Urine Concentration and Dilution Flashcards
Regulation of extracellular osmolality depends on
transport mechanisms
Excretion of dilute urine (when there is a large concentration of water in the body). The kidneys can excrete as much as ____ liters per day with a concentration as low as
20 liters per day with a concentration as low as 50 mOsm/L
- kidneys continue to reabsorb solutes - simultaneously fail to reabsorb large amounts of water
during water diuresis what remains constant
- plasma osmolarity
- Urinary solute excretion (mOsm/min)
The ascending thick limb of Henle is ____ to water
impermeable
Areas of the kidney that dilute urine
- Ascending thick limb of Henle
- Late distal convoluted tubule (in the absence of ADH)
What is readily reabsorbed in the Ascending thick limb of Henle
- Sodium
- Potassium
- Choride
In the ascending thick limb of Henle Tubular fluid becomes more ___ as it flows up the ascending loop of Henle
Dilute
Does ADH effect the ascending thick limb of Henle
No
what is osmolarity at the early distal tubular segment
100 mOsm/L
The late distal convoluted tubule reabsorbs
- Sodium chloride
- (reabsorbs water in the presence of ADH)
Osmolarity reaches ____ in the late distal convoluted tubule
50 mOsm/L
The kidney can produce a maximal urine concentration of
1200 to 1400 mOsm/L
Requirements for forming a concentrated urine
- presence of ADH
- High osmolarity of renal medullary interstitial tubule
- Estabilishes osmotic gradient necessary for water reabsorption to occur
a normal 70-kg human must excrete about ____ mOsm of solute each day in order to get rid of waste products of metabolism and ions that are ingested
600 mOsm
The maximal urine concentrating ability of humans is
1200-1400 mOsm/L (4 to 5 times the the osmolarity of plasma)
The proximal tubule reabsorbs about ____ % of filtered electrolytes
65%
Water permeability of the proximal tubule
highly permeable to water
Tubular osmolarity of proximal tubule
about 300 mOsm/L
Descending loop of Henle permeability
- highly permeable to water
- less permeable to sodium chloride and urea
Osmolarity of tubular fluid in the descending loop of Henle
about 1200 mOsm/L when (ADH) is high
Permeability of the thin ascending loop of henle
- Impermeable to water
- Reabsorbs sodium chloride
Tubular fluid in the thin ascending loop of henle
becomes more dilute
The thick ascending loop of henle permeability to water
The thick ascending loop of henle is impermeable to water
Permeability in the thick ascending loop of henle
- impermeable to water
- Large amounts of sodium chloride, potassium, and other iions are actively transported from tubule into medullary interstitium
The tubular fluid of the thick ascending loop of henle becomes
dilute: 100 mOsm/L
The early distal tubule is similar to
The thick ascending loop of henle
major functions of the kidneys include
-regulation of extracellular osmolality, including water loss and conservation
Major functions of the kidneys include
-regulation of extracellular osmolality, including water loss and conservation
After drinking 1 liter of what _____ decreases, ___ increases, and what two things remain constant
Urine osmolarity decrease, urine volume increases
Plasma osmolarity and urinary solute excretion (mOsm/min) remains the same.
Does ADH have an effect on the ascending thick limb
No
Ascending thick limb permeability to water
is impermeable to water
The thick ascending limb avidly reabsorbs
Sodium
potassium
Chloride
What is the osmolarity of the tubular fluid in the early distal tubule
100 mOsm/L
Fluid leaving the early distal tubular segment is ______, with an osmolarity of _____ that of the osmolarity of the plasma
Hypo-osmotic, only about 1/3 the osmolarity of the plasma
In a healthy kidney, fluid leaving the ascending loop of hence and early distal tubule is always ____, regardless of the levels of ADH
Dilute
The late distal convoluted tubule is impermeable to water in the
absence of ADH
Osmolarity in the late distal convoluted tubule reaches
50 mOsm/L
What is reabsorbed in the late distal convoluted tubule
Sodium chloride
Tubular fluid is ____ throughout proximal tubule
Isosmotic. This is because solutes and water are reabsorbed in equal proportions
What is the osmolarity in the proximal tubule
the same as in the plasma 300 mOsm/L
tubular fluid becomes _____ as it flows into the inner medulla
more concentrated
a normal 70-kg human must excrete about ____ most of solute each day in order to get rid of waste products of metabolism and ions that are ingested
600 mOsm
What is obligatory urine volume and how is it calculated
-the minimal volume of urine that must be excreted
- calculated by: (how much must be excreted each day/ maximum concentration ability)
(600/1200)=0.5 L/day
For every liter of seawater drunk, ___ liter of urine volume would be required to rid the body of 1200milliosmoles of sodium chloride ingested in addition to 600 milliosmoles of other solutes such as urea
1.5 Liters
Descending loop of Henle is highly permeable to ____ and less permeable to
water, sodium chloride and urea
The osmolarity of tubular fluid increases to ____ when ADH is high
1200 mOsm/L when {ADH} is high
The thin ascending loop of Henle is impermeable to ____ and reabsorbs
water and reabsorbs sodium chloride
Tubular fluid in the thin ascending loop of Henle becomes more
dilute
____ diffuses into the ascending limb
urea (comes from urea absorbed into interstitium from collecting ducts)
The more concentrated the urine, the ____ the urine specific gravity
higher
in most cases, urine specific gravity ___________ with increasing urine osmolarity
increases linearly
what is urine specific gravity
