urinary conc. and dilution, Lect 5 Flashcards
when body fluids are hypoosmotic, the kidneys exrete urine. What is the limit?
a dilute urine, (as low as 50 mOsm/L - water diuresis)
when body fluids are hyperosmotic, the kidneys exrete urine. What is the limit?
- water deficit
- concentrated urine (to 1200 mOsm/L) - antidiuresis
are the kidneys able to regulate water excretion independently of solute excretion?
yes
how much sodium reabsorbtion and water reabsorbtion occur in the loop of henle? active or passive?
- sodium: 25%, active
- water: 15%, passive, solute linked
how much sodium reabsorbtion and water reabsorbtion occur in the distal and collecting tubule? active or passive?
- sodium: 8%; active
- water: 20%; passive
active Na2+ reabsorption in the distal and collecting tubule is regulated by
aldosterone
passive water reabsorption in the distal and collecting tubule is regulated by
ADH
what creates a large gradient in the instertitial fluid from the corticomedullary border to the top of the papilla by multiplying a small local gradient created by the epithelium of the loop of henle
the counter-current multiplier
what is the purpose of the osmotic gradient from cortex to medulla in the interstitial space
used to remove water from urine in the collecting duct
the descending limb is to water but to NaCL
- very permeable to water
- no active transport of NaCl
the ascending limb is to water but to NaCl
- strucutre: thin to thick
- active reabsorbtion to NaCl occurs (lumen looses NaCl)
- impermeable to water
what happens to fluid as it flows down the descending limb
progressively concetrated
what happens to fluid as it flows up the ascending limb
progressively diluted
- NaCl is actively reabsorbed from lumen into capillary
what is the largest osmotic gradient that can be maintained across the wall of the ascending limb?
- you can only have a 200 mOsm/L difference between concentration in the tubule and that in the interstitial fluid
- this is due to back diffusion; NaCl will flow back into the tubule (lumen) if greater than a 200 mOsm/L difference is created
which part of the nephron is described as the countercurrent multiplier
Loop of henle
sodium potassium ATPase is always on which side of the tubule cell
basolateral side -> towards interstitial fluid
what is the essential component of the countercurrent multiplier
active transport
Describe the NKCC2 transporter
- Na2+, K+, 2 Cl- transporter on the luminal aspect of the tubule cell
what stimulates NKCC2 transporter
ADH
loop diuretics (furosemide (lasix)) has what effect on NKCC2 transporter
- blocks this transporter
- because of this kidney cant create corticopapillary gradient
what is characterized by hairpin loops
vasa recta
as blood flows down the capillary into papillary part of kidney, what happens to NaCl and water in the blood
- NaCl diffuses in and H2O flows out
- as blood flows up the capillary, the reverse occurs
function of vasa recta and countercurrent exchanges
protect the ISF gradient (corticopapillary gradient)
vasa recta and countercurrent exchanges is an active or passive process
entirely passive
what is urea generated by
hepatic protein catabolism
what is the importance of urea in the medullary interstitial fluid
contributes to hyperosmotic renal ISF and to concentration of the urine
- people on low protein diets cannot concentrate urine as well (due to reduced urea formation)
What happens to urea in the medulla of the kidney
it is recycled: reabsorbed and secreted
permeability to urea of the unner medullary portion of the collecting duct is controlled by
ADH
What transporters are present in the early distal convoluted tubule
- the Na+, K+, 2Cl- transporter (NKCC2) is NOT present
- there is a NaCl transporter (NCC) in the luminal membrane
- symport
describe what happens to NaCl and water in the early distal convoluted tubule
- NOT permeable to water
- has a transporter for NaCl (NNC)
- thus referred to as a Diluting segment
The NaCl transporter (NCC) in the early distal convoluted tubule is blocked by
Thiazide diuretics
The Late distal tubule and collecting duct are composed of what two cell types
- Principle cells
- Intercalated cells (type A)
what are the function of the Priniciple cells in the Late distal tubule and collecting duct
- reabsorb Na+
- secrete K+
- reabsorb Na+ in exchange for K+
- **site of aldosterone action
- ***this depends on the Na+, K+-ATPase in the basolateral membrane and apical channels for both ions
aldosterone acts on which cell types . MOA?
- Principle cells in the Late distal tubule and collecting duct
- MOA: increases the number of apical Na+ channels (ENaC) and Na+, K+ ATPase
What is the function of the Intercalated cells (type A) in the Late distal tubule and collecting duct
- secrete H+
- via H+-ATPase
- reabsorb K+
- via H+, K+ ATPase
water and urea permeability of the collecting duct is controlled by
vasopressin (ADH)
- **the collecting duct is impermeable to water and urea in the absense of ADH
MOA of ADH on water and urea permeability in the collecting duct
- ADH causes the insertion of aquaporins into the apical membranes of collecting duct cells via cyclic AMP messenger system
- ADH released when body fluids become concentrated: want to reabsorb water from urine
is the collecting duct permeable to water in the absence of ADH
No
- ADH create aquaporins
fluid in the early distal tubule has what osmolarity
hyposmotic
- no water reaborption
- some NaCl reabsorption
give osmolarity status of descending limp of LOH, ascending limb of LOH, early distal tubule
- descending limp of LOH: hyperosmotic
- ascending limb of LOH: hyposmotic
- early distal tubule: hyposmotic
why is the corticopapillary gradient strong when a person is dehydrated
- ADH allows for Na, K+, 2Cl- transporter which gives the intersitium more ions
- urea permability from lumen into interstitium
When ADH is present, what determines the osmolarity of the urine in the collecting duct
the osmolarity of the interstitial fluid because water flows down concentration gradient
when ADH is high, water is , and urine becomes
- water reabsorbtion is high
- urine becomes hyperosmotic
when ADH is low, water is , and urine becomes
- water is not reabsorbed
- urine is hypoosmotic
