OCR A: Excretion and The Kidneys

• How does blood enter the kidneys?

  Through the renal artery
• ultrafiltration


  The process where small molecules are forced from the blood out of the capillaries of the glomerulus, under high pressure, into the Bowman's capsule.
• What happens in ultrafiltration?

  -Blood enters glomerulus from afferent arteriole -Lumen narrows, blood pressure increases, increases water potential-Small molecules can pass through basement membrane and podocyte cells via slit pores-Smaller molecules into PCT
• Selective Reabsorption


  The absorption of certain selected molecules back into the blood from the fluid in the nephron tubule.
• how is the kidney adapted for Selective Reabsorption?

  -Membrane of the cells of PCT folded into microvilli -Increases SA
• What happens in selective reabsorption to PCT?

  -Na+ is actively transported out of basal membrane of cells into lumen -Na+ passively transported from the tubule lumen into the cells of the tubule wall using co-transport protein

  s-Allows accompanying movement of useful substances
• % of molecules selectively reabsorbed (4)

  -100% Amino acids -100% Glucose -85% Na+ -65% H2O
• Name 3 substances that are reabsorbed in PCT

  Sodium Glucose amino acids
• Where is the majority of water recovered?

  The loop of henle
• How is loop of henle adapted to recover water?

  -Ascending limb impermeable to water

  -Descending limb permeable to water
• How is water recovered?

  -In ascending limb, Na+ and Cl- ions actively pumped into medulla

  -Decreases water potential of surrounding tissues

  -causes water to diffuse into medulla from descending limb

  -water in medulla reabsorbed into blood through capillary network
• Why do some animals have a longer loop of henle?

  longer loop of henle = more water can be reabsorbed from the filtrate Longer ascending limb = more ions pumped out into medulla
• How is the water potential of the blood monitored?

  -Osmoreceptors in Hypothalamus
• What hormone is used in monitoring water potential of the blood?+How released

  ADH (antidiuretic hormone)Released by posterior pituitary gland
• What do the kidneys do when the body is dehydrated?

  -water potential drops

  -Detected by osmoreceptors, pituitary gland stimulated

  -More ADH released

  -DCT and Collecting duct more permeable, more water reabsorbed by osmosis

  -small amount of conc urine produced
• How does ADH help avoid dehydration?


  -Bind to receptors on plasma membranes of DCT and duct-Aquaporins inserted into membrane -protein channel allows water to pass through via osmosis -More water reabsorbed
• What does the kidneys do when the body is hydrated?

  -Water potential increases-detected by osmoreceptors, pituitary gland stimulated -Less ADH released -walls less permeable -less water reabsorbed-large amount of dilute urine produced
• What is kidney failure?


  when the kidneys can't carry out their normal functions because they don't work properly
• what is the difference between acute and chronic?

  acute: sudden onset, rapid changes, usually short term Chronic: slow progressive changes, usually long term
• What can acute kidney failure be caused by?


  -Infection -Sudden loss of a large volume of blood -Blockage such as kidney stones
• what can chronic kidney failure be caused by?


  -Hypertension-Diabetes (high blood glucose can thicken glomerulus wall)-Polycystic disease
• How can kidney failure be detected

  by measuring the Glomerular Filtration Rate the rate at which blood is filtered from glomerulus into the Bowman's capsule Urinanalysis
• Symptoms of acute kidney failure

  -Little urine output -Oedema
• Symptoms of chronic kidney failure

  -more urine produced -change in blood chemistry
• What can high blood pressure cause?

  -Damage to the glomeruli -can damage capillaries -Larger molecules can filter through into PCT
• accumulation of fluid in tissues

  -excess water can't be removed -parts of the body swells
• Unbalanced ions

  -blood may become acidic

  -an imbalance of calcium and phosphate can lead to brittle bones

  -salt build-up up can lead to water retention
• How can kidney failure be treated?

  By organ transplant or dialysis
• Types of Dialysis

  hemodialysis and peritoneal dialysis
• Haemodialysis

  Blood is taken from a vein and passed through a dialysis machine so that exchange can occur across an artificial partially permeable membrane.
• problems of haemodialysis


  -waste products in blood build up between sessions -patient feels unwell -long hours
• What is peritoneal dialysis?

  -Peritoneal membrane in stomach used as filter-Dialysate is warmed and infused into the peritoneal cavity. -Fluid fills the peritoneal cavity and remains in the peritoneal cavity for a prescribed amount of time-The fluid, along with the toxins are drained.
• Problems with peritoneal dialysis

  -operation needed to insert a tube into abdominal cavity -risk of infection -No dialysis-free days
• What is a kidney transplant?

  Where a new kidney is implanted into a patient's body to replace a damaged kidney
• Advantages of a kidney transplant over dialysis

  -cheaper in long term-more convenient
• disadvantages of a kidney transplant

  -patient will undergo a major surgery

  -immunosuppressant drugs
• what are anabolic steroids?

  Drugs that build up muscle tissue
• How to detect steroids in urine

  Gas Chromatography/ Mass Spectroscopy -Urine sample vaporised, and passed through a column containing a polymer-Different substances move through at different speeds-Separates -Mass spectrometer separates ions depending on mass
• How are recreational drugs tested for?

  -Sample of urine applied to a test strip -If a certain amount of a drug is present, a colour change will occur
• How does a pregnancy test work?

  -Embryo secretes hCG (mr 36,700)

  -stick used with monoclonal antibodies for hCG bound to a bead

  -When urine is applied, hCG will bind to antibodies

  -Urine moves up to test strip carrying beads

  -Test strip has hCG antibodies immobilised