Glomerular Filtration Flashcards
What are indicators of end-stage renal disease? (2)
- really low GFR
- high protein composition in urine
What is glomerular filtration?
filtration of fluid into Bowman’s space from glomerular capillary tuft (blood)
What is filtrate (ultrafiltrate)?
filtered fluid composed of H2O and electrolytes, glucose, creatinine (similar to plasma composition)
How is filtrate/ultrafiltrate different from plasma?
essentially no protein present – unless there is damage to filtration barrier
What is glomerular filtration rate (GFR)?
volume of plasma filtered (from glomerulus to bowman’s capsule) per unit time
What is the GFR range for healthy adults?
80-120 mL/min, or 115-173 L/day
What happens to GFR as you age? Why?
decreases
- reduced function of filtration
How does kidney disease affect GFR?
decreases GFR
What is filtration fraction (FF)?
fraction of plasma that is being filtered (overall quality of filtration function of kidney)
FF = GFR/RPF
What are the 3 layers of the glomerular filtration barrier?
- fenestrated endothelium – big openings found between endothelial cells
- glomerular basement membrane – determines what gets across barrier from blood, into tubule
- podocytes (visceral epithelium) – surround capillary
What specialized cells do glomerular capillary tufts require? Why?
intraglomerular mesangial cells
- glomerular capillary tufts are the only capillary beds not surrounded by interstitial tissue, therefore require unique structural support
How do intraglomerular mesangial cells function?
cells are connected to glomerular basement membrane, and have contractile properties that allow for regulation of GFR
contraction and relaxation change surface area available between podocytes for filtration to occur
What is the slit diaphragm?
thin structure near GBM that has proteins that connect adjacent podocyte foot processes
Is the slit diaphragm charged? Why?
negatively charged surface coat – helps with selectivity of barrier
What is podocin? What does it do?
protein component of slit diaphragm (filtration slits of podocytes) that helps with coordination and determination of what can can cross glomerular filtration barrier
What can cross the glomerular filtration barrier?
easier for smaller and positively charged substances (due to negative coating on barrier, which will repel negative charges) to cross
What substances are filtered out of blood plasma at the renal corpusce?
- Na+, K+, Cl- , Ca2+
- PO43- , H+ , HCO3- , NH4+
- H2O
- urea
- glucose
- creatinine, urobilinogen
- some proteins (trace amounts), amino acids
What is filtrate?
fluid and substances arriving to nephron from glomerulus – found in Bowman’s capsule
Can filtrate composition change?
NO – no way to change composition of fluid
Can filtrate be modified by reabsorption or secretion?
NO – only gets filtered
What is tubular fluid?
fluid in tubule along length of nephron, until it reaches end of collecting duct
Can tubular fluid composition change?
YES – lots of transport happening that will dramatically change fluid composition as we move along nephron
What substance is used to determine RPF?
RPF is physically measured – extrapolate what RBF would be from those values, using PAH
What substance is used to measure GFR?
inulin or creatinine
When looking at clearances, why do we use things that are largely excreted?
if largely excreted, we can remove renal vein component of equation (which is difficult to measure)
For GFR measurements, what’s important about the substance that is used?
important that it’s a substance that relies heavily on filtration for its excretion (ONLY FILTERED) – don’t want it to be something that is reabsorbed or secreted
Why is inulin or creatinine used to measure GFR?
~100% filtered (~100% excreted) – rely on filtration for their excretion
no tubular reabsorption or secretion
Is the amount of inulin or creatinine in an individual a good indication of filtration rate? Why?
numbers can fluctuate more depending on individual’s activity level – less precise measurement, but still good indication of filtration rate
How is the amount of inulin in an individual determined?
known amount is injected into person, then we can measure it in blood once it’s equilibrated, and in urine once it’s excreted
What is creatinine?
breakdown of skeletal muscle
assessed routinely if investigating kidney function