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BIOLOGY  
 
F214:  Communication,  Homeostasis  and  Energy      
1) Excretion  
a) Excretion  
i) Define  the  term  excretion  
(1) Egestion  –  removal  of  undigested  food  by  defecation  (never  enters  the  cell)  
(2) Excretion  –  removal  of  metabolic  waste  from  the  body  (formed  inside  cells)    
(a) Metabolic  waste  –  consists  of  waste  substances  that  are  unwanted  because  they  
may  be  toxic  by-­‐products  or  are  produced  in  excess  by  reactions  inside  cells  
(3) CO2  –  produced  in  every  living  cell  in  the  body  as  a  result  of  respiration  
(a) Passed  from  the  cells  of  respiring  tissues  into  the  bloodstream  
(b) Transported  in  blood  (mostly  in  the  form  of  hydrogencarbonate  ions)  to  the  lungs  
(c) Carbon  dioxide  diffuses  into  the  alveoli  to  be  excreted  as  we  breathe  out  
(4) Urea  –  excretory  product  formed  in  the  liver  from  breakdown  of  excess  amino  acids  
(a) Deamination  –  removal  of  amine  group  from  an  amino  acid  to  produce  ammonia  
(b) Amino  acid  +  oxygen  à  keto  acid  +  ammonia  
(c) Ammonia  +  carbon  dioxide  à  urea  +  water  
(d) 2NH3  +  CO2  à  CO(NH2)2  +  H2O  
(e) Urea  passed  into  the  bloodstream  in  the  plasma  to  be  transported  to  the  kidneys  
(f) In  the  kidneys,  urea  is  removed  from  blood  and  becomes  part  of  urine  
(g) Urine  stored  in  bladder  
(h) Urine  excreted  via  the  urethra  
 
ii) Explain   the   importance   of   removing   metabolic   wastes,   including   carbon   dioxide   and  
nitrogenous  waste,  from  the  body  
(1) Carbon  dioxide  –  toxic  in  excess  
(a) Reduce  oxygen  transport  
(i) Carried  in  the  blood  mainly  as  HCO3-­‐  ions    
(ii) HCO3-­‐  ions  can  form  H+  ions  with  the  help  of  carbonic  anhydrase  
(iii) H+  ions  outcompete  oxygen  and  combine  with  haemoglobin  in  red  blood  cells  
(iv) Haemoglobin  acts  as  a  buffer  –  forms  haemoglobinic  acid  on  combing  with  H+  
(b) Reduces  haemoglobin’s  normal  affinity  for  oxygen  
(i) CO2  combines  directly  with  haemoglobin  à  carbaminohaemoglobin  
(ii) Has  a  lower  affinity  for  oxygen  than  normal  haemoglobin  
(c) Respiratory  acidosis  
(i) Can  be  caused  by  diseases  in  the  lungs  themselves  
1
...
Chronic  bronchitis  
3
...
Severe  pneumonia    
5
...
Protein  buffers  in  blood  resist  change  in  pH  
2
...
Increase  in  breathing  rate  to  remove  excess  CO2  
(vi) Large  change  in  acidity  –  blood  drops  below  pH  of  7
...
Slowed,  difficult  breathing  
2
...
Drowsiness,  restlessness,  confusion  
4
...
Tremours  
(2) Nitrogenous  waste  
(a) Body   cannot   store   proteins   or   amino   acids   –   amine   group   of   amino   acids   is  
potentially  highly  toxic  and  very  soluble  
(b) Wasteful  to  excrete  amino  acids  –  almost  as  much  energy  as  carbohydrates  so…  
(c) Amino  acid  +  oxygen  à  keto  acid  +  ammonia  
(i) Amino  acids  deaminated  (removal  of  amine  group)  in  the  liver  
(ii) Keto   acids   formed   that   can   be   used   directly   in   respiration   or   converted   to   a  
carbohydrate  or  fat  for  storage  
(iii) Ammonia  formed  is  also  potentially  highly  toxic  and  very  soluble  
(d) Ammonia  +  carbon  dioxide  +  input  of  ATP  à  urea  +  water  
(i) 2NH3  +  CO2  à  CO(NH2)2  +  H2O  
(ii) Urea  transported  to  the  kidneys  
(e) Urea  can  be  excreted  safely  –  less  toxic  and  less  soluble  than  ammonia  
 
