B5 - Homeostasis and Response Flashcards
Homeostasis definition
> Regulation of the conditions inside your body to maintain a stable environment in response to conditions.
Why is homeostasis important?
> Cells need the right conditions to function properly including the right conditions for enzyme action.
The control systems
> Loads of automatic control systems regulate internal environment:
-include nervous and hormonal communication systems.
What do control systems monitor?
> Body temperature, blood glucose levels, water content.
Components of an automatic control system
> Automatic control systems are made up of 3 main components:
- Receptors
- Co-ordination centres (brain, spinal cord and pancreas)
- Effectors.
Stimulus definition
> A change in the environment.
Negative feedback definition
> Mechanism where the automatic control systems keep the environment stable.
It counteracts change.
Negative feedback
- Receptor detects stimulus - if the level is too high/low.
- coordination centre receives + processes the info then organises a response.
- Effector produces a response which counteracts the change + restores the optimum level - level decreases/ increases.
>Automatic process.
>Effectors will carry on producing response if stimulated by the coordination centre. Could cause opposite probem. Then receptor detects + changes.
The nervous system parts
> The nervous system detects + reacts to stimuli - parts:
- CNS.
- Sensory neurones.
- Motor neurones.
- Effectors.
The nervous system - CNS definiton
> In vertebrates this consists of the bran + spinal cord only. In mammals, the CNS is connected to the body by sensory neurones + motor neurones.
The nervous system - Sensory neurones
> Neurones that carry information as electrical impulses from the receptors to the CNS.
The nervous system - Motor neurones
> Neurones that carry electrical impulses from the CNS to the effectors.
The nervous system - Effectors
> All your muscles and glands, which respond to nervous impulses.
Receptor definiton + info
> Cells that detect stimuli.
Different types of receptors, e.g. taste in tongue and sound in ears.
Receptors can form part of larger, complex organs, e.g. the retina in the eye is covered in light receptors.
Effectors info
> They respond to nervous impulses and bring about a change.
Muscles and glands are known as effectors - they respond in different ways. Muscles contract in response to a nervous impulse, whereas glands secrete hormones.
The central nervous system definition
> A coordination centre - it recieves information from the receptors and then coordinates a response. The response is carried out by effectors.
Stimulus - Receptor - Sensory neurone - CNS - Motor neurone - Effector - Response.
Synapse definition
> A connection between 2 neurones.
Synapse info
> The nerve signal is transferred by chemicals which diffuse across the gap.
These chemicals set off a new electrical signal in the next neurone.
Reflexes definition + info
> Rapid, automatic responses to certain stimuli that don’t involve the conscious part of the brain.
Reflexes help prevent injury.
E.g. bright light - pupils get smaller - prevent damage.
E.g. shock - body releases adrenaline automatically.
Reflex arc definition
> Passage of information in a reflex (from receptor to effector).
Quicker than a normal response as you don’t think about it.
Reflex Arc - Sequence
> The neurones in the reflex arc go through the spinal cord or unconscious part of the brain.
- When the stimulus is detected by receptors, impulses are sent along a sensory neurone to a relay neurone in the CNS.
- When impulses reach a synapse between the sensory and relay neurone, they trigger chemicals to be released. These chemicals cause impulses to be sent along the relay neurone.
- When the impulses reach a synapse between the relay and motor neurone they trigger chemicals to be released. These chemicals cause impulses to be sent along the motor neurone.
- The impulses travel along the motor neurone to the effector and the response is triggered.
Practical - Investigating Reaction Time - Steps
- Caffeine is a drug that can speed up a reaction time. Its’ effect can be measured:
- The person being tested sits with their arm resting on the edge of the table.
- Hold the ruler vertically between their thumb and forefinger, making sure the zero end of of the ruler is level with their thumb.
- Without warning, let go. Person catches the ruler as fast as they can.
- Reaction time is measured by the number on the ruler where caught - read from top of the thumb.
- The further down it’s caught, the slower the reaction time.
- Repeat a few times and then calculate the mean distance.
- Person should drink a caffeinated drink. After 10 mins repeat.
Investigating reaction times practical - what variables need to be controlled to ensure a fair test?
> Control any variable to make sure it’s a fair test.
