Term
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Definition
Freely permeable to water
Impermeable to Na+, Cl- |
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Term
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Definition
Always impermeable to water
Thin segment: passive NaCl reabsorption
Thick segment: active Na+, K+, 2Cl- cotransport |
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Term
Transport in thick ascending limb of Henle's loop:
- what transporters/channels are on the basolateral membrane?
- apical membrane? |
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Definition
- Na+/K+ ATPase: sets up conc gradient
K+/Cl- cotransporter (out of cell)
K+, Cl- channels (out of cell)
- Na+/K+/2Cl- symporter brings these ions into the cell
K+ is secreted through "leaky" channels |
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Term
Transport in first half of distal convoluted tubule
- what transporters/channels are on the basolateral membrane?
- the apical membrane? |
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Definition
- Na+/K+ ATPase sets up the concentration gradient
K+ and Cl- are reabsorbed through channels
- Na+/Cl- cotransporter reabsorbs NaCl
K+ channel secretes K+ into tubular urine
K+/Cl- cotransporter secretes these ions into the tubular urine |
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Term
What is the major site of physiological control of salt and water balance in the nephron?
What three hormones affect this balance at this site? |
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Definition
Late DCT and collecting duct
ALDOSTERONE stimulates Na+ reabsorption, K+ secretion, H+ secretion
ANP (atrial natriuretic peptide) inhibits Na+ reabsorption (medullary collecting duct)
ADH (VASOPRESSIN) stimulates H2O reabsorption |
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Term
Transport in late DCT, collecting duct
- what transporters/channels lie on the basolateral membrane?
- the apical membrane?
what is the function of the cell that contains these carriers? |
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Definition
- Na+/K+ ATPase
K+ channel (reabsorbs)
- Na+ channel (reabsorbs)
K+ channel (secretes)
PRINCIPAL CELLS reabsorb NaCl and secrete K+. Na+ reabsorption generates a lumen-negative voltage which provides the driving force for Cl- reabsorption across the paracellular pathway |
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Term
| If more Na+ is being reabsorbed in the DCT, more __ will be secreted. |
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Definition
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Term
| How does aldosterone increase Na+ reabsorption in the collecting duct? |
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Definition
Aldosterone crosses the cell membrane, gets into nucleus, activates transcription of mRNA that encode proteins involved in Na+ reabsorption,
mRNA provides template for synth of Na+ channels (placed in luminal membrane) and
also increases the amount of Na+/K+ ATPases on the basolateral membrane
Aldosterone increases the cells' capacity to reabsorb Na+ by stimulating the creation of more Na+ channels on the luminal membrane and more Na+/K+ ATPase ion pumps on the basolateral membrane |
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Term
What is ADH's role in physiological regulation of water reabsorption?
Which cells are responsive to ADH? |
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Definition
ADH binds to receptors on PRINCIPAL CELLS -> adenylate cyclase produces cAMP -> activates cAMP kinase A --> creation of aquaporins in the luminal membrane that allow reabsorption of H2O via passive diffusion
So ADH increases H2O absorption of the collecting duct cells; water moves across apical membrane, can move across basolateral membrane by a number of ways
It's the permeability of the luminal membrane that's under physiological control |
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Term
Where is solute concentration greatest in the nephron?
What type of fluid (in terms of solute concentration relative to plasma) is inside the cortex? |
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Definition
INNER MEDULLARY INTERSTITIAL FLUID
When substances are reabsorbed, they're first transported into interstitial fluid, from there substance is taken up by peritubular capillaries/vasa recta and returned to systemic circulation
Cortex - isotonic fluid (same osmolality as plasma)
Solute conc gradient is generated by countercurrent multiplier mechanism |
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Term
Describe the countercurrent multiplier mechanism
What are its 3 components? |
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Definition
Concentrates solute in medullary interstitium
Kidneys excrete highly concentrated urine to conserve water during periods of dehydration
This mechanism requires integrated function of 3 components:
- Descending, ascending limbs of Henle’s loop (generate solute gradient)
- Vasa recta capillaries (preserve solute gradient)
- Collecting ducts (use solute gradient to retain water) |
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Term
Solute concentrations during antidiuresis
how do solute concentrations inside the nephron (and in the interstitial fluid) change as we move down towards the collecting duct?
where along the tubule are H2O and NaCl reabsorbed? |
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Definition
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Term
During ANTIDIURESIS, what happens in:
- the descending limb?
