Homeostasis -> topic 1

What does homeostasis mean?

• The regulation of internal conditions of a cell or organism to maintain the optimum conditions for function in response to internal and external changes.

What homeostasis consist of?

• Automatic control systems making sure that internal conditions of the body stay as constant as possible.

In the human body, these include control of:

• blood glucose concentration

• body temperature

• water levels

What do all control systems include?

• cells called receptors, which detect stimuli (changes in the environment)

• coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors

• effectors, muscles or glands, which bring about responses which restore optimum levels

Structure of the nervous system

1. Receptors detect a stimulus (change in environment) and send electrical impulses down neurones (nerve cells) to the central nervous system (co-ordination centre).

2. This now send electrical impulses sown other neurones to effectors which bring about a response.

What are effectors usually?

A muscle which contract or a gland that secretes hormones.

What does the nervous system allow humans to do?

• React to their surroundings and coordinate their behaviour.

• One way it does this is through the reflex arc.

What is the reflex arc?

1. When you touch a hot object the stimulus is detected by a receptor. In this case the stimulus is heat and the receptor is the skin.

2. Electrical impulses now pass from the receptor along a sensory neurone to the CNS.

3. Sensory neurones are connected to receptors and at the end of the sensory neurone is a junction called synapse. At the synapse a chemical is released and this chemical now diffuses into a relay neurone in the CNS where it triggers and electrical impulse.

4. The electrical impulse passes across the relay neurone and reaches another synapse. Once again a chemical is released.

5. This chemical triggers an electrical impulse in a motor neurone.

6. The electrical impulse now passes down the motor neurone to an effector. In this case the effector is the muscle.

7. The muscle now contracts and pulls the hand away from the heat. (response)

What makes reflexes automatic and rapid which protects us from danger?

The fact that they don’t involve the conscious part of the brain.

The brain

• Controls complex behaviour such as language.

• This is why the brain is made of billions of interconnected neurones and has different parts that carry out different functions.

Cerebral cortex

• Highly folded outer part of the brain.

• Functions:

  • Language

  • Memory

  • Consciousness

Cerebellum

• Responsible for muscle co-ordination and movement

Medulla

• Controls unconscious activities such as breathing and heart rate

Why is it difficult to investigate brain function and treat brain damage and disease?

• The brain is protected by the skull, making it very tricky to access.

• The structures of the brain are extremely complex, making it difficult to work out exactly which parts of the brain carry out specific functions.

• The brain is extremely delicate and easy to damage.

Ways that scientists investigate the brain

1. Many scientists look at patients who have suffered brain damage.

   They then look to see where the damage has taken place and try to link that part of the brain to it’s function.

2. Electrically stimulate different parts of the brain and look at the effects on the person’s behaviour.

   That allows us to narrow down specific regions to their functions.

3. MRI scanning to look at which parts of the brain are most active during different activities.

The eye

• Is a sense organ

• Contains receptors which are sensitive to light intensity and the colour of light.

How does light pass through the eye.

1. Passes through the transparent front of the eye called the cornea which refracts light as it enters the eye.

2. The light rays then pass through the pupil in the centre of the iris.

3. The light rays then pass through the lens.

4. The light rays are now focus onto the back of the eye-retina.

5. The receptor cells in the retina now send electrical impulses down the optic nerve to the brain.

How does light pass through the eye?

1. Passes through the transparent front of the eye called the cornea which refracts light as it enters the eye.

2. The light rays then pass through the pupil in the centre of the iris.

3. The light rays then pass through the lens.

4. The light rays are now focus onto the back of the eye-retina.

5. The receptor cells in the retina now send electrical impulses down the optic nerve to the brain.

Cornea

Function: Refracts light as it enters the eye

• Transparent outer layer at the front of the eye

Iris

Coloured part of the eye.

Function: To control how much light reaches the retina. It contains muscles that allow it control the diameter of the pupil.

Lens

Function: To focus the light rays onto the retina.

Retina

Contains receptor cells sensitive to light intensity and colour.