E.g:
-same person with same hand.
-ruler dropped from the same height.
-person hasn’t had any caffeine or something else that may affect their reaction time before the start of the experiment.
Investigating reaction times practical - safety
> Too much caffeine can lead to unpleasant side effects so avoid caffeine for the rest of the day.
Investigating reaction times alternative methods
> Can be measured using a computer.
Simple computer tests can also be used to measure reaction time.
E.g. person clicks mouse when they see a stimulus on the screen.
Benefits of using computer to measure reaction time than ruler drop test.
> More precise as it removes the possibility of human error from the measurement.
More accurate as the computer can record the reaction time in milliseconds.
Removes the possibility that a person can predict when to respond, e.g. anticipate drop due to tester’s body language.
The brain - info
> The brain is responsible for complex behaviours.
Along with the spinal cord, the brain is part of the CNS.
It’s made up of billions of interconnected neurones.
The brain is in charge of all our complex behaviours. It controls and co-ordinates everything you do.
Different regions of the brain carry out different functions.
The brain - parts
> Different regions of the brain carry out different functions:
- Cerebral Cortex
- Medulla
- Cerebellum
- Spinal Cord
Regions of the brain - Cerebral Cortex
> This is the outer wrinkly bit.
>It’s responsible for things like consciousness, intelligence, memory and language.
Regions of the brain - Medulla
> Controls unconscious activities like breathing and your heartbeat.
Regions of the brain - Cerebellum
> Responsible for muscle coordination.
Methods of studying the brain
> Studying patients with brain damage.
Electrically stimulating the brain.
MRI scans.
Methods of studying the brain - studying patients with brain damage
> If a small part of the brain has been damaged, the effect this has on the patient can tell you a lot about what the damaged part of the brain does.
E.g. if an area at the back of the brain was damaged by a stroke and the patient went blind, then that area has something to do with vision.
Methods of studying the brain - electrically stimulating the brain
> The brain can be stimulated electrically by pushing a tiny electrode into the tissue and giving a small zap of electricity.
By observing what stimulating different parts of the brain does, it’s possible to get an idea what those parts do.
E.g. when a certain part of the brain (known as the motor area) is stimulated, it causes muscle contraction and movements.
Methods of studying the brain - MRI scans
> A magnetic resonance imaging (MRI) scanner is a bug tube-like machine that can produce a very detailed picture of the brain’s structure.
Scientists use it to find out what areas of the brain are active when people do things like listening to music or trying to recall a memory.
Consequences of studying the brain
1) Knowledge of how the brain works has led to the development of treatments for disorders of the nervous system.
- E.g. electrical stimulation of the brain can help reduce muscle tremors caused by nervous system disorders such as Parkinson’s disease.
2) However, the brain is incredibly complex and delicate so the investigation of brain function and any treatment of the brain without damage or disease is difficult.
- It also carries risks, e.g. physical damage to the brain or increased problems with brain function (e.g. speech difficulties).
What is the Eye
> It is sense organ.
The Eye - parts
- The SCLERA is the tough, supporting wall of the eye.
- The CORNEA is the transparent outer layer found at the front of the eye. It refracts light into the eye.
- The IRIS contains muscles that allow it to control the diameter of the PUPIL (the hole in the middle) and therefore how much light enters the eye.
- The LENS focuses the light onto the RETINA (which contains receptor cells sensitive to light intensity and colour.
- The shape of the lens is controlled by the CILIARY MUSCLES and SUSPENSORY LIGAMENTS.
- The OPTIC NERVE carries impulses from the receptors on the retina to the brain.
How does the eye deal with bright light?
> The Iris Reflex - adjusting for bright light.
Very bright light can damage the retina - so you have a reflex to protect it.
1. When light receptors in the eye detect very bright light, a reflex is triggered that makes the pupil smaller. The circular muscles in the iris contract and the radial muscles relax. This reduces the amount of light that can enter the eye.
2. The opposite process happens in dim light. This time, the radial muscles contract and the circular muscles relax, which makes the pupil wider.
How does the eye focus on near and distant objects.
> Focusing on near and distant objects use another reflex.
The eye focuses light on the retina by changing the shape of the lens - this is known as accommodation.
