B5 - Homeostasis and Response

• Homeostasis - the regulation of internal conditions in response to changes in external and internal conditions
• Negative feedback:

  1. Receptor detects a stimulus - a level is too high / low
  2. Coordination centre receives and processes the information to organise a response
  3. Effector produces a response that counteracts the change - lowering / raising the level
  4. The effectors carry on producing theresponse, which may push the level too far the other way, and the negative feedback starts again
• Nervous system detects and reacts to stimuli
• Nervous system:

  • Central Nervous System (CNS) - brain and spinal cord
  • Sensory Neurones - neurones that carry info as electrical impulses from receptors to CNS
  • Motor Neurones - neurones that carry electrical impulses from CNS to effectors
  • Effectors - muscles and glands which respond to nervous impulses
• Receptors - the cells that detect stimuli. E.g taste, sound, and light receptors
• Effectors - respond to nervous impulses and bring about a change. E.g muscles contract and glands secrete hormones
• Nervous system reaction steps:

  1. Stimulus
  2. Receptor
  3. Sensory neurone
  4. CNS
  5. Motor neurone
  6. Effector
  7. Response
• Hormones are chemical messengers released by endocrine glands
• Synapses:

  • The connection between two neurones
  • Nerve signal is transferred by chemicals which diffuse across the gap
  • These chemicals set off a new electrical signal in the next neurone
• Reflexes - rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain
• Reflex arc - The passage of information in a reflex ( from receptor to effector )
• Reflex arc:

  1. Stimulus
  2. Receptor
  3. Sensory neurone
  4. Relay neurone
  5. Motor neurone
  6. Effector
  7. Response
• Reaction time required practical:

  1. Subject holds out a hand level with the end of a ruler
  2. Ruler is dropped and subject must catch it
  3. Number on the ruler where it is caught is recorded
  4. Repeat and calculate mean
  5. Repeat all after subject has drunk a caffeinated drink
• Hormones:

  • Chemical molecules released directly into the blood
  • Carried in the blood to the organs
  • Control things that need constant adjustment
  • Produced and secreted in endocrine glands
  • Lomg-lasting effects
• Endocrine glands:

  • Pituitary - hormones that cause other glands to release hormones
  • Thyroid - thyroxine (metabolism, heart rate, temp)
  • Adrenal - adrenaline (fight or flight response)
  • Pancreas - insulin (blood glucose level)
  • Ovaries - oestrogen (menstrual cycle)
  • Testes - testosterone (puberty, sperm production)
• Nerves - fast action, short lasting, act in a precise area

  Hormones - slow action, long lasting, act in a general way
• Insulin and Glucagon:

  • Insulin, exercise - lowers glucose levels
  • Glucagon, eating sugar - raises glucose levels
  • Excess glucose is stored as glycogen in liver and muscles
• Type 1 diabetes:

  • Pancreas produces little / no insulin
  • Blood glucose can rise to a level that can kill
  • Sufferers need regular insulin injections to remove glucose from the blood
  • Varied insulin quantities needed depending on diet and exercise
• Type 2 diabetes:

  • Normal insulin production, but cells no longer response to it
  • Can also cause fatally high glucose levels
  • Obesity can increase chance of developing it
  • Can be controlled by diet and exercise
• Stages of menstrual cycle:

  1. (Days 1 - 4) Menstruation starts. Uterine lining breaks down
  2. (Days 4 - 14) Uterine lining builds up again
  3. (Day 14) ovulation
  4. (Days 14 - 28) Uterine lining maintained
• Menstrual cycle hormones:

  • FSH (follicle-stimulating hormone)
  • Oestrogen
  • LH (luteinising hormone)
  • Progesterone
• FSH (follicle- stimulating hormone):

  • Produced in pituitary glands
  • Causes an egg to mature in a follicle in an ovary
  • Stimulates the ovaries to produce oestrogen
• Oestrogen:

  • Produced in the ovaries
  • Causes the lining of the uterus to grow
  • Stimulates the release of LH and inhibits release of FSH
• LH (Luteinising Hormone):

  • Produced by pituitary glands
  • Stimulates the release of an egg
• Progesterone:

  • Produced in ovaries (by the remains of the follicle after ovulation)
  • Maintains uterine lining during second half of the cycle
  • When level of progesterone drops, lining breaks down
  • Inhibits release of LH and FSH
• Reducing fertility:

  • Oestrogen can be used to prevent egg release because it stops FSH from maturing eggs
  • Progesterone can be used to stimulate production of thick mucus which blocks sperm
• Combined oral contraceptive pill contains oestrogen and progesterone, however it has side effects which a progesterone-only pill doesn't
• Contaceptives:

  • Patch - lasts 1 week on the skin, contains oestrogen and progesterone
  • Implant - last 3 years under the skin, uses progesterone
  • Injection- lasts 2-3 months, uses progesterone
  • IUD - plastic ones use progesterone and copper ones kill sperm
• Barrier contraception:

  • Condom - used to block sperm and SWISS
  • Diaphragm - used over cervix to block sperm. Used with spermicide
• Other contraception:

  • Sterilisation - permanent severing of fallopian tubes or sperm duct
  • Calendar methods - to plan when women are fertile/not
  • Abstinence
• Increasing fertility:

  • Giving FSH and LH to stimulate ovulation
  • Increased chance of pregnancy, but also of multiple pregnancies e.g twins
• IVF:

  • Collecting eggs and sperm to combine in a lab
  • Growing them into embryos then inserting into uterus
  • Success rate is low and it causes multiple pregnancies which is risky
  • Technology can help - micro tools, monitoring
  • Some think it is inertial because of wasted embryos
• Thyroxine:

  • Regulates basal metabolic rate, stimulates protein synthesis
  • Released in response to thyroid stimulating hormone (TSH) from pituitary gland
  • Negative feedback system used to keep levels steady
• Adrenaline:

  • Released in response to stress and fear
  • Increases supply of oxygen and glucose to brain and muscles