iii) Describe,  with  the  aid  of  diagrams  and  photographs,  the  histology  and  gross  structure  of  
the  liver  
(1) Functions  of  the  liver  
(a) Control  of  levels  of  blood  glucose,  amino  acids,  lipids  
(b) Turnover   and   transport   of   lipids   and   plasma  
lipoproteins    
(c) Transformation  of  glucose  to  glycogen  
(d) Synthesis   of   red   blood   cells   (in   the   foetus),   bile  
salts,   proteins,   plasma   proteins   (eg
...
  drugs,  
alcohol  and  insecticides  
(h) Destruction  of  senescent  red  blood  cells  

(i) Breakdown  of  hormones  
(2) Hepatic  blood  vessels  
(a) Hepatic   artery   –   leads   from   the   aorta   and   delivers   oxygenated   blood   from   the  
heart  (essential  for  aerobic  respiration)  
(b) Hepatic   portal   vein   –   leads   from   the   small   intestine   and   delivers   deoxygenated  
blood  rich  in  uncontrolled  levels  of  absorbed  nutrients  under  low  pressure  
(c) Sinusoids  –  long,  blood  chambers  that  both  artery  and  vein  eventually  branch  into  
(i) Break  up  of  flow  –  large  surface  area  for  the  hepatocytes  to  work  
(ii) In  close  contact  with  the  hepatocytes  
(iii) Extremely  porous  –  highly  fenestrated  endothelial  lining  
(d) Hepatic  vein  –  through  which  blood  leaves  the  liver,  rejoins  the  vena  cava  
(3) Lobules  –  hexagonal  functional  unit  of  liver  tissue  (further  division  of  lobes)  
(a) Rows  of  hepatocytes  arranged  in  a  radial  pattern  around  central  vein  
(b) Bile  canaliculi  –  small  channels  through  which  bile  that  is  produced  can  flow  
(i) Join  together  to  form  the  bile  duct  
(ii) Bile  duct  –  transports  bile  from  the  liver  to  the  gall  bladder  where  it  is  stored  
(iii) Bile  –  secretions  from  the  liver  with  both  digestive  and  excretory  functions  eg
...
 Breakdown  product  of  haemoglobin,  bilirubin,  is  excreted  as  part  of  bile  and  
in  faeces  (the  brown  pigment)  
 
iv) Describe  the  formation  of  urea  in  the  liver,  including  an  outline  of  the  ornithine  cycle  
(1) Urea  –  excretory  product  formed  in  the  liver  from  breakdown  of  excess  amino  acids  
(2) Deamination  –  removal  of  amine  group  from  an  amino  acid  to  produce  ammonia  
(a) Amino  acid  +  oxygen  à  keto  acid  +  ammonia  
(3) Ornithine  cycle  –  process  in  which  ammonia  is  converted  to  urea  

(a) 2NH3  +  CO2  à  CO(NH2)2  +  H2O  
(b) Occurs  partly  in  the  cytosol  and  partly  in  mitochondria  (ATP  is  used)  
(4) Urea  is  both  less  soluble  and  less  toxic  than  ammonia  
(5) Urea  is  released  from  the  hepatocytes,  into  the  blood,  transported  around  the  body  
and  to  the  kidneys  
(6) In  the  kidneys,  urea  is  filtered  out  of  the  blood  and  concentrated  in  urine  
(7) Urine  stored  in  the  bladder  until  it  is  released  from  the  body  via  the  urethra  
 
