Osmoregulation and kidney faliure

Osmoregulation and kidney faliure

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Altering the permeability of collecting duct

Osmoregulation - control of water and salts in the body


  • cool day ---> conserve less water ---> walls of collecting duct LESS permeable ---> dilute urine  

Therefore LESS ADH ---> cell surface membrane folds inwards ---> creating new vesicles that remove water- permeable channels from the membrane.

  • walls are then less permeable, less water reabsorbed by osmosis into the blood---> more water in urine. dilute urine!
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Altering the permeability of collecting duct

Hot day ---> conserve more water ---> collecting ducts are MORE permeable ---> conc urine then the walls of collecting ducts respond to ADH in the blood

  • there are ADH receptors in the membrane of the cells that make up the walls of the collecting duct 
  • ADH binds to these receptors and cause a chain of enzyme controlled reactions in the cell
  • The result ---> insert vesicles containing water permeable channels (AQUA PORINS) into the cell membrane. Walls are more permeable

Therefore more ADH ---> more permeable channels inserted ---> more water reabsorbed by osmosis into the blood ---> less urine of a lowered water potential passes out of the body

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Adjusting the concentration of ADH in the blood

Water potential of the blood is monitored by OSMORECEPTORS in the HYPOTHALAMUS of the brain. These cells respond to the effects of osmosis.

When the water potential is LOW the OSOMORECEPTOR CELLS lose water by osmosis. The cells SHRINK and STIMULATE NEUROSECRETORY CELLS in the hypothalamus.

  • Half life- The half life of a substance is the time taken for it's concentration to drop half its original value.
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Adjusting the concentration of ADH in the blood

NUEROSECRETORY CELLS are specialised nerve cells ---> produce and release ADH

  • ADH manufactured in the cell body of these cells and pass down the axon to the terminal bulb in the POSTERIOR PITUITARY GLAND. ADH is stored here till its needed
  • When NUEROSECRETORY CELLS are activated (stimulated) action potentials are sent down the axon causing ADH to release.
  • ADH enters the blood capillaries running through the POSTERIOR PITUITARY GLAND. It's transported around the body and acts on the cells of the collecting ducts
  • once water potential is increased less ADH is released ADH is slowly broken down it's half life is 20 mins the ADH present in blood is broken down and collecting ducts receive less stimulation
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Kidney faliure

  • Kidney failure- due to Diabetes mellitus, hypertension and infection
  • Dialysis- the use of a partially permeable membrane to filter blood
  • Dialysis membrane- is a partially permeable membrane that separates the dialysis fluid from the patients blood in a dialysis machine.Dialysis is a complex fluid that matches the composition of body fluids
  • Heamodialysis- is blood taken from a vein and passed through a dialysis machine so that exchange can occur across an artificial partially permeable membrane. I
  • Peritoneal dialysis- dialysis fluid is pumped into the blood cavity so that exchange can occur across the peritoneal membrane
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  • removes waste, excess fluid and salt from the blood by passing the blood over a DIALYSIS MEMBRANE.
  • The DIALYSIS MEMBRANE is a PARTIALLY PERMEABLE MEMBRANE that allows exchange between blood and DIALYSIS FLUID.
  • DIALYSIS FLUID contains the right amount of salts urea water and other substances in blood plasma
  • Any substances in excess diffuse into the dialysis fluid and substances which are too low in concentration diffuse from the dialysis fluid into the blood. Dialysis must be combined with a carefully monitored diet
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  • blood from a vein is passed in a machine which contains an artificial dialysis membrane
  • Heparin is added to prevent clotting and any bubbles are removed before the blood returns to the body.
  • Haemodialysis is performed in a clinic 3 times a week for several hours at each session.


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Peritoneal Dialysis

Peritoneal dialysis

  • The filter is the body's own abdominal membrane (peritoneum)
  • An permanent tube is implanted in the abdomen
  • Dialysis solution is poured through the tube and fills the space between the abdominal walls and organs.

Pd is performed in several consecutive sessions daily as people can walk around and have dialysis.


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Kidney transplant


  • freedom from time consuming dialysis
  • diet less limited
  • feel physically better
  • better quality of life e.g able to travel
  • no longer seeing oneself as chronically ill
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Kidney transplant


  • need immunosuppressants to help prevent rejection as the immune system may see the new organ as foreign object and produce a reaction
  • need major surgery under general anaesthetic
  • risks of surgery; infection, bleeding, and possible damage to surrounding organs
  • frequent checks for signs of organ rejection
  • Side effects of immunosuppressant increase risk of infection
  •  anti-rejection medicines cause fluid retention and high blood pressure
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Excretion summary

Order of nephron travelling - Blood from the Renal Artery goes into the glomerulus which creates glomerulus filtrate in the Bowman's Capsule. It then travels down the first convoluted tubule (distal convoluted tubule - ultra-filtration) and through the loop of Henle and then up the second convoluted tubule (proximal convoluted tubule - selective re-absorption). Finally, it goes into the uterus and down towards the bladder.

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