- ascending limb?
- distal convoluted tubule?
- cortical collecting duct?
- medullary collecting duct?
- how does interstitial fluid osmolarity change as we move down into the inner medulla? |
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Definition
- tubular osmolarity i/c, H2O is reabsorbed
- tubular osmolarity d/c, NaCl is reabsorbed
- osmolarity d/c, NaCl is reabsorbed
- osmolarity i/c, H2O and NaCl are reabsorbed
- osmolarity i/c, H2O and NaCl are reabsorbed
*NaCl is reabsorbed via active transport, H2O via passive diffusion*
- it INCREASES (is isotonic to tubular osmolarity in the bend of Henle's loop, and as it exits the medullary collecting duct, ~1400) |
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Term
| What is the effect of ADH on urea? |
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Definition
ADH promotes urea reabsorption from the inner medullary collecting duct
- by the time we exit the PCT, 50% of the filtered urea has been reabsorbed
- it is completely re-secreted by the time we reach the DCT
- 80% is reabsorbed by the time we exit the collecting duct; 50% back to the ascending limb, 30% returns to the systemic circulation
ADH recycles urea! |
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Term
| How is physiological control exerted during antidiuresis? |
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Definition
| ADH makes the collecting duct epithelium highly water permeable. Water is reabsorbed in this segment, and a low volume, highly concentrated urine is excreted |
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Term
How is physiological control exerted during water diuresis?
What is the osmolarity in the medullary interstitium during diuresis, compared to antidiuresis? |
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Definition
Low ADH
A high volume of dilute urine is excreted
Collecting duct epithelium is impermeable to water
Lower solute concentrations in the medullary interstitium |
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Term
Luminal osmolality: diuresis vs. antidiuresis
How does ADH affect osmolarity in the loop of Henle, distal tubule, collecting tubule & duct, and urine? |
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Definition
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Term
| what is the contribution of the vasa recta to the osmotic gradient and the countercurrent multiplier? |
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Definition
VASA RECTA MAINTAIN SOLUTE GRADIENT
H2O and NaCl are exchanged between descending and ascending limbs
Solute gradient is maintained while small amounts of NaCl and H2O are returned to systemic circulation
the vasa recta remove more H2O, solute from the medulla than they bring in and return that reabsorbed material to the systemic circulation |
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Term
Obligatory water loss
How much waste does the body make?
What is maximum urine excretion?
What is minimum urine excretion to eliminate waste?
what if the kidneys couldn't concentrate urine above plasma solute concentration? |
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Definition
600 milliosmol/day
1200 mOsm/L
(600 mOsm/day)/(1200 mOsm/L)= .5 L/day
(600 mOsm/day)/(300 mOsm/L)= 2 L/day |
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Term
Osmolar clearance (Cosm)
when kidneys excrete excess solute, Cosm ________.
when solute is retained, Cosm __________. |
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Definition
Cosm = Uosm x V/Posm
when kidneys excrete excess solute, Cosm increases
when solute is retained, Cosm falls |
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Term
Free water clearance (CH2O)
If Uosm < Posm, CH2O is ____; pure water is ______
If Uosm > Posm, CH2O is ____; pure water is ______
How does ADH affect CH2O? |
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Definition
CH2O is excretion of water in excess of amount needed to excrete isosmotic urine, i.e. clearance of solute-free water by the kidneys
CH2O = V - Cosm
If Uosm < Posm, CH2O is positive; pure water is cleared
If Uosm > Posm, CH2O is negative; pure water is retained
ADH lowers free water clearance |
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Term
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Definition
The fraction of the filtered amount of a substance that is excreted in urine
Fex = (Ux • V)/(Px • GFR) = (Ux • Pcr)/(Px • Ucr) |
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