Tubular Transport I Flashcards
Are H+ and para-aminohippuric acid (PAH) both filtered at the glomerulus and secreted at the PCT?
YES
For H+ and PAH, prior to the inflection or saturation point, are they being reabsorbed or secreted efficiently?
YES
What happens to H+ and PAH after the saturation point?
the excretion rate and filtration rates become proportional.
** What is clearance?
the rate at which the kidneys clear various substances from the plasma (ml/min). Same equation as GFR (when using inulin) :)
*Clearnace= concentration of urine ‘substance’ x flow of urine/ concentration of plasma ‘substance’
** What substance is used to measure GFR?
INULIN, because the only way for it to be eliminated is via filtration. It cannot be reabsorbed or secreted.
** What is a more clinically useful way to measure GFR?
- creatinine= by-product of muscle metabolism that is cleared from the body fluids almost entirely by glomerular filtration (it is partly secreted and not reabsorbed).
- plasma creatinine concentration= 1 mg/dL
What happens to creatinine if you decrease GFR by 50% (aka you lose a kidney)?
It will increase in the blood to double the amount.
What molecule is used to measure renal plasma flow?
PAH because 90% of it is cleared in one pass through the kidney (due to the ability for the kidney to both filter and secrete this molecule).
*Use same formula as inulin clearance (GFR). This comes out to be about 650 ml/min (after dividing by 0.9, because you’re correcting for the 10% that is not cleared), which is about equal to the renal plasma flow.
How do you calculate TOTAL BLOOD FLOW through the kidneys using the renal PLASMA flow?
take the renal plasma flow/ (1- hematocrit)
* should be around 1200 ml/min
Is there a Tm for inulin?
NO (duh because it is not reabsorbed).
*** If Cx/C inulin = 1, is substance x being filtered, reabsorbed or secreted?
FILTERED only because it’s behaving just like inulin.
*** If Cx/C inulin > 1, is substance x being filtered, reabsorbed or secreted?
FILTERED and SECRETED because this rate is greater than that of inulin and the only way to do that is to also secrete the substance (just like PAH).
*** If Cx/C inulin
FILTERED AND REABSORBED (just like glucose).
What are the 2 paths that water and electrolytes can be reabsorbed by the kidney?
- paracellularly (between cells)
2. trancellularly (through the cell itself)
What percent of kidney energy consumption does the kidney expend to move Na+?
80%
What channels does water move through?
aquaporins
What are the 4 types of Na+ entry into the tubular cells at the PCT?
- Na+/H+ antiporter= major transporter
- Na+ nutrient pump (how glucose uses Na+ entry energy to also enter).
- Na+/phosphate pump
- Na+ sulfate pump
Note Cl- follows to maintain equal charge through its own channel.
How does Na+ exit out of the tubular cells at the basolateral membrane?
- Na+/K+ ATPase= major transporter
- Na+/HCO3- cotransporter
Note Cl- passively diffuses to maintain equal charge
Is there a lot of movement through the cells of the descending loop of henle in the CORTICAL nephrons?
NO because there isn’t a large change in concentration gradient in the interstitium.
*Remember only the juxtamedullary nephrons are the only ones that can concentrate the urine.
What happens to the filtrate as it moves through the descending loop of henle in the JUXTAMEDULLARY nephrons?
it will increase from 300 to 1200 mOsm/kg because water is permeable but solutes are not in this area of the loop of henle.
What happens tot he osmolarity of the filtrate as it moves up the ascending limb of the loop of henle?
it decreases because this portion is impermeable to water but Na+, K+, and 2 Cl- are moved out via their cotransporter. Aka this is diluting the filtrate (making it hypoosmotic).
*Remember this is where loop diuretics (furosemide) work.
*** Is the filtrate in the early DCT isotonic, hypotonic, or hypertonic with respect to the blood plasma?
HYPOOSMOTIC
Are there more or less Na+ channels on the luminal side of the the tubular cells at the DCT?
very few but the ones that are there are Na+/Cl- cotransporters. Thus, there is little water reabsorbed here also.
*Remember this is what thiazide diuretics inhibit.
** What specific cells are primarily involved in the transport of Na+, Cl-, and water in the distal tubule?
PRINCIPLE CELLS of the cortical collecting tubules and collecting duct.
- Remember this is mainly where ADH (increases transcription/translation and upregulation of aquaporins to increase water reabsorption), ALDOSTERONE (increases Na+ and thus water reabsorption), and ANP/BNP (decrease Na+ reabsorption) act.
- This is also the site remember for K+ sparing diuretics like spirinolactone (inhibits aldosterone), and amiloride (Na+ reabsorbing channel blocker).