If the lens cannot refract the light by the right amount (so that t focuses on the retina), the person will be short or long-sighted.
Accommodation - definition
> Where the eye focuses light on the retina by changing the shape of the lens.
Process that allows the eye to look at near objects
- The ciliary muscles contract, which slackens the suspensory ligaments.
- The lens becomes fat. (more curved).
- This increases the amount by which it refracts the light.
Process that allows the eye to look at distant objects
- The ciliary muscles relax, which allows the suspensory ligaments to pull tight.
- This makes the lens go thin (less curved).
- So it refracts light by a smaller amount.
Why do people need reading glasses when they are older?
> As you get older, your eye’s lens loses flexibility, so it cant easily spring back to a round shape. This means light can’t be focused well for near viewing, so older people often have to use reading glasses.
Long-sighted
> Long-sighted people are unable to focus on near objects:
- This occurs when the lens is the wrong shape and doesn’t refract the light enough or the eyeball is too short.
- The images near objects are brought into focus behind the retina.
- You can uses glasses with a convex lens (a lens which curves outwards) to correct it. The lens refracts the light rays so they focus on the retina.
- The medical term for long-sightedness is HYPEROPIA.
Convex lens - definition
> A lens which curves outwards.
Hyperopia - definition
> Medical term for long-sightedness.
Short-sighted
> Short-sighted people are unable to focus on distant objects:
- This occurs when the lens is the wrong shape and the refracts the light too much or the eyeball is too long.
- The images of distant objects are brought into focus in front of the retina.
- You can use glasses with a concave lens (a lens which curves inwards) to correct it, so that the light rays focus in the retina.
- The medical term for short-sightedness is MYOPIA.
Myopia - definition
> The medical term for short-sightedness.
What treatments are there for vision defects?
> Wearing glasses.
Contact lenses.
Laser eye surgery.
Replacement lens surgery.
Treatments for Vision Defects - Contact Lenses.
> Contact lenses are thin lenses that sit on the surface of the eye and are shaped to compensate for th efault in focusing.
They’re popular because they are lightweight and almost invisible.
They’re also more convenient than glasses for activities like sports.
The 2 main types of contact lenses are hard lenses and soft lenses.
Soft lenses are generally more comfortable, but carry a higher risk of eye infections than hard lenses.
Treatments for Vision Defects - Laser Eye Surgery
> A laser can be used to vaporise tissue changing the shape of the cornea (and so changing how strongly it refracts light into the eye.)
Slimming it down, makes it less powerful and can improve short sight.
Changing the shape so it’s more powerful will improve long sight.
The surgeon can precisely control how much tissue the laser takes ff, completely correcting the vision.
However, like all surgical procedures, there is risk of complications, such as infection or the eye reacting in a way that makes your vision worse than before.
Treatments for Vision Defects - Replacement lens surgery.
> Sometimes long-sightedness may be more effectively treated by replacing the lens of the eye (rather than altering the shape of the cornea with laser eye surgery)
In replacement lens surgery, the natural lens of the eye is removed and an artificial lens, made of clear plastic, is inserted in its place.
As it involves work inside the eye, replacing a lens carries higher risks than laser eye surgery, including possible damage to the retina (which could lead to loss of sight).
What temperature does the body have to keep its insides?
> At around 37C - the optimum temperature for enzymes in the body.
Keeping body temperature constant
> The body has to balance the amount of energy gained (e.g. through respiration) and lost to keep the core body temperature constant.
There is a thermoregulatory centre in the brain, which contains receptors that are sensitive to the temperature of the blood flowing through the brain.
The thermoregulatory centre also receives impulses from temperature receptors in the skin, giving information about skin temperatures.
What part of the brain detects temperature change?
> The thermoregulatory centre.
Process if body temperature is too high/low
- Temperature receptors detect that the core body temperature is too high/low.
- The thermoregulatory centre acts as a coordination centre - it receives information from the temperature receptors and triggers the effectors automatically.
3.Effectors, e.g sweat glands or muscles, produce a response and counteract the change.
>Some effectors work antagonistically.
Effectors that work antagonistically.
.Some effectors work antagonistically, e.g. one effector heats and another cools.
>They will work at the same time to achieve a very precise temperature.
