B5 - homeostasis + response (homeostasis, pg 59 onwards) Flashcards
why is homeostasis important?
your cells need the right conditions in order to function properly including the right conditions for enzyme action
what is homeostasis?
maintaining optimum internal conditions for enzyme action and all cell function
what are three things that are controlled in homeostasis?
body temperature, blood glucose level and your water content
what are the two examples of automatic control systems?
nervous and hormonal communication systems
what is reaction time?
the time it takes to respond to a stimulus - it’s often less than a second
what can reaction time be affected by?
factors such as age, gender or drugs
what are the 8 steps to measuring the effect of caffeine on reaction time?
- the person being tested should sit with their arm resting on the edge of a table (to stop their arm moving up or down)
- hold a ruler vertically between their thumb and forefinger. Make sure that the zero end of the ruler is level with their thumb and finger. Then let go without giving any warning
- the person being tested should try to catch the ruler as quickly as they can - as soon as they see it fall
- reaction time is measured by the number on the ruler where it’s caught. The number should be read from the top of the thumb. The further down the ruler it’s caught (i.e. the higher the number), the slower their reaction time
- repeat the test several times then calculate the mean distance that the ruler fell.
- the person being tested should then have a caffeinated drink (e.g. 300 ml of cola). After ten minutes, repeat steps 1 to 5.
- you need to control any variables to make sure that this is a fair test. For example, you should use the same person to catch the ruler each time, and that person should always use the same hand to catch the ruler. Also the ruler should always be dropped from the same height, and you should make sure that the person being tested has not had any caffeine (or anything else that may affect their reaction time) before the start of the experiment
- too much caffeine can cause unpleasant side-effects, so the person being tested should avoid drinking any more caffeine for the rest of the day
how can reaction time be measured using a computer?
simple computer tests can be used to measure reaction time. For example, the person being tested has to click the mouse (or press a key) as soon as they see a stimulus on the screen, e.g. a box change colour
why can computers give a more precise reaction time?
- because they remove the possibility of human error from the measurement
- computers can record the reaction time in milliseconds, which gives a more accurate measurement
- using a computer removes the possibility that the person can predict when to respond - using the ruler test, the catcher may learn to anticipate the drop by reading the tester’s body language
what are hormones?
chemical molecules released directly into the blood - they are chemical messengers sent in the blood
where are hormones carried to in the blood, and what do they effect?
they are carried in the blood to other parts of the body, but only affect particular cells in particular organs (called target organs)
what do hormones control?
things in organs and cells that need constant adjustment
where are hormones produced and secreted from?
endocrine glands
what do your endocrine glands make up?
your endocrine system
how long do the effects of hormones last?
a long time
name 6 endocrine glands
- the pituitary gland
- ovaries
- testes
- thyroid
- adrenal gland
- the pancreas
what does the pituitary gland do?
it produces many hormones that regulate body conditions. It is sometimes called the ‘master gland’ because these hormones act on other glands, directing them to release hormones that bring about change
what do ovaries produce?
oestrogen, which is involved in the menstrual cycle
what do testes produce? what does this product do?
testosterone, which controls puberty and sperm production in males
what does the thyroid gland produce? what does this product do?
thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature
what does the adrenal gland produce?
adrenaline, which is used to prepare the body for a ‘fight or flight’ response
what does the pancreas produce?
insulin, which is used to regulate the blood glucose level
what are 3 differences between nerves and hormones
- nerves have a very fast action, whereas hormones have a slower action
- nerves act for a very short time whereas hormones act for a long time
- nerves act on a very precise area, whereas hormones act in a more general way
what happens at puberty (hormone wise)?
at puberty, your body starts releasing sex hormones that trigger secondary sexual characteristics (such as the development of facial hair in men and breasts in women) and cause eggs to mature in women
what is the reproductive hormone in men? where is it produced? what does it do?
the main male reproductive hormone is testosterone. It’s produced by the testes and stimulated sperm production
what is the main reproductive hormone in women? where is it produced? what does it do?
in women, the main reproductive hormone is oestrogen. It’s produced by the ovaries. As well as bringing about physical changes, oestrogen is also involved in the menstrual cycle
how many stages does the menstrual cycle have?
four
what happens in stage 1 of the menstrual cycle?
Day 1 - menstruation starts. The uterus lining breaks down for about 4 days
what happens in stage 2 of the menstrual cycle?
the uterus lining builds up again, from day 4 to day 14, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg
what happens in stage 3 of the menstrual cycle?
an egg develops and is released from the ovary at day 14 - this is called ovulation
what happens in stage 4 of the menstrual cycle?
the wall 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 and the whole cycle starts again
what are the 4 hormones that control the menstrual cycle?
