Urine Concentration- Exam 4 Flashcards
What is the major controlling agent for water in the body?
ADH
Extracellular fluid must have a constant concentration of what?
Electrolytes and other solutes
What is solute concentration and osmolarity determined by?
Total amount of solute / volume of extracellular fluid
Changing extracellular water has significant effect on what?
Solute concentration and osmolarity
What is body water determined by?
Fluid intake (controlled by thirst) Renal excretion of water (controlled by changing GFR and tubular reabsorption)
If ECF solute concentration increases, kidneys hold onto water so ECF volume __________(increases/decreases), _________ECF solutes.
Increases, diluting
If ECF solute concentration decreases, kidneys excrete more water so ECF volume (increases/decreases), ________ ECF solutes.
decreases, concentrating
Assuming normal solute intake and metabolic production: what will happen to solute excretion each day? What will happen to total amount of solute in ECF?
Solute excretion will remain relatively constant each day.
Total amount of solute in ECF relatively constant.
What is adjusted each day to keep solute concentration of ECF constant?
Quantity of water excreted each day is adjusted
Increased ECF [solute]: ________ECF osmolarity
increased
What responds to changes in ECF osmolarity by changing ADH release?
Posterior pituitary
Increased ECF osmolarity results in what?
Increased release of ADH
Decreased ECF osmolarity results in what?
decreased release of ADH
Quantity of water excreted is controlled by what?
ADH
Increased ADH results in an increase in water reabsorption by what?
Distal tubule & collecting duct
Decreased ADH results in a decrease in water reabsorption by what?
Distal tubule & collecting duct
What controls urine volume and urine solute concentration?
Changes in water reabsorption
Increased water reabsorption means less water enters what part of the nephron? What does this do to the volume of urine?
Collecting duct; decreases overall volume of urine
What is the max concentration? (mls/day and osmolarity)
500 mls/day
osmolarity of 1200 to 1400 mOsm/L
TOtal solute excreted: 700 mOsm/day
What is the minimum concentration of urine? How many L/min?
20L/day with osmolarity of 50 mOsm/L
If you have dilute urine, how much ADH do you have?
Low amounts
Describe the reabsorption of solutes with the present of dilute urine.
Normal amounts of solutes are reabsorbed
When producing dilute urine, there is limited water reabsorption in what parts of the nephron?
Late distal tubule and collecting ducts
If you drink 1 Liter of water, changes being to occur within how long?
45 minutes
During water diuresis, there is a slight _______in solute excretion.
Increase
During water diuresis, there is a slight _________ is plasma osmolarity.
decrease
During water diuresis, there is a large _________ in urine osmolarity
decrease
What is the decrease in urine osmolarity in water diuresis?
600 mOsm/L to 100 mOsm/L
During water diuresis, there is a large ______ in urine output.
increase
How much of an increase in urine output occurs in water diuresis?
1 ml/min to 6 mls/min
In the production of dilute urine, filtrate osmolarity is equal to what?
Plasma osmolarity; 300 mOsm/L
To produce dilute urine, what has to happen?
Solute has to be reabsorbed at a faster rate than water
In the proximal tubule, how does the rate of solute reabsorption compare to the rate of water reabsorption?
Reabsorbed at the same rate; no change in osmolarity
In the descending loop, what drives water to be reabsorbed?
Gradient into hypertonic interstitial fluid
How much does the osmolarity increase in the descending loop?
2 to 4x osmolarity of plasma
What is reabsorbed in the ascending loop? [Production of dilute urine]
Sodium, potassium, chloride reabsorbed
How much water is reabsorbed in the ascending loop? [Production of dilute urine]?
No water reabsorbed, regardless of [ADH]
How much does the tubular osmolarity change in the ascneding loop? [ Production of dilute urine ] How does this compare to the osmolarity of plasma?
Decreases to 200 mOsm/L
1/3 osmolarity of plasma
Describe the water reabsorption in the distal tubule and the collecting tubules. [Production of dilute urine]
Variable amount of water reabsorption based on [ADH]
No ADH = no water reabsorption
Describe the solute reabsorption in the distal tubule and the collecting tubules. [ Production of dilute urine]
Solute reabsorption continues further decreasing tubular osmolarity
What is the max dilution in the distal tubule and collecting tubules? [ Production of dilute urine]
Max dilution of 50 mOsm/L
In what ways are we already losing water?
Breathing, sweat, feces, urine
What must we be able to do when water intake is limited?
Concentrate urine
We can excrete ______mls/day with maximum concentration of ______ to______ mOsm/L
500 mls/day ; 1200 to 1400 mOsm/L
Describe the level of ADH when excreting concentrated urine.
High concentration of ADH
Describe the reabsoprtion of solutes during excrete of concentrated urine.
Reabsorb normal amounts of solute
Describe the water absorption in the late distal tubule and collecting ducts during the excretion of concentrated urine.
Increased
What is meant by obligatory urine volume?
Some urine has to be produced each day to excrete the waste products of metabolism and ingested ions
What dictates the obligatory urine volume?
Ability to concentrate urine
A normal 70 kg person needs to excrete how many mOsm/day
600 mOsm/day
A normal 70 kg person needs to excrete how many L/day?
600mOsm/day / 1200mOsm/L = 0.5L/day
What is the salt content in sea water?
3.5%
If the only water you have is sea water and you drink 1 L of sea water each day you need to remove how many mOsm salt + how many mOsm of waste each day?
1200 mOsm salt
600 mOsm of waste each day
When drink a liter of sea water each day, you are losing how many mls of volume each day?
500 mls; which means you would become quickly dehydrated
What is needed to produce concentrated urine?
High concentration of ADH
High osmolarity of renal medullary interstitial fluid
What sets up interstitial osmolarity in renal medullary interstitial fluid?
Countercurrent mechanism
What is important about interstitial fluid surrounding collecting ducts being hyperosmotic?
Provides the gradient for water reabsorption
What picks up water once water leaves the distal tubule and collecting ducts?
Vasa recta capillary network
Countercurrent mechanism is made possibly by anatomical arrangement of what?
Loops of henle
Corresponding vasa recta capillaries
Collecting ducts
Countercurrent Mechanism: Loops of Henle
Especially loops of the juxtamedullary nephrons that go deep into the renal medulla
(25% of the total nephrons)
Where are the vasa recta capillaries?
Parallel the loops
What do the collecting ducts to?
Carry urine through the renal medulla
Urine osmolarity cannot exceed osmolarity of what?
Interstitial fluid in the renal medulla
To produce concentrated urine of 1200 mOsm/L the osmolarity at the bottom of the renal medulla must be at least what
1200 mOsm/L
What must happen to create a hyperosmotic renal medulla?
Must accumulate solute in the medulla
Once solute is accumulated, hyperosmolarity is maintained by what?
By a balanced inflow/outflow of water and solutes