>This mechanism allows a more sensitive response.
Response that alter body temperature when you’re too hot.
- Sweat is produced by sweat glands and evaporates from the skin. This transfers energy to the environment.
- The blood vessels supplying the skin dilate so more blood flows close to the surface of the skin. This is called vasodilation. This helps transfer energy from the skin to the environment.
- Hair erector muscle relaxed.
Response that alter body temperature when you’re too cold.
- Hairs stand up to trap an insulating layer of air.
- No sweat is produced.
- Blood vessels supplying skin capillaries constrict to close off skin’s blood supply. Vasoconstriction.
- When you’re cold you shiver too (your muscles contract automatically). This need respiration which transfers some energy to warm the body.
Hormones - definition
> Hormones are chemical molecules released directly into the blood.
Chemical messengers sent in the blood.
Hormones - information
> Hormones are chemical molecules released directly into the blood. They are carried in the blood to other parts of the body, but only affect particular cells in particular organs (called target organs).
Hormones control things in organs and cells that need constant adjustment.
Hormones are produced in and secreted by various glands, called endocrine glands. These glands make up your endocrine system.
Hormones tend to have relatively long lasting effects.
List of glands in the endocrine system
>The pituitary gland >thyroid >adrenal gland >ovaries - females only >the pancreas >testes - males only
Endocrine glands - the pituitary gland.
> The pituitary gland 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.
Located in brain.
Endocrine glands - thyroid
> Produces thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature.
Located in neck as meets chest.
Endocrine glands - ovaries
> Females only.
>Produce oestrogen, which is involved in the menstrual cycle.
Endocrine glands - testes
> Males only.
>Produces testosterone, which controls puberty and sperm production in males.
Endocrine glands - adrenal glands
> This produces adrenaline which is used to prepare the body for a ‘flight or fight’ response.
Endocrine glands - the pancreas
> This produces insulin, which is used to regulate the blood glucose level.
Difference between hormones and nerves
> Nerves: very fast action, act for very short time, act on a very precise area.
Hormones: slower action, act for a long time, act in a more general way.`
How are blood glucose levels controlled?
> By homeostasis.
>Insulin and glucagon are the two hormones involved.
Why blood glucose levels change
> 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 in 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.
Process if blood glucose level is too high
- Blood with too much glucose.
- Insulin secreted by the pancreas.
- Too much glucose but insulin as well.
- Insulin stimulates liver to turn glucose into glycogen.
- Glucose moves from blood into liver where stored as glycogen and muscle cells where used.
- Blood glucose reduced.
Process if blood glucose level is too low
- Blood with too little glucose.
- Glucagon secreted by the pancreas.
- Too little glucose but glucagon as well.
- Glucagon makes liver turn glycogen into glucose.
- Glucose released into blood by the liver.
- Blood glucose released.
What id diabetes?
> A condition that affects your ability to control blood sugar levels.
There are two types -1 and 2.
Diabetes - type 1
> Type 1 diabetes is where the body produces little or no insulin.
This means a person’s blood glucose level can rise to a level that can kill them.
People with T1 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 body quickly once the 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 T1 diabetes need to think about limiting the intake of food rich in simple carbohydrates.
.E.g. sugars (which causes the blood glucose to rise rapidly) and taking regular exercise (which helps to remove excess glucose from the blood).
Diabetes - type 2
> T2 diabetes is where a person becomes resistant to their own insulin (they still produce insulin but their body cells don’t respond properly to the hormone).
This can also cause a person’s blood sugar level to rise to a dangerous level.
Being overweight can increase your chance of developing T2 diabetes, as obesity is a major risk factor in the development of the disease.
T2 diabetes can be controlled by eating a carbohydrate-controlled diet and getting regular exercise.
What do the kidneys do?
> Kidneys basically act as filter to ‘clean the blood’.
The kidneys make urine by taking waste products (and other unwanted substances) out of your blood.
Substances are filtered out of the blood as it passes through the kidneys.
This process is called filtration.
Useful substances like glucose, some ions and the right amount of water are then absorbed back into the blood.
This process is called selective reabsorption.
The substances that are removed from the body in urine are urea, ions and water.
What is filtration?
