Topic 5 - Homeostasis

• Homeostasis = an organism's ability to regulate its internal conditions so crucial reactions can happen at optimum rates
• What needs to be regulated:

  • Blood glucose regulation
  • Internal temperature
  • Water levels
• CNS: Central Nervous System (brain and spinal cord)

  PNS: Peripheral Nervous System (all other nerves)
• Stimulus - Receptor - Sensory Neurone - Relay Neurone - Brain - Motor Neurones - Effector - Response
• Reflex arc - signal bypasses brain - much quicker
• Glands are also effectors - they secrete chemicals
• Reaction Time Practical:

  • Drop ruler between finger and thumb
  • Measure distance fallen before caught, repeat and calculate a mean
  • Independent variable: stimulant increases neurotransmission or depresssant decreases neurotransmission
• Cerebral cortex:

  Higher functions

  • memory
  • speech
  • problem-solving
• Cerebellum:

  Motor skills

  • movement
  • balance
  • coordination
• Medulla Oblongata:

  Unconscious actions

  • heart and breathing rate
  • signals to adrenal glands to release adrenaline
• MRI scans allow doctors to see brain activity without surgery. Issues with the brain are difficult to treat safely
• Accommodation: eyes ability to change the shape of the lens in order to focus light from objects of different distances onto the retina
• Far: ciliary muscles relax, suspensory ligaments tighten, thin lens

  Close: CM contract, SL slacken, thick lens
• Retina cells:

  • Rods only detect light intensity
  • Cones sensitive to red, blue or green wavelengths of light so provide colour information
  • These signals travel to the brain via the optic nerve
• Myopia = short sightednesss

  Hyperopia = long sightedness

  Both can be treated with contact lenses, glasses or laser eye surgery
• Thermoregulation - body controlling internal temperature by the brain sensing blood temperature then sending nervous and hormonal signals to effectors
• Too hot: sweat glands produce water which evaporates, taking away heat. Blood vessels dilate - vasodilation
• Too cold: hairs stand on end to trap hair - layers of insulation. Shivering makes muscles produce more heat. Blood vessel contract - vasoconstriction
• Endocrine system - system of glands that secret hormones to send signals to effectors transported via blood so are slower than the nervous system
• Pituitary gland = master gland that sends signals to other glands
• Pancreas - secrets insulin and glucagon to control blood sugar
• Thyroid - controls growth, metabolism and more
• Adrenal Glands - releases adrenaline
• Ovaries - release eggs and secrete hormones
• Testes - produces sperm
• Pancreas:

  Too high - Islet cells release insulin. Tissue cells absorb more glucose for respiration. Liver converts excess glucose into glycogen as energy store

  Too low - islet cells secrete glucagon. Liver and muscle cells covert glycogen back into glucose. Example of negative feedback
• Type 1 diabetes: Pancreas cannot produce enough insulin. Injections needed

  Type 2 diabetes: Cells don't absorb enough glucose as they should. Obesity increases risk
• Water is lost through exhalation, sweating and urinating. Excess water is removed from blood by kidneys to the bladder
• Water is mixed with urea to make urine. Urea contains ammonia from amino acids obtained from excess proteins broken down in the liver
• Too much water - water moves in by osmosis and the cell become turgid - could burst

  Too little water - water moves out by osmosis and cell becomes flaccid
• Kidneys also filter out glucose and useful minerals and ions for the body to use
• Too much water:

  Detected by hypothalamus of the brain - pituitary gland increases secretion of ADH into blood - increased permeability of kidney tubules - more water reabsorbed into blood - small volume of concentrated urine
• Too little water:

  Detected by hypothalamus of brain - pituitary gland reduces secretion of ADH into blood - reduced permeability of kidney tubules - less water absorbed into blood - larger volume of concentrated urine
• Negative feedback - the response to a change is such that conditions return to normal
• If kidneys don't work properly, dialysis is needed where blood is filtered by a machine. If not done - ammonia/urea buildup will be poisonous
• Menstrual cycle:

  • FSH from pituitary gland causes egg to mature and the ovaries to produce
  • Oestrogen causes the uterus lining to thicken, and it inhibits FSH so no more eggs mature until the next cycle. It also causes the pituitary gland to secrete
  • LH causes egg to be released which starts to travel towards the uterus. A sperm cell can fertilise it while in the oviduct
  • Progesterone secreted by the ovaries maintains the uterus lining
• Contraception:

  • FSH-inhibiting pills - no egg matures
  • Progesterone injection/implant - stops eggs being released
  • Condoms/diaphragms - stops sperm entering vagina
  • IUD (copper coil) - stops egg embedding in lining
  • Avoiding sex for a time after egg is released
  • Clamping oviduct or vasectomy
• Fertility treatments:

  • FSH/LH injections - simple
  • IVF (in-vitro fertilisation) - hard and expensive
• IVF:

  • Eggs collected after inducing release with LH to be fertilised in a lab
  • Viable embryos are inserted back into the woman's uterus

  Cons - very low success rate and can potentially cause multiple embryos to develop
• The adrenal glands (attached to top of kidney) release adrenaline into your body which increases blood flow and breathing rate, to prepare you for 'fight or flight'