Homeostasis and Response

  • Created by: benitaxx
  • Created on: 18-02-18 17:21
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  • Homeostasis and Response
    • Homeostasis and body temperature
      • Homeostasis
        • The maintenance of a constant internal enviroment
          • Body temperature
          • Blood glucose concnetration
          • Water and Ion levels
        • Keeps conditions constant for enzyme action and cell functions
      • Control centres
        • Have cells called receptors that detect change in enviroment
          • This mechanism is called negative feedback
        • Co-ordination centers which receive and process info from receptors
          • This mechanism is called negative feedback
        • Receptors which bring levels back to optimum
      • Body temperature
        • Human body temperature should be kept around 37 degrees
          • This is the optimum temperature for enzymes
        • The thermoregulatory system in the brain:
          • Monitors and controls body temp
          • Has receptors that monitor temp of blood flowing through brain
          • Receives information from temperature receptors i  the skin
        • If body temperature gets too low
          • Blood vessels narrow
            • Vasoconstriction
          • Sweating stoops
          • Skeletal muscles contract and relax quickly  transferring more heat to blood
            • Shivering
    • The nervous system and the eye
      • The nervous system
        • Enables humas to react to their surroundings and coordiante better
        • How it works:
          • Pain stimulus is detected by receptors
            • Impulses pass along sensory neuron to CNS
              • Impulse passes through relay neuron
                • Motor neuron carries impulse to effector
                  • Effector responds by drawing limb away from source of pain
              • Central nervous system- brain and spinal cord
      • Brain and the eye
        • The brain controls complex behavior and has 3 main regions
          • Cerebral cortex- responsible for consciousness, language, memory and intelligence
          • Cerebellum-Coordinates movement and balance
          • Medulla- controls automatic actions such as heartbeat and breathing
        • The eye is an organ and in it:
          • Retina-contains receptor cells sensitive to light
          • Optic nerve carries impulses from retina to brain
          • Sclera forms a tough outer layer with front region called cornea
          • Iris controls size of pupil and amount of light hitting retina
          • Ciliary muscles and sensory ligaments change shape of lense to focus light on retina
      • Accomodation
        • The process of changing the shape of the lense to focus on a near or distant object
        • To focus on a near object:
          • Ciliary muscles contract
          • Suspensory ligaments loosen
        • To focus on a far object
          • Ciliary muscles relax
          • Suspensory ligaments pulled tight
          • Lens is pulled thin and only slightly refracts light rays
      • Required practical
        • Drop a ruler and see how fast you can catch it. Record results by looking at the number your fingers land on
        • The further the ruler travels, the slower the reaction time of the participant
      • Defects of the eye
        • Myopia (short sighted)
          • Can generally be treated with glasses
            • New technologies include laser surgery and contact lenses
        • Hyperopia (long sighted)
          • Can generally be treated with glasses
            • New technologies include laser surgery and contact lenses
    • Hormones and Homeostasis
      • The endocrine system
        • Made up of glands that secrete hormones back into bloodstream
          • Hormones are chemical messengers carried in the blood, to an organ where they produce an effect
          • The effect of hormones are slower and act for longer than the nervous system
        • The pituitary gland in the brain is the master gland
          • Secretes several hormones in response to body conditions
        • Adrenaline
          • Produced in adrenal glands in times of fear
          • Prepares for 'fight or flight'
          • Increases heart rate., increasing the delivery of oxygen and glucose to  orgnas and muscles
        • Thyroxine
          • Produced in thyroid gland
          • Increases metabolic rate
          • Controls growth and development in young animals
          • Controlled by negative feedback
      • Control of blood glucose
        • Blood glucose concentration is monitored and controlled by pancreas
        • If blood glucose is too high:
          • Pancreas releases more insulin
            • Insulin caused glucose to be from blood into cells
          • In liver and muscle cells excess glucose is converted into glycogen for storage
        • If blood glucose is too low:
          • Pancreas releases glucagon
            • Stimulates glycogen to be converted into glucose
      • Water Balance