> The process where substances are filtered out of the blood as it passes through the kidneys.
What is selective reabsorption?
> The process where useful substances like glucose, some ions and the right amount of water are then absorbed back into the blood.
What does urine contain?
- Urea
- Ions
- Water
Urine - urea
> Proteins (and the amino acids that they are broken down into) can’t be stored by the body - so any excess amino acids are converted into fats and carbohydrates, which can be stored. This occurs in the liver and involves a process called deamination.
Ammonia is produced as a waste product from this process.
Ammonia is toxic so it’s converted to urea in the liver. Urea is then transported to the kidneys, where it’s filtered out of the blood and excreted from the body in urine.
A small, unregulated amount of urea is also lost from the skin in sweat.
Urine - ions
> Ions such as sodium are taken into the body in food, and then absorbed into the blood.
If the ion (or water) content of the body is wrong, this could upset the balance between ions and water, meaning too much or too little water is drawn into cells by osmosis. Having the wrong amount of water can damage cells or mean they don’t work as well as normal.
Some ions are lost in sweat. However, this amount is not regulated, so the right balance of ions in the body must be maintained by the kidneys. The right amount of ions is reabsorbed into the blood after filtration and the rest is removed.
Urine - water
> The body has to constantly balance the water coming in against the water going out.
We lose water from the skin in sweat and from the lungs when breathing out.
We can’t control how much we lose in these ways, so the amount of water is balanced by the amount we consume and the amount removed by the kidneys in urine.
Deamination
> The process where amino acids are converted into fats and carbohydrates in the liver.
How is the concentration of urine controlled?
> The concentration of urine is controlled by a hormone called anti-diuretic hormone (ADH). This is released into the bloodstream by the pituitary gland.
The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed.
The whole process of water content regulation is controlled by negative feedback. This means that if the water content gets too high or too low a mechanism will be triggered that brings it back to normal.
Process if water content is too high
> A receptor in the brain detects that the water content is too high.
The coordination centre in the brain receives the information and coordinates a response.
The pituitary gland releases less ADH, so less water is reabsorbed from the kidney tubules.
Process if water content is too low
> A receptor in the brain detects that water content is too low.
The coordination centre in the brain receives the information and coordinates a response.
The pituitary gland releases more ADH, so more water is reabsorbed from the kidney tubules.
What are the 2 treatments if your kidneys stop working?
> Regular dialysis.
>Transplant.
Role of the kidneys
> The kidneys remove waste substances from the blood.
If the kidneys don’t work properly, waste substances build up in the blood and you lose your ability to control the levels of ions and water in your body, eventually resulting in death.
People with kidney failure can be kept alive by having dialysis treatment - where machines do the jobs of the kidneys. Or they can have a kidney transplant.
Dialysis - disadvantages
> Dialysis has to be done regularly to keep the concentrations of dissolved substances in the blood at normal levels, and to remove waste substances.
Many people with kidney failure have to have a dialysis session 3 times a week. Each session takes 3-4 hours - not much fun.
Plus, dialysis may cause blood clots or infections.
Being on a dialysis machine isn’t pleasant experience and it’s expensive for the NHS to run.
Dialysis - advantages
> It can buy a patient with kidney failure valuable time until a donor organ is found.
Dialysis
> Dialysis machines filter the blood.
Dialysis has to be done regularly to keep the concentrations of dissolved substances in the blood at normal levels, and to remove waste substances.
In a dialysis machine the person’s blood flows between partially permeable membranes, surrounded by dialysis fluid. It’s permeable to things like ions and waste substances, but not big molecules like proteins (just like in Kidneys).
The dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood.
This means that useful dissolved ions and glucose won’t be lot from blood during dialysis.
Only waste substances (such as urea) and excess ions and water diffuse across the barrier.
Kidney transplant
> At the moment, the only cure for kidney failure is to have a kidney transplant.
Healthy kidneys are usually transplanted from people have died suddenly.
The person who has died has to be on the organ donor register or carry a donor card (provided their relatives agree too).
TKidneys can also be transplanted from people who are still alive but there’s a small risk to the person donating the kidney.
Kidney transplant - advantage
> Transplants are cheaper in the long run than dialysis.
>And they can put an end to the hours patients have to spend on dialysis.