Ciliary muscles and suspensory ligaments

Change the shape of the lens allowing us to focus on objects at different distances.

How does the eye adapt to dim light?

• The drop in light intensity is sensed by light receptors in the retina.

• The light receptors send electrical impulses to the brain.

• The brain send electrical impulses to specific muscles in the iris.

• The radial muscles contract and the circular muscles relax, causing the pupil to become larger.

• This now allows more light to enter the eye.

• Reflex action/iris reflex-doesn’t involve the conscious part of the brain.

Accommodation

The ability to change the shape of the lens in order to focus on near or distant objects.

OR

A reflex that changes the refractive power of the lens in order to focus on distant or near objects

How does accommodation take place?

The lens are surrounded by ciliary muscle.

By contracting or relaxing, the ciliary muscle can change the thickness of the lens.

When the ciliary muscle contracts, the suspensory ligaments loosen.

The lens is now thicker and refracts light rays more strongly.

However, when the ciliary muscle relaxes, the suspensory ligaments are pulled tight.

As a result the lens are pulled thin and only slightly refract light rays.

• Focusing on distant objects:

  • Light from distant objects only needs to be focused/refracted a small amount which means after light has been refracted by the cornea, the lens doesn’t need to do as much. So in this case the ciliary muscle relaxed and the suspensory ligaments are pulled tight, meaning that the lens are pulled thin. Because the lens are pulled thin, the light rays are only slightly refracted. The light rays are now focused to a point on the retina called the fovea.

• Focusing on near objects:

  • Light from near objects needs to be focused/refracted a large amount. This means that even though it’s been refracted by the cornea it needs a powerful lens to refract it more. In this case, the ciliary muscle contracts inwards towards the lens, causing the suspensory ligament to slacken, meaning that the lens is thicker and refracts the light rays more strongly. The light rays are now focused to a point on the retina called the fovea.

In some people, the light rays do not focus correctly on the retina, they can be either long-sited or short-sited.

What are the lens surrounded by?

Ciliary muscle

This is connected to the lens by fibres which are called suspensory ligaments.

Long sightedness

Long sight/hyperopia- No problem focusing on distant objects but they cannot focus on nearby objects.

In many cases of long sight, the eyeball is too short so the light is focused at a point behind the retina causing blurriness.

However, in some cases- especially the elderly- the lens becomes less elastic.

This means that the lens cannot become thick enough refract strongly enough to focus on near objects so the light focuses on a point behind the retina causing blurriness.

Long sight can be treated by using glasses with convex lenses.

These partially refract the light before it enters the eye, which refracts the light rays so that they do focus on the retina rather than behind it.

Short sightedness

Short sightedness/ myopia- Can focus on nearby objects but not distant objects.

In people with short sightedness the eyeball can be too long so the light is focused at a point in front of the retina, causing blurriness.

Short sight can also be caused when the lens is too thick meaning it refracts too much and the image appears in front of the retina, causing blurriness.

Can be treated using glasses with concave lenses to partially unfocus the light, by refracting outwards (counteracting the over refraction of the lens) before the light rays enter the eye so that when it does enter the eye the light rays refract so that they do focus on the retina.

Contact lenses

Hard or soft contact lenses can be used as an alternative to glasses.

These lenses sit on the eyeball and refract the light so that the light rays do focus on the retina, in the same way as glasses do.

Laser surgery

• Can change the shape of the cornea so it refracts the light to a greater or less extent.

Artificial lenses

Lenses that replace the lenses in the eye.

Reaction Time Practical

Investigate affect of factor on reaction time

• Get two people

• One of the people (person 1)have to sit on a stool with good upright posture.

• They then place the forearm of their dominant hand across the table with their hand overhanging the edge.

• The other person (person 2) holds a ruler vertically.

• The 0cm mark should be between person 1’s thumb and first finger.

• Person 2 then tells person 1 to prepare to catch the ruler.

• Person 2 now drops the ruler at a random time and person 1 has to catch the ruler with their thumb and first finger as quickly as possible when it drops.

• Person 2 now records the measurement on the ruler that is level with the top of person 1’s thumb.

