Homeostasis and Response AQA Biology topic 5
5.1 Homeostasis
Homeostasis: An introduction Wow it s hot here! What would happen if I stand here for too long? What would happen if I drank too much water? Homeostasis means controlling internal conditions in order to maintain optimum conditions for bodily responses
Homeostasis Some examples of homeostasis in our bodies: Internal conditions that need controlling + how Temperature Ion content Water content Blood glucose Increased by shivering, lost by sweating Increased by eating, lost by sweating + urine Increased by drinking, lost by sweating + urine Increased and decreased by hormones These conditions are controlled by our control systems: Cells called receptors detect a stimulus (change in the environment) Coordination centres such as the brain coordinate the body s response Effectors such as muscles and glands bring about the response
5.2 The Nervous System
The Nervous System The NERVOUS SYSTEM enables us to react to our surroundings. It consists mainly of the brain, the spinal chord, nerve cells ( neurones ) and receptors. Where do we have receptors? 1) Light receptors in the eyes 2) Sound receptors in the ears 3) Taste receptors on the tongue 4) Smell receptors in the nose 5) Touch, pressure and temperature receptors in the skin 6) Changes of position receptors in the ears (balance)
Nervous Reactions When we react to a stimulus the Central Nervous System (CNS brain and spinal chord) in our body uses the following pattern: Stimulus Receptor Coordinator Effector Response For example, consider a man and a camel: Oh No! What are the stimulus, receptor, coordinator, effector and response in this situation?
Examples of reactions Stimulus Receptor Effector Response (i.e. the thing that detects the stimulus) (i.e. the thing that will do the reaction) (i.e. action taken) Bright light Sour taste Losing balance Sit on a drawing pin
Conscious actions A conscious action is one where the brain makes a considered response. Here s what happens: 3) Here another sensory neurone carries the electrical signal to the brain 2) The impulse is carried as electrical impulses by SENSORY NEURONES to the spinal chord 1) Receptors in your skin detect a stimulus 4) The brain decides to move away the hand 5) This electrical impulse is sent by MOTOR NEURONES to the hand muscles (the effectors) via the spinal chord 6) Which then moves the hand away (the response) Stimulus Receptor Sensory Neurone Coordinator Motor Neurone Effector Response
Reflex actions Sometimes conscious action is too slow to prevent harm, e.g In situations like this the body bypasses the brain to produce a quicker response. Here s how it works
Reflex actions 2. Sensory neurone 3. Relay neurone in the spinal chord 1. Receptor 4. Motor neurone 5. Effector By bypassing the conscious part of the brain, this response is much quicker.
Types of nerve cell Nucleus Cell body Muscle strands (effector) Nerve cells (neurones) are elongated with branched endings to connect to many muscles fibres. 1) Motor neurone 2) Sensory neurone 3) Relay neurone Impulse Impulse
Synapses Neurones never each other there is a small gap between them called a. A signal is sent from one to the next by a transmitter across the synapse. These transmitters are then. Words chemical, synapse, neurone, touch, destroyed
The Brain (Biology only) The brain controls complex behaviour and is made of billions of neurones and different regions: Cerebral cortex responsible for thought, intelligence etc Cerebellum coordinates movement and balance Medulla controls automatic actions like breathing and circulation
Studying the Brain (Bio HT only) The cerebral cortex is the part of our brain most concerned with intelligence, memory and consciousness. By studying the effects (e.g. memory/sight loss) when different parts of the brain are damaged scientists have been able to identify which parts of the brain control which functions.
Other techniques of studying the brain 1) An electroencephalogram (EEG) is a visual record of the electrical activity generated by neurons in the brain. It works by amplifying and detecting the electrical signals from the brain. What are the risks of these methods? 2) Magnetic resonance imaging (MRI) scanning is a new technique that produces images of different cross sections of the brain and uses colours to represent activity.