Kidney transplant - diadvantage
> There’s also a risk that the donor kidney can be rejected by the patient’s immune system.
The patient is treated with drugs to prevent this but it can still happen.
There are long waiting lists for kidneys.
Hormones - puberty
> At puberty, your body starts releasing sex hormones that trigger off secondary sexual characteristics (such as the development of facial hair in men and breasts in women) and cause eggs to mature in women.
Hormones - women
> 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.
Hormones - men
> In men, the main reproductive hormone is testosterone.
>It’s produced by the testes and stimulates sperm production.
The menstrual cycle - the stages
> The menstrual cycle has 4 stages:
- Day 1 - menstruation starts. The uterus lining breaks down for about 4 days.
- The uterus lining builds up again, from day 4 to 14, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg.
- An egg develops and is released from the ovary at day 14 - this is could ovulation.
- 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.
Ovulation
> Stage 3 or menstrual cycle where an egg develops and is released from the ovary.
Hormones involved in the menstrual cycle plus order
- FSH (Follicle-Stimulating Hormone).
- Oestrogen.
- LH (Luteinising Hormone).
- Progesterone.
The menstrual cycle - FSH
> Follicle-Stimulating Hormone.
Produced in the pituitary gland.
Causes an egg to mature in one of the ovaries, in a structure called a follicle.
Stimulates the ovaries to produce oestrogen.
The menstrual cycle - -LH
> Luteinising Hormone.
Produced by the pituitary gland.
Stimulates the release of an egg at day 14. (ovulation).
The menstrual cycle - Oestrogen
> Produced in the ovaries.
Causes the lining of the uterus to grow.
Stimulates the release of LH (which causes release of an egg) and inhibits release of FSH.
The menstrual cycle - progesterone
> Produced in the ovaries by the remains of the follicle after ovulation.
Maintains the lining of the uterus during the 2nd half of the cycle. When the level of progesterone falls, the lining of the uterus breaks down.
Inhibits the release of LH and FSH.
Methods of controlling fertility
>Hormones >Barrier methods >Sterilisation >Abstinence >'Natural' methods
Controlling fertility - hormonal methods list
>Oestrogen >Progesterone >The pill >Progesterone-only pill >Contraceptive patch >Contraceptive implant >Contraceptive injection >An intrauterine device
Contraception - oestrogen
> Oestrogen can be used to prevent the release of an egg - so it can be used as a method of contraception.
If oestrogen is taken everyday 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.
Contraception - progesterone
> Progesterone also reduces fertility
>E.g. by stimulating the production of thick mucus which prevent any sperm getting through and reaching an egg.
Contraception - the pill
> The pill is an oral contraceptive containing oestrogen and progesterone.
Known as the combined oral contraceptive pill.
It’s over 99% effective at preventing pregnancy.
But it can cause side effects like headaches and nausea and it doesn’t protect against sexually transmitted diseases.
Contraception - progesterone-only pill
> Fewer side effects than the ill, and is just as effective.
Contraception - contraceptive patch
> Contains oestrogen and progesterone.
It’s a small 5x5cm patch that is stuck to the skin.
Each patch lasts one week.
Contraception - contraceptive implant
> Inserted under the skin of the arm.
It releases continuous amounts 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.
Lasts for 3 years.
Contraception - contraceptive injection.
> Contains progesterone.
>Lasts for 2 to 3 months.
Contraception - IUD
> An intrauterine device is a T-shaped device tha’s inserted into the uterus to kill sperm and prevent implantation of a fertilised egg.
There are 2 main types - plastic IUDs that release progesterone and copper IUDs that prevent the sperm surviving in the uterus.
Contraception - barrier methods
> Condoms
A diaphragm
Spermicide
Contraception - condoms
> Condoms are worn over the penis during intercourse to prevent the sperm entering the vagina.
There are also female condoms that are worn inside the vagina.
Condoms are the only form of contraception that will protect against STDs.
Contraception - a diaphragm
> a diaphragm is a shallow plastic cup that fits over the cervix to form a barrier.
It has to be used with spermicide.
Contraception - spermicide
> Spermicide can be used alone as a form of contraception.
>But it isn’t as effective (only about 70-80%).