• Then person 1 can have a short rest and this test is repeated several time so a mean can be calculated.

• From these experiments the results can be converted into a reaction time using a conversion table.

• At the end, the 2 people switch places with person 1 testing the reaction time of person 2.

• This allows us to see whether the two people have different reaction times.

• Control variables:

  • Starting distance between the thumb and first finger should be kept constant.

  • We should always measure the ruler at the top of the thumb

  • Keep conditions in the room the same e.g. the lighting and the level of background noise.

• Key point: Several other independent variables could be investigated such as the effect of practice.

• Or investigate whether the reaction time depends on the hand catching the ruler.

• Or whether certain chemicals affects reaction time. Give the test subject a measured amount of cola half an hour before the experiment and compare this with their normal reaction times.

• The problem is that there could be some other chemical in the cola so they need to be given a caffeine free cola first and this reaction time can be compared to their normal reaction time.

• Because we are giving test subject something to drink, we need to be certain that this is safe by checking they have no medical issue that may be affected by caffeine e.g. an allergy.

• The test should also be carried out in a lab where hazardous chemicals are not normally used.

How does the eye adapt to bright light?

• The increase in light intensity is sensed by light receptors in the retina.

• The light receptors send electrical impulses to the brain.

• The brain send electrical impulses to specific muscles in the iris.

• The radial muscles relax and the circular muscles contract, causing the pupil to become smaller.

• This now allows less light to enter the eye, protecting it from damage.

• Reflex action/iris reflex-doesn’t involve the conscious part of the brain.

Optic nerve

Function: Carries impulses from he receptors on the retina to the brain.

Sclera

The white part of the eye.

Function: protects the eye, supports the eye giving it shape.

What is normal human body temperature?

37 degrees C

What monitors and controls body temperature?

• The brain

• This part of the brain is called the thermoregulatory centre.

What receptors does the thermoregulatory centre contain.

Receptors which are sensitive to the temperature of blood. (Temperature receptors)

• The skin also contains temperature receptors and these send electrical impulses down the sensory neurone to the thermoregulatory centre.

What happens when body temperature gets too high (e.g. via exercise)?

• Sweat glands release sweat onto the surface of the skin. The sweat now evaporates, taking temperature from the body, cooling it down.

• Vasodilation

  • Under the skin we have a fine network of capillaries which are supplied with blood by blood vessels deeper in the skin.

  • If we get too hot the blood vessels supplying the capillaries dilate (get wider)(vasodilation).

  • Because the blood vessels have dilated this means more blood can flow through the capillaries and heat can now transfer out of the blood, cooling the body down.

What happens when body temperature is too low?

• Vasoconstriction:

  • Under the skin we have a fine network of capillaries which are supplied with blood by blood vessels deeper in the skin.

  • The blood vessels supplying the capillaries construct (become narrower) when body temperature decreases. (Vasoconstriction)

  • This means less blood now flows through the capillaries and less heat is lost from the body.

• Shivering:

  • When we shiver our skeletal muscles contract.

  • To generate energy for this contraction the muscle cells increase their rate of respiration.

  • This releases heat which warms the body.

• We also stop sweating

What is the endocrine system?

• A key system in the body which contains a number of glands.

• These glands secrete chemicals called hormones directly into the bloodstream.

• The blood carries the hormone to a target organ where it produces an effect.

• These effects are slower compared to the nervous system but more long lasting.

Nervous system vs Endocrine system

• The nervous system uses electrical impulses which travel down neurones whereas the endocrine system uses hormones which are chemicals and these are carried in the bloodstream.

• The signalling in the nervous system is extremely fast but the effects tend to be short lived.

• Contrastingly the endocrine system tends to produce a much slower effect but it’s more long lasting.

Name the glands in the endocrine system that you’re expected to know.

• Pituitary gland

• Thyroid

• Ovaries

• Adrenal gland

• Pancreas

• Testes

Pituitary gland

• It’s located in the brain

• It produces many hormones that regulate the body conditions.

• These hormones act on other glands, directing them to release hormones that bring about a change.

