4 Tubular Transport Flashcards
Review: what are the components of rena function?
- Glomerular filtration (filtering the plasma of proteins)
- Tubular reabsorption (from tubular lumen to PTC)
- Tubular secretion (from PTC to tubular lumen)
- Excretion (not secretion….loss from body in the urine)
Filtered load is the amount of material in _____________: FL = ? (formula)
glomerular filtrate;
FL = (GFR)(Px)
Excretion rate is the amount of material ___________.
ER = (formula) ?
lost in urine;
ER = (Ux)(V)
Secretion vs. Reabsorption: Transport rates (Tx) are amount of material added to (secreted) or removed (reabsorbed) from glomerular filtrate
Tx = ? (formula)
Tx = FL - ER
Secretion vs. Reabsorption:
If the transport rate (Tx) is positive, then some material was ___________.
Reabsorbed (removed from the filtrate)
Secretion vs. Reabsorption:
If the transport rate (Tx) is negative, then some material was ___________.
secreted (added to thhe filtrate)
Fractional Excretion is the ratio of excretion rate over _________.
filtered load
FE = ER / FL
Fractional excretion:
If FE < 1, then some material was __________.
Reabsorbed (opposite of transport rate: negative –> secretion)
Fractional excretion:
If FE > 1, then some material was __________.
secreted (added to the filtrate) (opposite of transport rate which if positive –> reabsorption)
Tubular reabsorption:
Name 2 routes of reabsorption though the tubular epithelial cells
Paracellular (between cells) - “leaky” epithelium
Transcellular (through cells) - crosses 2 barriers –> luminal __membrane (apical) and basolateral membrane
About ____% of Na+ (active) and water (passive;solute-linked) are absorbed in the proximal tubule.
Loop of henle has ____% (Na+) and ___% (water) absorption
The distal and collecting tubes have ____% Na+ and ___% water reabsorption
Proximal tube: Na+: 67% (active) Water: 65% (passive; solute-linked)
Loop of henle: Na+: 25% (active) Water: 15% (passive; solute-linked)
Distal and Collecting Tube: Na+: 8% (active; aldosterone) Water: 20% (passive; NOT soulte-linked; regulated by ADH)
In the proximal tubule, LOH, and the distal and collecting tubules, Na+ reabsorption is _________. (active/passive?)
Active
Water reabsorption in the proximall, LOH, and distal and collecting tubules is _________. (passive/active?)
passive
By what mechanisms does Na+ enter the proximal tubule fromt the PTC? How does it leave the cell?
Cotransport with organics and a **Na+/H+ ion exchanger (NHE) **(Na+ reabsorption and H+ secretion)
Na+/K+ ATPase and through cotransport with HCO3-
How does Cl- enter the PTC?
It travels through paracellular routes (inbeetween cells)
What 3 hormonal and neural influences affect Na+ reabsorption by the PT? What are the effects?
Angiotensin II - stimulates Na+/H+ exchange across apicl membrane –> stimulates Na+ reabsorption and H+ secretion
Sympathetic nerve activity - stimulates Na+ reasorption
Parathyroid hormone - inhibits Na+-phosphate cotransport –> increases urinary escretion of phosphate
TF/P ratios for freely filtered solutes are ___ in Bowman’s space (proximal tubule).
Water and solute are ________ along length of PT.
Inulin ratio (not secreted or reabsorbed) shows that the volume of tubule fluid is ___________.
Reabsorption can produce very _____ TF/P ratios.
Note that the osmolarity _________.
1
reabsorbed
decreasing
small
doesn’t change
TF/Px Ratio
If TF/Px = 1.0, then reabsorption has been ______________ to the reabsorption of water.
If TF/Px < 1.0, then reabsorption of the substance has been ______ than water.
If TF/Px > 1.0, then reabsorption of the substance has been ______ than water OR there has been net ________ of the substance.
TF/P(inulin) is used as a marker. Since it is only filtered, it’s concentration in the tube is solely detemined by the movement of ________.
exactly proportional
greater
less; secretion
water
Tubular Maxima
Tubular maximum (Tm) - maximal rate at which a renal transport system can _________ a __________.
The rate is limited due to saturation of ________ ________ ________.
Below Tm, all of the filtered load is ___________.
The portion of the load above Tm is __________.
Tm’s are foudn primarily in the _________ ________.
transport; solute
membrane transport proteins
reabsorbed
excreted
proximal tubule
The threshold for the glucose tubular maximum is the plasma concentration where glucose first ________________. Depends on ______.
“Splay” - due to _______ of nephrons. Not all nephrons have the same Tm.
appears in urine
GFR
heterogeneity
The Effect of Changing GFR on Threshold
Decreasing the GFR _________ (increases/decreases) the threshold.
decreases
Other Solutes with Tm’s
- Sugars (fructose, galactose)
- Amino acids
- Metabolic intermediates
- Phosphate ions
- Water-soluble vitamins
- Proteins peptide
Osmotic Diuresis - Proximal Tubule
Excess reabsorbed solute (e.g. mannitol) __________ osmotic water flow from lumen to basolateral spaces.
Causes Na+ ________ into lumen of tubule w/ increased Na+ and water loss (diuresis).
Causes _________ loss of water and electrolytes in urine.
inhibits
back-diffusion
increased
Osmotic Diuresis can result in a rapid loss of _____ and _____.
Can accompany;
- a high filtered load of _____
- when glucose load _______ Tm in diabetic patients (excess glucose in filtrate)
________, a non-reabsorbed carbohydrate can be given IV to induce an osmotic diuresis.
sodium and water
urea
exceeds
Mannitol
Tubular Secretion
Two routes?
Two main transport mechanisms present…**VERY NON-SPECIFIC **
- One for organic ______
- One for organic ______
Commpounds secreted
- metabolites
- waste products
- foreign chemicals (tagged by liver e.g. with glucuronic acid or sulfate)
Paracellular, transcellular
- organic cations
- organic anions
Secretion of Organic Anions - PAH
Draw out the secretion of organic anions - PAH
- Organic anions are secreted via _______ _______ transport.
- PAH is taken up into the celll in exchange for _______
- PAH leaves the cell on the _______ side via a ________.
Tertiary active transport
alpha-KG
apical; PAH-anion antiporter
Clinical Tidbits - Anion Transport
All organic anions compete for the same _______.
Thus, elevated _______ _______ of one anion will inhibit the secretion of others.
Ex: infusion of PAH inhibits the secretion of PCN, thus _________ PCN’s half-life.
During WWII, when PCN was in short supply, ________ were infused to extend the drug’s therapeutic effect.tranpo
transporter
plasma levels
extend
