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Physiology > Urine Concentration > Flashcards

Urine Concentration Flashcards

1
Q

Maintaining Normal Cellular Environment Extracellular fluid must have a constant

A

concentration of electrolytes and other solutes

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2
Q

Maintaining Normal Cellular Environment Solute concentration & osmolarity determined by:

A

Total amount of solute / Volume of extracellular fluid

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3
Q

Maintaining Normal Cellular Environment Changing extracellular water has significant effect on

A

solute concentration and osmolarity

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4
Q

Maintaining Normal Cellular Environment body water determined by

A 
Fluid intake (controlled by thirst)
 Renal excretion of water (controlled by changing GFR and tubular reabsorption
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5
Q

If ECF solute concentration increases, kidneys

A

hold onto

water so ECF volume increases diluting ECF solutes

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6
Q

If ECF solute concentration decreases kidneys

A

excrete more water so ECF volume decreases concentrating ECF solutes

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7
Q

Assuming normal solute intake and metabolic production

A

Solute excretion will remain relatively constant each day
 Total amount of solute in ECF relatively constant. Quantity of water excreted each day adjusted to keep solute concentration of ECF constant

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8
Q

Increased ECF [solute] (i.e. increased ECF osmolarity)

A

 Normal amount of solute dissolved in less water
 Holding onto water will spread the total amount of solute over larger volume of water thus decreasing solute concentration of ECF

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9
Q

Decreased ECF [solute] (i.e. decreased ECF osmolarity)

A

 Normal amount of solute dissolved in too much water
 Getting rid of water will spread the total amount of solute over smaller volume of water thus increasing solute concentration of ECF

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10
Q

Posterior pituitary responds to changes in ECF osmolarity by changing ADH release. what effects ADH release?

A

Increased ECF osmolarity results in an increased release of ADH
 Decreased ECF osmolarity results in a decreased release of ADH

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11
Q

Quantity of water excreted controlled

A

ADH. Increased [ADH] results in an increase in water reabsorption by the distal tubule & collecting duct
 Decreased [ADH] results in a decrease in water reabsorption by the distal tubule & collecting duct

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12
Q

Changes in water reabsorption control

A

urine volume and urine solute concentration.

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13
Q

Increased water reabsorption means

A

less water enters collecting duct decreasing overall volume of urine - Normal amount of excreted solutes now dissolved in less volume  production of small amount of very concentrated urine
 At max concentration: 500 mls/day with osmolarity of 1200 to 1400 mOsm/Liter

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14
Q

Decreased water reabsorption means

A

more water enters collecting duct increasing overall volume of urine – Normal amount of excreted solutes now dissolved in less volume  production of large amount of very dilute urine
 At min concentration: 20 Liters/day with osmolarity of 50 mOsm/Liter

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15
Q

Excretion of Dilute Urine

 Can excrete 20 liters/day with

A

minimal concentration of 50 mOsm/Liter.Low Antidiuretic Hormone concentration
 Reabsorb normal amounts of solute
 Limit water reabsorption in late distal tubule and collecting ducts

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16
Q

Water Diuresis process drink 1 liter of water…

A

Changes begin to occur within 45
minutes
 Slight increase in solute excretion
 Slight decrease in plasma osmolarity
 Large decrease in urine osmolarity [600 mOsm/L to 100 mOsm/L]
 Large increase in urine output [1 ml/min to 6 mls/min]

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17
Q

Production of Dilute Urine

 Filtrate osmolarity =

A

Plasma osmolarity

 ≈ 300 mOsm/L

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18
Q

o produce dilute urine, solute has to be

A

reabsorbed at a faster rate than water

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19
Q

Production of Dilute Urine

Proximal Tubule

A

Solute & water reabsorbed at same rate

 No change osmolarity

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20
Q

Production of Dilute Urine Descending Loop

A

Water reabsorbed following gradient into hypertonic interstitial fluid
 Osmolarity increases 2 to 4 times osmolarity of plasma

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21
Q

Production of Dilute Urine

Ascending Loop

A

 Sodium, potassium, chloride reabsorbed
 No water reabsorbed regardless of [ADH]
 Tubular osmolarity decreases to 100 mOsm/L
 1/3 osmolarity of plasma

