Chapter 27 Flashcards
reabsorption is quantitatively ____
large
reabsorption is _____
selective
controlling reabsorption allows kidneys to regulate what
excretion of various solutes independently from one another
for a substance to be reabsorbed, what are the steps (what must be crossed to transport it?)
x
transcellular transport includes
diffusion and active transport
paracellular transport includes
diffusion
water moves by
osmosis
describe the steps of active transport of sodium
- Na enters cell due to electrochemical gradient
- Na transported out of cell (against the gradient) by Na-K atpase
- reabsorption completed withmovement from interstitial fluid into peritubular capillary
reabsorption of Na is governed by
hydrostatic and colloid osmotic pressure gradients
what helps keep the Na concentration
Nna-K ATPase
the amount of protein in filtrate is ____
low
why is it important for proteins to be reabsorbed?
because this low amount that is filtered adds up to a significant amount
what is the mechanism of protein reabsorption
pinocytosis; requires energy so this is active transport
once the proteins are inside the cell, cytosolic enzymes break them down into amino acids, the amino acids leave the cell via transporters and are returned to the blood
protein reabsorption mechanism: can it be saturated?
yes, in pathologic diseases you can have proteinuria
actively reabsorbed substances exhibit what
transport (tubular) maximum Tm
why is there an upper limit on how much of a particular substance can be actively transported from the tubular fluid in a given period of time
because a limited number of each carrier type is present in the cells lining the tubules
what is the transport maximum
when all the carriers specific for a particular substance are fully occupied
what is the renal threshold
the plasma concentration at which Ttm is reached and the substance starts to appear in the urine
what is the Tm of glucose
375 mg/min
what is the renal threshold for glucose
200-300 mg/dl
is glucose regulated by the kidney
the kidney does not maintain the plasma glucose in a specific range; not insulin dependent
how is this different from the Ph?
Ph is regulated by the kidney so Ph doesnt have to go over normal plasma concentration by much to have Ph excreted
what is the based law of conservation of mass
for any substance that is not synthesized or metabolized, the amount that enters the kidney in renal arterial blood is equal to the amount that leaves the kidney in renal venous blood plus urine
concentration =
mass/volume
what is renal clearance
the plasma clearance of any substance is defined as the volume of plasma completely cleared of that substance by the kidneys per minute (volume/minute)
clearance of substance is equal to
concentration of substance in urine x urine flow rate/ concentration of substance in plasma
what is more informative of function of kidneys than looking at composition of urine
measuring how effectively the kidneys are clearing
what is inulin
plant polysaccharide that is freely filtered and not reabsorbed, secreted or metabolized
iohexol clearance test
by measuring the plasma or serum disappearance of iodine follwoing IV dose of iohexol, GFRr can be estimated
RPF is equal to
PAH
Inulin
=GFR
Glucose
<GFR
PAH
> GFR
URrea
<GFR
H
> GFR
creatinine
=GFR
effect of reducing GFR by 50% on serum creatinine
serum creatinine increases, then levels off
a fall in GFR is followed by
an increase in plasma creatinine
the proximal tubules reabsorb about ______ of filtered _______
65%; sodium, chloride, bicarbonate, and potassium
proximal tubules reabsorb approximately all
filtered glucose and amino acids
the proximal tubules secrete ___________-
organic acids, bases, and hydrogen ions
review solute reasborption coupled to sodium
x
Na uptake into the cell of a proximal tubule is coupled with
either H or organic solutes like glucose, amion acids, P and lactate
Na-H antiporter
couples Na entry with H extursion
what is the source of the Hh
from carbonic anhydrase reaction
The H secretion results in absorption of
NaHCO3
Na-glucose symporter
Na and glucose enter cell together; glucose leave via glucose transporter on basolateral surface (GLUT)
Proximal tubule reabsorption is ______
isoosmotic
what is fanconi’s syndrome
an inherited disease that affects the proximal renal tubule (impaired Na, glucose, Ca, P, HCO3, and AA reabsorption; increased amount of solutes in the urine causes osmotic diuresis and inability to concentrate urine)
fanconi’s syndrome can be mimicked by
toxins and drugs that affect the proximal tubule and interrupt normal reabsorbtive functioning
_______ are secreted into PT
organic anions and cations
this includes what?
end products of metabolism and xenobiotics
secretion of these is important for what
removal of toxins and drugs
many organic compounds are protein bound. Why is this significant?
