Homeostasis and Response

A mind map of the whole AQA Homeostasis and Response topic

?
View mindmap
  • Homeostasis and Response
    • Homeostasis
      • The Human Nervous System
        • The Central Nervous System
          • Key components of the CNS are the brain, the spinal cord and neurones
        • Synapses
          • They are gaps between neurones for electrical impulses to travel across
          • They can be found at each junction of a reflex arc
          • First an electrical impulse reaches the end of the neurone before the synapse
            • Then it triggers the release of neurotransmitters that diffuse across the synapse
              • At the other end of the synapse, the neurotransmitters bind to receptors and their presence causes the release of more electrical impulses
        • Reflexes
          • Reflexes allow us to respond quickly to situations without conscious thought. This means that the impulses go through a reflex arc which doesn’t include the brain
            • E.g. blinking, sneezing, dropping hot objects etc
          • Components of a reflex arc
            • Stimulus - change in the environment
            • Receptor - detect stimuli
            • Neurones - carry electrical impulses
              • Can be  sensory neurones (carries impulse to the CNS), relay neurones (really signals from sensory neurone to motor neurone  in CNS), or motor neurone (carries impulse from CNS to effector)
            • Effector - brings about the response to the stimulus
            • Response - an action that helps you avoid a dangerous situation
          • Can be tested with the reaction time practical
            • One person sits down while the other holds the ruler with 0cm at the top of the person sitting’s hand
              • Then the standing person drops the ruler and the sitting person catches it
                • Record the measurement at which the person catches it and use a conversion table to find their reaction time. Then repeat the experiment and find the mean reaction time
        • The brain
          • The brain is a complex organ made of many neurones and split into different sections
            • Medulla - responsible for unconscious activities
            • Cerebellum - muscle coordination
            • Cerebral Cortex - conscious thought
          • Lots of studies have been done on the brain and electrical impulses and MRI scans have helped treat brain diseases and increase understanding of the brain
        • The Eye
          • Eye Anatomy
            • Link to eye diagram
          • Accommodation
            • When the lens changes shape in order to refract light at varying distances and focus on objects
              • Close up - ciliary muscles contract and suspensory ligaments relax  making the lens thicker and rounder causing greater refraction
              • Far away - ciliary muscles relax and suspenseful ligaments contract making the lens flatter and thinner causing less light refraction
          • Iris causes adaptation to different light levels by changing the size of the pupil to reduce or increase the amount of light that reaches the retina
          • Eye Defects
            • Myopia - short sightedness
              • Light is focused in front of the retina
            • Hyperopia - long sightedness
              • Light focused behind the retina
            • Fixed by using lenses in glasses or contact lenses to refract light better. Laser eye surgery and replacement lenses are also options
        • Control of Body Temperature
          • The thermoregulatory centre of the brain monitors temperature as blood flows through it
          • Receptors in the skin monitor body surface temperature
          • Ideal body temperature is 37 degrees Celsius
          • Too cold
            • Muscle contractions increase (shivering)
              • Requires energy through respiration which produces heat, warming us up
            • Hairs stand on end
              • Traps an insulating layer of air around the body
            • Vasoconstriction
              • Less blood goes to your extremities so less can be transferred to the surroundings
          • Too hot
            • Sweat
              • Goes onto the surface of the skin and holds heat energy. When it has enough energy it evaporates, taking heat with it and cooling us down
            • Hairs lie flat
            • Vasodilation
              • More blood goes to the capillaries at the edge of our skin making more heat to be transferred to the surroundings
      • Homeostasis is all the processes within a cell or body that help to maintain optimal conditions
      • The conditions that need to be regulated
        • Water
        • Blood Sugar
        • Internal body temperature
        • CO2 levels
        • Urea concentration (in urine)
      • Control systems
        • They are made up of effectors, receptors and control centres
          • Effectors are muscles or glands that carry out the responses to stimuli in order to maintain optimum levels
          • Receptors detect changes in the external or internal environment
          • Coordination centres receive and process information from receptors
        • They can be either nervous or chemical
        • They use a negative feedback loop
    • Hormonal Coordination in Humans
      • The Endocrine System
        • Coordinates the body’s response to changes in the environment using hormones
          • Hormones are chemical messengers released into the blood to be sent to organs
        • There are lots of different endocrine glands
          • Thyroid - in the neck and releases thyroxine which controls metabolism, heart rate and temperature
          • Ovaries - female only, produce oestrogen and controls puberty an the menstrual cycle
          • Testes - male only, helps control puberty and sperm release
          • Pancreas - produces glucagon and insulin and help regulate blood sugar
          • Pituitary gland - master gland, produces hormones in response to changes in the hypothalamus, triggers other  glands to release hormones
          • Adrenal Glands - above each kidney, produce adrenaline for fight or flight response
        • Different to nervous system in many ways...
          • Slower response
          • Uses chemical messengers in the blood
          • Response can be long lasting
          • Can act on large areas of the body
      • Blood Glucose
        • It is important to keep glucose levels within a range because too little can cause tiredness as glucose is needed for respiration which provides energy and too much can damage osmosis
        • As blood flows through the pancreas, the body detects the glucose concentration and releases hormones in a negative feedback loop if it is too high or too low