Contraception -sterilisation
> Sterelisation involves cutting or tying the fallopian tubes in a female or the sperm duct in a male.
This is a permanent procedure.
However there is a very small chance that the tubes can rejoin.
Contraception - natural methods
> Pregnancy may be avoided by finding out when in the menstrual cycle the woman is most fertile and avoiding sexual intercourse those days.
It’s popular with people who think that hormonal and barrier methods are unnatural, but it’s not very effective.
Contraception - abstinence
> The only way to be completely sure that the sperm and egg don’t meet is to not have intercourse.
What can be used to increase fertility?
> Hormones can be used to increase fertility.
Some women have levels of FSH that are too low to cause the eggs to mature. This means no eggs are released and the women can’t get pregnant.
The hormones FSH and LH can be given to women in a fertility drug to stimulate ovulation.
Pros of using hormones to increase fertility
> It helps a lot of women to get pregnant when previously they couldn’t.
Cons of using hormones to increase fertility
> 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).
Other than hormones, how else can couples be helped to have children?
> IVF
>In Vitro Fertilisation
IVF
> If a woman can’t get pregnant using medication, she may chose to try IVF.
IVF involves collecting eggs from the woman’s ovaries and fertilising them in a lab using the man’s sperm.
IVF treatment can also involve a technique called ICSI, where a sperm is injected directly into an egg. It’s useful if the man has a very low sperm count.
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 can be collected).
IVF - ICSI
> Intra-Cytoplasmic Sperm Injection.
>A technique that can be used in IVF where sperm is injected directly into an egg.
IVF - Pros
> Fertility treatment can give an infertile couple a child.
IVF - Cons
> 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, stilbirth…).
The success rate of IVF is low - the average success rate in the UK is about 26%. This makes the process incredibly stressful and often 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 the the hormones - e.g. abdominal pain, vomiting, dehydration.
How have advancement in techniques helped IVF?
> Advances in microscope techniques have helped to improve the techniques and therefore the 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 (to check it’s healthy).
More recently, the development of time-lapse imaging means that the growth of the embryos can be continuously monitors 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’s 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.
Adrenaline
> Adrenaline prepares you for ‘fight or flight’.
Adrenaline is a hormone released by the adrenal glands, which are just above the kidneys.
Adrenaline is released in response to stressful or scary situations - our brain detects fear or stress and sends nervous impulses to the adrenal glands, which respond by secreting adrenaline.
It gets the body ready for ‘fight of flight’ by triggering mechanisms that increase the supply of oxygen and glucose to sells in the brain and muscles. For example, adrenaline increases heart rate.
Hormones and negative feedback
> Hormone release can be affected by negative feedback.
Your body can control the level 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.
An example is with thyroxine.
What is thyroxine?
> A hormone released by the thyroid gland, which is in the neck.
It regulates the metabolism.
Thyroxine is made in the thyroid gland from iodine and amino acids.
What role does thyroxine play?
> 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 loads of processes in the body, such as stimulating protein synthesis for growth and development.
Release of thyroxine
> Thyroxine is released in response to the thyroid stimulating hormone (TSH), which is released from the pituitary gland.
What system keeps the amount of thyroxine in the blood at the right level?
> 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 of blood falls back towards normal.
- Too low, secretion of TSH stimulated.
Definition of Auxin
> Auxin is a plant hormone that controls growth near the tips of shoots and roots.
Auxin
> It controls the growth of a plant in response to light (phototropism) and gravity (gravitropism/geotropism).
Auxin is produced in the tips and moves backwards to stimulate the sell elongation process which occurs in the cells just behind the tips.
If the tip of a shoot is removed, no auxin is available and the shoot may stop growing.
Extra auxin promotes growth in the shoot but inhibits growth in the root -producing the desired result.
Phototropism
> Shoots grow towards light.
When a shoot tip is exposed to light, more auxin accumulates on the side that’s in the shade than the side that’s in the light.
This makes the cells grow (elongate) faster on the shaded side, so the shoot bends towards the light.
Gravitropism/geotropism
> Shoots grow away from gravity and roots grow towards gravity.
When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side.
This causes the lower side to grow faster, bending the shoot upwards.
A root growing sideways will also have more auxin on its lower side.