it means filtration alone will only remove a small proportion
the specificity of the transport mechanisms of organic anions and organic cations is _____
low
why is this significant
because compounds can compete for the same secretory pathway
competition for transport mechanisms between two cations or two anions can lead to what
drug toxicity
what is the only part of loop permeable to water
descending thin loop
drugs are _____ because they are not really filtered
actively secreted
because they are actively secreted, what occurs
must use a transporter
specifity for transports is
very low
descending thin segment of the loop of Henle permeability
highly permeable to water and moderately permeable to most solutes
mitochondria of descending thin loop
few mitochondria and little or no active reabsorption
thick ascending limb of the loop of henle reabsorbs about _____ of the filtered loads of ___________
25; sodium, chloride, and potassium, large amounts of Ca, bicarbonate, and Mg
what transporters/channels are present in the thick ascending limb
Na-K-Cl symporter (apical) K channel (apical) Na-H antiporter (apical) Vvoltage Na-K ATPase (basilateral)
Na-K-Cl symporter (apical)
Na and Cl gradient is to drive K into cell (against its concentration gradient)
K channel
recycles the K back into tubular fluid to drive the Na-K-Cl symporter
Na-H antiporter
Na reabsorption and H absorption
Voltage
positive charge in tubular fluid drives cation reabsorption
Na-K ATPase
Maintains low Na in cell thus providing a favorable gradient for Na entry
The loop reaborbs ______ of filtered NaCl
25%
the loop reabsorbs _____ of filtered water
20%
does the descending thin limb reabsorb NaCl
No because the gradient not favorable, no active transport
ascending thin limp functions in
passive reabsorption of NaCl (concentration gradient)
Thick ascending limb functions in
NaCl reabsorption by transcellular and paracellular pathways
the acending limb is referred to as the ______ segment
diluting
what is the net result at the end of the descending limb
[NaCl] increase in tubule fluid
why is the fluid in the ascending thin limb passive reabsorbed
the fluid delivered has increased [NaCl] and thus there is a gradient
what is the net result at end of ascending limb
[NaCl] decreases in tubule fluid- a “dilution effect”
what occurs in the distal tubule
dilutes or concentrates urine (fine adjustments to urine; where hormones take effect)
reabsorption of Na adn Cl occurs ____ in distal tubule
early
principal cells and ntercalated cells are in the _____
late distal tubule
Late DT is grouped with
collecting duct
what transports are in the early distal tubule?
Na-Cl cotransporter (apical)
Na-K ATPase (basolateral)
Cl Channel (basolateral)
Net osmotic effect of early distal tubule
continued dilution of urine
Na-Cl contransporter
Na and chloride entry
Na-K ATPase
Na leaves the cell
Cl channel
Cl leaves cell
Principal cells
reabsorb Na, Cl, and water; secrete K
Intercalated cells
Secrete H; Reabsorb K
permeability of late DT and CD to water is controlled by the concentration of
ADH
TOPICS OF COLLECTING DUCT
Fig. 27-11, 12, 10
Fig 27-13
Principal cells are the site of action of _____
aldosterone
late DT and CD is impermeable to ____
urea
water reabsorption controlled by
ADH concentrations
principal cells contain what
Na-K ATPase
Na channel
K channel
Water reabsorption
Na-K ATPase in principal cells
Keeps [Na] in cell low to facilitate entry of Na
Na reabsorption
K entry into cell
Na channel (principal cells)
Na entry into cell creates negative charge in tubular fluid
K channel (principal cells)
passive diffusion through channel from high [K] in cell to low [K] in tubular fluid
Water reasportion in principal cells
varies depending on ADH
Function of medullary collecting duct
NaCl Reabsorption
Permeable to Urea
Water Reabsorption, Controlled by ADH concentrations
study tables
4 of them
solute and water reabsorbed across _____
apical membrane
flow into interstitial space then into ____
capillary
some solute and water re-enter the _____
tubular fluid
proximal tubular and peritubular capillary reabsorption are affected by
peritubular capillary hydrostatic pressure or peritubular capillary colloid osmotic pressure (see chart)
knwo factors that can influence peritubular capillary reabsorption
x
aldosterone site of action
late DT and CD
Aldosterone effects
increase NaCl, H2O reabsorption, Increased K secretion (aldosterone can change K without changing Na and water, and vice versa)
agiotensin II site of action
PT, TAL, Late DT, and CD
Angiotensin II effects
Increased NaCl, H20 reabsorption
ADH site of action
late DT and CD
ADH effects
increased water reabsorption
atrial natriuretic hormone site of action
late DT and CD
atrial natriuretic hormone effects
decreased NaCl reabsorption
what are the stimuli for release of these hormones
renin, angiotensin, aldosterone
direct effects of angiotensin II to increase proximal tubular sodium reabsorption
see figure
what is the mechanism of ADHh
aquaporins are inserted on the apical side
Changes in GFR markedly alter the filtered load of ____
Na
what 2 mechanisms counter these changes so that there isnt a marked repsonse in Na excretion, which could disturb ECFV and blood pressure
- starling forces in the PT
2. filtred load of organic solutes
starling forces in the PTt
colloid oncotic pressure in peritubular capillary will increase with increased filtration fraction, thereby promoting greater reabsorption in the PT
filtered load of organic solutes
filtered load of organic solutes (like glucose and amino acids) will also increase with increased filtration fraction; since Na reabsorption is coupled to their reabsorption in PT, it promotes reabsorption of Na
_________ corrects GFR to also guard against too much Na excretion
tubuloglomerular feedback
_____ can be differentially absorbed (Ch. 30)
Na and Cl
what is the primary mechanism in renal regulation of acid-base balance
Net Cl excretion relative to net Na excretion; since sodium reabsorption is strongly related to renal regulation of ECFV