• Because it releases hormones which act on other glands causing other hormones to be released, the pituitary gland is called the master gland.

Thyroid

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

• It’s also involved in growth.

Ovaries (females only)

• Produce oestrogen which is involved in the menstrual cycle (more broadly puberty and reproduction)

Testes (males only)

• Produce testosterone which controls puberty and sperm production in males.

Adrenal gland

• This produces adrenaline in times of fear or stress.

Pancreas

• Produces hormones insulin and glucagon which are involved in controlling the concentration of blood.

Why is it important that the concentration of blood glucose is kept as constant as possible?

Because glucose is needed by every cell (to release energy by respiration).

What monitors the blood glucose concentration?

Pancreas

Describe what happens to a non diabetic person when their blood glucose level rises e.g after a carbohydrate-rich meal.

• The pancreas senses the increase in blood glucose and produces the hormone insulin.

• Insulin travels in the bloodstream all around the body and triggers body cells to take up glucose from the blood.

• Insulin also triggers liver and muscle cells to store excess glucose as a storage molecule glycogen.

• As a result the blood glucose concentration returns to it’s normal level (homeostasis has taken place).

What type of people’s blood glucose control doesn’t work effectively?

Diabetic people.

Type 1 diabetes

• The pancreas produces little or no insulin so their blood glucose levels can rise too high to a level that can kill the person.

• People with type 1 diabetes take insulin therapy and are ADVISED to monitor their blood glucose concentration to prevent it from rising too high.

• Insulin therapy- they inject themselves with insulin if blood glucose rises too much throughout the day e.g. after a carbohydrate-rich diet.

• The amount of insulin depends on the person’s diet and how active they are.

• Monitoring blood glucose concentration can be done via exercise (as it helps remove excess blood glucose for the process of respiration) as well as by limiting the carbohydrates in their diet (as it causes blood glucose to rise rapidly).

Type 2 diabetes

• A person becomes to their own insulin as the body cells stop responding to insulin produced by the pancreas so their blood glucose levels can rise too high to a dangerous level.

• Obesity is a major risk factor of type 2 diabetes.

• Type 2 diabetes is often treated with a diet containing a controlled level of carbohydrates to prevent the blood glucose levels from rising too high.

• They’re also advised to take regular exercise.

What happens when blood glucose concentration falls e.g. between meals?

• Pancreas senses decrease in blood glucose levels and produces the hormone glucagon into the bloodstream.

• Glucagon triggers liver cells to convert glycogen stores back to glucose and this glucose is released into the blood, causing the blood glucose concentration to return to normal.

Why does the blood glucose level of someone without diabetes rise and fall slightly throughout the day?

• Because the blood glucose concentration is controlled by a balance between insulin and glucagon.

• When the blood glucose concentration rises the pancreas releases insulin which work to reduce the blood glucose levels but when then the blood glucose concentration falls, the pancreas produces glucagon to increase the blood glucose levels.

• Because the insulin and glucagon have opposite effects on the blood glucose concentration scientists say they form a negative feedback cycle.

Why is it important that the body keeps the level of water in the blood as constant as possible?

• If the blood becomes to dilute, then water moves into cells by osmosis.

• If the blood becomes too concentrated, then water moves by osmosis out of cells.

• And if body cells gain or lose too much water by osmosis then they don’t work efficiently.

How does the body take in water?

Via food and drinks

How many ways can the body lose water?

• 3 ways

• 1. Via the lungs when we exhale- the body can’t control this water loss.

• 2. Sweating removed water through the skin.

• 3. Via the kidneys in urine.

• The body can control how much body is lost in urine.

• So if the blood is too dilute, the kidneys remove the excess water and they produce a greater volume of urine.

• If the blood is less dilute, the kidneys produce less urine so that more water can be obtained in the blood.

What does sweat contain?

• Water

• Ions such as the sodium ion.

• Waste product urea

• The body can’t control how much water, ions or urea is lost by sweating.

• This is because sweating is part of the body’s temperature control system.

