chapter 5 - biology - homeostasis and response

58 - homeostasis

• homeostasis - maintaining a stable internal environment

• your body has to keep things stable inside even when the environment outside changes, so things such as enzyme action can take place

• your body contains automatic control systems that regulate things such as your temperature, your blood glucose and your water levels

• automatic control systems are made up of a receptor, co-ordination center and an effector

• negative feedback is used by automatic control systems to regulate things when they get too high or too low to bring it back to normal

• for example: receptor detects a stimulus, level is too high

• co-ordination center gets info and organises a response

• effector carries out response, which counteracts change and make level return to normal

• this also works the opposite way, when the level is too high negative feedback will ensure that the level returns to normal

• the effector will continue to produce the response until the level is too high/low again, but your receptor will detect this and cause negative feedback to occur again

• it’s automatic, you don’t think about it

59 - the nervous system

• single celled organism respond to stimuli (changes in the environment) but multicellular organisms (like us) have to communicate with the rest of the body

• in vertebrates (animals with a backbone) the CNS (central nervous system) is made up of the spinal cord and brain only, whereas in mammals, the CNS is connected to the rest of the body with sensory and motor neurones

• sensory neurones - carry information as electrical impulses from the receptors to the CNS (coordinator)

• motor neurones - carry info from CNS to effectors

• relay neurones - connect sensory neurones to motor neurones

• effectors - all the muscles and glands in your body

• muscles - expand and retract to react

• glands - secret hormones to react

• receptors - cells that detect stimuli

• receptors can form complex organs, e.g light receptor cells are found in the retinas of the eyes

• an example of the nervous system working - a bird sees a cat (stimulus), its light receptor cells in it’s eyes detect the stimulus and sensory neurones carry this info as electrical impulses to the coordinator (the brain/CNS) which organises a response, this info is carried to the effectors by motor neurons, which carry out the response, making the bird’s muscles expands and contract to allow it to fly away

60 - synapses and reflexes

• the connection between 2 neurones is called a synapse, info is carried across the synapse as chemicals the diffuse across the gap, which sets off another electrical signal in the other neurone

• reflexes as fast and automatic that don’t require the consciense part of your brain, they don’t require you to think

• the neurones in reflex arcs go through the spinal cord or the unconscience part of the brain

• a stimulus is detected by receptors, which causes impulses to be sent along a sensory neurone to a relay neurone in the CNS

• a relay neurone is used to connect sensory and motor neurones

• when a synapse is reached, the impulse is diffused as a chemical along the gap, which stimulates another impulse onto the next relay neurone, which carries it to a motor neurone, where it diffuses it as chemicals along a synapse again

• the motor neurone then carries the impulse to the effector

61 - investigating reaction time - practical

• reaction time is the time it takes for your body to respond to a stimulus

• can be affected by factors such as age, gender and drugs

• method : the person being tested should sit with their arm resting in the table with their hand on the edge of it to stop them from moving their arm randomly

• hold a ruler between their thumb and forefinger and make sure the zero end of the ruler is being held, then drop it without giving any warning

• the person should then catch the ruler as soon as it’s dropped and the hold at still at the point they caught it

• read off from where they’ve caught it, the larger the measurement, the slower their reaction time, e.g if someone catches the ruler at 5cm their reaction time is faster than someone who catches it at 10cm

• redo the experiment afew times and calculate the mean reaction time

• alternatively, they could be asked to drink caffine for the second part of the experiment to see how it alters their reaction time, after 10 mins, repeat the experiment

• control variables - the length of the ruler used, the person being tested, the hand they catch the ruler in, the height the ruler is dropped from

• ensure the person doesn’t drink too much caffine, as it has unpleasant side effects

• alternative method - using a computer to measure reaction time

• use a program in which the person being tested has to click the mouse when a coloured square appears on the black, computer screen

• since computers rule out human errors and can calculate reaction time to the nearest millisecond, it is a more accurate experiment and stops the person being tested from the reading the body language of the person, as they may know when they’re going to drop the ruler after a few tries

• 62 - the endocrine system

• the endocrine system is made up of glands called endocrine glands

• glands secrete and produce hormones that have long last effects and target certain organs (called target organs)

• glands are different from nerves, the reactions are slower, long-lasting and they act in a more general way instead of on a very precise area (muscle)

• the glands in the endocrine system are - the pituitary gland (called the master gland, produces and secretes hormones that instruct the other glands on when to produce their hormones) - found in the brain, the thyroid gland (produces thyroxine that regulates body temperature, metabolic rate and heart rate) - found in the throat, the adrenal gland (produces adrenaline which prepares the body for fight or flight response and quickens heart rate) found by the pancreas - the pancreas (produces insulin which regulates blood glucose) - the ovaries (produces oestrogen which causes the lining of the uterus to grow) and the testes (produces testosterone which produces sperm and controls puberty in males)

63 - controlling blood glucose

• eating carbohydrates puts glucose into your bloodstream

• normal metabolism removes glucose from ya bloodstream but excersising vigourously removes even more glucose from your bloodstream

• excess glucose is stored as GLYCOGEN in the liver and muscles

• the pancreas regulates blood glucose levels, so secretes hormones insulin (reduces blood glucose level) and GLUCAGON (increases blood glucose cycle) in a negative feedback cycle

• when blood glucose level is too high : insulin is added to your bloodstream, insulin moves glucose from your blood to your liver and muscle cells, where it is turned into GLYCOGEN and stored

• when blood glucose level is too low : GLUCAGON is added to your bloodstream, which makes GLYCOGEN turn into GLUCOSE from the liver and muscle cells, which then secrete the GLUCOSE back into your bloodstream!!

