrogen and progesterone.

The pituitary gland, in the brain.

It stimulates a follicle to develop in the ovary, so an egg matures inside it.

It also stimulates the follicle to produce oestrogen.

It causes the uterus lining to grow and repair.

It inhibits FSH and, at a high enough level, stimulates the release of LH.

It triggers ovulation, usually around day 14 of the cycle.

Oestrogen rising to a high enough level.

The empty follicle left after ovulation.

It produces progesterone.

It maintains the thickness of the uterus lining, ready to receive a fertilised egg.

The corpus luteum breaks down, so progesterone falls.

The uterus lining then breaks down, causing menstruation.

The corpus luteum keeps producing progesterone, so the lining is maintained and the pregnancy continues.

It stops further follicles maturing, so normally only one egg is released in a cycle.

Around day 14 of a 28-day cycle.

A drop in progesterone causes the uterus lining to break down at menstruation.

After ovulation the empty follicle becomes the corpus luteum.

False.

LH stimulates ovulation. FSH matures the egg in the follicle.

True.

It keeps the uterus lining intact so the pregnancy can continue.

Methods used to prevent pregnancy.

Oestrogen and progesterone.

High oestrogen inhibits FSH, so no eggs mature.

Progesterone also stops eggs being released and thickens mucus so sperm cannot reach an egg.

A progesterone-only contraceptive pill, which has fewer side effects than the combined pill.

They slowly release progesterone, which stops eggs maturing and being released, for months or years at a time.

It lasts for years, so there is no risk of forgetting to take it each day.

They physically stop sperm from reaching the egg.

The condom, the femidom and the diaphragm.

It is the only method that also protects against sexually transmitted infections.

Avoiding intercourse during the fertile part of the menstrual cycle, around ovulation.

Stress, illness or lifestyle changes can alter the menstrual cycle, so the fertile period is hard to predict.

Vasectomy — the sperm ducts are cut, so semen contains no sperm.

Female sterilisation — the oviducts are cut or tied, so eggs and sperm cannot meet.

It is very difficult to reverse.

The implant, the IUD and sterilisation.

Only complete abstinence is 100% effective.

They can cause side effects such as headaches, mood changes, weight gain or irregular periods.

A method used incorrectly may fail — for example a condom that splits, or a pill taken at the wrong time.

The combined pill works mainly by inhibiting FSH so that no eggs mature.

False.

Only condoms act as a barrier to sexually transmitted infections.

False.

An IUD works by preventing implantation. Some types also release progesterone, but the device itself is not a hormonal method.

FSH and LH.

It stimulates eggs to mature in the ovaries.

It stimulates ovulation, so a mature egg is released.

Where too few eggs mature, or where no egg is released at ovulation.

In vitro fertilisation — 'in vitro' means 'in glass'.

FSH and LH are given to stimulate egg production, and the eggs are collected from the ovary.

The eggs are fertilised with sperm in a dish, and the resulting embryos are placed into the uterus.

To increase the chance that at least one develops into a pregnancy.

Several eggs may be released at once, raising the chance of a multiple birth such as twins or triplets.

It is expensive, so not every couple can afford it.

Implanting several embryos raises the risk of multiple births.

Multiple pregnancies carry greater health risks for both the parent and the babies.

When someone still cannot conceive after taking fertility drugs, or where both partners have fertility problems.

In IVF, eggs are fertilised outside the body and the resulting embryos are placed in the uterus.

FSH is given to stimulate eggs to mature before they are collected for IVF.

False.

The egg and sperm are combined in a dish outside the body, which is what 'in vitro' means.

True.

Several eggs may be released, and in IVF several embryos are implanted.