The Eye (Bio HT only) Iris Sclera Lens Retina Pupil Optic nerve Cornea Ciliary muscles Suspensory ligaments
Seeing things The eye is a sense organ containing receptors sensitive to light intensity and colour. How do they work? Rays of light are refracted (bent) first by the cornea and then by the lens. They focus on the retina.
Focussing on different distances ( accommodation ) For distant objects the ciliary muscles relax and the suspensory ligaments pull tight making the lens pull thin the light doesn t refract as much. For close objects the ciliary muscles contract allowing the lens to go fat, thus bending the light more.
The Iris Reflex Q. How does the eye respond to light? When the light is bright the radial muscles relax, the circular muscles contract and the pupil increases in size. When the light is bright the radial muscles, the circular muscles and the pupil in size.
Using lenses to correct vision Short sighted myopia Long sighted hyperopia
Using Lasers in Surgery Lasers are being increasingly used in laser eye surgery: What are the advantages and disadvantages of this treatment compared to using glasses or contact lenses?
Controlling Body Temperature (Bio only) Wow it s hot! The thermoregulatory centre in the brain detects warm blood. Also, temperature sensors in the skin detect the heat and send information to the brain. When the brain detects the high temperature it takes two main steps...
Body Temperature (Bio only) Nerve endings in the skin (receptors) detect the external temperature Temperature detectors in the brain detect the blood temperature The brain coordinates a response using hormones Effectors (muscles and sweat glands) carry out the response
Maintaining Body Temperature Cold Hot Vasodilation Vasoconstriction
5.3 Hormonal Condition in Humans
Hormones Hormones are chemical messengers produced by endocrine. They control the way in which parts of the body work and are transported to their target organs in the. The effects are slower compared to the nervous system but last for longer. Some examples... The pancreas produces The adrenal gland produce The pituitary gland produces FSH and LH Testes produce Ovaries produce progesterone The adrenal gland Words testosterone, glands, bloodstream, insulin, adrenaline
The Endocrine System Where are the following glands and organs in our body? Adrenal Kidney 2. Hypothalamus 1. Pituitary Thyroid 3. Thyroid Pituitary Hypothalamus 4. Adrenal Testes Ovaries 5. Kidney 6. Pancreas 7. Ovaries Pancreas 8. Testes
The Pituitary Gland in more detail The pituitary gland is a gland which secretes several into the in response to body conditions. These hormones act in turn on other in order to cause different hormones to be and bring about other responses. Words secreted, glands, hormones, master, blood
Controlling Blood Sugar levels We need glucose in our bodies to help our cells to respire and produce energy. The amount of it in our blood is controlled by the pancreas. What happens if we have too much glucose? If blood sugar is too high the pancreas releases insulin, which causes glucose to move from the blood into cells The liver then converts glucose into insoluble glycogen and is removed from the blood
Diabetes What is diabetes? What do the pens (above right) do? What does an insulin injection (above left) do? What is the difference between Type 1 and Type 2 Diabetes? How does physical activity affect Type 1 and Type 2 Diabetics?
Diabetes Diabetes is a in which a person s blood sugar (i.e. glucose) level may rise to a level. Type 1 diabetes is when the doesn t produce enough, whereas type 2 diabetes is when the body no longer responds to its own insulin or doesn t make enough of it. Type 1 diabetes can be controlled using insulin whereas type 2 diabetes can be controlled by careful and exercise. Diabetics have to test their blood sugar level before they decide how much insulin to themselves with. Diets high in fibre and complex carbohydrates can help to maintain a healthy sugar level. Words insulin, disease, inject, dangerous, eating, pancreas, injections
Diabetes and Obesity What conclusions can you draw from this data? % obesity of US population No. of people (in millions) with Diabetes
More interesting statistics No. of fast food outlets No. of people (in millions) with Diabetes
Glucogen and Negative Feedback (HT only) What happens if we don t have enough glucose? If blood sugar levels fall then the pancreas produces glucagon instead, which causes glycogen to be converted back into glucose and released back into the blood. This is an example of a negative feedback system where an output (in this case, the production of insulin or glucagon) controls the level of glucose in the blood.