But in a root the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards.
Practical - investigating plant growth responses - method
> You can investigate the effect of light on the growth of cress seeds like this:
- Put 10 cress seeds into 3 different Petridishes, each lined with moist filter paper. (remember to label your dishes, e.g. A, B, C.)
- Shine a light onto one of the dishes from above and two of the dishes from different directions.
- Leave your cress seeds alone for 1 week until you can observe their responses - you’ll find the seedlings grow towards the light.
- You know that the growth response of the cress seeds is due to light only, if you control all other variables.
Practical - investigating plant growth responses - variables
> Number of seeds: use the same number of seeds in each dish.
Type of seed: use seed that all come from the same packet.
Temperature: Keep your Petri dishes in a place where the temperature is stable.
Water: use a measuring cylinder to add the same amount of water.
Light intensity: keep the distance between the bulb and the dish the same.
Practical - investigating plant growth responses - 2
> You can also investigate the effect of gravity on plant growth.
Just place 4 seedlings on damp cotton wool in a Petri dish, each with their roots pointing in a different direction, and store the Petri dish vertically for a few days in the dark.
You should find that the roots of each seedling grow downwards.
Uses of auxin
> Auxins are useful for controlling plant growth. Here are some of the ways they come in handy:
- Killing Weeds
- Growing from cuttings with root powder
- Growing cells in tissue culture
Uses of auxins - killing weeds
> Most weeds growing in fields of crops or in a lawn are broad-leaved, in contrast to grasses and cereals which have very narrow leaves.
Selective weedkillers have been developed using auxins, which only affect broad-leaved plants.
They totally disrupt their normal growth patterns, which soon kills them, whilst leaving the grass and crops.
Uses of auxins - growing from cuttings with root powder
> A cuttings is part of a plant that has been cut off it, like the end of a branch with a few leaves on it.
Normally, if you stick cuttings in the soil they won’t grow, but if you add rooting powder, which contains auxins, they will produce roots rapidly and start growing as new plants.
This enables growers to produce clones of a really good plant quickly.
Uses of auxins - growing cells in tissue culture
> Tissue culture can be used to grow clones of a plant from a few of its cells.
To do this, hormones such as auxins need to be added to the growth medium (along with nutrients) to stimulate the cells to divide to form both roots and shoots.
The 3 plant hormones i need to know
- Auxins
- Gibberellin
- Ethene
Gibberellin
> Gibberellin stimulates plants stems to grow.
>Gibberellin is another type of plant growth hormone. It stimulates seed germination, stem growth and flowering.
Uses of Gibberellin
- Controlling dormancy
- Inducing flowering
- Growing larger fruit
Uses of Gibberellin - controlling dormancy
> Lots of seeds won’t germinate until they’ve been through certain conditions (e.g. a period of cold or of dryness).
This is called dormancy.
Seeds can be treated with gibberellin to alter dormancy and make them germinate at times of the year that they wouldn’t normally.
It also helps to make sure all the seeds in a batch germinate at the same time.
Uses of gibberellin - inducing flowering
> Some plants require certain conditions to flower, such as longer days or low temperatures.
If these plants are treated with gibberellin, they will flower without any change in their environment.
Gibberellin can also be used to grow bigger flowers.
Uses of gibberellin - growing larger fruit
> Seedless varieties of fruit often don’t grow as large as seeded fruit.
However, if gibberellin is added to these fruit, they will grow larger to match the normal types.
Ethene
> Stimulates ripening of fruit.
Ethene is a gas produced by aging parts of a plant.
It influences the growth of the plant by controlling cells division.
It also stimulates enzymes that cause ripe fruit to ripen.
Utility of ethene
> Commercially, it can be used to speed up the ripening of fruits - either while they’re still on the plant or during transportation to the shops.
This means that fruit can be picked while it’s still unripe (and therefore firmer and less easily damaged). The gas is then added to the fruit on the way to the supermarket so that it will be perfect just as it reaches the shelves.
Ripening can also be delayed while the fruit is in storage by adding chemicals which block ethene’s effect on the fruit or reduce the amount of ethene that the fruit can produce. Alternatively, some chemicals can be used to react with ethene to remove it from the air.