v) Describe  the  roles  of  the  liver  in  detoxification  
(1) Detoxification  –  conversion  of  toxic  molecules  to  less  toxic  or  non-­‐toxic  molecules  
(a) Can  be  done  via  oxidation,  reduction,  methylation  or  a  combination  
(b) Liver  detoxifies  hydrogen  peroxide  using  catalase  to  produce  oxygen  and  water  
(c) Liver  can  also  detoxify  ethanol  –  consumed  rather  than  produced  by  the  body  
(2) Mainly  takes  place  in  the  SER  in  hepatocytes  
(a) Ethanol  à  ethanal  by  ethanol  dehydrogenase  
(b) Ethanal  à  ethanoate  ions  (ethanoic  acid)  by  aldehyde  
(ethanal)  dehydrogenase  
(c) Acid  combines  with  coenzyme  A  à  acetyl  coenzyme  A  
(d) Ethanoic  acid  enters  the  Krebs  Cycle  to  produce  ATP  
(3) Ethanol  is  a  good  source  of  energy    
(4) But   conversion   of   ethanol   to   ethanoic   acid   and   Krebs  
Cycle  need  NAD  to  accept  H+  ions  released  
(a) Too   much   alcohol   =   insufficient   NAD   to   oxidise   and  
break  down  fatty  acids  for  respiration  
(b) Fatty  acids  accumulate  
(c) Fatty  acids  are  converted  back  to  lipids  
(d) Lipids  deposited  in  the  hepatocytes  in  the  liver  –  enlarged,  fatty  liver  
(e) =  Cirrhosis  or  alcohol-­‐related  hepatitis  –  result  of  enlarged  liver  due  to  excess  fats  
 
vi) Describe,  with  the  aid  of  diagrams  and  photographs,  the  histology  and  gross  structure  of  
the  kidney  

(1) Two  kidneys  on  either  side  of  the  spine  just  below  the  lowest  rib  
(a) Held  in  place  by  fat  layers  
(b) Cortex  and  medulla  are  surrounded  by  a  tough  capsule  
(c) Pelvis  –  connects  the  collecting  duct  and  the  ureter  
(d) Renal  artery  –  supplies  oxygenated  blood  and  nutrients  to  the  kidney  
(e) Renal  vein  –  carries  away  filtered  blood  to  the  heart  
(2) Role  
(a) Remove  waste  products  from  the  blood  
(b) Produce   urine   –   passes   out   of   the   kidney,   down   the   ureter   and   to   the   bladder  
(stored  before  release  via  the  urethra)  
 
vii) Describe,   with   the   aid   of   diagrams   and   photographs,   the   detailed   structure   of   a   nephron  
and  its  associated  blood  vessels  
(1) Nephron   –   functional   unit   of   the   kidney   involved   in   regulating   salt   content   of   the  
blood,  blood  pressure  and  the  pH  of  urine  
(a) Microscopic  tubule  
(b) Receives  fluid  from  the  blood  capillaries  in  the  cortex  
(c) Converts  the  fluid  into  urine  to  be  drained  into  the  ureter  
(2) 6  types  of  blood  vessels  associated  with  the  nephron  
(a) Afferent  arteriole  –  brings  blood  from  the  renal  artery  (wider  than  the  efferent)  
(b) Glomerulus  –  fine,  knot-­‐like  network  of  capillaries  that  increases  the  local  blood  
pressure  and  so  acts  as  the  site  of  ultrafiltration  (squeezes  fluid  out  of  the  blood)  
(c) Efferent   arteriole   –   narrow   vessel   that   is   muscular   and   so   can   constrict   to   restrict  
blood  flow,  which  allows  it  to  generate  a  higher  blood  pressure  in  the  glomerulus  
than  in  the  Bowman’s  capsule  
(d) Peritubular   capillaries   –   low   pressure   capillary   bed   that   runs   around   the  
convoluted  tubules,  absorbing  fluid  from  them  
(e) Vasa  recta  –  unbranched  capillaries  that  are  similar  in  shape  to  the  loop  of  Henle,  
carries  blood  from  the  glomerulus  to  the  renal  vein  
(i) Descending  limb  carries  blood  deep  into  the  medulla  

(ii) Ascending  limb  that  carries  blood  back  into  the  cortex  
(f) Venules  –  carry  blood  to  the  renal  vein  