Osmosis recap Osmosis is a special kind of. It s when water diffuses from a area to a less concentrated area through a partially permeable (i.e. one that allows water to move through but not anything else): Water Sugar solution In this example the water molecules will move from left to right (along the concentration ) and gradually the sugar solution. Words membrane, concentrated, dilute, diffusion, gradient If body cells lose too much water by osmosis they do not function efficiently.
Excreting Products (Bio only) Our bodies need to get rid of surplus amounts of: 1) Water removed by the lungs during exhalation and through sweating. 2) Urea produced when excess amino acids are broken down in the liver and is transferred to the bladder. Also lost via sweating. 3) Ions excreted through the skin via sweating. There is no control over water, ion or urea loss by the lungs or skin. Excess water, ions and urea are removed by the kidneys via urine instead. Q. How is the removal of these products affected by: - The amount of water we drink - The outside temperature - The amount of exercise we do?
Amino Acids in Digestion (HT only) Mmmm that s a nice steak. What happens if I eat too much protein? The digestion of proteins causes excess amino acids. In the liver, these amino acids are deaminated to form ammonia, which is toxic, so it is immediately converted into urea for safe excretion. Amino acids Ammonia Urea
Kidneys (Bio only) Kidneys are responsible for controlling ion, urea and water content. Blood in Kidneys are made up of two important tissues BLOOD VESSELS and TUBULES. Ureter (tube that takes urine down to bladder) Blood out
Kidneys Blood vessel Kidneys work in 3 stages: Tubule 1. ULTRAFILTRATION - Lots of water and products of digestion are squeezed out of the blood and into tubules under pressure. 2. SELECTIVE REABSORPTION the blood takes back the things it wants (e.g. glucose and ions) even though this means going against a concentration gradient. 3. WASTE excess water, excess ions and any urea are now removed through the ureter
Controlling Water Content (Bio only) Another example of a negative feedback mechanism: Low blood water level causes a high salt concentration Receptors in the brain detect the high salt content More ADH is secreted by the kidneys into the blood The kidney tubules becomes less permeable to water so more is absorbed into the blood. The bladder fills with a smaller quantity of urine Normal blood water level is achieved.
High blood water level causes a low salt concentration Controlling Water Content 2 (Bio only) Receptors in the brain detect the low salt content Less ADH is secreted into the blood The kidney becomes more permeable to water so more is reabsorbed. The bladder fills with a large quantity of urine Normal blood water level is achieved.
Dialysis fluid Blood Dialysis fluid Dialysis (Bio only) Sometimes kidneys can fail due to infections, toxic substances or genetic reasons. One possible answer is to use a dialysis machine: Partially permeable membranes Urea Sugar Sugar Urea Urea and salt diffuse out of the blood into the dialysis fluid. Also, the dialysis fluid contains the same concentration of sugar and minerals as the blood so these don t diffuse.
Kidney transplants (Bio only) Instead of dialysis a kidney could be transplanted into the patient. This option is cheaper than dialysis but it requires a (a normal person can still function with one kidney). This donor must have a similar type to the patient. Also, the new kidney might be rejected by the body s system which will try to destroy the new organ. To work around this problem the patient can take immunosuppresant which suppress the immune system. Transplanted kidneys only work for around nine years and then the patient has to return to. Words dialysis, donor, immune, tissue, drugs
Hormones in Human Reproduction During puberty reproductive hormones cause the development of secondary sex characteristics. The testes make the hormone testosterone. This hormone stimulates sperm production. The ovaries produce the hormone oestrogen. At puberty eggs begin to mature and one is releases every 28 days ( ovulation )
Hormones in the Menstrual Cycle Several hormones are also involved in the menstrual cycle, where hormones can... 1) cause an egg to mature (the hormone FSH) 2) stimulate the release of eggs (the hormone LH) 3) maintain the lining of the uterus (oestrogen and progesterone) FSH and LH are produced by the pituitary gland whereas oestrogen and progesterone are produced by the ovaries.
