Homeostasis and Response

  • Created by: India.02
  • Created on: 06-06-19 11:40

Homeostasis

- Conditions inside the body need to be kept steady because your cells need the right conditions in order to function properly, including the right conditions for enzyme action

- Homeostasis is the regulation of the conditions in the body and cells to maintain a stable environment, in response to changes in internal and external conditions

- There are automatic control systems in your body that regualte your internal environment - nervous and hormonal communication systems - there are systems that control body temperature, blood glucose level and water content

- All automatic control systems are made up of three main components - these are cells that are called receptors, coordination centres (brain, spinal cord and pancreas) and effectors 

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Negative Feedback

- Automatic control systems keep your internal environment stable by using a mechanism called negative feedback - when the level of something is too high or too low, the negative feedback system is used to bring the level back to normal

- Receptor detects a stimulus (level is too high or too low)

- The coordination centre receives and processes the information, and then organises a response

- The effector produces a response, which counteracts the change and restores the optimum level (level decreases or level increases)

- The effectors will carry on producing the responses for as long as they are stimulated by the coordination centre - this may cause the opposite problem because making the level change too much (away from the ideal) - the receptor will detect the change in level and the negative feedback will start again

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Nervous System Components

- Organisms need to respond to stimuli in order to surive - a single-celled organism can respond to its environment but multicellular organisms need to communicate with each other - as multicellular organisms evolved, they developed nervous and hormonal communication systems

- Central Nervous System (CNS) - in verterbrates (animals with backbones) this consists of the brain and spinal cord only - in mammals, the CNS is connected to the body by sensory neurones and motor neurones

- Sensory Neurones - the neurones that carry information as electrical impulses from the receptors to the CNS

- Motor Neurones - the neurones that carry electrical impulses from the CNS to the effectors

- Effectors - all muscles and glands, which respond to nervous impulses

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Receptors and Effectors

- Receptors are cells that detect stimuli - there are different types of receptors, such as taste receptors on the tongue and sound receptors in the ear - they can form part of larger, complex organs, such as the retina of the eye being covered in light receptor cells

- Effectors 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

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The CNS and Synpases

- The CNS receives informations from receptors and coordinates a response, which is carried by the efectors

- The stimulus is detected by receptors - sensory neurones carry the information from the receptors to the spinal cord and brain (CNS) - a response is coordinated - the response information is sent to the effectors, along the motor neurones - the response is carried out

- The connection between two neurones is called a synapse - the nerve signal is transferred by chemicals which diffuse across the gap - the chemicals then set off a new electrical signal in the next neurone

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Reflexes

- They are rapid and automatic responses to certain stimuli that don't involve the conscious part of the brain - they can reduce chances of being injured

- If someone shines a bright light in your eyes, your pupils get smaller so less light gets in the eye, which stops it getting damaged

- If you get a shock, your body automatically releases the adrenaline hormone - it doesn't wait for you to decide if you were shocked

- The passage of information in a reflex (from receptor to effector) is called a reflex arc

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The Reflex Arc

- The neurones in the reflex arc go through the spinal cord or through an unconscious part of the brain

- When a stimulus is detected by receptors, impulses are sent along a sensory neurone to the spinal cord and/or brain (CNS)

- When the impulses reach a synapse between the sensory and and relay neurone,they trigger chemicals to be released - these chemicals cuase impulses to be sent along the relay neurone

- When the impulses reach a synapse between the relay and motor neurone, the same thing happens - chemicals are released an cause impulses to be sent along the motor neurone 

- The impulses then travel along the motor neurone to the effector - the effector then carries out the response

- You don't have to think about the response because it is quicker than normal responses

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The Brain

- The brain is part of the central nervous system, and is made up of billions of interconnected neurones - it is in charge of all complex behvaiours

- Cerebral Cortex - main part of the brain - responsible for consciousness, intelligence, memory and language

- Medulla - controls unconscious activities, like breathing and your heartbeat

- Cerebellum - responsible for muscle coordination

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Studying the Brain

- Studying patients with brain damage - the effect of brain damage on a patient can tell you about what the damaged part of the brain does - if an area at the back of the brain was damaged by a stroke and the patient went blind, you would know that the area has something to do with vision

- Electrically stimulating the brain - stimulated electrically by pushing a tiny electrode into the tissue and giving it a small shock - by observing what stimulating different parts of the brain does, it is possible to understand what those parts do