(3) Key  features  of  the  nephron  
(a) Bowman’s  capsule  –  cup-­‐shaped  capsule  which  acts  as  the  ultrafiltration  unit  
(i) Surrounds  the  glomerulus  
(ii) Leads  into  the  nephron  
(iii) Filters   blood   by   separating   larger   particles   (stay   in   the   blood   vessels)   from   the  
smaller  ones  (pass  into  the  nephron)  
(b) Proximal   (closest   to   glomerulus)   convoluted   (bent   and   coiled)   tube   –   site   of  
selective  re-­‐absorption  to  ensure  valuable  substances  are  not  lost  in  the  urine  
(i) 85%  of  fluid  is  selectively  reabsorbed  –  all  sugars,  most  salts  and  some  water    
(c) Loop   of   Henle   –   countercurrent   exchange   mechanism   that   creates   a   low   water  
potential  in  the  medulla  of  the  kidney  so  water  is  reabsorbed  
(i) Descending  limb  –  water  potential  of  the  fluid  is  decreased  by  the  addition  of  
salts  and  the  removal  of  water  
(ii) Ascending  limb  –  water  potential  of  the  fluid  is  increased  as  salts  are  removed  
by  active  transport  
(d) Distal   (furthest   from   the   glomerulus)   convoluted   tube   –   concerned   with  
osmoregulation  as  it  varies  the  amount  of  water  reabsorbed  into  the  blood  
(e) Collecting   duct   –   high   water   potential   of   fluid   is   decreased   by   the   removal   of  
water  so  the  urine  has  a  higher  concentration  of  solutes  than  in  blood/tissue  fluid  
 
viii) Describe   and   explain   the   production   of   urine,   with   reference   to   the   processes   of  
ultrafiltration  and  selective  reabsorption  

(1) Ultrafiltration   –   high   pressure   filtration   at   a   molecular   level   whereby   large   molecules  
and  cells  are  left  in  the  blood  and  smaller  molecules  pass  into  the  Bowman’s  capsule  
(a) Ultrafiltration   unit   –   endothelium   of   the   capillary,   basement   membrane   and  
epithelium  of  the  Bowman’s  capsule  
(i) Pores/fenestrations   –   100nm   in   diameter  
between   the   endothelial   cells   in   the   wall  
of   the   capillaries   which   allow   plasma   and  
dissolved  substances  to  pass  through  
(ii) Basement   membrane   –   fine   mesh   of  
collagen   and   glycoproteins   that   act   as   a  
filter   to   prevent   proteins   (or   other  
molecules   with   RMM   >   69000)   from   being  
filtered  out  of  the  blood  
(iii) Podocytes   –   specialised   cells   forming   the  
inner  lining  of  the  Bowman’s  capsule  
(iv) Major   processes   –   finger-­‐like   projections  
that   wrap   around   the   capillaries   of   the  
glomerulus  to  ensure  there  are  gaps  between  the  cells  
(v) Foot   processes   –   many   short   side   branches   that   prevent   large   molecules   from  
being  filtered  out  of  the  blood  
(b) Process  
(i) Blood  enters  the  glomerulus  at  a  high  pressure  through  the  afferent  arteriole  
from  the  renal  artery  
(ii) Pressure  in  glomerulus  is  higher  than  pressure  in  the  Bowman’s  capsule  
(iii) Pressure   is   kept   high   because   the   arteriole   leaving   the   glomerulus   is   narrower  
than  the  one  entering  it  
(iv) Pressure  forces  glucose,  amino  acids,  urea,  salts  and  some  water  through  the  
basement  membrane  and  into  the  Bowman’s  capsule  
(v) Glomerular  filtrate  is  formed  
(c) Glomerular  filtrate  –  solution  that  passes  into  the  nephron  that  is  almost  identical  
to  the  blood  in  composition,  consisting  of…  
(i) Some  water  
(ii) Amino  acids  
(iii) Glucose  
(iv) Urea  
(v) Inorganic  ions  (salts)  –  sodium,  chloride  and  potassium  ions  
(d) NO  (red)  blood  cells  and  large  proteins  pass  through   –  left  in  the  blood  capillaries  
so   blood   has   a   very   low   water   potential   which   means   some   fluid   is   retained,  
aiding  reabsorption  later  
(2) Selective  reabsorption  –  useful  substances  are  reabsorbed  from  the  nephron  into  the  
bloodstream  while  other  excretory  substances  remain  in  the  nephron  
(a) How  the  PCT  epithelial  cells  are  specialised  

