Reabsorption/Secretion in the Proximal Tubule Flashcards
How many times is the entire plasma filtered through the glomerulus every day?
60 times, equivalent to 5 times for whole body fluid
What percentage of reabsorption of glomerular filtrate is absorbed through the proximal tubule?
2/3rd
What is the primary role of the proximal tubule?
reabsorbtion of most of the filtered water and solutes
What is the gold standard for mesasuring GFR?
Inulin
Why is inulin the gold standard for measuring GFR?
It is neither reabsorbed or secreted in the tubules.
Is reabsorption in the proximal tubule is iso-osmotic?
yes
what are the major solutes that contribute to the isotonic reabsorption in the proximal tubule?
sodium, choride, bicarbonate
Does the concetration of inulin decrease or increase compared to the distance from the glomerulus?
increase
What absorption requires the most amount of energy?
sodium, using active transport, accounting for the majority of oxygen consumption in the kidney
where does sodium reabsorption occur?
throughout the entire nephron,
Is the concentration of sodium high or low in the tubular lumen, tubular epithelial cells and the renal interstitium?
high in tubular lumen
low in the tubular epithelial cells
high in the renal interstitium
In the tubular epithelial cell, where is the only place the na/k atpase pump located?
on the basolateral membrane, near the renal interstitium
what are the two results and overall purpose of the nka pump?
- decrease the intracellular sodium conc.
- decreased membrane potential
allows for the driving force for na absorption
why does sodium flow through the apical membrane without energy?
it’s flowing down it’s electrochemical gradient
the passive diffusion of sodium down it’s electrochemical gradient allows for what?
a passive, coupled transport of other solutes from the renal epithelial cell into the lumen for reabsorption. either through antiport or cotransport
what is the only quantitatively important substance whose transport is directly coupled to metabolic energy in proximal tubule?
sodium, all others are secondarily related.
what solutes are related to metabolic energy through secondary means?
bicarbonate, glucose, amino acids, organic acids
Na reabsorption is coupled with an equivalent movement of what to allow ofor electroneutrality?
anions
What drives the movement of chlorine out of the tubule?
the rapid na reabsorption leaves the lumen with a -5mv charge. This charge this pushes the chlorine into the renal interstitium.
Explain the general idea behind a leaky epithelium of the proximal tubule.
it favors anion transport via paracellular space. leaky in the context of allowing more anions to move on purpose…
In the straight proximal tubule, how does the absorption of chlorine change?
chlorine absorption is reduced.
what is absorbed more rapidly within the straight proximal tubule than chlorine?
hco3-, outcompetes the chlorine
What drives water reabsorption?
the osmotic gradient, facilitated by the lekay epithelium with high hydraulic conductivity (high kf value).
What does massive solute reabsorption lead to in terms of osmolarity?
slight decrease in osmo of tubular luminal fluid and increase in interstitial fluids
what is the name of the type of corce that is involved in capillary uptake of fluid from the interstitium?
starling forces
what are starling forces?
acoss the peritubular capillary endothelium that drives rapid uptake of fluid from the interstitial compartment
what three pressures allow for uptake of fluid into the capillaries from the interstitial spaces? aka peritubular factors
positive interstitial fluid pressure
low hydrostatic pressure in peritubular capillaries
high oncotic pressure in peritubular capillaries
In the proximal tubule, absorption of mculs is iso-osmotic but it is selective?
yes, not all mculs are absorbed to the same extent
Is bicarbonate preferred in over chlorine for absorption in proximal tubule?
yes
where is H+ actively secreted into?
pt, dt, cd
how is proton secretion regulate in pt?
at the apical membrane, na-h exchanger (driven by na gradient)
on the basolateral membrane, hco3 is secreted into interstitial space, through the hco3-na cotransporter
how is glucose reabsorbed?
it is through a cotransporter na-glucose
what are the names of the two na glucose co transporters?
sglt1 sglt2
what is the threshold level for glucose?
200-220 mg/dl
what is the transport maximum?
where secretion rate d.n change.
compared to threshold, which is when you’re going to start seeing gluocse in the urine.
what does glucosuria cause?
thirst and nocturia (due to osmotic diuresis)
what are the causes of glucosuria?
pregnancy
diabetes mellitus
renal glucosuria (mut in sglt1 and sglt2)
what is amino acid reabsorption coupled to
soidum
where is the sodium-amino acid transport located on the epithelial cells?
apical membrane
what three conditions have high protein excretion?
multiple sclerosis
hemoglobinemia
myoglobinemia
in what condition will you have excessive excretion of organic acids?
diabetic ketoacidosis
is phosphate never excreted or continuously excreted in the urine? why?
continuously, because the threshold for phosphate is very low
what are the two reasons chlorine is passivley absorbed?
concentration gradient created by water reabsorptino
electrochemical potential gradient created by sodium reabsorption
what are the absorption characteristics of diuretics?
they are freely filtered and not reabsorbed, can increase osmolarity and cause diuresis
what is mannitol
a diuretic, not produced or metabolized in the body, no transporters for mannitol
