Homeostasis and response

• homeostasis

  maintaining a stable internal environment, in response to changing internal and external conditions
• negative feedback loop


  responds when a system moves away from optimum levels
• central nervous system


  consists of the brain and spinal chord
• synapse


  the connection between two neurons

  chemicals are released across the gap when the electrical impulse reaches the end of the neuron
• reflex arc

  automatic responses to stimuli, which mainly reduce the chance of injury

  e.g adrenaline release
• Brain

  Cerebral cortex:

  • large wrinkled section
  • in charge of consciousness, memory, intelligence and language

  Cerebellum:

  • the section under the cerebral cortex, next to the spinal chord
  • in charge of muscle coordination

  Medulla:

  • runs down, out the bottom, alongside the spinal chord
  • controls subconscious activities like breathing and heart rate
• menstrual cycle stages

  1. uterus lining breaks down (days 1-4)
  2. lining rebuilds (days 4-14)
  3. egg develops and is released - ovulation (day 14)
  4. wall is maintained in case the egg is fertilised. If there is no fertilised egg, the wall will break down again and the cycle repeats (days 14-28)
• FSH


  the first hormone

  released from the pituitary gland

  causes an egg to mature

  stimulates the release of oestrogen
• Oestrogen 


  the second hormone

  released from the ovaries

  causes the uterus lining to grow

  stimulates LH

  stops FSH
• LH


  The third hormone

  released from the pituitary gland

  stimulates egg release
• Progesterone 


  released from the ovaries

  maintains the uterus lining

  stops LH and FSH
• controlling fertility - the pill

  • contains oestrogen (to stop FSH) and progesterone (which causes a thick mucus to stop sperm getting through
  • 99% effective
  • lots of side effects such as headaches, sickness
  • there is also a progesterone only pill, which is just as effective
  • these do not prevent STDs
• controlling fertility - contraceptive patch

  • contains oestrogen and progesterone
  • goes on the skin
  • lasts for a wekk
• controlling fertility - contraceptive implant

  • inserted in the arm
  • contains progesterone
  • lasts 3 years
• controlling fertility - contraceptive injection

  • contains progesterone
  • each injection lasts 2 or 3 months
• controlling fertility - IUD (intrauterine device)

  • T-shaped
  • goes in the uterus
  • kills the sperm
  • plastic ones: release progesterone
  • copper ones: stop sperm living, it creates an environment too hostile for them
• barrier methods of contraception

  condoms - only form of contraception that stops STD's

  diaphragms - fits over the cervix. Has to be used with spermicide

  spermicide - shouldn't be used alone as only 60-70% effective
• other forms of contraception

  steralisation

  natural method

  abstinence
• adrenaline

  released by the adrenal glands which are above the kidneys

  triggers a fight or flight response

  - increases heart rate

  - increases oxygen and glucose supply to the cells

  reflex arc

  released when in a scary or stressful situation
• thyroxine

  works in a negative feedback loop

  released by the thyroid glands in the back of the throat

  a response to the release of thyroid stimulating hormone (TSH)

  regulates the metabolism
• gibberellin 


  stimulates plant cells to grow

  commercial uses:

  • to grow larger fruit
  • induce flowers
  • control dormancy
• ethene

  a gas

  stimulates a fruit to ripen

  commercial uses:

  • speed up ripening
• auxin

  controls plant growth

  commercial uses:

  • killing weeds (grow too much too quick)
  • growing cuttings with rooting powder
  • growing cells in tissue culture
• phototropism 


  growth in response to a light stimulus

  shoots have positive phototropism (grow towards the light)

  roots have negative phototropism
• geotropism


  growth in response to gravity

  shoots have negative geotropism (grow away from gravity)

  roots have positive geotropism
• endocrine glands


  pituitary - master gland, can control other glands

  pancreas - insulin

  thyroid - thyroxine

  adrenal glands - adrenaline

  ovaries - oestrogen

  testes - testosterone
• hormones

  chemical messengers which travel in the blood to activate target cells
• nerves v hormones

  nerves

  • fast action
  • act for a short time
  • act in a precise area

  hormones

  • slower action
  • longer effect
  • general area
• Type 1 diabetes


  when the pancreas does not produce enough/any insulin
• Type 1 treatment

  insulin therapy:

  • injecting insulin throughout the day
  • amount injected is based on diet and exercise

  limit intake of high simple carbohydrate food

  • these cause high glucose increases

  regular exercise

  • helps remove excess glucose

  Pancreas transplant

  • modern cure
  • issues with transplantation such as organ rejection and having to take immunosuppressant
• Type 2 diabetes


  caused by someone's lifestyle, like obesity

  body still produces insulin but it does not respond to it
• Type 2 treatments


  eat a carbohydrate controlled diet

  regular exercise
• glucose increase

  1. pancreas receptors detect the change
  2. insulin is produced
  3. it works in the liver
  4. glucose is converted to glycogen (a carbohydrate store)
  5. glucose levels return to normal
• glucose decrease

  1. pancreas receptors detect the change
  2. glucagon is produced
  3. this works in the liver
  4. glycogen is turned into glucose
  5. glucose levels return to normal
• diabetes testing

  1. urine test - look at glucose level in urine
  2. blood test - more reliable and shows the current blood levels
• ADH (anti-diuretic hormone)


  released from the pituitary gland

  It effects how much water is reabsorbed
• Hypothalamus detects: 


  body temperature change

  water levels
• controlling water levels

  water levels are too high:

  1. pituitary releases less ADH
  2. tubules become less permeable
  3. less water is reabsorbed
  4. urine is more dilute

  water levels are too low

  1. pituitary releases more ADH
  2. tubules become more permeable
  3. more water is reabsorbed
  4. urine is more saturated
• kidneys


  make urine out of the bodies waste products

  they filter out all the substances from the blood

  the correct amounts are reabsorbed ( selective reabsorption)

  substances: (all are also removed through sweat)

  • urea - made from ammonia which is toxic
  • ions - affect osmosis if there is too high a concentration in the blood
  • water - lost through sweat and lungs in an uncontrolled manner so the kidneys control the rest of the water content
• accommodation


  far objects:

  • ciliary muscles relax
  • suspensory ligaments tighten
  • lens gets thinner
  • light refracts less

  near objects

  • ciliary muscles contract
  • suspensory ligaments slacken
  • lens gets fatter
  • light refracts more