(i) Microvilli   –   microscopic   folds   increase   the   surface   area   of   cell   surface  
membrane  in  contact  with  tubule  fluid  for  reabsorption  
(ii) Co-­‐transporter  proteins  in  cell  surface  membrane  –  allow  facilitated  diffusion  
of   simple   sodium   ions   to   be   accompanied   by   transport   of   larger   glucose   or  
amino  acid  molecules  from  the  tubule  to  the  cell    
1
...
 small  proteins  will  be  reabsorbed  by  endocytosis  
 
ix) Explain,  using  water  potential  terminology,  the  control  of  the  water  content  of  the  blood,  
with   reference   to   the   roles   of   the   kidney,   osmoreceptors   in   the   hypothalamus   and   the  
posterior  pituitary  gland  
(1) Osmoregulation   –   control   and   regulation   of   water   potential   (water   levels   and   salt  
levels)  of  the  blood  and  body  fluids  
(2) Correct  water  balance  between  cells  and  surrounding  fluids  must  be  maintained  to  
prevent  problems  with  processes  where  osmosis  is  involved  
(3) Amount  of  water  reabsorbed  depends  on  the  needs  of  the  body  
(4) Ways  water  is  gained  from  the  body  
(a) Food  
(b) Drink  
(c) Metabolism  eg
...
 by  drinking  lots  of  water  
(i) Detected  by  osmoreceptors  (monitor  blood  water  potential)  in  hypothalamus  
1
...
Osmoreceptor  cells  lose  water  by  osmosis  
3
...
Stimulates  neuro-­‐secretory  cells  (specialised  neurons)  in  the  hypothalamus  
5
...
ADH   is   released   and   flows   down   the   axon   of   the   cell   to   the   terminal  
bulb  in  the  posterior  pituitary  gland  
b
...
Neuro-­‐secretory  cells  send  action  potentials  down  their  axons  to  cause  the  
release  of  ADH    
a
...
ADH  transported  around  the  body  
(ii) More  ADH  in  the  bloodstream,  so  the  more  permeable  the  collecting  duct    
1
...
ADH  binds  to  these  receptors  –  peptide  hormone  
3
...
Result  is  the  insertion  of  vesicles  containing  aquaporins  (water  permeable  
channels)  into  the  cell  surface  membrane  
5
...
More  water  is  allowed  to  be  reabsorbed  by  osmosis  into  the  blood  
7
...
ADH   slowly   broken   down   with   a   half-­‐life   of   20   minutes   –   time   taken   for   its  
concentration  to  drop  to  half  its  original  value  
2
...
Collecting  ducts  will  receive  less  stimulation  
(f) Blood  water  level  is  too  high  eg
...
Water  potential  of  the  blood  is  high  
2
...
Osmoreceptor  cells  don’t  shrink  
4
...
Neuro-­‐secretory  cells  don’t  manufacture  ADH  
6
...
Neuro-­‐secretory   cells   don’t   send   action   potentials   down   their   axons   to  
cause  the  release  of  ADH    
(ii) Less  ADH  is  released  into  the  bloodstream  
(iii) Less  permeable  collecting  duct  
(iv) Less  water  is  reabsorbed  by  the  kidneys  –  more  water  enters  the  kidneys  via  
the  afferent  arteriole  than  leaves  via  the  efferent  arteriole  
(v) Large  volume  of  dilute  urine  produced  
(vi) Blood  water  level  returns  to  normal  
 