- MRI scans - a magnetic resonance imaging scanner can produce a very detailed picture of the brain's structures - scientists can use it to find out what parts of the brain are active during certain activities

- Knowledge of the brain has led to development of treatments for disorders - electrical stimulation can reduce muscle tremors caused by Parkinson's disease

- It is complex and delicate - investigating brain function has risks, such as physical damage to the brain or increased problems with brain function

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The Eye

- Sclera - tough, supporting wall of the eye

- Cornea - transparent outer layer found at the front of the eye - it refracts light into the eye

- Iris - contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye

- Lens - focuses light onto the retina, which contains receptor cells that are sensitive to light and colour

- Ciliary muscles and suspensory ligaments - control the shape of the lens

- Optic nerve - carries impulses from the recpetors on the retina to the brain

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Iris Reflex

- Very bright light cn damage the retina so this refle helps to protect it

- Whenlight recpetors in the eye detect very bright light, a reflex is triggered that makes the pupil smaller - circular muscles in the iris contract and the radial muscles relax, which reduces the amount of light that can enter the eye

- The opposite process occurs in dim light - radial muscles contract and cicular muscles relax, which makes pupils wider

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Focusing on Objects

- Accomodation - when the shape of the lens is changed to focus light on to the retina

- To look at close objects - ciliary muscles contract, which slakens the suspensory ligaments - the lens becomes more curved, which increases the amount by which it refracts light

- To look at far objects - ciliary muscles relax, which allows the suspensory ligaments to pull tight - the lens becomes less curved, which means it refracts light by a smaller amount

- If the lens cannot refract light by the right amount, the person will be short or long-sighted

- As you get older, your lens loses flexibility so it can't spring back to shape easily - this means that light cna't be focused well for near viewing so older people often have to wear reading glasses

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Long and Short-Sight

- Long-sighted people have trouble seeing close objects (hyperopia) - lens is the wrong shape and doesn't refract the light enough or the eyeball is too short - images of close objects are brought into focus behind the retina - you can use glasses with a convex lens (outward curve) to correct it - the lens refracts the light rays so they focus on the retina

- Short-sighted people have trouble focusing on far objects (myopia) - lens is the wrong shape and refracts the light too much or the eyeball is too long - images of objects are brought into focus infront of the retina - you can use glasses with a concave lens (inward curve) to correct it so that the light rays foucs on the retina

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Vision Defect Treatments

- Contact Lenses - thin lenses that sit on the surface of the eye and are shaped to compensate for the fault in focusing - popular because they are lightweight and almost invisible - more convenient than glasses for activities like sports - soft lenses are more comfortable but they carry a higher risk of infection than hard lenses

- Laaser Eye Surgery - a laser can be used to vaporise tissue, changing the shape of the cornea and changing how strongly it refracts light into the eye - slimming it down can make it less powerful so it is good for short sight - changing the shape so that it is more powerful is good for long sight - surgeon can control how much tissue is taken off by the laser, which completely corrects vision - there is a risk of complications, such as infection or a reaction that means the vision is worse

- Replacement Lens Surgery - long-sightedness can be more effectively treated by replacing the lens of the eye, rather than alterin the shape of the cornea - natural lens of the eye is removed and an artificial lens, which is made of plastic, is inserted in its place - carries higher risks than laser eye surgery because it involves work in the eye - possible damage to retina, which could lead to a loss of sight

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Controlling Body Temperature

- The body has to balance the amount of energy gained through respiration and lost to keep the core body temperature constant - thermoregulatory centre in the brain contains receptors that are sensitive to temperature of the blood flowing through the brain - also receives impulses from temperature receptors in the skin

- Temperature receptors detect change to core body temperature - TRC acts as a coordination centre so it recevies information and triggers the effectors automatically - effectors produce a response to counteract the change

- Some effectors work antagonistically - one effector heats and another cools so they will work at the same time to achieve a very precise temperature - this mechanism allows a more sensitive response

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Vasodilation and Vasoconstriction

- When you are too hot, the blood vessels supplying the skin dilate so that more blood flows close to the surface - vasodilation - helps to transfer energy to the environment - hairs also lie flat - sweat is produced by glands and then evaporates form the skin

