Homeostasis

• Homeostasis


  The regulation of the internal conditions of a cell or organism to maintain optimum conditions for functions in response to internal and external changes
• Homeostasis


  1. Maintaining a stable internal environment

  2. Enzymes and cells require stable conditions to work

  3. Can't work well if conditions change too much

  4. Automatic control systems making sure internal conditions stay constant
• Homeostasis


  • Involves the nervous system or hormones
  • Receptor cells detect changes in the environment which is a stimulus
  • Receptor cells pass information to a coordination centre (brain, spinal cord, pancreas) which processes the information
  • The coordination centre sends instructions to the effectors (muscles or glands) to carry out a response and restore optimum level
• Nervous system


  • Enables humans to react to their surroundings
  • Reflex arc reactions
• Reflex arc


  1. Stimulus detected by receptor

  2. Electrical impulse passes from receptor along sensory neurone to CNS

  3. Electrical impulse passes from CNS along motor neurone to effector

  4. Effector (muscle or gland) carries out response
• Reflexes are rapid and automatic reactions that help prevent danger
• Measuring human reaction time


  1. Person 1 sits with arm overhanging edge of table

  2. Person 2 holds ruler vertically and drops it

  3. Person 1 has to catch ruler as quickly as possible

  4. Person 2 records measurement on ruler at top of Person 1's thumb

  5. Repeat several times and calculate mean reaction time
• Independent variable


  The thing that is changed (the person)
• Dependent variable


  The one that is measured for each change in the independent variable (reaction time)
• Control variable


  Not allowed to change (starting distance between thumb and finger, measurement at top of thumb, conditions in room)
• Endocrine system


  • Body controlled by hormones
  • Consists of glands that secrete hormones directly into the bloodstream
• Endocrine glands and their hormones

  • Pancreas releases insulin to control blood glucose concentration
  • Ovaries and testes release hormones involved in puberty and reproduction
  • Thyroid gland produces hormones involved in growth and regulating basal metabolic rate
  • Adrenal glands release adrenaline in times of fear or stress
  • Pituitary gland (master gland) releases different hormones that act on other glands
• Control of blood glucose concentration

  1. Blood glucose monitored by pancreas

  2. After a meal, pancreas produces insulin which triggers body cells to take up glucose from blood

  3. Excess glucose stored as glycogen, returning blood glucose to normal level
• Type 1 diabetes


  Pancreas doesn't produce enough insulin
• Type 2 diabetes


  Body cells stop responding to insulin produced by pancreas
• Treating diabetes


  1. Type 1 - Inject insulin

  2. Type 2 - Controlled carbohydrate diet, exercise
• Risk factor for Type 2 diabetes is obesity
• Controlling blood glucose concentration

  1. Pancreas releases glucagon which triggers liver to convert glycogen to glucose

  2. Blood glucose concentration controlled by balance between insulin and glucagon
• The menstrual cycle


  1. During puberty, reproductive hormones cause secondary sexual characteristics to develop

  2. Eggs mature in ovaries and are released every 28 days (ovulation)

  3. If egg is fertilised, it implants in uterus lining

  4. If not fertilised, egg and uterus lining is released (period)
• FSH


  Causes egg to mature in ovary
• LH


  Causes ovulation
• Oestrogen and progesterone


  Involved in maintaining uterus lining
• Contraception methods


  1. Oral contraception - prevents FSH production

  2. Implant/patch/injection - contain progesterone

  3. Barrier methods - prevent sperm reaching egg

  4. IUD/coil - prevent embryo implanting

  5. Sterilisation - prevents egg reaching uterus or sperm leaving penis
• IVF treatment


  1. Woman treated with FSH/LH to mature multiple eggs

  2. Eggs collected and fertilised with sperm in lab

  3. Fertilised eggs (embryos) inserted into woman's uterus
• Negative feedback


  • Adrenal glands produce adrenaline in response to fear/stress, increasing heart rate and oxygen/glucose delivery
  • Thyroid gland releases thyroxine which stimulates basal metabolic rate
  • Thyroxine level controlled by negative feedback - measured by brain, pituitary gland releases TSH to trigger thyroid to release more thyroxine
• Metabolism is the sum of all chemical reactions in a cell or the body
• Metabolic rate is how fast chemical reactions take place