homeostasis

• homestasis

  regulation of constant internal environment.

  conditions are maintained to ensure optimum conditions for metabolism and changes in response to fluctuations.

  regulates blood glucose, temperature, co2 and water levels.
• stimulus 


  change in environment
• receptor

  detects the stimulus

  EG: Skin, eye
• sensory neurone

  sends electrical impulses to the nervous system
• nervous system 


  comprised of the brain and spinal cord.

  allows a fast, short-lived response to stimulus in the surroundings.
• parts of typical neurone/nerve cell

  dendrites: branched endings that connect to the the neurones together to make a network.

  axons: long, stretched out fibre of cytoplasm that the electrical impulse travels along.

  some are surrounded in myelin sheath & it helps insulate the electrical impulse.
• effector

  receives the impulse and carries out a response.

  EG: Muscle, gland
• role of effectors

  muscles: contract to make a movement.

  glands: releases a chemical into the body.
• relay neurones

  allow sensory & motor neurones to communicate.
• motor neurone

  transmits impulses from the CNS to effectors.

  directly control our muscle movements.
• endocrine system

  pituitary gland

  thyroid gland

  parathyroid gland

  adrenal gland

  pancreas

  ovaries

  testes
• glands

  Pituitary gland: ‘master gland’ produces hormones that travel to other glands in the body so they can produce certain chemicals. 

  
  

  Pancreas: Makes sure that blood glucose levels aren’t too high or too low:

  
  

  Thyroid: releases Thyroxine, which controls the body’s metabolic rate.

  
  

  Adrenal: releases adrenaline, the hormone that increases heart and breathing rate in stressful situations to prepare body for ‘fight or flight’.

  
  

  Ovaries: release eggs

  
  

  Testes: produce sperm
• hormones

  chemical messengers transported in the bloodstream to an effector where they can activate a response.
• Detailed role of pancreas

  if too high it: secretes insulin, which causes glucose to move from blood into liver & muscle cells for respiration.  Any excess glucose is converted into glycogen, by the liver.

  if too low it: secretes glucagon, which causes liver and muscles to convert glycogen back into glucose & released into the blood.

  Glucagon and insulin interact as art of a negative feedback cycle.
• detailed role of thyroid

  If Thyroxine levels are too low hypothalamus in your blood releases TRH, which causes the pituitary gland to release TSH, which causes the thyroid to release more thyroxine. 
• type 1 diabetes

  pancreas does not produce enough insulin.

  treated by insulin injections.

  childhood or teenage years.

  lifelong condition.
• type 2 diabetes 


  resistant to insulin - cells won take in glucose from the blood stream.

  older people - unhealthy diets.

  lifelong condition.

  treated by: healthy, low sugar diet. regular exercise
• menstrual cycle

  occurs in females, approximately every 28 days.

  It is a cyclical process of the building of the lining of the uterus and ovulation.

  If the egg become fertilised by a sperm, then pregnancy follows.

  If the egg is not fertilised, then the lining of the uterus is shed away and leaves the body as the menstruation.
• menstrual cycle - reproductive hormones

  FSH - follicle stimulating hormone

  oestrogen

  LH - luteinising hormone

  progesterone
• FSH


  FSH: produced in pituitary gland

  response caused: an egg to develop one of the ovaries

  Interaction w hormones: stimulates production of oestrogen
• Oestrogen

  produced: ovaries

  response caused: the lining of uterus builds up and thickens

  interaction w hormones: stimulates production of LH & inhibits production of FSH
• LH

  produced: pituitary gland

  response caused: ovulation - day 14

  interaction w hormones: stimulates progesterone
• Progesterone

  produced: ovaries

  response caused: maintains uterus lining

  interaction w hormones: inhibits production of LH
• types of contraception

  hormonal

  non hormonal
• the pill

  contains hormones to inhibit FSH so that egg does not mature.

  pros - easy, can be reversed, reliable

  cons - side effects, causes pregnancy if missed, doesn't protect against STI's.
• coil

  The device is attached to the lining of the uterus and releases hormones or prevents the implantation of an embryo.

  pros - Requires little to no aftercare, Very reliable.

  cons - May take some time for effects to be reversed, Does not protect from STIs.
• condoms

  Creates a physical barrier to prevent the sperm from reaching the egg.

  pros - easy, reliable, Provides protection from most STIs.

  cons - can fail.
• spermicidal agents 


  Contains chemicals to kill or immobilise sperm cells.

  pros - Easy to use, Short-term effects.

  cons - Does not protect from STIs, Less effective when used as the only method.
• abstaining from intercourse 


  Avoiding sexual intercourse when there is a likelihood of an egg being present in the oviduct.

  pros - inexpensive

  cons - not reliable
• surgery

  In males, the vas deferens tubes are sealed or blocked to prevent the passage of sperm from the testes.

  In females, the fallopian tubes (oviducts) are sealed

  or blocked to prevent the passage of the egg from the ovaries.

  cons - risk of infections, difficult to reverse, time consuming
• infertility treatments

  fertility drugs - LH & FSH

  IVF
• IVF

  The woman is given FSH and LH to stimulate the ovaries to mature and release several eggs.

  The eggs are then collected from the woman and fertilised using sperm collected from the man. This is done in the lab

  The fertilised eggs develop into embryos.

  At the early stage of development, one or two embryos are inserted into the woman’s uterus for implantation.

  If successful, the pregnancy progresses as normal.
• Cons of fertility treatments

  stressful and emotional.

  success rates are low.

  underlying causes of fertility are not treated.

  high chance of multiple births ( twins, triplets etc ) which carries risk to both mother and babies.
• negative feedback 


  the body works to counteract the change and return conditions to the optimum.
• vasoconstriction.


  The blood vessels that supply the skin constrict.

  reduces blood flow to the skin.

  This means that less heat energy is lost to the surroundings.

  The body also shivers, which releases energy, warming the body.
• kidney failure 


  treated by: kidney implants, dialysis

  cons of dialysis: expensive, risk of infections, needed three times a week, takes a long time
• liquids lost from kidney's and skin

  K: urine

  S: sweat
• How do we replace ions that are lost

  by drinking

  by eating food
• Thermoregulatory centre


  part of the brain that detects an increase in blood temperature in our bodies.
• how does sweating lower body temperature

  sweat evaporates from the skin.

  This means that heat is lost to the environment and so the body cools down.