Muster: Loop of Henle, Distal Tubule, Collecting Duct Flashcards
The loop of Henle dives into what part of the kidney?
Medulla
The loop of Henle reabsorbs what % of filtered sodium?
25 %
Is more sodium or water reabsorbed in the Loop of Henle?
Sodium is absorbed in excess of water! Allows for excretion of urine with osmolality that is different from the plasma (so more H2O stays in the Loop!) Part of the loop is not permeable to water.
What is the descending limb permeable to?
ONLY water! Solute cannot leave!
What is the osmolarity of fluid that enters the descending limb?
300 mOsms
Which part of the loop of Henle is not permeable to water? why?
Thick ascending limb.
It is composed of huge, fat, cuboidal cells
What special pump is found in the Thick Ascending Limb of the Loop of Henle?
NKCC pump
Na+ K+ Cl- Cl-
What is the osmolarity of the fluid in the bottom of the loop that is in the deep medullary space?
1400 mOsms
What is the osmolarity of the fluid in the thick ascending limb?
100 mOsms
What does fluid enter after it leaves the thick ascending limb?
Macula Densa (part of the early distal tubule)
Where does the fluid go after the macula densa?
Distal convoluted tubule and then the collecting duct
The NKCC pump uses secondary transport dependent on which ion?
Sodium
sodium is going down its gradient while K+ and Cl- are going up their gradients
What channels ARE NOT present in the thick ascending limb?
Aquaporins
What % of the filtered load of sodium does the NKCC pump reabsorb?
20 %
What is the rate limiting ion in the NKCC pump?
Choride
The affinity for Na+ and K+ is very high!
What ions get transported paracellularly in the thick ascending limb?
Na+
Ca2+
Mg+
What disease is caused by genetic mutations in any of the transporters in the Thick Ascending Limb?
Bartter Syndrome
What is the fate of Chloride after the NKCC pump?
It is reabsorbed into the peritubular capillary
What is the fate of Potassium after the NKCC pump?
Some is reabsorbed into the peritubular capillary and some is filtered back out into the lumen.
Describe Bartter Syndrome.
Genetic mutation in any transporter in thick ascending limb.
Can be seen early or later in life.
Growth retardation and mental retardation.
Volume depletion w/ low BP.
Hypokalemia.
Metabolic Acidosis.
Normal or elevated urinary calcium excretion.
What drug blocks the NKCC pump?
In what conditions would you use it?
Furosemide
CHF, Hypertension, Hypernatremia etc.
Are there aquaporins in the distal tubule?
NO. So it contributes to urinary dilution!
What % of filtered sodium is reabsorbed in the distal tubule?
5 %
What transported can be mutated in the distal tubule to cause disease?
What is the disease?
NaCl symporter.
Gitleman Syndrome
Describe the key features of Gitleman Syndrome.
Normal BP Metabolic Alkalosis Hypocalciuria Hypomagnesemia Hypokalemia
What drug works in the distal tubule to block the NaCl transporter?
Hydrochlorothiazide
What is the sodium reabsorption in the collection duct?
Explain.
Variable! 0-5 %
The first area that is directly controlled to determine urinary electrolyte concentration.
Variable permeability to water too!
What are the 2 primary cell types in the collecting duct?
Principal cell
Intercalated cell
What is the role of the Principal cell?
Salt, Chloride, and Potassium reabsorption/excretion
Which channel is present on the principal cell to bring in Sodium?
ENaC (epithelial Na+ channel)
What channel is present on the principal cell to remove K+?
ROMK (renal outer medullar K+ channels)
What are the %’s of sodium reabsorption for the proximal tubule, Loop of Henle, Distal tubule, and collecting duct respectively?
65 % Proximal
20 % loop
5 % distal
0-4.9 % collecting duct
What is the filtered load in mM/day?
25,000
If we reabsorb 99.9 %, what amount is excreted?
.1 % = 25 mM
What is the primary mechanism of controlling salt reabsorption in the collecting duct?
Aldosterone
What cells release Renin?
Juxtaglomerular cells
What do sympathetic nerve fibers attach to?
Afferent arteriole
What 3 things stimulate renin release?
Sympathetics (NE)
Decreased stretch in afferent arteriole
Decreased chloride delivery to macula densa
What are the primary actions of Angiotensin II?
Stimulates aldosterone
Systemic vasoconstrictor
Stimulates proximal tubule reabsorption of Na+
Increases sympathetic activity
What does aldosterone bind to (its receptor)?
Steroid response element (SRE)
What is the result Aldosterone binding SRE?
Increase transcription, translation, and insertion of the 3 channels on the principal cell (Na+/K+ ATPase, ENaC, ROMK)
What property of aldosterone allows it to cross freely through the cell?
Lipophilic
What are the stimuli for aldosterone release? What does this cause?
Stimuli: Low sodium, High potassium
Causes: Increased sodium reabsorption, potassium secretion
What is Little’s Syndrome?
Increase in ENaC channels that can’t shut off!
What is Type 1 pseudo-hypo aldosteronism?
Decrease in ENaC function
What is the equation for fractional excretion of sodium?
Excreted Na/Amount Filtered x 100
What is the Equation for Clearance of Na+?
Excretion rate/[plasma]
In what state is aldosterone stimulated?
low salt state
Why would a genetic mutation in the distal tubule suck less than a genetic mutation in the thick ascending limb?
Distal tubule only reabsorbs 5 % of sodium whereas the thick ascending limb reabsorbs 20 % of it.
Equation for Filtered Na load:
GFR x Serum sodium
Equation for Na excretion rate:
Urine sodium x Total urine output
