Homeostasis and response

• give a definition of homeostasis 


  the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• what is maintain of optimum enzyme activity and cell function

  blood glucose concentration (sugar levels)

  body temperature

  water levels
• explain three control systems

  receptor cells detecting stimuli

  coordination centres receiving and processing info e.g brain, spinal cord

  effectors bringing about responses retorting optimum levels
• describe the physilogical, psychological and results of hypothermia

  too cold

  shiver, vasconstricin, goosebumps-phy

  drink less, seek warmth, change clothes-psy

  coma, confusion, drowsy- results
• describe the physilogical, psychological and results of hyperthermia

  too hot

  sweat, less urination, vasodilation-phy

  drink more, seek shade, change clothes-psy

  heart stroke, dehydration, dizziness- results
• what is the endocrine system 


  composed of glands secreting hormones into the bloodstream
• what is the target organ

  the organ a particular hormone acts on
• what is the pituitary gland 


  master gland secreting several hormones into the bloodstream
• what is a hormone

  a chemical produces by a gland secreted into the blood having a biological effect on the target organ
• endocrine system facts

  chemical signal carried by bloodstream

  slower speed of response usually a long duration of response

  effectors = target cells / organs

  response = varied usually
• nervous system facts 


  electrical signal carried by neurones

  very fast speed response short duration of response

  effectors = muscles / glands

  responses = contraction / secretion
• pituitary gland 


  master gland stimulates other glands
• thyroid gland 


  produces thyroxine

  rate of metabolism

  heart rate

  temp
• adrenal gland 


  produces adrenaline
• testes 


  produced by testosterone

  puberty

  sperm production
• pancreas 


  produces insulin
• ovary 


  produces oestrogen and is involved in the menstrual cycle
• what happens when blood glucose is too high

  pancreas monitors blood glucose concentration

  ⬇️

  blood glucose is too high

  ⬇️

  insulin is released by the pancreas

  ⬇️

  insulin tells the liver to take glucose out of the blood turn it into glycogen and stores it

  ⬇️

  blood glucose back to normal
• what happens when blood glucose is too low

  pancreas monitors blood glucose concentration

  ⬇️

  blood glucose to low

  ⬇️

  glycogen is released by the pancreas and insulin stops being released

  ⬇️

  glucagon tells the liver to break down glycogen into glucose and release it into the blood

  ⬇️

  blood glucose back to normal
• type 1 diabetes

  pancreas fails to produce sufficient insulin characterised by uncontrolled high blood glucose level
• type 1 diabetes treatment

  injecting insulin before meals

  extra glucose allows glucose into cells for respiration and for the rest to be stored in the liver correcting blood glucose levels
• type 2 diabetes 


  is when the body no longer responds to insulin produced by the pancreas
• type 2 diabetes treatment

  carbohydrate controlled diet + exercise regime is usual treatment and insulin injections if this fails to work
• risks of type 2 diabetes

  obesity
• glucose tolerance test (type 2)


  no food for 8-14 hours

  blood sugar levels

  given known amount of sugar

  blood sugar tested in intervals
• fasting glucose test 


  no food / drink 8 hours

  test for blood glucose levels
• describe how the water content of the blood is controlled (opposite for more ADH released)


  osmoregulation- the process of water regulation

  less ADH ⬅pituitary gland

  released

  ⬇️

  kidney tubules

  reabsorbs less

  water

  ⬇️

  lots of urine is produced

  ↘️ normal water conc in blood ⬆️
• what happens when ion concentration is too low or high

  high - move into cells causing them to burst

  low - drawn out of cells causing them to shrink (osmosis)
• how does the kidneys control ion concentration - ultrafiltration at the nephron 


  blood passes through and ions are filtered out large molecules remain
• how does the kidneys control ion concentration - selective reabsorption 


  required molecules are reabsorbed e.g glucose, H2O
• how does the kidneys control ion concentration - collecting duct

  excess minerals + H2O not reabsorbed into the blood are passed into the bladder
• describe how urea is made and excreted

  During digestion, proteins are broken into amino acids so they con pass through the gut wall easily

  the blood carries away the amino acid to cells, so they can be used for building new products

  Excess amino acids cannot be stored

  The liver breaks down excess into ammonia (NH3) through the process DEAMINATION

  NH3 is the converted into nirogenous waste ,UREA

  urea is toxic in high concentration, so transported to the kidney, filtered out

  of the blood

  the blood and excreted in urine
• how does out body control water levels

  We cannot control the amount of water lost from the skin in sweat and by the lungs in breathing. Therefor, water is balanced by the amount we consume and the amount removed by the kidneys.
• describe how dialysis machines filter blood for a person with kidney failure

  in a dialysis machine the persons blood flows between a partially permeable membrane surrounded by dialysis fluid

  ⬇️

  ions and waste substances diffuse through

  ⬇️

  dialysis fluid had same ion/ glucose concentration as healthy blood so nothing useful is lost during dialysis

  ‼️must be done regularly
• what is tropism

  the growth response to stimulus responsible for direction a plant faces

  positive - towards stimulus

  negative - away from stimulus
• what are the three types of tropism

  phototropism - light stimulus

  geotropism - gravity stimulus

  hydrotropism - water stimulus
• what causes tropism

  the hormone auxin promotes growth near tips do shoots and roots - unevenly distributed
• two ways auxin controls growth

  geotropism - gravity produces an unequal distribution of auxin more auxin on lowers side this causes shoots go upwards roots go downwards phototropism - the side with no light accumulates auxin more quickly then the side with light bending the shoot to the light
• how can auxins have commercial uses

  kills weeds

  induces flowering

  cloning cells
• gibberellin 


  a plant hormone that stimulates seed germination stem growth and flowering