          • If too high, the pancreas releases insulin to bring it down
            • Insulin converts excess glucose into glycogen to be stored in the liver
          • If too low, the pancreas produces glucagon to bring it up
            • When glucagon is detected, the liver turns glycogen back into glucose and sends it into the blood
        • Some people have a condition called diabetes which means they are unable to regulate their blood sugar
          • Type 1 - a person doesn’t produce enough insulin, probably caused by the body attacking pancreas cells, develops in childhood
            • Treated by regulating diet and injecting insulin
          • Type 2 - a person’s body no longer responds to insulin, this is usually caused by being overweight or old age, develops in adulthood
            • Treated by regulating diet and exercise
      • Kidneys
        • Control of water balance
          • It is important to control the amount of water and ions diffusing in and out of cells
            • Balance can be disrupted by: sweating, illness, exhaling and eating too much salt
          • Ion levels must be kept constant to keep normal diffusion between cells
          • Water  volume is monitoring by the hypothalamus
          • If there is too much water, the hypothalamus inhibits the release of ADH which means less water is reabsorbed
        • Main functions to filter blood and produce urine to get rid of urea and excess water
          • Urea is toxic to cells and is formed by: excess amino acids and ammonia produced by deamination
        • Kidneys contain nephrons in which the two stages of urine production take place
          • Ultrafiltration - the blood is filtered and all urea, water and salts move into a nephron tubule as the blood cells and proteins are too big
          • Selective Reabsorption - useful  substances are reabsorbed into the blood . This leaves urea and excess salts and water to form urine which is collected be the kidneys and travels to the bladder to be excreted
        • If there is too little water, the hypothalamus triggers ADH to be released which increases the permeability of the tubules to more water is reabsorbed
        • Some people’s kidneys don’t filter blood properly so they need to have kidney dialysis which replicates what the tubules do
          • Disadvantages: takes 3-4 hours, three times a week, increased risk of blood clots and infections, expensive
          • Advantages: lifesaving process, gives the patient more time to find a kidney donor
          • Some people get transplants if one becomes available. People usually choose to get one from a family member as their body is less likely to reject it but they will still need to take immunosuppressants
            • Advantages: cheaper than dialysis, patient doesn’t need dialysis anymore
            • Disadvantages: need to take immunosuppressants, kidney may be rejected by the body, long waiting list
      • Puberty and hormones
        • In girls it stimulates the production of oestrogen and the menstrual cycle as well as breast development and pubic hair growth
        • In boys the hormone testosterone rises causing sperm production, facial and pubic hair grows, voice deepens
        • The menstrual cycle is the process in women which involves the maturation and release of an egg. If sexual intercourse occurs then pregnancy may occur
          • One egg matures each month once a female reaches puberty. There are many hormones involved in menstruation
            • They are: FSH, LH, oestrogen and progesterone
              • FSH: causes the eggs to mature and stimulates the production of oestrogen
              • LH:  released by pituitary gland and stimulates ovulation
              • Oestrogen: produced in ovaries, builds up the uterus lining, inhibits the release FSH and stimulates the production of LH
              • Progesterone: produced in the ovaries, maintains uterus lining (days 14-28) and inhibits the production of LH and FSH
        • Contraception
          • Pharmaceutical companies have designed contraceptive methods to reduce the likelihood of a pregnancy
            • progesterone only pill, stimulates production of thick mucus that stops sperm getting through, stops FSH which means eggs don’t mature
            • Combined pill, contains progesterone and oestrogen and taken daily, produces enough FSH to stop eggs maturing. It has more side-effects than the progesterone only pill
            • Contraceptive implant - lasts for three years, placed under the skin, slowly releases progesterone
            • Contraceptive injection - lasts up to three months, contains progesterone
            • Intrauterine devices - inserted into the uterus, stop implantation, some release progesterone
            • Diaphragms - shallow plastic cups, sit at entrance to uterus, prevent sperm coming past, sometimes covered in spermicide
            • Condoms - worn by the male on his penis during sexual intercourse which prevents sperm entering the female, has spermicide to kill sperm
            • Sterilisation - permanent, for a woman means having fallopian tubes cut, for a man means having the sperm duct cut
            • There are also natural methods such as avoiding sexual intercourse when the woman is ovulating or abstinence
          • Contraceptive patch - only changed once a week, worn on skin, slowly releases progesterone
        • Treating infertility
          • Some people have low hormone levels which means that they are unable to have children
            • This can be treated by prescribed fertility drugs or IVF
              • Fertility drugs - contain FSH and LH to stimulate the growth of more eggs
              • IVF - patients are given fertility drugs, the eggs are collected and so are some of the male’s sperm before being fertilised in a laboratory. It grows into an embryo and is then implanted into the uterus
    • Plant Hormones
      • Gibberellins are important in starting of the germination process of plants
        • Used to increase flower and fruit size and initiate germination
      • Auxins change growth patterns to allow plants to grow away fro m or towards a stimulus (tropisms)
        • Tropisms can be split into phototropismsand gravitropisms which are either positive or negative
          • A positive phototropism grows towards the light, a negative grows away from the light
          • A positive gravitropism grows in the direction of gravity and a negative away
        • Used in weed killers
      • Ethene - controls cell division and ripening of fruits
        • It is used in the food industry to control the ripening of fruit

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Homeostasis resources »