Renal lecture 2 glomerular filtration, tubular reabsorption/secretion, concept of clearance Flashcards
What are the 3 barriers in glomerular filtration?
What gets filtered by glomerular filtration?
1.-endothelial cells
2.-BM
3.-podocytes
-water and low molecular weight substances
Wht cannot get filtered (should not be in urine)
-cells
-proteins (albumins, globulins)
-protein bound substances (1/2 of calcium ion and fatty acid)
What does it mean when albumin is in urine?
Why should onyl half of Ca2+ ions not be filtered?
-means filtration barrir is messed up (protein uria)
-1/2 of them are bound to large proteins so they should not get filtered, only 1/2 should be filtered
What is RBC in urine and WBC in urine called?
What does this mean damage is in?
alot of RBC in blood=hematuria, which means damage to glomerulus
alot of WBC=piuria
what forces favor and oppose filtration?
What is the value of each force in mmhg
favor filtration=glomerular capillary BP (Pgc)=60 mmhg
opposing filtration (pushes against fluid trying to get in:
fluid in bowmans space (Pbs)=15 mmhg
-osmotic foce due to protein in plasma (pi gc)=29mmhg
What is the formula for net glomerular filtration pressure?
What is the value?
=Pgc-Pbs-PIgc=16mmhg
What is the definition of glomerular filtration rate?
Glomerular filtration rate (GFR): the volume of fluid
filtered from the glomeruli into Bowman’s space per unit
time
What is GFR regulated by, what are the 3 things (what pressure, permeability,etc)?
GFR is regulated by: NMS
N-net filtration pressure
M-membrane permeability
S-surface area available for filtration
What is the normal GFR value for a 70kg person?
What is plasma volume of this person?
How often is plasma filtered in glomeruli?
-Normal GFR (70 kg person): 180 L/day (125 ml/min)
-3.5L (5% of body weight)
-51 times a day
What does decreased GFR cause? What do you dilate and constrict?
What does this cause to glomerular capillary BP?
-constrict the left side of the afferent arteriole
-dilate the efferent arteriole
-causes a decrease in Pgc
What does an increase in GFR mean and cause in terms of constriction/dilation?
What does this cause to glomerular capillary BP?
-it means increased filtration
-constrcit efferent arteriole
-dilate afferent arteriole to increase blood flow
-increase in Pgc
What is the definition of filtered load?
What is the formula for filtered load?
What is the filtered load of glucose?
Filtered load: total amount of any freely filtered substance
Filtered load = GFR x plasma concentration of the substance
ex.Filtered load of glucose = 180 L/day x 1 g/L = 180 g/day
What does it mean when filtered load is greater than amount excreted in urine, and vice versa?
Filtered load > amount excreted in the urine: net reabsorption
Filtered load < amount excreted in the urine: net secretion
What is the definition of reabsorption?
What does transcellular vs paracellular mean/
-it is when you go from the tubular luomen to the peritubular capillaries
-transcellular=going through tubular lumen and tubular epithelial cells
-paracellular goes from tubular lumen through tight junction
What is the amount of water, sodium, glucose, and urea that is reabsorbed?
What can having too much potassium cause?
water=99%
sodium=99.5%
glucose=100%
urea=44%
-too much K+ can stop your heart
What are the first 2 most imporant points about tubular reabsorption (what is large and incomplete)?
- Filtered loads are enormous, generally greater than the amounts of the substance in the body.
- Reabsorption of waste products is relatively incomplete (e.g. urea).
What aer the last 2 important points about tubular reabsorption?
- Reabsorption of most useful plasma components (e.g. water, inorganic ions, and organic nutrients) is relatively complete
- Reabsorption of some substances are not regulated (e.g. glucose, amino acids), while others are highly regulated (water, inorganic ions).
Where does reabsorption by diffusion occur?
Where does urea reabsorption occur, and where is it filtered (what part of kidney)
Reabsorption by diffusion: often across the tight junctions connecting the tubular epithelial cells
-e.g. urea reabsorption in the proximal tubule
-Urea is freely filtered at glomerulus
Where does water reabsorption occur?
Whre does urea concentration become higher?
where does urea diffuse along the conc. gradient across Tj into?
-In the proximal tubule, water reabsorption occurs.
-Urea concentration in the tubular fluid becomes higher.
-Urea diffuses into the interstitial fluid and peritubular capillaries.
What are the 2 mechanisms of reabsorption?
diffusion and mediated transport
where does reabsorption by mediated transport occur?
What does it normally require the participation of?
what is it usually coupled with?
-Reabsorption by mediated transport occurs across tubular
cells (transcellular epithelial transport)
-Requires the participation of transport proteins in the plasma membrane of tubular cells.
-Usually coupled to the reabsorption of sodium
Where is the Na, K ATPase in mediated transport?
Where does glucose pass along concentration gradient?
How do amino aciids leave tubular epithelial cells/
-it is on the basal side of the membrane
-on the basolateral side
-via amino acid transporters
What is the definiton of transport maximum (Tm)
What is an example of when this can occur, what happens in this example?
What happens to the urine as a result of this example?
When the membrane transport proteins become saturated, the tubule can not reabsorb the substance any more.
- in people with uncontrolled diabetes mellitus, the plasma concentration of glucose can become very high and the filtered load of glucose exceeds the capacity of the tubules to reabsorb glucose (Tm is exceeded).
As a result, glucose appears in the urine (glucosuria).
What is the definition of tubular secretion?
What are the 2 mechanims that mediate secretion?
Tubular secretion moves substances from peritubular capillaries into the tubular lumen (opposite of reabsorption)
-diffusion and transcellular mediated transport