What’s removed in urine

• Water

• Urea

• Excess ions

Describe how the kidneys remove the waste product urea and also adjust the levels of water and ions.

• Humans have two kidneys.

• Blood (containing urea) enters the kidney through an artery.

• The kidneys removed this urea as well as excess ions and excess water.

• These leave the kidneys as urine- which is stored in the bladder.

• Blood (not containing urea) now leaves the kidney through a vein.

How do the kidneys adjust the level of molecules in the blood?

• First the blood passes through capillaries where small molecules are filtered out of the blood.

• These molecules include: urea, ions, water and the sugar glucose.

• Then these molecules pass into tiny tubules.

• Now all of the glucose, some of the ions and some of the water is re absorbed back into the blood- this is called selective reabsorption.

• Urea, excess ions and excess water are released as urine.

Describe the concentration change of glucose in the blood before and after it has passed through the kidneys.

• Concentration of glucose in the blood doesn’t change as the kidneys filter glucose out of the blood but then reabsorb it all back into the blood.

Describe the concentration change of ions in the blood before and after it has passed through the kidneys

• Concentration of ions in the blood has decreased as the kidneys filter ions out of the blood but only reabsorb a certain amount of ions back into the blood- depending on the needs of the body.

Describe the concentration change of urea in the blood before and after it has passed through the kidneys

• Concentration of urea in the blood falls to zero as all of it’s filtered out by the kidneys and none of it is reabsorbed.

What does the body do when too much protein is eaten?

• The liver breaks down the excess amino acids and produces the chemical ammonia.

• This process is called deamination.

• Ammonia is a very toxic chemical so the liver immediately converts it to urea which can be safely excreted by the kidneys.

If the blood becomes too concentrated/the level of water in the blood falls, what does the body do in response.

• The hypothalamus triggers the pituitary gland to release the hormone ADH into the bloodstream.

• ADH travels to the kidneys and it causes the kidney tubes to become more permeable to water.

• In other words, more water can pass out of the kidney tubules, meaning more water will be reabsorbed from the tubules back into the blood.

• Because of this, less urine is produced and the amount of water in the blood rises back to its normal level.

• As the level of water in the blood returns to normal, the pituitary gland stops releasing ADH.

• This is a negative feedback cycle.

If the blood becomes too dilute, what does the body do as a response?

• The pituitary gland stops releasing ADH.

• This means that the kidneys reabsorb less water into the blood, meaning more urine is produced and the concentration of water in the blood returns back to normal.

What happens if someone’s kidneys, fail?

• A machine is used to adjust the levels of water, ions and urea in the persons blood.

• This is called kidney dialysis.

How does kidney dialysis work?

• When a patient has kidney failure, their blood will contain a higher concentration of water ions and urea than it should.

• In kidney dialysis, the patients blood passes over a semi-permeable membrane.

• This allows urea, ions and water through but it will not allow larger molecules such as proteins or blood cells through.

• On the other side of the membrane, we have dialysis fluid.

• This contains the normal concentrations of water and ions but it doesn’t contain any urea.

• Because of the concentration gradient, the urea diffuses from the blood into the dialysis fluid.

• The dialysis fluid is constantly refreshed, maintaining the large concentration gradient for urea.

• The dialysis fluid contains the normal concentration of water and ions, so some of the water and ions in the blood will diffuse into the dialysis fluid, as the blood contains high levels of water and ions.

• Because of this diffusion, the concentrations of water and ions in the patients blood will return to normal.

Advantages and disadvantages of kidney dialysis

• Can be inconvenient as patients have to visit a hospital several times a week.

• They also have to eat a controlled diet so they do not produce too much urea.

• Advantage is that it successfully removes urea from the blood and adjusts the level of water and ions in the blood.

• No shortage of dialysis machines.

• Expensive in the long term.

What happens during a kidney transplant?

• Diseased kidney is replaced with a healthy kidney from a donor.

Advantages and disadvantages of kidney transplant

• Donated kidney may be rejected by patients immune system.

• Shortage of kidney donors.

• Allows patient to lead normal life.

• Only expensive initially.