- FSH (follicle-stimulating hormone)
- LH (luteinising hormone)
- oestrogen
- progesterone
where is FSH produced?
in the pituitary gland
what does FSH cause/stimulate
it causes an egg to mature in one of the ovaries, in a structure called a follicle. It also stimulates the ovaries to produce oestrogen
where is oestrogen produced?
the ovaries
what does oestrogen cause/stimulate/inhibit?
it causes the lining of the uterus to grow. It also stimulates the release of LH and inhibits release of FSH
where is LH produced?
the pituitary gland
what does LH do?
it stimulates the release of an egg at day 14 (ovulation)
where is progesterone produced?
in the ovaries by the remains of the follicle after ovulation
what does progesterone do?
it maintains the lining of the uterus during the second half of the cycle. When the level of progesterone falls, the lining breaks down. It also inhibits the release of LH and FSH
what are the two hormones that can be used to reduce fertility?
oestrogen and progesterone
why can oestrogen be used as a method of contraception?
it can be used to prevent the release of the egg. This may seem strange (as it naturally stimulates release of eggs), but if oestrogen is taken every day to keep the level of it permanently high, it inhibits the production of FSH, and after a while egg development and production stop and stay stopped
how does progesterone reduce fertility?
it stimulates the production of thick mucus which prevents any sperm getting through and reaching an egg
what is the pill?
an oral contraceptive containing oestrogen and progesterone (known as the combined oral contraceptive pill)
how effective are oral contraceptives?
over 99% effective at preventing pregnancy
what are some downsides to oral contraceptives?
they can cause effects like headaches and nausea and they don’t protect against sexually transmitted diseases
why do some people use a progesterone-only pill?
it has fewer side effects and is just as effective
name 4 methods of contraceptives (other than oral contraceptives) that use hormones
- the contraceptive patch
- the contraceptive implant
- the contraceptive injection
- an intrauterine device (IUD)
what is the contraceptive patch?
a small (5cm x 5 cm) patch containing oestrogen and progestone that’s stuck to the skin
how long does a contraceptive patch last?
each patch lasts 1 week
how does a contraceptive implant work?
it is inserted under the skin of the arm. It releases a continuous amount of progesterone, which stops the ovaries releasing eggs, makes it hard for sperm to swim to the egg, and stops any fertilised egg implanting in the uterus.
how long can a contraceptive implant last for?
three years
what hormone does the contraceptive injection contain?
progesterone
how long does a contraceptive injection last?
2 to 3 months
what is an intrauterine device (IUD)?
a T-shaped device that is inserted into the uterus to kill sperm and prevent implantation of a fertilised egg.
what are the 2 types of IUDs?
plastic IUDs that release progesterone and copper IUDs that prevent the sperm surviving in the uterus
what happens if a woman has too low levels of FSH?
their eggs don’t mature, which means that no eggs are released and the woman can’t get pregnant
which hormones can be given to women in a fertility drug? how do they work?
the hormones FSH and LH can be given to women in a fertility drug to stimulate ovulation
what are the cons of fertility drugs?
- it doesn’t always work - some women may have to do it many times, which can be expensive
- too many eggs could be stimulated, resulting in unexpected multiple pregnancies (twins, triplets, etc.)
what does IVF stand for?
in vitro fertilisation
what does IVF involve?
- collecting eggs from the woman’s ovaries and fertilising them in a lab using the man’s sperm
- it can also involve a technique called intra-cytoplasmic sperm injection (ICSI), where the sperm is injected directly into an egg
what is intra-cytoplasmic sperm injection (ICSI)? when is it useful?
it’s a form of IVF where the sperm is injected directly into an egg. It’s useful if the man has a very low sperm count
what are the 4 stages of IVF?
- collecting eggs from the woman’s ovaries and fertilising them in a lab using the man’s sperm
- The fertilised eggs are then grown into embryos in a laboratory incubator
- once the embryos are tiny balls of cells, one or two of them are transferred to the woman’s uterus to improve the chance of pregnancy
- FSH and LH are given before egg collection to stimulate several eggs to mature (so more than one egg can be collected)
what are the cons of IVF?
- multiple births can happen if more than one embryo grows into a baby - these are risky for the mother and babies (there’s a higher risk of miscarriage, stillbirth…)
- the success rate of IVF is low - the average success rate in the UK is about 26%. This makes the process incredibly stressful and oftwn upsetting, especially if it ends in multiple failures
- as well as being emotionally stressful, the process is also physically stressful for the woman. Some women have a strong reaction to the hormones - e.g. abdominal pain, vomiting, dehydration
how have advances in microscopic techniques helped to improve the techniques (and therefore success rate) of IVF?
specialised micro-tools have been developed to use on the eggs and sperm under the microscope. They’re also used to remove single cells from the embryo for genetic testing. More recently, the development of time-lapse imaging (using a microscope and camera built into the incubator) means that the growth of the embryos can be continuously monitored to help identify those that are more likely to result in a successful pregnancy
why are some people against IVF?
