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What are hormones?

Chemical messengers sent in the blood.


What are target organs?

A specific organ on which a hormone, drug, or other substance acts.

The hormones affect particular cells in particular organs.


Where are hormones produced?

In endocrine glands. These glands make up your endocrine system.


Name the types or endocrine glands

1. Pituitary gland
2. Thyroid gland
3. Ovaries
4. Adrenal glands
5. Testes
6. The pancreas


What does the pituitary gland produce?

It produces many hormones that regulate body conditions. For example ACTH, FSH, LH and growth hormones.

It’s sometimes called the master gland because these hormones act on other glands, directing them to release hormones that bring about change.



What does the thyroid gland produce?

This produces thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature.

Low, from neck


What do the ovaries produce?

Produce oestrogen, which is involved in the menstrual cycle.


What do the adrenals glands produce?

They produce adrenaline, which is used to prepare the body for a ‘fight or flight’ response.

Top of each kidney


What do the testes produce?

They produce testosterone which controls puberty and sperm production.


What does the pancreas produce?

This produces insulin, which is used to regulate the blood glucose level.

Across the back of the abdomen


What’s the difference between hormones and neurones?

Neutrons -
Very fast action.
Act for a very short time.
Act on a very precise area.

Hormones -
Slower action.
Act for a long time.
Act in a more general way.


What does adrenaline do?

Prepares you for ‘fight or flight’. Standing you ground or running.

It does this by activating processes that increase the supply of oxygen and glucose to cells.
When you brain detects a stressful situation, it sends nervous impulses to the adrenal glands, which respond by secreting adrenaline. This gets the body ready for action.


Give an example of how adrenaline works

1. Adrenaline binds to specific receptors in the heart. This causes the heart muscle to contact more frequently and with more force,so heart rate and blood pressure increase.
2. This increases blood flow to the muscles, so the cells receive more oxygen and glucose for increased respiration.
3. Adrenaline also binds to receptors in the liver. This causes the liver to break down its glycogen stores to release glucose.
4. This increases the blood glucose level, so there’s more glucose in the blood to be transported to the cells.


How is hormone release affected by negative feedback?

Your body can control the levels of hormones (and other substances) in the blood using negative feedback systems. When the body detects that the level of a substance has gone above or below the normal level, it triggers a response to bring the level back to normal again.


What does thyroxine regulate?



What happens when a negative feedback system keeps the amount of thyroxine in the blood at the right level

1. When the blood thyroxine level is lower then normal the hypothalamus (structure in the brain) is stimulated to release thyrotropin releasing hormone (TRH).
2. TRH stimulates the pituitary gland to release thyroid stimulating hormone (TSH).
3. TSH stimulates the thyroid gland to release thyroxine so the blood thyroxine level rises back towards normal.
4. When the blood thyroxine level becomes higher than normal, the release of TRH from the hypothalamus is inhibited, which reduces the production of TSH, so the blood thyroxine level falls.


Name and explain the 4 stages of the menstrual cycle.

Stage 1: Day 1 is when the menstruation starts. The lining of the uterus breaks down and is released.

Stage 2: the uterus lining is repaired, form day 4 to day 14 until it becomes a thick spongy layer full of blood vessels ready fro a fertilised egg to implant there.

Stage 3: an egg develops and is released from the ovary (ovulation) at about day 14.

Stage 4: the lining is then maintained for about 14 days, until day 28. If no fertilised egg has landed on the uterus wall by day 28, the spongy lining starts to break down again and the whole cycle starts over.


Name the 4 hormones that the menstrual cycle is controlled by

1. FSH (follicle-stimulating hormone)

2. Oestrogen

3. LH (luteinising hormone)

4. Progesterone


What does FSH (follicle-stimulating hormone) do in the menstrual cycle?

1. Released by the pituitary gland.

2. Causes a follicle (an egg and its surrounding cells) to mature in one of the ovaries.

3. Stimulates oestrogen production.


What does oestrogen do in the menstrual cycle?

1. Released be the ovaries.

2. Causes the lining of the uterus to thicken and grow.

3. A high level stimulates an LH surge (a rapid increase).


What does LH (luteinising hormone) do in the menstrual cycle?

1. Released by the pituitary gland.

2. The LH surge stimulates ovulation at day 14 - the follicle ruptures and the egg is released.

3. Stimulates the remains of the follicle to develop into a structure called a corpus luteinising - which secretes progesterone.


What does progesterone do in the menstrual cycle?

1. Released by the corpus luteum after ovulation.
2. Maintains the lining of the uterus.
3. Inhibits the release of FSH and LH.
4. When the level of progesterone falls, and there’s a low oestrogen level, the uterus lining breaks down.
5. A low progesterone level allows FSH to increase and then the whole cycle starts again.


What does infertile mean?

Means you cant reproduce naturally.

There are methods an infertile couple can use to become pregnant, many of which involve hormones. For example:

1. Clomifene therapy
2. IVF (in vitro fertilisation)


What does clomifene therapy involve?

Some women are infertile because they don’t ovulate or they don’t ovulate regularly. These women can take a drug called clomifene.

This works by causing more FSH and LH to be released by the body, which stimulate egg maturation and ovulation. By knowing when the woman will be ovulating, the couple can have intercourses during this period to improve the chance of becoming pregnant.


What does IVF involve?

IVF involves collecting eggs from the women’s ovaries and fertilising them in a lab using the mans sperm.
These are then grown into embryos. Once the embryos are tiny balls of cells, one or two of them are transferred to the women’s uterus to improve the chance of pregnancy.
FSH and LH re given before egg collection to stimulate egg production (so more than one egg can be collected).

IVF is an example of Assisted Reproductive Technology (ART) - a fertility treatment that involves eggs being handled (and usually fertilised) outside of the body.


How is oestrogen used as a contraceptive?

1. It can prevent the release of an egg.

2. Naturally it helps stimulate the release of eggs, but if its taken every day to keep the level of it permanently high, it inhibits the production of FSH.

3. After a while egg development and production stop and stay the stopped.


How is progesterone used as a contraceptive?

1. It reduces fertility. It works in several different ways:

2. One of which is by stimulating the production of thick cervical mucus, which prevents any sperm getting through the entrance to the uterus (the cervix) and reaching an egg.


Name some of contraceptives?

1. The combined pill (both oestrogen and progesterone).

2. The mini pill (progesterone only).

3. Barrier methods (put a barrier between the sperm and egg so they don’t meet) - e.g - condom.


What are the pros and cons of hormonal and barrier contraceptives?

1. Generally, hormonal methods are more effective at preventing pregnancy than barrier methods. Also, hormonal methods mean the couple don’t have to think about contraceptives each time.

2. However, hormonal methods can have unpleasant side-effects, such as headaches, acne and mood changes. Also hormonal methods don’t protect against STI’s - (only condoms can do this)


What is homeostasis?

It’s maintaining a constant internal environment.