• If successful, provides patient with a healthy kidney which successfully removes urea and adjusts levels of water and ions in the blood.

• Patients have to take anti-rejection drugs for the rest of life.

What do reproductive hormones cause during puberty?

• Cause secondary characteristics to develop e.g. pubic hair

What does testosterone stimulate the testes to produce?

Sperm

What do eggs in the ovaries begin to do once puberty begins?

• They start to mature

  • Every 28 days an egg is released

  • This is called ovulation.

  • The release of an egg every 28 days is part of the menstrual cycle.

What happens during the menstrual cycle?

• Every 28 days, the ovary releases an egg/ovulation takes place.

• In preparation for this the uterus lining becomes thick and spongy.

• The egg now makes its way down the uterus.

• If sperm is present, then the egg can be fertilised.

• If this happens, the fertilised egg can be implanted into the uterus wall and develop into a baby.

• However, if the egg does not get fertilised then both the egg and uterus lining are released.

• This is called a period.

What does FSH (follicle stimulating hormone) do?

• Causes an egg to mature in the ovary.

What does luteinising hormone (LH) cause the egg to do?

To be released/ ovulate

What does oestrogen (produced by the ovary) and progesterone do?

• They’re involved in maintaining the uterus lining, in case the egg is fertilised and implants.

Menstrual cycle stages:

• In the first stage, FSH is released by the pituitary gland.

• FSH travels in the blood to the ovaries where it causes an egg to mature and at the same time it also triggers the ovaries to make oestrogen.

• Oestrogen causes the lining of the uterus to become thick and it also stops the pituitary gland from releasing any more FSH.

• Instead the pituitary gland now releases luteinising hormone (LH).

• LH triggers ovulation/ triggers the mature egg to be released.

• Once the ovary has released its egg, the ovary now produced the hormone progesterone.

• Progesterone has two effects

• It stops the pituitary gland from releasing FSH and LH, to prevent more eggs from maturing or being released.

• Progesterone keeps the lining of the uterus thick, incase a fertilised egg implants and if fertilisation doesn’t take place then the level of progesterone falls.

• This causes the uterus lining and the egg to be released and the women now has a period.

Interpret graphs of these hormones during the menstrual cycle.

• Level if FSH rises and this trigger the ovaries to release oestrogen so the level of oestrogen increases.

• As the level of oestrogen increases, this inhibits the production of FSH so the level of FSH falls.

• Oestrogen triggers the release of LH to the LH level rises to a peak around day 14.

• LH triggers ovulation and once this happens, the ovaries release progesterone, so the level of progesterone increases.

• The level of FSH and LH them fall as a result.

• Progesterone levels also fall if fertilisation doesn’t happen and the woman has her period.

What is contraception?

Artificial methods used to prevent fertilisation.

Examples of contraception: Oral contraceptives (this is a hormonal form of contraception)

• Oral contraceptives such as the pill.

• These contain hormones such as oestrogen which prevent the body from producing the hormone FSH therefore preventing any eggs inside the woman’s body from maturing.

• Others contain hormones such as progesterone which stimulates the production of thick mucus in the cervix (the entry to the uterus) preventing sperm from entering the uterus and reaching the egg.

• An advantage of this pill is that it’s highly effective if it’s taken correctly.

• A disadvantage is that it must be taken every day otherwise there’s a risk of pregnancy.

• Certain contraceptive pills also have a risk of side effects such as an increased risk of breast cancer or blood clots- these risks are small though. Also has other side effects such as headaches and nausea.

• Doesn’t protect against STIs such as HIV

Examples of contraception: (hormonal form of contraception) an implant, skin patch or an injection

• These cause progesterone to be slowly released, preventing eggs from maturing or being released

• Contraceptive patch is like a small sticker that you stick on your upper arm which slowly releases progesterone.

• Each patch lasts one week.

• Contraceptive injection is an injection of progesterone into the upper arm.

• Each injection dose lasts 13 weeks.

• Contraceptive implant involves a small device being placed under the skin of the arm.

• This slowly releases progesterone for 3 years.