x) Outline  the  problems  that  arise  from  kidney  failure  and  discuss  the  use  of  renal  dialysis  
and  transplants  for  the  treatment  of  kidney  failure  (HSW6a,  6b,  7c)  
(1) Common  causes  for  kidney  failure  
(a) Diabetes  mellitus  –  types  1  and  2  
(b) Hypertension  
(c) Infection  
(2) Consequences  of  kidney  failure  
(a) Cannot  remove  excess  waste  products  from  the  blood  
(i) Damage  to  internal  organs  –  urea  becomes  toxic  at  very  high  concentrations  
(ii) Cells  dehydrate  –  excess  salts  will  lower  blood  water  potential  
(iii) Drugs  and  toxins  in  diet  cannot  be  expelled  
(b) Cannot  regulate  levels  of  water  and  salts  in  the  body  
(i) High  blood  pressure  –  water  will  not  be  expelled  
(ii) Acidosis  –  other  metabolites  eg
...
 sodium  chloride  
(ii) Minimise  fluid  intake  eg
...
 ambulatory  PD  
(a) Filter  –  body’s  own  abdominal  membrane  (peritoneum)    
(b) Surgeon  implants  a  permanent  tube  in  the  abdomen  
(c) Dialysis  solution  is  poured  through  the  tube  
(d) Solution  fills  the  space  between  the  abdominal  wall  and  organs  
(e) Solution  is  drained  after  several  hours  from  the  abdomen  
(f) Daily  sessions  at  home  or  work  –  mobility  
(6) Haemodialysis  vs
...
 patient’s  peritoneum  
(d) Artery  vs
...
 daily  
(f) Tied  to  a  machine  vs
...
 ability  to  travel  

(v) No  longer  seen  as  chronically  ill  
(g) Disadvantages  
(i) Major  surgery  –  risk  of  infection,  bleeding  and  damage  to  surrounding  organs  
(ii) General  anaesthetic  holds  its  own  risks  
(iii) Immune  system  could  recognise  the  new  organ  as  foreign  and  could  reject  it  
(iv) Need  to  regularly  take  many  immunosuppressant  drugs  to  prevent  rejection  
(v) Immunosuppressant   drugs   could   cause   fluid   retention,   high   blood   pressure  
and  increase  susceptibility  to  infection  
(vi) Need  frequent  checks  for  signs  of  organ  rejection  
 
xi) Describe   how   urine   samples   can   be   used   to   test   for   pregnancy   and   detect   misuse   of  
anabolic  steroids  (HSW6a,  6b)  
(1) Small  molecules  (RMM  <  69  000)  can  be  tested  for  as  they  pass  into  the  urine  from  
the  bloodstream  (so  long  as  they  are  not  reabsorbed  further  down  the  nephron)  
(2) Pregnancy  testing  
(a) Human   chorionic   gonadotropin   (hCG)   –   hormone   secreted   by   human   embryos  
implanted  in  the  uterine  lining  
(i) Can  be  found  in  mother’s  urine  as  early  as  6  days  after  conception  
(ii) Small   glycoprotein   (RMM   =   36   700)   and   so   will   easily   pass   into   bowman’s  
capsule  of  nephron  
(b) Monoclonal  antibodies  are  specific  and  complementary  –  will  only  bond  to  hCG    
(i) Monoclonal  –  all  identical  because  they  have  been  produced  by  cells  that  are  
clones  of  one  original  cell  
(c) Antibodies  are  tagged  with  a  blue  bead  
(d) Urine  tested  by  soaking  a  portion  of  the  test  strip  in  it  
(e) Any  hCG  in  urine  acts  as  an  antigen  and  attaches  to  antibody  
(f) hCG  antibody  complex  moves  up  the  strip  
(g) Complex  will  stick  to  a  band  of  immobilised  antibodies  at  the  top  
(h) All  tagged  antibodies  attached  to  hCG  are  held  in  place  to  form  a  blue  line  
(i) Control  blue  line  –  used  for  comparison  to  second  blue  line  indicating  pregnancy  
(3) Anabolic  steroid  testing  
(a) Anabolic  steroids  –  drugs  that  mimic  the  action  of  steroid  hormones  
(i) Increase  protein  synthesis  in  cells  
(ii) Results  in  a  build  of  cell  tissue  and  increased  muscle  growth  
(iii) Remain  in  body  for  many  days  –  half  life  of  16  hours  
(iv) Small  molecules  –  will  easily  pass  into  bowman’s  capsule  of  nephron  
(b) Analyse   urine   sample   in   a   laboratory   using   gas   chromatography   (aka
...
 paper  or  gel  
(viii) Standard  samples  of  drugs  are  run  to  identify  and  quantify  drugs  tested  for  
(ix) Use   standard   samples   of   drugs’   chromatograms   to   identify   their   presence   in  
the  urine  sample  being  tested  
 



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