• diabetes makes you unable to control your blood glucose levels

• type 1 - you pancreas produces little to no insulin, can be treated by regular insulin injections (usually after mealtimes) as it makes the insulin lower your blood sugar levels to normal after eating ,the amount of insulin someone has to take depends on how active they are and their diet, avoiding high carb meals is also good, as a lot of carbs can make your blood sugar spike and excersising regularily

• type 2 - your pancreas still produces inslulin but your body no longer reacts to it, obesity is a large risk factor in developing type 2 diabetes, can be controlled by eating a controlled carb diet and excercising often

64 - puberty and the menstrual cycle

• at puberty, your body produces hormones that set off secondary-sex charcateristics

• in girls, breasts growing, pubic hair and periods beginning

• in boys, growing facial hair and voice deepening

• the main sex hormone in men is testosterone and the main sex hormone in women is oestrogen

• the menstrual cycle - day 1, the lining begins to break down for around 4 days (this is when you bleed) day 4 - 14, the lining the uterus begins to build up again, ready for an egg to be released by the ovaries, day 14- this is called ovulation and is when an egg is released, ready to be fertilised, the wall is maintained but if the egg if not fertilised, on day 28, the lining of the uterus will begin to break down and the cycle begins again

• the menstrual cycle is controlled by 4 hormones: FSH, oestrogen, LH and progesterone

• they are produced in this order: FSH, made by the pituitary gland, causes egg to mature in one of the ovaries in a structure called a follicle, stimulates the release of oestrogen, OESTROGEN, made by the ovaries, causes the lining of the uterus to grow in preparation for the egg to be released, stimulates the release of LH and inhibits FSH, LH, made by the pituitary gland, causes an egg to be released on ovulation (day 14), PROGESTERONE, produced by the ovaries, keeps the lining of the uterus thick, inhibits release of LH and FSH

65 - controlling fertility

• the pill

• the combined contraceptive pill is over 99% effective, containing oestrogen and progesterone, these hormones limit the chances of pregnancy

• oestrogen inhibits FSH, so when taken daily in the pill, it keeps levels of oestrogen high, so gradually egg development and production will slow and then stop

• progesterone produces a thick mucus which prevents sperm meeting the egg and will stop the ovaries producing eggs (as it inhibits LH and FSH)

• however, the pill has some side effects and doesn’t protect against STDs

• there is a progesterone-only pill, it’s just as effective with fewer side effects

• other hormone contraceptives:

• the patch - contains progesterone and oestrogen, each patch lasts one week and sticks to the skin

• the implant - stuck under the skin of the arm, produces a constant amount of progesterone, stops eggs being produced, makes it hard for the sperm to swim to the egg and stops eggs implanting in the uterus, can last up to 3 years

• the injection - contains progesterone, each dose lasts 2-3 months

• the IUD (intrauterine device) - places inside the uterus to kill sperm and prevent implantation of the egg, 2 types: plastic (releases progesterone) and copper (kills sperm)

• barrier contraception:

• the condom - worn over penis to prevent sperm entering vagina, there is a female condom, only method that prevents against STDs

• the diaphragm - shallow plastic cup that fits over the cervix, stops sperm entering the vagina, has to be used with spermicide, a substance that kills or disables sperm

• spermicide - a substance that kills/disables sperm, can be used on its own but its around 70-80% effective

• other methods:

• sterilisation - cutting or tying the fallopian tubes or cutting the sperm duct, permanent procedure, very small chance the tubes will rejoin

• natural methods - not having sex when the woman is at her most fertile, popular with those who think hormonal and barrier methods are unnatural, isn’t very effective

• abstinence - not having sex (boring)

66 - more on controlling fertility

• hormones can be given to a woman to increase her fertility (fertility drug)

• FSH and LH are given, as they stimulate egg production, release and development

• can help women get pregnant but isn’t always successful, and many tries is very expensive, too many eggs could also be stimulated causing multiple pregnancies

• IVF can also be used to help a woman get pregnant

• FSH and LH are given to the woman to stimulate egg production and development

• those eggs are then collected and put in lab incubator before being fertilised with the man’s sperm, which is also collected from him

• ICSI (intra-cytoplasmic sperm injection) can be used for males with a low sperm count, as the sperm is injected directly into the eggs

• these eggs grow into embryos in the lab incubator

• once they are tiny balls of cells, one or two of them are implanted in the woman’s uterus to improve chance of pregnancy

• microscopes can be used to help monitor the development of the embryos: can also be used to remove single cells for genetic testing to check that they’re healthy, time-lapse imaging means that the growth of the embryos can be constantly monitored

• some people are against the process, as unused embryos are destroyed, and as they are potential human life, some view it as murder (bullshit)

• some also argue that the genetic testing of the embryos to ensure they’re healthy may lead to allowing parents to chose preferred characteristics (eye colour and gender)

• IVF can help women get pregnant, but the success rate is low, 26% in the UK, it is also a very mentally stressful process for both parents, and women can react badly to hormones, causing side-effects such as vomiting, dehydration and abdominal pain, multiple births can also occur, increasing the chance of stillbirth and miscarriage

67 - adrenaline and thyroxine

• adrenaline is produced when your brain detects fear or stress, and sends nervous impulses to the adrenal glands, causing adrenaline to be produced

• adrenaline gets the body ready for fight or flight by triggering mechanisms that transport oxygen and glucose to the brain and muscles, it also increases heart rate

• thyroxine is made in the thyroid gland is is made up of iodine and amino acids!

• plays an important role in regulating the body’s basal metabolic rate, the speed at which chemical reactions in the body occur when the body is at rest, e.g protein synthesis for growth and development

• the thyroid gland uses negative feedback to regulate the levels of thyroxine in the blood, when it’s too high, TSH (thyroid stimulation hormone) produced by the pituitary gland is inhibited, which reduces the amount of thyroxine in the blood and regulates it back to normal