Mechanisms to Adjust Urine Conc Flashcards
TF:U = 1
The concentration of the substance in the tubule is the same as the plasma
The TF:U greater than 1
Substance is reabsorbed to a lesser extent than water
TF:U less than 1
Substance is reabsorbed more avidly than water
The loop of henle descending limb thin segment is permeable to? But impermeable to what
Water; NaCl which becomes more concentrated during descent
The primary cilia does what
Senses changes in osmolarity
The loop of henle ascending limb is permeable to what? Impermeable to what
NaCl (serves to dilute gradient); water
What is the main transporter in the thick ascending limb that we care about
NKCC and NaH antiporter
What ion drives luminal electrical voltage
K
What diuretics act on the thick ascending loops
Loop diuretics
When the luminal positive potential is reduced absorption of what is affected
Mg, Ca
The early segment of the distal tubule is permeable to what? Impermeable?
Na, Cl, Ca; water
The late segment of the distal tubule contains what cell types
Principal and intercalated
What do principal cells do
Na and water reabsorption; K secretion
What do intercalated cells do
Acid/base balance
What diuretics act on the early distal tubule and what transporter do they act on
Thiazide diuretics; NCC transporter
What diuretics act on the late segment DT principal cells?
Aldosterone antagonists and ENaC
What is more specific and binds tighter than spironolactone
Eplerenone
What diffuses down its gradients in the late segment DT of principle cells
Na, K, Cl
α intercalated cells function to change pH by doing what
Secrete H and resorb HCO3 during acidosis
Late segment DT β intercalated cells function in what
Alkalosis
Bicarb is secreted; H reabsorbed
What does water and chloride normally follow in the nephron
Na
Where is Cl active reabsorption
NaCl co-transporter (distal tubule)
Na-K-2Cl co-transporter (TAL)
What inhibits NaCl co-transporter
Thiazide in the distal tubule
What inhibits the NKCC co-transporter
Loop diuretics in the thick ascending loop
Na reabsorption causes what
Water reabsorption and increased lumen negative potential, increased luminal Cl concentration, increased luminal urea concentration
Which causes passive Cl and urea reabsorption
What 3 spaces are regulated independently to concentrate urine
Tubular space, vascular space, interstitial space
What two things function to concentrate the urine
Counter current multiplier and exchanger
What is the single effect
NaCl leaves the ascending loop where water is impermeable
What is fluid flow
Descending limb and collecting duct leak water to try and dilute the interstitium
What determines the size of the gradient in the nephron
Length of the loop of henle
The passive reuptake of water from interstitium is called
Countercurrent exchange
What are the transporters of urea in the medullary CD
UT-A1 and UT-A3
What are the urea transporters in the thin limb
UT-A2
What are the urea transporters activated by
ADH
If you eat high protein what is the urea conc in the medulla? Low protein?
High urea, low
What is the location in which urea is reabsorbed mostly
thick ascending limb
What 2 things lead to the salty medulla
NaCl and urea
How do we calculate obligatory urine volume
Minimum solute exretion per day / max urine concentrating ability
Antidiuresis requires high ____ and high ______ of the renal medullary intersitial fluid
ADH; osmolality
What is the contribution of urea and NaCl the hyperosmolality of the medulla
50/50
High levels of ADH leaves to high levels of permeability of what
Water at the collecting duct and NA in the thick ascending limb
An increase/decrease in blood flow dissipates the medullary gradient
Increase
Reduced O2 causes what in the medullary interstitium
Reduced medullary gradient
What 2 things cause a decrease in the medullary gradient
Decreased blood (O2 reduction) and increased vasa recta flow
Where does ADH start changing the Osm
Medullary collecting duct on
How do you calculate osmolar clearance
U_osm * V / P_osm
How do you calculate free water clearance
C_h2o = V - C_osm
When C_h2o is negative? Positive?
Excess solute removed and water is conserved; water is being excreted forming dilute urine
How do you calculate fractional excretion
Clearance_x / GFR
What does it mean when fractional excretion is greater than 1? Less than?
Secreted; reabsorbed
What if the fractional excretion of Na is below 1%? Above 2?
Pre-renal; intra or post renal
What does SIADH result in
Euvolemic hyponatremia
What causes SIADH to give you euvolemic hyponatremia
ADH is secreted when it isn’t supposed to —> compensatory mechanisms —> volume and Na excreted
What are the possible causes euvolemic hyponatremia
SIADH, COPD, malignancy
What are some common causes of hypervolemic hyponatremia
CHF, renal impairment, cirrhosis
What is central diabetes insipidus
Deficient secretion of ADH from hypothalamus or pituitary
What is nephrogenic diabetes insipidus
Lack of renal response to ADH
What are the symptoms of diabetes insidpidous
Polyuria, polydipsia, polyphagia
How do you differentiate diabetes insipidus cases
ADH challenge test
Inject ADH and see if the body responds appropriately
