Sweep 1.3 Flashcards
Reabsorption in the proximal tubule
1. Glucose and amino acids are rebsorbed with
Na+ using symporters
Reabsorption in the proximal tubule
2. Active transport on ——–, keeps intracellular —– low
basal side
Na+
Reabsorption in the proximal tubule
3. Water (and solutes) move via ——–; keeps the osmolarity of the tubular fluid —-
paracellular transport
constant
Reabsorption in the proximal tubule
4. Na+ reabsorption also occurs in conjunction with bicarbonate reabsorption using a ———-
Na+/H+ antiporter
reabsorption is not direct……
H+ secretion = HCO3- reabsorption
To summarize: by the end of the proximal tubule –
K+ and divalent cations reabsorbed by solvent drag
bicarbonate reabsorbed due to activity of Na+ / H+ transporter
In the ascending thick limb (ATL; see diagram at right), fluid is diluted via
Na+ K+ 2Cl- symporter in apical membrane
Na+ K+ ATPase in basolateral membrane
ascending thick limb
paracellular transport of monovalents and divalents NOT due to
solvent drag. Tubular fluid becomes positive when Cl- reabsorbed so cations diffuse along an electrical gradient
ATL
Fluid leaving loop is ——–, but the renal countercurrent mechanism has established an osmotic gradient required for formation of hyperosmotic urine. Concentration of the tubular fluid will occur in the collecting duct if antidiuretic hormone (ADH/vasopressin) is present.
hyposmotic
More NH4+ can be added to the urine by diffusion trapping.
Much of the NH4+ leaving the proximal tubule is
reabsorbed by the ascending limb of the loop of Henle
More NH4+ can be added to the urine by diffusion trapping.
NH4+ substitutes for———- and enters the interstitial fluid in the ——— where it is in equilibrium with NH3
K+ in the Na+K+2Cl- symporter
medulla
NH4+ is produced in the ———- by metabolism of glutamine. The NH4+ that is produced is transported into the ———– and the HCO3- moves into blood.
proximal tubules
tubular fluid
The peritubular capillaries are permeable to ——- so plasma osmolarity changes as the
NaCl and water
capillaries follow the loop, but the osmolarity of the blood leaving the kidney (to veins) is normal.
The initial segment of the distal tubule, reabsorbs ~8% of filtered NaCl via a————- and———–
Na+ Cl- symporter in apical membrane
Na+ K+ ATPase in basolateral membrane
There are two cell types in the collecting duct and late distal tubule
principal cells have
epithelial sodium channels (ENaC) that reabsorb Na+ and secrete K+
There are two cell types in the collecting duct and late distal tubule
Principal cells
K+ secreted due to
Na+ K+ ATPase activity in basal membrane
Principal cells
Na+ reabsorption drives
paracellular Cl- reabsorption
There are two cell types in the collecting duct and late distal tubule
intercalated cells involved with acid-base balance; can also
reabsorb K+
Hormonal regulation of blood volume -
ADH
Actions of ADH
increases the permeability of the late ———— to water by increasing ——— into the apical membrane (basolateral membrane is freely permeable to water)
distal tubule and the collecting duct
aquaporins
ADH
also increases permeability of
medullary collecting duct to urea
ADH
If ADH low (diuresis) –
solutes reabsorbed in distal tubule and collecting duct, but no water reabsorption; urine as dilute as 50 mOsm/kg H2 O 18L pee
If ADH high (antidiuresis) –
water reabsorbed as fluid passes through collecting duct; urine can be concentrated up to 1200 mOsm/kg H2O ½ L pee
Alcohol inhibits
ADH secretion**
How the system works…..
renin released in response to a drop in
perfusion pressure, decreased NaCl delivery to macula densa, or sympathetic input to juxtaglomerular cells
aldosterone from the adrenal cortex acts to increase ———— in the distal tubule and collecting duct by increasing ————
NaCl reabsorption
transport protein synthesis
Natriuretic peptides are hormones secreted when the
heart dilates (during volume expansion)
Natriuretic peptides
Atrial natriuretic peptide from the atria
Brain natriuretic peptide from the ventricles (first found in brain)
The effects of natriuretic peptides include
vasodilation of afferent arterioles
vasoconstriction of efferent arterioles
inhibition of renin (and aldosterone)
inhibition of ADH secretion
Natriuretic peptide
Net effect is to increase the
excretion of NaCl and water.
Why is potassium regulation important?
hyperkalemia will
depolarize Vm
hypokalemia will
hyperpolarize Vm
In the thick ascending limb have reabsorption of K+ by
Na+K+2Cl- symporter and paracellular transport (non-solvent drag)
In the late distal tubule and collecting duct
K+ secreted by
principal cells depending on ATPase activity, K+ gradient, and/or apical K+ permeability
Late distal tubule and collecting duct
—————- reabsorb K+ when potassium is depleted
intercalated cells
Cells of the proximal tubule detect ——– can alter ———— accordingly.
intracellular pH and
CA activity
Factors affecting excretion of potassium include
plasma [K+] - increased K+ stimulates
aldosterone release, and aldosterone increases Na+ K+ ATPases in principal cells
Factors affecting excretion of potassium include
flow rate of tubular fluid –
increased flow rate increases K+ secretion
-local response to bending of cilia
↑ flow —–> ↑ —— in collecting duct —> ↑ —– reabsorption —–> favors ↑ ———
Na+
Na+
K+ secretion
nonvolatile acids
must be neutralized with
HCO3-
nonvolatile acids
——— within tubular cells eliminates H+ and produces an HCO3- that is reabsorbed
ammonium production
Bicarbonate reabsorption begins in the ———, and —– of filtered HCO3- is reabsorbed here.
proximal tubule
80%
CA activity in the tubular epithelium produces H+ and HCO3-
H+ is secreted via ———-
also have ———— operating to secrete H+ (not illustrated)
Na+ / H+ antiporter
H+ ATPase pumps and H+/K+ ATPase pumps
HCO3- is transported/reabsorbed across
basolateral membrane
In the late distal tubule and the collecting duct CA activity in the ——— cells produces bicarbonate and H+
intercalated
Intercalated cells
H+ is secreted via an
H+ ATPase pumps and an H+/K+ ATPase pump (not illustrated)
A less common type of intercalated cell reverses the position of the
H+ and HCO3- transporters to the basolateral and apical membranes, respectively. These cells reabsorbs H+ and secretes HCO3- ; activity of this cell type is normally very low.
If the body is alkaline, the kidney must produce alkaline urine which requires
incomplete reabsorption of HCO3- (figure on right)
increase excretion of HCO3- by not neutralizing all the HCO3- that is in the tubular fluid