        • The control of water levels in the body is an example of negative feedback
        • Water leaves the body through lungs when breathing, sweat through skin and in urine
        • The balance of water and ions is regulated by the kidneys who also excrete urea, produced by the liver from breakdown of proteins
          • Kidneys produce urine by:
            • Filtering blood
              • Selective absorption of useful substances e.g. glucose
                • Takes place in millions of tiny tubes called tubules
                • Leaves urea, excess water and ions to form urine
                  • Takes place in millions of tiny tubes called tubules
            • Selective absorption of useful substances e.g. glucose
              • Leaves urea, excess water and ions to form urine
            • If kidneys fail a transplant can be offered
              • Patient has to be on anti rejection drugs for rest of life
              • Until transplant is available, a patient may be offered dialysis
                • A machine that does the kidneys fuction
                • Is very time consuming as it must happen 3 times a week for up to 8 hours
            • Digestion of food proteins results in excess amino acids
              • In liver, amino acids converted to ammonia- deamination
                • Ammonia is toxic so is quickly converted into urea
          • Water level in the body is controlled by a hormone ADH
            • Released by pituitary gland when blood concentration is too high
            • Passes in blood, to kidney tubles where it causes more water to be absorbed by blood
      • Hormones and reproduction
        • Sex hormones
          • Oestrogen (found in the ovaries) is the main female sex hormone
          • Testosterone (produced in the testes) is the main male sex hormone
        • Control of the menstrual cycle
          • Follicle stimulating hormone (FSH)
            • secreted by pituitary gland
            • matures eggs
            • Stimulates ovaries to produce oestregen
          • Oestregen
            • Inhibits FSH release
            • Stimulates LH release
            • Makes lining of uterus regrow after menstruation
          • Luteinising hormone (LH)
            • Secreted by pituitary gland
            • Stimulates ovulation
          • Progesterone
            • Secreted by empty follicle in ovaries
            • Maintains lining of uterus
            • Inhibits FSH and LH release
        • Reducing fertility
          • Hormonal methods
            • Oral contraceptives that contain Oestrogen and progesterone
              • Inhibits FSH release so no eggs are released
            • Injection, implant or skin patch
              • To slow release progesterone to stop release of eggs
          • Non-hormonal methods
            • Spermicidal creams
              • Kill sperm
            • Not having intercourse during ovulation
            • surgical methods
            • Contraception
            • intrauterine devices
              • stop embryos implanting into uterus
        • Increasing fertility
          • FSH and LH can be given in a drug to stimulate release of egg
          • In  Vitro fertilisation (IVF) involves:
            • Giving woman FSH and LH to stimulate growth of may eggs
              • Collecting eggs
                • Fertilising eggs from fathers sperm
                  • Inserting 1 or 2 embryo's into the uterus
          • Problems with IVF
            • Emotionally and physically stressfull
            • Success rates are not high
            • Can lead to multiple births-high risk
      • Plant hormones
        • Functions of plant hormones
          • roots and shoots growing towards or away from a stimulus
          • Ripening of fruits
        • Tropism
          • When a pant grows in a particular direction
          • Controlled by a group of plant hormones called auxins
          • Phototrphism
            • response to light
            • More light reaches one side of shoot
              • More auxin sent down shaded side of root
                • Cells on shaded side elongate more
                  • The shoot grows towards light
          • Gravitropism
            • Response to gravity
            • Auxin moves to one side of root
              • Growth becomes inhibitted
                • Root grows downwards
        • Required practical
          • Plant 10 cress seeds in each plastic container with a  hole in one side. Place in even lighting and leave for several days
          • Look at what directions the roots and shoots grow in
        • Uses of plant auxins
          • weed killers
            • Makes weeds grow so quick they exhaust  food supply
          • Rooting powers
          • Promoting growth in tissue culture
        • Ethene
          • Gas and plant hormone
          • Controls ripening fruits
        • Gibberellines
          • Increase fruit size
          • Initiate germination
          • Promote flowering

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