- the process of IVF often results in unused embryos that are eventually destroyed. Because of this, some people think it is unethical because each embryo is a potential human life
- the genetic testing of embryos before implantation also raises ethical issues as some people think it could lead to the selection of preferred characteristics, such as gender or eye colour
what do insulin and glucagon control?
blood glucose level
describe how your blood glucose level fluctuates, and how the body reacts to these changes
- eating foods containing carbohydrate puts glucose into the blood from the gut
- the normal metabolism of cells removes glucose from the blood
- vigorous exercise removes much more glucose from the blood
- excess glucose can be stored as glycogen in the liver and the muscles
- the level of glucose in the blood must be kept steady. Changes are monitored and controlled by the pancreas, using the hormones insulin and glucagon, in a negative feedback cycle
which hormone is released when the blood glucose level is too high?
insulin
which hormone is added when the blood glucose level is too low?
glucagon
how does insulin work?
- when the blood glucose level is too high, insulin is secreted by the pancreas
- insulin moves the glucose from the blood into the muscle cells and liver (insulin makes the liver turn glucose into glycogen so it can be stored)
- the blood glucose level is reduced
how does the hormone glucagon work?
- when the blood glucose levels are too low, glucagon is secreted by the pancreas
- glucagon makes the liver turn glycogen into glucose, which is released into the blood
- the blood glucose increases
what does insulin do?
remove glucose from the blood
is glucagon a hormone or a store of glucose?
a hormone
is glycogen a hormone or a store of glucose?
a store of glucose
what is type 1 diabetes?
type 1 diabetes is where the pancreas produces little or no insulin. This means that a person’s blood glucose level can rise to a level that can kill them. People with Type 1 diabetes need insulin therapy - this usually involves several injections of insulin throughout the day, most likely at mealtimes. This makes sure that glucose is removed from the blood quickly once food has been digested, stopping the level getting too high. It’s a very effective treatment. The amount of insulin that needs to be injected depends on the person’s diet and how active they are. As well as insulin therapy, people with Type 1 diabetes need to think about limiting the intake of food rich in simple carbohydrates, e.g. sugars (which cause the blood glucose to rise rapidly) and taking regular exercise (which helps to remove excess glucose from the blood)
what is diabetes?
a condition that affects your ability to control your blood sugar level
what is Type 2 diabetes?
where a person becomes resistant to their own insulin. This can also cause a person’s blood sugar level to rise to a dangerous level. Being overweight can increase your chance of developing Type 2 diabetes, as obesity is a major risk factor in the development of the disease. Type 2 diabetes can be controlled by eating a carbohydrate-controlled diet and getting regular exercis
what are non-hormonal forms of contraception designed to do?
to stop the sperm from getting to the egg
what is the only form of contraception that will protect against sexually transmitted diseases?
condoms
what is a diaphragm (in contraception)?
a shallow plastic cup that fits over the cervix (the entrance to the uterus) to form a barrier. It has to be used with spermicide (a substance that disables or kills the sperm)
what is spermicide?
a substance that disables or kills sperm
can spermicide be used alone as a form of contraception? If it were to be used alone, how effective would it be?
Spermicide can be used alone as a form of contraception, but it is not as effective (only about 70-18%)
give 3 more drastic ways to avoid pregnancy
- sterilisation
- ‘natural’ methods
- abstinence
what does sterilisation involve?
sterilisation involves cutting or tying the fallopian tubes (which connect the ovaries to the uterus) in a female, or the sperm duct (the tube between the testes and penis) in a male. This is a permanent procedure. However, there is a very small chance that the tubes can rejoin
what are ‘natural’ methods of avoiding pregnancy? who are these methods popular with?
pregnancy may be avoided by finding out when in the menstrual cycle the woman is most fertile and avoiding sexual intercourse on those days. It’s popular with people who think that hormonal and barrier methods are unnatural, but it’s not very effective
what is adrenaline?
a hormone released by the adrenal glands, which are just above the kidneys
what is adrenaline released in response to?
stressful or scary situations - your brain detects fear or stress and sends nervous impulses to the adrenal glands, which respond by secreting adrenaline
what does adrenaline do?
it gets the body ready for ‘fight or flight’ by triggering mechanisms that increase the supply of oxygen and glucose to cells in the brain and muscles. For example, adrenaline increases heart rate.
give an example of a negative feedback system
thyroxine regulating metabolism
where is thyroxine made? what is it made from?
thyroxine is made in the thyroid gland from iodine and amino acids
how does thyroxine regulate metabolism?
- thyroxine is a hormone released by the thyroid gland, which is in the neck
- it plays an important role in regulating the basal metabolic rate - the speed at which chemical reactions in the body occur while the body is at rest. Thyroxine is also important for lots of processes in the body, such as simulating protein synthesis for growth and development
- Thyroxine is released in response to thyroid stimulating hormone (TSH), which is released from the pituitary gland
- a negative feedback system keeps the amount of thyroxine in the blood at the right level - when the level of thyroxine in the blood is higher than normal, the secretion of TSH from the pituitary gland is inhibited. This reduces the amount of thyroxine released from the thyroid gland, so the level in the blood falls back towards normal
where is the thyroid gland?
in the neck
