describe what happens when water potential of blood increases
- detected by osmoreceptors in hypothalamus
- hypothalamus releases less ADH
- DCT and collecting duct walls become less permeable to water
- less water is reabsorbed into the blood and more is lost in the urine
describe what happens when water potential of blood decreases
- detected by osmoreceptors in hypothalamus
- hypothalamus releases more ADH which is released into blood by posterior pituitary gland
- DCT and collecting ducts become more permeable to water
- more water is reabsorbed into the blood and less is lost in the urine
why is urine used to test?
urine is composed of substances that are filtered out of the blood
what is urine used to test?
- diabetes
- pregnancy
- anabolic steroids
- drugs
what does a pregnancy test use?
monoclonal antibodies to detect the presence of human growth hormone
how does a pregnancy test work?
- absorbent end of the pregnancy test submerged in urine sample
- first antibody complementary to human growth hormone has a coloured dye attached
- second antibody complementary to antigen is immobilised in the test
- third antibody is immobilised and is complementary in shape to the first antibody
what is haemodialysis?
uses a dialysis machine for many hours multiple times a week
- filters blood and returns it
describe how haemodialysis works
- blood comes out of artery into artificial renal artery
- anticoagulants added (stops blood clotting)
- enters the machine (artificial kidney)
- flows in spaces in between the partially permeable dialysis membranes which mimic the basement membrane
- into artificial renal vein and back into body
- blood & dialysis fluid separated by a partially permeable membrane (countercurrent system)
- blood cells and large proteins cannot pass through
- urea & excess salt diffuses out of blood down concentration gradient
how does dialysis fluid allow dialysis to take place effectively?
- contains no urea so there is a steep conc gradient so all urea diffuses out of blood
- normal plasma levels for glucose and mineral ions so there is no net movement of glucose out of the blood and only excess mineral ions are removed
why do patients have to have a careful diet on haemodialysis?
keep blood levels as constant as possible
where does peritoneal dialysis occur?
inside the body
what is GFR?
glomerular filtration rate
- rate at which substances are filtered out of the blood in the glomerulus into the renal capsule
what does a rate of filtration below the normal range indicate?
kidneys are not functioning properly
how is ultrafiltration rate measured?
- blood test to measure concentration of creatinine
what is creatinine?
breakdown product from muscle cells, usually filtered out of the body by the kidneys
- concentration used to estimate GFR
what are the units for eGFR?
cm3min-1
what does it suggest if creatinine concentration in the blood increases?
kidneys are not functioning properly
- small molecules should be removed during ultrafiltration
what factors affect eGFR?
- age
- gender (males have more muscle so more creatinine)
- fitness levels (more active = more muscle tissue)
describe how peritoneal dialysis works
- occurs inside body using peritoneum membrane which forms abdomen lining
- dialysis fluid introduced into abdomen using a catheter, left for a few hours
- dialysis occurs across peritoneal membrane
- urea, excess mineral salts and water diffuse out of blood capillaries inside tissue fluid and into dialysis fluid
- dialysis fluid drained out and discarded
why is peritoneal dialysis less effective than haemodialysis?
little movement of fluid
so less concentration gradient
what is the main problem when someone receives a kidney transplant?
- rejection
- surface antigens on cells of the donated kidney may be different to the antigens on the cells of the recipient
- causes an immune response - destruction of new kidney
how can kidney transplant rejection be overcome?
- matching of tissue types as closely as possible
- recipient given immunorepressant drugs for the rest of their life to prevent the immune attack
