Kidney Processes Flashcards
what is the hydrostatic pressure in the glomeruli?
50mmHg
what is the oncotic pressure difference between the bowman’s capsule filtrate and the glomerulus?
25mmHg
what is the net perfusion pressure in the kidney?
the difference between the hydrostatic pressure in the glomerulus (pressure favouring filtration) and the hydrostatic pressure of the bowman’s space and oncotic pressure of glomerulus (forces favouring reabsorption)
in other words the net pressure trying to push fluid out
why does oncotic pressure of glomerulus increase throughout filtration?
As more water leaves the glomerulus the protein conc is increasing
where does the blood in the efferent arteriole go?
leaves the glomerulus, it enters a portal vein and travels to a second capillary bed surrounding the Loop of Henle; (vasa recta ) here, the hydrostatic pressure is much more similar to a systemic capillary, while the osmotic (oncotic) pressure is much higher
what are the 3 layers between the glomerulus and the bowman’s space?
endothelial cells (with fenestrations)
negatively charged glycocalyx
Basement membrane containing thick negatively charged proteins such as collagen
podocytes
what is the main form of solute movement into the bowman’s capsule?
Bulk flow
(solvent drag occurs as filtrate is forced out)
what is the GFR?
120ml/min
what is the renal plasma flow rate?
600ml/min
what are the 2 main mechanisms of increasing glomerular GFR?
dilate afferent arteriole
contract efferent arteriole
what is proteinuria and what does it suggest?
protein in the urine suggests glomerular nephritis (dysfunction in the glomerulus) and or nephrotic syndrome (severe renal failure)
what is the classification of epithelial cells of the PCT?
simple columnar epithelium, with microvilli (to aid absorption)
what is the basolateral and apical surface in the PCT?
Apical side = filtrate side
Basolateral = interstitial space
how is water transported in the PCT?
paracellularly, through aquaporin 1 channels
drawn by oncotic pressure into interstitial space
how is glucose reabsorbed in the PCT?
Under normal conditions when glucose conc in the filtrate is high glucose is reabsorbed by SGTL2 which is a Na+ glucose symporter
High affinity / low capacity
further down the tubule when glucose conc is lower SGTL1 transports the glucose but it requires 2Na+ to do this as its moving against a large conc gradient. Low affinity / high capacity
what is the value for glucose Tm and why is it useful?
380mg/min-1
tubular maximum - max amount of glucose that can be reabsorbed, prevents excess glucose entering the blood by stopping too much being reabsorbed
how does canagliflozin act and what are it side effects?
inhibits SGTL2 transporter, decreases glucose reabsorption
used to treat diabetes mellitus
increase glucose in urine = increase risk of UTI because glucose is available as a bacteria metabolite
how are amino acids reabsorbed?
through various cotransporters, a lot of which use Na+
how is Cl reabsorbed in the PCT?
anion exchanger (antiporter)
example is methanoic acid (charged form enters filtrate in exchange for Cl, combines with H+, so it now lipid soluble, renters the epithelial cell to redo process)
also via the paracellular route (solvent drag and passive diffusion, mainly occurs further down as water is lost and delivered to interstitial space so conc gradient is set up)
explain how organic ions such as penicillin are secreted into the urine
Organic ion transporters present on the basolateral membrane transport the organic ions into the cell
Multidrug resistance associated protein transport inorganic ions from the cells into the filtrate in exchange for another anion e.g. Cl, HCO3 (antiporter system)
Organic ions compete with each other for excretion at both transporters
explain the transporters / properties of epithelial cells on the thick Ascending limb
Uses NA/2CL/K cotransporter to move ions out of the filtrate (NKCC2 transporter)
there is K+ leak channels present on the apical side because there is a limited amount of K
multiple active ion transporters on the basal lateral side
lots of tight junctions to prevent paracellular movement of water etc
how does water mainly leave the descending limb?
paracellular route
what is the action of
Furosemide
acts on thick ascending limb
Blocks the NKCC2 cotransporter = less being pumped into interstitial space causing enormous diuresis and natriuresis
what is furosemide used to treat?
hypertension, so used to treat cardiac and renal failure/ dysfunction
what are the side effects of furosemide?
dehydration, excess K+ loss (hypokalaemia)
can result in cardiac arrythmias especially when applied with digoxin
how is water reabsorbed in the collecting ducts?
paracellularly and through AQP2 (apical) then AQP3 (basolateral)
what effect does aldosterone have on the collecting ducts?
stimulates increase synthesis of sodium potassium and NA/K ATPases in the collecting duct
This increases sodium and water reabsorption
what effect does spironolactone have why is it used?
Spironolactone blocks the effects of aldosterone and therefore acts as a diuretic
It has used In heart failure as it’s a K+ sparing diuretic
what is Urea Counter current Multiplication and how is it useful?
Urea transported out of the collecting ducts
increases the osmolarity of the medullary interstitial space to aid water reabsorption
then reabsorbed again in the loop of hele
How is H+ secreted into urine?
Na+/H+ antiporter
(formed from carbonic anhydrase)
how is HCO3 absorbed in the PCT?
forms CO2 in filtrate, diffuse into cell, forms HCO3 via CA then Na+ HCO3 symporter back
what diuretic targets CA?
acetazolamide blocks carbonic anhydrase meaning no H+ is generated to travels into the filtrate, decreasing HCO3 absorption