- When you are too cold, the blood vessels supplying the skin constrict to close off the sin's blood supply to keep blood flow close to important organs - vasoconstriction - hairs stand up to trap an insulating layer of air - no sweat is produced - you shiver (muscles contracting automatically) because this needs respiration, which transfers some energy to warm the body

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Endocrine System

- Hormones are chemical moleucles released directly into the blood - carried to other parts of the body, but only affect particular cells in particular organs (target organs) - control things that need adjustment - produced in endocrine glands

- Pituitary gland - sometimes called the 'master gland' because the hormones released can act on other glands, which direct them to produce a hormone, which brings about a change - LH and FSH

- Thyroid - thyroxine, which is involved in regulating things like rate of metabolism, heart rate and temperature

- Adrenal gland - adrenaline, which prepares body for a 'fight or flight' response

- Ovaries - oestrogen, which is involved in the mentrual cycle

- Pancreas - insulin, which is used to regulate blood glucose level

- Testes - testosterone, which controls puberty and sperm production in males

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Nerves and Hormones

- Both nerves and hormones carry information and instructions around the body

- Nerves have a very fast action - they act for a short time - they act on a very precise area

- Hormones have a slower action - they act for a long time - they act in a more general way

- Really quick reaction is nervous - information needs to be passed to receptors quickly - pain signals - hormones carry a message too slowly

- Long-term response is hormonal - when you get a shock, adrenaline is released into the body, which triggers the 'fight or flight' action that gets you ready for action - you can identify the hormonal response because it kicks in quickly but you feel the effects for a while

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Controlling Blood Glucose

- Eating foods containing carbohydrates puts glucose into the blood from the gut - normal metabolism of cells removes glucose from blood - vigorous exercise removes more glucose from the blood - excess glucose can be stored as glycogen in the liver and in the muscles - blood glucose level must be kept steady - changes are monitored and controlled by pancreas, using insulin and glucagon in a negative feedback cycle

- High blood glucose level - insulin secreated by pancreas - insulin and glucose travel in blood to the liver - glucose moves from blood into liver and muscle cells - insulin makes the liver turn glucose into glycogen - blood glucose is reduced

- Low blood glucose level - glucagon is secreated by the pancreas - glucagon travels in blood to the liver - glucagon moves into the liver and makes it turn glycogen into glucose - glucose released into blood by liver - blood glucose increased

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Diabetes

- A condition that affects your ability to control your blood sugar level

- Type 1 - pancreas produces little or no insulin - blood glucose level can rise to a level that is fatal - insulin therapy is needed - this usually involves several injections of insulin throughout the day, most likely at mealtimes - makes usre that glucose is removed from the blood quickly once food has been digested - insulin dosage depends on their diet and how active they are - people can also think about limiting the intake of food that is rich in simple carbohydrates (sugars, whcih cause blood glucose level tor rise rapidly) and taking regualr exercise, which helps remove excess glucose from the blood

- Type 2 - person becomes resistant to their own insulin - they produce it but the cells don't respond properly to the hormone - blood glucose level can rise to a dangerous level - being overweight can increase your chance of getting type 2 diabetes , as obesity is a major risk factor of the disease - can be controlled by eating a carbohydrate-controlled diet and taking regular exercise

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The Kidneys

- They make urine by taking waste products and other unwanted substances out of the blood - substances are filtered out as it passes through the kidneys - this is called filtration - useful substances like glucose, some ions and the right amount of water are then reabsorbed back into the blood - selective reabsorbtion

- Concentration of urine controlled by ADH - anti-diuretic hormone - released into the bloodstream by the pituitary gland - brain monitors water content of blood and instructs the pituitary gland to release ADH into the blood according to how much is needed

- Receptor in brain detects water content that is too high or too low - coordination centre receives information and coordinates response - pituitary gland can release less ADH so that less water is reabsorbed from the kidney tubules or it can release more so that more water is reabsorbed

- If they don't work properly, waste substances build up in the blood and you lose the baility to control ion and water levels in the blood, which results in death - kidney failure patients cn be kept alive with dialysis or they can have a kidney transplant

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Substances Removed in Urine

- Urea - proteins and the amino acids that they are broken down into can't be stored in the body - excess amino acids are converted into fats and carbs, which can be stored - occurs in the liver by deamination - ammonia is a toxic waste product of this process - ammonia is converted into urea in the liver, which is then transported to the kidneys, where it is filtered out of the blood 

