Kidney Flashcards
how many nephrons do humans have
500 thousand to 1 million
the nephron
afferent arteriole, (glomerulus/bowmans capsule) efferent arterole, proximal convoluted tubule, loop of henle, distal convoluted tubule
which are the specialised cells and where are they
podocytes - specialised epithelial cells - between the basement membrane the the urinary space
glomerular filtration barrier
blood - fenestrated endothelium - basement membrane - podocytes - urinary space
what kind of permeability - and what passes
selective permeability - H2O, electrolytes pass
Not proteins
why don’t proteins pass through the membrane?
they are negatively charged, and so is the basal membrane - proteins are maintained on the blood side
what is the primary urine
pressure coming to of the bowman capsule - efferent arteriole
loop of hence permeability
defending - v permeable to water
ascending (thick limb) no permeable to water but permeable to salts (sodium, potassium and 2 chloride ions) - 90% sodium is reabsorbed
how is water reabsorbed in DCT?
through aquaproins
what is th concentration gradient important for?
urea recycling
approximately how much Na is filtered each day?
25 000 mEq
approximately how much H2O is filtered each day?
180 litres
how much Na is excreted each day?
150 mEq
how much H2O is excreted each day?
1.5 litres
what % of the sodium and water is reabsorbed?
more than 99%
why would you filter and reabsorb that much?
to remove wate and toxin
what are the 5 groups of diuretics?
- osmotic
- carbonic anhydrase inhibitors
- loop
- thiazides
- potassium sparing
what % of the top 200 drugs in the US are diuretics?
10%
what are diuretics?
drugs that increase urine output by the kidney
when would you use diuretics
oedema of any origin, congestive heart failure, hypertension
when would you use diuretics
oedema of any origin, congestive heart failure, hypertension
how do most diuretics work?
inhibit reabsorbtion of sodium at different levels of the renal tubular system
more sodium excreted, more water excreted
what is a synergistic effect
when a combination of therapies are used
where do osmotic diuretics act?
on the first part of the glomerulus
glomerular capillary permeability
high permeability to water and electrolytes
what % of plasma is filtered into Bowman space and PCT
20%
which pump is the first part os the PCT/glomerulus
H+/Na exchange - Na out (reabsorbed) and H in
an example of an osmotic diuretic
mannitol
what pharmacological value does mannitol have
pharmacologically inert
doesn’t bind to a receptor and doesnt interfere with any channel
how does mannitol work?
- increases plasma osmolarity
- filtered at glomerulus and poorly reabsorbed
- increases osmotic pressure in glomerular filtrate
- decreases H2O reabsorption from nephron
- stays in the tubule - water moves into tubule and is excreted
why can’t salt or glucose be used as osmotic diuretics?
they are osmotic substances that are reabsorbed and taken up into cells - we don’t want the diuretic to be reabsorbed
why would you give mannitol with a slow infusion?
too fast you will drag water from inside the cells – bad - dehydrate the own cells suffer even more
what os glaucoma and which diuretic would you use?
accumulation of liquid in the eye
mannitol
where does mannitol enter and where does it draw liquid from?
does not enter the brain or eye - draws liquid from tissues
what would you use mannitol for?
forced diuresis e.g. in poisonings
acute glaucoma
cerebral oedema
how would you administer mannitol
slow IV. Infusion of 5 – 20% solution
what is reabsorbed in the PCT?
sodium, water and bicarbonate
what % of sodium is reabsorbed in the PCT?
65-70%
2/3
what does carbonic anhydrase do?
catalyses the dissociation reaction
H2CO3 –> CO2 + H2O
formula for carbonic acid
H2CO3
which exchanger is used between PCT and epithelial cells
Exchanger for sodium and hydrogen
Exhange hydrogen ion – sodium into the blood – atpase
what happens if you inhibit the carbonic anhydrase?
don’t form the hydrogen ion – sodium doesn’t have anything to exchange with – doesn’t get into the cell so then doesn’t get into the blood – sodium and the water stay in the tubule - excretion
where does carbonate come from and where does it diffuse into?
comes from the dissociation of NaHCO3 or H2O +CO2 joining - diffuses into the blood
what is crucial about Carbonic anhydrase inhibitor diuretics?
the H+ isn’t forms anymore
why would carbonic anhydrase be slightly redundant?
So many mechanisms to regulate hydrogen ions – that the H ions still apear in the cell – so is redundant
what sort of drug is Acetazolamide?
Carbonic anhydrase inhibitor
what effect would Acetazolamide have on the urine? why?
cause mildly alkaline urine - increase excretion of HCO3-
What does Acetazolamide do?
Suppresses H+ production and thus reduce Na+-H+ exchange
– less Na+ reabsorption
Increases excretion of HCO3- (accompanied by Na+, K+ and H2O)
– causes mildly alkaline urine
– metabolic acidosis
Effect is self-limiting
what are the uses for Acetazolamide?
Glaucoma
– inhibits CA in eyes to reduce the formation of aqueous
humour
- Adjunct therapy in metabolic alkalosis (inc. excretion of bicarbonate (acidosis))
Prophylaxis (treatment) of altitude sickness
what are the adverse effects of Acetazolamide?
Dizziness and light headache
Blurred vision
Loss of appetite and stomach upset
why do you get altitude sickness?
Less oxygen, saturation blood oxygen needs to be constant, hyperventelate, eliminate too much co2, metabolic alkilosis - hangover sensation
how does acetazolamide help altitude sickness?
increases the excretion of bicarbonate