Fertility (HT only) Four hormones are involved in the menstrual cycle: oestrogen, LH, FSH and progesterone. Here s how: Step 1: FSH produced by the pituitary gland causes both an egg to mature and the ovaries to start producing oestrogen Step 2: The rising levels of oestrogen cause the pituitary gland to stop producing FSH and produce LH instead Step 3: LH stimulates the release of the mature egg in day 14 of the menstrual cycle ( ovulation ). Step 4: Progesterone: This is produced in the ovaries by the remains of the follicle after ovulation. It maintains the lining of the uterus during the second half of the cycle and inhibits the release of FSH and LH.
The 4 stages of the menstrual cycle: Day 1: Bleeding starts when the lining of the uterus breaks down and passes out the vagina Having a period Day 4: The lining starts to build up again and thickens into a spongy layer of blood cells Day 14 (approx): An egg is released and lasts for around 3 days Day 28: The lining stays thick awaiting the arrival of a fertilised egg. If one doesn t come then the lining breaks down again.
Thickness of uterus lining The Menstrual Cycle Day 0 Day 7 Day 14 Day 21 Day 28 Day 4 Hormone concentration FSH LH Oestrogen Progesterone
Or planning when to abstain from sexual intercourse. Methods of Contraception Oral contraceptives that contain hormones to inhibit FSH production so that eggs can t mature. Implants that slowly release progesterone to inhibit the maturation and release of eggs. Barrier methods such as condoms, that prevent sperm reaching the egg. Intrauterine devices which prevent the implantation of an egg. Spermicidal agents that kill sperm. Surgical methods of sterilisation.
Evaluating Contraceptive Methods The Pill Implants Barriers Pros and cons of different methods Intrauterine devices Spermicides Sterilisation operations Planning by calendar
Fertility Drugs and IVF (HT only) Women may be able to boost fertility with drugs, which contain FSH and LH. If that doesn t work then IVF is another option. Here s how it works: 2. Sperm is added 1. FSH and LH are given to the mother to stimulate the release of mature eggs. They are removed from the womb and placed in a solution of oxygen and water to keep them alive 3. The fertlised egg is allowed to grow into an embryo (a group of 4-8 cells) 4. Usually 3 of these embryos are transferred back into the uterus
Evaluating fertility treatment Risks: 1) Stress 2) Low success rates 3) Risk of multiple births Benefits: New babies! Fertility treatment Moral issues: 1) What happens to unused embryos 2) Storage time of frozen embryos 3) The use of sperm or embryos after the death of a partner
Adrenaline and Thyroxine (HT only) Adrenaline is produces by the adrenal glands in times of fear or stress. It increases the heart rate and delivery of oxygen and glucose ready for a fight or flight response. Thyroxine from the thyroid gland stimulates the basal metabolic rate and plays an important role in growth and development. Its levels are another example of negative feedback.
5.4 Plant Hormones (Bio only)
Plant Hormones The growth of roots and shoots is controlled by hormones: In the shoots the hormone auxin is destroyed by light, so the shoot will bend towards the light as the cells on the shaded side grow quickest. In the roots hormones slow down growth of the cells in the lower region, which makes the root bend down.
Some Definitions Shoots grow towards light (positive phototropism) and against gravity (negative geotropism). Roots grow away from light (negative phototropism) and in the direction of gravity (positive geotropism). Two more important plant hormones: Ethene is a hormone that helps fruit to ripen Gibberellins are important in starting seed germination
More on Plant Hormones (HT only) 1) Auxin Auxins are used as killers, rooting powders and tissue 2) Ethene Controlled use of this hormone can help control the of fruit during transport to 3) Gibberellins can be used to end seed, promote flowering and increase size Words fruit, dormancy, weed, growth, shops, ripening