- Ions - ions are taken into the body in food and are then absorbed into the blood - if ion or water content of the body is wrong, the balance can be disrupted so too much or too little water is drawn into cells by osmosis - wrong amount of water can damage cells or mean they don't work well - some ions are lost in sweat - this amount is not regualted so the right balance of ions must be maintained by the kidneys - right amount if reabsorbed into the blood after filtration and the rest is removed in urine

- Water - water is lost from skin in sweat and from the lungs when breathing out - we can't control how mcuh we lose in these ways so the amount of water is balanced by the amount we consume and the amount removed by the kidneys

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Dialysis

- Has to be done regularly to keep concentrations of dissolved substances in the blood at normal levels and to remove waste substances

- In the machine, the blood flows between partially permeable membranes, which are surrounded by dialysis fluid - the membranes are permeable to things like ions and waste but not big molecules like proteins (like the kidneys) - dialysis fluid has the same concentratin of dissolved ions and glucose as healthy blood so that useful dissolved ions and glucose won't be lost from the blood - only waste substances (urea) and excess ions and water diffuse cross the barrier

- Patients with kidney failure have to have the treatment three times a week and each session can take up to 4 hours

- May cause blood clots or infections

- Not a pleasant experience and is expensive for the NHS, but it can prolong life until a donor is found

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Kidney Transplants

- Only cure for kidney failure

- Healthy kidneys are transplanted from someone who has died suddenly

- The person who died has to be on the organ donor register or carry a donor card (provided that relatives agree too)

- Kidneys can be transplanted from people who are still alive, but there is a small risk to the person donating the kidney

- There is a risk of rejection by the patient's immune system - patient treated with drugs to prevent this but it can still happen

- Transplants are cheaper than dialysis and they can put an end to the hours that patients have to spend on dialysis, but there are long waiting lists

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Adrenaline and Thyroxine

- Adrenaline is released in response to stressful or scary situations - brain detects fear or stress and sends nervous impulses to adrenal glands - gets body ready for 'fight or flight' by triggering mechanismsthat increase the supply of oxygen and glucose to cells in the brain and muscles (increases heart rate)

- Thyroxine plays an important role in regulating basal metabolic rate (speed at which chemical reactions occur in the body while it is at rest) - it is also important for other processes, such as stimulating protein synthesis for growth and development

- Released in response to thyroid stimulating horone (TSH), which is released from the pituitary gland

- Negative feedback keeps the amount of thyroxine in the blood at a normal level - when the level is too high, the secretion of TSH is inhibited, which reduces the amount of thyroxine released from the thyroid gland - level falls back to normal

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Controlling Fertility with Hormones

- Oestrogen can be used to prevent the release of an egg - normally it is used to stimulate release but if it is taken every day to keep the level permanently high, it inhibits the function of FSH, and after a while egg development and production stop

- Progesterone reduces fertitlity - by stimulating the production of thick mucus which prevents any sperm getting through and reaching an egg - there is a progesterone-only pill, which has fewer side effects and is effective

- The pill is an oral contraceptive that contains oestrogen and progesterone (combined oral contraceptive pill) - 99% effective at preventing pregnancy but can cause side effects like headaches and nausea and it doesn't prevent against STDs

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Controlling Fertility with Hormones

- Contraceptive patch contains oestrogen and progesterone - sticks to skin and lasts a week

- Contraceptive implant - under skin of the arm - releases continuous amount of prgesterone, which stops egg production, makes it hard for sperm to swim to egg, stops fertilised egg implanting in uterus - lasts 3 years

- Injection contains progesterone, which can last for 3 months

- Intrauterine device (IUD) - device inserted into uterus that kills sperm and prevents implantation of fertislised egg - plastic ones release progesterone and copper ones prevent sperm surviving

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Other Ways to Control Fertility

- Barrier methods - condoms worn over penis to prevent sperm entering vagina - female condoms worn inside vagina - condoms are the only contraceptive that protect against STDs - a diaphragm is a shallow plastic cup that fits over the cervix to form a barrier - it has to be used with a spermicide (disables or kills sperm) - spermicide can be used as a contraceptive alone but it isnt as effective (70%

- Sterilisation - cutting or tying the fallopian tubes or the sperm duct - permanent procedure but there is a small chance that the tubes rejoin

- Natural methods - finding out when in the menstrual cycle the woman is most fertile and avoiding sex - popular with those who don't like other methods but it isn't very effective

