renal 3 Flashcards
what determines the final urine concentration and volume (3)
- ultrafiltration at glomerulus
- selective reabsorption in tubules (water and solutes)
- tubular secretion of solutes
- *simultaneously determine ECF concentration and composition as well**
define glomerular filtration (ultrafiltration)
- bulk flow of fluid from glomerular caps to bowman’s
what are freely filtered in glomerular filtration
- low molecular weight substances such as:
- ions, Na, K, Cl, HCO3, glucose, urea etc
what does filtration depend on in glomerular caps
starling forces
What is different about the glomerular cap than the other caps
- Hydrostatic pressure is higher at the glomerular cap
What is the ONLY job of the glomerulus
FILTRATE (no reabsorption)
what are the layers that a filtrate passes
- overall filtration passes from capillary lumen –> bowman’s capsule
- needs to pass through endothelial layer, basement membrane, podocytes and epithelial layer of bowmans.
what is the only barrier to RBC
- highly spaced epithelial cells of the cap (not big enough for RBC)
Define Congenital nephrotic syndrome
- mutation in podocin gene –> lose protein/edema
What effect does charge have to do with glomerular filtration
- part of a barrier
- endothelial layer is lined with NEGATIVE charged mucopolysaccharides to prevent filtering proteins (everything else is fair game)
- this is why proteins are much LESS PERMEABLE
- also filtration slits in podocytes are negatively charged
- -> results in repeling large neg. charged proteins
What forces favor filtration
- capillary hydrostatic pressure (cap. BP) because glomerulus is between 2 high pressure circuits
What force opposes glomerular filtration
- capillary oncotic pressure because it pushes filtrate out on afferent side and into glomerulus so there is more protein on the efferent side, so more oncotic pressure
- Hydrostatic Pressure in Bowman’s (important if there is renal obstruction-stones)
Where are the forces favoring net filtration biggest?
Forces favoring filtration biggest on AFFERENT END
–> decrease to near 0 at end of efferent end
what are the effects of filtration if polyanionic substance lose a charge?
- lots of (-) charge so no filtration (like protein)
- start filtering the proteins causing edema
- proteinuria and albuminuria occurs
describe colloid osmotic pressure
- normally it is always increasing because it only filters
- only goes down if starting to reabsorb water
what are the substances that constrict both afferent and efferent arterioles
- NE and Epi
- decrease GFR and RBF (only occurs in extreme conditions like hemorrhage)
describe angiotensin II
- consticts Afferent arterioles
- maintains GFR and decrease RBF by constricting afferents
- effect is on efferent despite constriction of the afferent
What happens if you raise hydrostatic pressure
The GFR increaes
What occurs if the plasma oncotic pressure increases
Increase in plasma oncotic pressure –> GFR will decrease (bolus or protein) –> GFR decrease
what occurs if you start sweating alot
sweat a lot, lose all but proteins so oncotic pressure increases –> GFR DECREASE
what is the result on filtration of a Person with GI illness with vomit/diarrhea
vomitting/diarrhea cause the loss of protein-free fluid so get SAME
What occurs in the case of kidney stone obstruction
kidney stones obstruct ureter so hydrostatic in bowman’s rise –> causing a DECREASE in GFR
define filtration fraction
- FF=GFR/RPF
- percent of renal plasma flow (RPF) filtered at glomerulus
- if FF increased, oncotic pressure at efferent end increases above normal
define transport maximum
- max rate at which glucose can be reabsorbed in the lumen
- a person with very high blood glucose levels will also have high urine volume due to transport max being reached and glucose spills into urine
- -> since glucose is osmotically active and keeps Na and thus water in the urine (resulting in high levels of urine)
