Homeostasis & response

• Homeostasis


  regulation of conditions inside the body to maintain a stable internal environment in response to both internal and external conditions
• Automatic control 


  Detect a change in optimal condition and send a signal to reverse the change

  receptor (nerve) — coordination centre(brain)— effectors (muscles)
• Negative feedback


  Does the opposite or the change

  e.g if sugar too high = signal to decrease it
• Nervous system


  nerve cells (neurone) = carry electrical impulses, long + thin w lots of branch connections

  synapse = EI travels along axon, then neurotransmitters are released, diffuse across synapse + bind to membrane of other nerve, the receptor stimulates the nerve to transmit its EI
• Central nervous system (CNS)


  Brain + spinal cord

  receives info from sensory neurones and organises response to send out via motor neurones to effectors
• Reflex arc


  An unconscious action (reflex)

  rapid and automatic to avoid harm

  stimuli - receptor -CNS - relay neurone - motor neurone - effector
• The brain

  cerebral cortex - consciousness, intelligence, memory, language and senses (left hem = right muscles & right hem = left muscles)

  Cerebellum - balance + muscle coordination

  hypothalamus - regulate body temp + send signals to pituitary gland

  medulla - unconsious activity e.g breathing
• Studying the brain

  -study ppl w brain damage e.g stroke damages area and can no longer hear = part of brain controlling hearing

  -electrically stimulate areas and see if anything happens to locate where it controls

  -scanning e.g MRI (magnetic field) CT scans (x rays) PET scan (radioactive chemicals)
• Treatment of the brain

  -wide range of things can go wrong in the brain

  -fragile, complex and surrounded by skull = hard to treat
• the eye


  Cornea - transparent so light passes through, O2 diffuses in, refracts light a certain amount

  iris - controls the size of pupil

  lens - refract light and can change shape so light hits the retina

  retina -cone cells (colour light) rod cells (black and white light)

  fovea - only cone cells, if light hit = can see most clearly

  optic nerve - transmits impulses from receptor to brain
• iris reflex


  Bright = radial muscles relax + circular contract = less light in

  dark = radial muscles contract + circular relax = more light in
• Accommodation


  Changes refracted power of lens, suspensory ligaments connect to circular muscles

  Close = lens is short and fat (curved) as circular contract+ suspensory slacken = more refraction

  distant = lens is long and thin as circular relax + suspensory taut = less refraction
• long sighted 


  Can’t refract enough

  can’t focus on nearby objects so appears blurry

  use glasses w convex lenses
• Short sighted


  Refracts too much

  Forms image before hitting the retina so appears blurry

  use glasses w concave to counter act the refraction
• Thermoregulation


  Control of our internal body temperature

  Human body is at 37 degrees as its optimum for enzyme activity
• Thermonregulatory centre 


  In hypothalimus acts as a thermostat

  Receptors in skin and blood vessels let us know if to hot or cold so negative feedback occurs
• Mechanisms


  Warm up: vasoconstriction so less heat lost, hairs stand on end to trap air as insulator, shiver

  Cool down: vasodualate, hairs lay flat, sweat to evapourate removing heat
• Endocrine system


  Series of glands to secret hormones in bloodstream
• Glands


  Pituitary - master gland, tells body and glands what to do

  Thyroid - release thyroxine for metabolism,growth and development

  TSH - if pituitary detects low levels it releases TSH to stimulate thyroxine levels

  Adrenal - release adrenaline to increase heart rate (fight or flight)

  Pancreas - release insulin for glucose
• Glands pt2


  Testies - release testosterone (controls puberty) and produce sperm

  Overies - release oestrogen (control puberty + menstrual cycle) and produce eggs
• Endo vs nervous


  Endo : hormone based , transported in blood , slower but lasts longer , more general

  Nervous : electrical impulses , transported via nerve cells , fast and short lasting , specific/precise
• Blood glucose conc


  Too high = rise in levels detected by pancrease so insulin released into blood , tells cells to absorb glucose e.g muscles + liver Store it as glycogen = conc decrease
• Blood glucose conc


  Too low : detected by pancrease and releases glycagon (opposite of insulin) in blood and bind to liver cells, break down glycogen to glucose molecules = increase conc
• Glucose in blood


  Used for respiration

  Too high can damage cells
• Insulin x glycagon


  Create neg feedback loop

  Levels if glucose fluctuate
• Type 1 diabetes


  Cant regulate blood glucose

  In childhood or teen years and is life long

  Pancreas makes little or no insulin = levels to high results in feeling ill or death

  Treat by injecting insulin after meal
• Injectinv insulin


  Depends on meals eaten e.g if very sugary = more insulin needed

  Exersice done e.g does lots of exersice = less needed as its used in respiration
• Type 2 


  Happens to older ppl with unhealthy diets

  Cells resistant to insulin so less glucose absorbed

  Treat by healthy low sugar deit and lots of exersice
• Kidneys


  Filter blood to remove waste e.g urea from liver

  Regulate levels of water and ions (sodium + potassium in diet) if too high or low it damages cells
• Water regulation


  Gain in drink and foods

  Lose from sweat breathing and urine

  Cells lose/gain water by osmosis

  Too high = burst

  Too low = shrink
• Nephron


  Tubules absorb water glucose amino acids and urea (small) = filtration

  As it moves through we reabsorb anything we want to keep e.g glucose and some water = selective reabsorbtion
• ADH


  Hypthalimus detects water levels

  If too low signal sent to pituitary gland to release ADH this tells kidneys to reabsorb more water + less urine

  If too high signal stops so less ADH so less water is reabsorbed by blood and more urine made
• Urinary system


  Renal vein + artery cycle blood to kidneys

  Kidneys filter out urea which pass down ureters to bladder and out urethra
• Kidney failure


  Build up of waste = become sick and if untreated die

  Treatmenta are dialysis or kidney transplants
• Dialysis


  Machine or artificial kidneys

  Connected to pateints blood supply and passes through past the dialysis fluid seperated by a partially permiable membrane

  Dialysis fluid = same conc of water and molecules as healthy blood (constantly replaced)

  Diffuse stuff from blood to fluid to bring levels down to normal
• cons dialysis


  Time consuming:

  Have to be in hospital 3-4 times a week for 3-4 hours

  Can cause blood clots

  Unpleasant experience

  Expensive to run

  Continually for rest of life
• Transplants


  Surgical proceedure

  Healthy kindey usually from dead person but can be a living donar

  Small risk in surgery

  Larger risk if rejection from body so medication used but doesnt always work

  Not enough donars
• Puberty


  Adolescents start to develope secondary sexual characteristics

  E.g facial hair or breasts

  Controlled by testosterone in men and oestrogen in women
• Menstraul cycle


  Stage 1 (day 0 to 4) is break down of uterus linning = menstruation

  Stage 2 (day 4 to 14) is linning builing up preparing for egg

  Stage 3 (day 14) is ovulation when the egg ia released

  Stage 4 (day 14 to 28) is maintaining uterus linning for egg to embed if fertilised
• Menstrual hormones


  Oestrogen = produced in ovaries increase in stage 2

  Progesterone = produced in ovaries increases in stage 4 to maintain uterus

  FSH = produced in pituitary gland stimulates egg to mature

  LH = produced in pituitafy gland stimulates release of egg