- Abstinence - don't have sex

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Increase Fertility

- Some women have levels of FSH that are too low to cause their eggs to mature - no eggs released and woman can't get pregnant

- FSH and LH can be given as a fertility drug to stimulate ovulation

- It helps a lot of women get pregnant when previously they couldn't

- It doesn't always work - some women may have to do it many times which can be expensive

- Too many eggs can be stimulated, resulting in multiple unexpected pregnancies

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IVF

- Involves collecting eggs from the woman's ovaries and fertilising them in a lab using the man's sperm - can also involve a technique called intra-cytoplasmic sperm injection (ICSI), where pserm is directly injected into an egg - useful with a low sperm count - fertilised eggs grown into embryos in a incubator - once they are balls of tiny cells, one or two are transplanted into the uterus to improe chance of pregnancy - FSH and LH are given before egg collection to stimulate the maturing of several eggs

- It can give an infertile couple a child

- Multiple births can happen if more than one embryo grows into a baby, which is risky for the mother and babies as there is a higher risk of miscarriages and stillbirths

- Success rate is low (26%) - stressful and upsetting if it ends in multiple failures

- Emotionally and physically stressful - some women have strong reactions to the hormones (abdominal pain, vomiting, dehydration)

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IVF Pros and Cons

- Advances in microscopic techniques have improved the techniques and therefore successs rate of IVF

- Specialised micro-tools have been developed to use on eggs and sperm under the microscope - used to remove single cells from the embryo for genetic testing (check that it is healthy)

- Development of time-lapse imaging means that the growth of embryos can be continuously monitored to help identify those that are more likely to result in a successful pregnancy

- IVF often results in unused embryos being destroyed - some think that it is unethical because it is a potential human life

- Genetic testing before implantation also raises ethical issues as some think that it could lead to the selection of preferred characteristics, such as gender or eye colour

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Plant Hormones

- Auxin is a plant hormone that controls growth near the tips of shoots and roots - controls growth of plant in response to light and gravity - phototropism and gravitropism - produced in tips and moves backwards to stimulate the cell elongation process, which occurs in cells just behind the tips - if tip is removed then no auxin is available so the shoot may stop growing - extra auxin promotes growth in the shoot but inhibits growth in the root

- When shoot tip is exposed to light, more auxin accumulates on the side that is in the shade than the side that is in the light - makes cells grow faster on the shaded side, so the shoot bends towards the light

- When shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side - lower side grows faster, bending the shoot upwards

- A root growing sideways will also have more auxin on it's lower side - in a root extra auxin inhibits growth so the cells on the top grow faster and bend downwards

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Auxins and Ethene

- Killing weeds - most weeds in fields of crops or in a lawn are broad-leaved, in contrast to grasses and cereals, which have narrow leaves - selective weedkillers have been developed using auxins, which only affect the broad-leaved palnts - disrupt normal growth patterns, which kills them 

- Growing from cuttings with rooting powder - sticking cuttings in soil means they won't grow but if you add rooting powder, which contains auxins, they will rapidly produce roots and start growing as new plants - enables production of lots of clones very quickly

- Growing cells in tissue culture - tissue culture can be used to grow clones of a plant from a few of its cells - hormones like auxins need to be added to the growth medium, with nutrients, to stimulate cell divison to form roots and shoots

- Ethene - gas produced by aging parts of plants that influences growth by controlling cell division - stimulates enzymes that cause ripening - can ripen fruit whilst still on the plant or during transport - bananas can be picked while unripe so they are less easily damaged - gas is added to the fruit during travel so they are perfect in store - ripening can be delayed by adding chemicals that delay the effect of ethene - chemical reaction to remove from air

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Gibberellin

- Plant growth hormone that stimulates seed germination, stem growth and flowering

- Controlling dormancy - seeds won't germinate until they have been through certain conditions (cold or dry period) - dormancy - seeds can be treated with gibberellin to alter dormancy and make them germinate at times of year that they wouldn't normally - makes sure all the seeds in a batch germinate at the same time

- Inducing flowering - some plants require certain conditions to flower (longer days or low temperatures) - if plants are treated with gibberellin, they will flower without anny change in their environment - gibberellin can also be used to grow bigger flowers

- Growing larger fruit - seedless varieties of fruit (grapes), often don't grow as larger as seeded fruit - if gibberellin is added, they will grow much larger the match the normal types

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