is a measure of the weight of solutes in a given volume of urine and is therefore determined by the number and size of the solute molecules
The proximal tubule reabsorbs about ____ % of filtered electrolytes
65%
the tubular osmolarity of the proximal tubule is
300 mOsm/L
The proximal permeability to water
highly permeable to water
The descending loop of Henle is highly permeable to _____ and less permeable to ___ and ____
water, and less permeable to sodium chloride and urea
Osmolarity of the tubular fluid increases to about _____ mOsm/L in the descending loop of Henle when ADH is high
1200 mOsm/L
The thin ascending loop of henle is impermeable to ____ and reabsorbs ____
impermeable to water and reabsorbs sodium chloride
Tubular fluid becomes more ____ in the thin ascending loop of Henle
more dilute
____ diffuses into the ascending limb
Urea, comes form urea absorbed into interstitial from collecting ducts
The thick ascending loop is impermeable to _____. Meanwhile large amounts of ____, _____, and _____ are actively transported form tubule into medullary interstitium
water, sodium chloride, potassium, and other ions
Tubular fluid in the thick ascending loop of Henle becomes ____ with an osmolarity of about
dilute, 100 mOsm/L
The early distal tubule is similar to
the ascending loop of Henle
Tubular fluid in the early distal tubule becomes more ___ with osmolarity about
dilute, with osmolarity of about 50 mOsm/L
The late distal tubule and cortical collecting tubules osmolarity depends on
ADH
Urea in the late distal tubule and cortical collecting tubule
is not very permeant
The osmolarity of fluid in the inner medullary collecting duct depends on
ADH and surrounding interstitium osmolarity
What is the osmolarity in the thick ascending tubule
about 100 mOsm/L
The limit of the thick ascending limb on the loop of Henle to reduce the concentration inside the tubule is _____ because ______. How is this overcome to achieve maximum concentration
200 mOsm/L because paracellular diffusion of ions back into the tubule eventually counterbalances transport of ions out of the lumen when the 200-mOsm/L concentration gradient achieved. The countercurrent multiplier system allows for 200 mOsm/L to be added to the interstitium everytime a cycle occurs
Are the ascending loop of Henle and distal cortical collecting tubule permeable to urea
No
What is the role of Urea of concentrating urine
ADH in the cortical collecting tubule. leads to increased water absorpition and a higher concentration of urea in the tubule fluid. ADH in the medullary collecting duct leads to more water and urea reabsorption into the interstitial fluid. Urea absorption is mediated by facilitated by UT-A1 and UT-A3 (ADH-activated) transporters
The passive secretion of urea into the thin loops of Henle is facilitated by
The urea transporter UT-A2
Urea transporters___ and ___ facilitate diffusion of urea out of the of the medullary collecting ducts and are activated by
UT-A1 and UT-A3, ADH
simultaneous movement of water and urea out of the inner medullary collecting ducts maintains
a high concentration of urea in the tubular fluid and, eventually, in the urine, even though urea is being reabsorbed
is the cortical collecting duct permeable to urea
no
The vasa recta does not create the medullary hyperosmolarity but
prevent it from being dissipated
what are two special features of the renal medullary blood flow that contribute to the preservation of the high solute concentrations
- ) The medullary blood flow is low, accounting for less than 5 percent of the total renal blood flow. This sluggish blood flow is sufficient to supply the metabolic needs of the tissues but helps to minimize solute loss form the medullary interstitium
- ) The vasa recta serve as countercurrent exchangers, minimizing washout of solutes from the medullary interstitium
What is the osmoreceptor-ADH feedback stystem
-When osmolarity (plasma sodium concentration) increases above normal because of water deficit, for example, this feedback system operates as follows:
increase in extracellular fluid osmolarity (which means an increase in plasma sodium concentration)—-> shrinking of osmoreceptor cells in anterior hypothalamus —> action potential—-> Release of ADH (from posterior pituitary) —–> increases water permeability in distal nephron segments
ADH is formed in .
magnocellular neurons in the supraoptic and paraventricular nuclei of the hypothalamus (note 5/6 in the supraoptic nuclei)
Where are osmoreceptor cells located
in the vicinity of the AV3V region (anterior region of 3rd ventricle)
a decrease in effective blood volume or an increase in extracellular fluid osmolarity stimulates _____.
ADH secretion.
ADHS is considerably more sensitive to small changes in _____ than to similar percentage changes in _____
osmolarity, blood volume. For example, a change in plasma osmolarity of only 1 percent is sufficient to increase ADH levels. By contrast, after blood loss, plasma ADH levels do not change appreciably until blood volume is reduced by about 10 percent
___ and ___ together maintain precise control of extracellular fluid osmolarity and sodium concentration
thirst and osmoreceptor-ADH mechanism
Angiotensin II and aldosterone have ______on sodium concentration in the extra cellular fluid.
little effect, because although they increase sodium reabsorption they also increase water reabsorption. Also as long as the ADH-Thirst mechanism is functional, any tendency toward increased plasma sodium concentration is compensated for by increased water intake or increased plasma ADH secretion, which tens to dilute the extracellular fluid back toward normal