• Advantages are that they’re more convenient than taking a daily pill.

• Disadvantages are that they can have side effects

• Doesn’t protect against STIs such as HIV.

When does the egg ovulate?

After two weeks

Examples of contraception: condom or diaphragm (barrier methods of contraception)

• Prevent the sperm from reaching an egg.

• Advantage is that it’s effective if used correctly.

• Advantage is that because they don’t use hormones they don’t have side effects.

• Condoms can also reduce the risk of STIs.

• However one disadvantage of condoms is that they can break or slip off.

• Both condoms and a diaphragm are more effective if they’re used with a spermicide gel.

What do spermicides do?

• Kill or disable sperm, reducing the risk of fertilisation.

Examples of contraception: intrauterine device/ IUD ( can be hormonal method)

• These can prevent an embryo from implanting.

• Some coils also release hormones such as progesterone to reduce the chances of fertilisation.

• Some coils don’t release hormones but release spermicide to kill or disable sperm, preventing the chance of fertilisation.

• Highly effective and can prevent pregnancy 3-10 years.

• Also have very few side effects.

• However an IUD doesn’t protect against STIs

Examples of contraception: (surgical forms) sterilisation

• In the case of women, this prevents the egg from reaching the uterus.

• In the case of men this prevents the spark from leaving the penis.

• Both are highly effective

• But very difficult to reverse so a person should be certain they never want children before going ahead.

• Surgical methods do not protect against STIs.

Examples of contraception: natural method

• Abstaining from sexual intercourse during the time after ovulation.

• Problem is that it’s very hard to tell when a woman has ovulated.

• Doesn’t protect against STIs.

What’s the Catholic Church’s view on contraception?

• All contraception is unethical except natural methods.

• Other people oppose this view as they believe it’s that persons right to choose whichever form of contraception is best for them.

• People also oppose this view because some forms of contraception such as condoms also prevent risk of STIs.

Why do some people struggle with infertility?

• Some men have a reduced sperm count

• Some women find it difficult to conceive

• Many of these people undergo fertility treatment as a result.

Describe a form of fertility treatment: fertility drug

• FSH and LH are given to a woman.

• This combination is called a fertility drug.

• This causes the woman to ovulate more than usual, increasing her chances of becoming pregnant through sexual intercourse.

Describe a form of fertility treatment: in-vitro fertilisation or IVF

• In this case, fertilisation takes place outside the body.

• During IVF, the mother is first treated with FSH and LH.

• This causes several eggs to mature.

• These eggs are then collected from the mother and taken to a laboratory.

• At this point, sperm from the father is collected and it’s used to fertilise the eggs in the laboratory.

• The fertilised eggs then develop into embryos.

• Once the embryos are tiny balls of cells, these are inserted into the mothers uterus (womb).

• These embryos can then develop in the mother in the usual way.

Advantages and disadvantages of IVF

• Gives a woman the chance to have a baby of her own.

• Success rates are not high.

• IVF is emotionally stressful for both parents.

• Physically demanding on the mothers e.g. during the treatment with fertility drugs and te collection of eggs.

• Can lead to multiple births which is risky for the babies and the mother.

• Not all of the embryos that are created will be transferred into the mother, meaning many embryos are destroyed and some people find that unethical.

• IVF is expensive and many believe this money should be spent on other medical issues such as treatment for cancer.

What do the adrenal glands do ?

• Produce the hormone adrenaline during times of fear or stress.

• The adrenaline is released into the blood.

• One of the main effects of adrenaline is to increase the heart rate.

• Because the heart is beating faster, more oxygen and glucose and delivered in the blood to the brain and muscles.

• Because both oxygen and glucose are needed for aerobic respiration, this prepares the body to either fight or runaway.

• This is called fight or flight.

What does the thyroid gland do?

• Releases the hormone thyroxine

• Thyroxine has 2 main effects:

  • It stimulates the body’s nasal metabolic rate- makes the body’s chemical reactions take place at a faster rate while the body is at rest.

  • Also plays an important role in growth and development.

• The level of thyroxine in the blood is controlled negative feedback.