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22
Q

Production of Dilute Urine

Distal Tubule & Collecting Tubules

A

 Variable amount of water reabsorption based on [ADH]
 NoADH–Nowater reabsorption
 Solute reabsorption continues further decreasing tubular osmolarity
 Max dilution of 50 mOsm/Liter

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23
Q

Excretion of Concentrated Urine Always losing water (breathing, sweat, feces, urine). Must be able to concentrate urine when water intake

A

is limited

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24
Q

Excretion of Concentrated Urine Can excrete 500 mls/day with maximum

A

concentration of 1200 to 1400 mOsm/Liter. High ADH concentration Reabsorb normal amounts of solute

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25
Q

Excretion of Concentrated Urine Increased water reabsorption in

A

late distal tubule and collecting ducts

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26
Q

Obligatory Urine Volume
 Some urine has to be produced each day to excrete the waste products of metabolism and ingested ions
 Volume dictated by

A

ability to concentrate the urine

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27
Q

 Normal 70 kg person needs to excrete

A

600 mOsm/day

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28
Q

Sea water has salt content of

A

3.5%

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29
Q

salt molarity

A

58.5g/mole

30
Q

osmolarity of salt water

A

1200 mOSM/liter

31
Q

If the only water you have is sea water and you drink 1 Liter of sea water each day you need to remove

A

1200 mOsm of salt PLUS 600 mOsm of waste each day

32
Q

if you drink salt water you lose

A

500 mls of volume each day which means you quickly become dehydrated

33
Q

What Is Needed To Produce

Concentrated Urine?

A

High concentration of ADH  Increased permeability of distal tubules & collecting ducts
 High osmolarity of renal medullary interstitial fluid  Water reabsorption is driven by osmotic forces  Interstitial osmolarity setup by the countercurrent mechanism
 Interstitial fluid surrounding collecting ducts normally hyperosmotic which provides the gradient for water reabsorption
 Once water leaves the distal tubule & collecting ducts it is quickly picked up by the vasa recta capillary network

34
Q

Countercurrent Mechanism

Made possible by

A

anatomical arrangement of:  Loops of Henle
 Especially the loops of the juxtamedullary nephrons that go deep into the renal medulla
 25% of total nephrons

35
Q

Collectingducts

 Carry urine down

A

through the renal medulla

36
Q

Corresponding vasa recta capillaries

 Parallel

A

the loops

37
Q

Urine osmolarity cannot exceed

A

osmolarity of interstitial fluid in
renal medulla
 To produce concentrated urine of 1200 mOsm/Liter the osmolarity at the bottom of the renal medulla must be at least 1200 mOsm/L

38
Q

Creating A Hyperosmotic Renal Medulla

 Must accumulate

A

solute in the medulla

39
Q

Creating A Hyperosmotic Renal Medulla Once solute accumulated,

A

hyperosmolarity maintained by a balanced

inflow/outflow of water and solutes

40
Q

Creating A Hyperosmotic Renal Medulla. factors:

A

 Active ion transport & co-transport (Na+, K+, Cl-) out of thick portion of ascending loop into medullary interstitium
 Able to create a 200 mOsm concentration gradient  Thin descending limb highly permeable to water – As water is reabsorbed, osmolarity of
tubular fluid decreases until it matched osmolarity of interstitial fluid
 Active transport of ions from collecting duct into medullary interstititum  Facilitated diffusion of urea from inner medullary collecting ducts into
medullary interstitium  More solute is reabsorbed into medullary interstitium than wate

41
Q

Osmolarity of tubular fluid entering distal tubule is

A

low. NO water permeability in thick ascending segment

 Minimal water permeability in late distal tubule

42
Q

Collecting duct water permeability depends on

A

ADH conc.

43
Q

HIGH ADH

A

IGH ADH  Large quantity of water reabsorbed by
cortical collecting duct
 Reabsorbed water carried away by peritubular capillaries
 Medullary collecting duct highly permeable to water but only small percentage of water is left
 Since amount of water relatively small, water permeability is high, and vasa recta able to carry water away, osmolarity inside collecting duct quickly equilibrates with interstitial osmolarity

44
Q

Affects of Urea on Medullary Osmolarity

 Urea accounts for

A

40 to 50% of total osmolarity of inner renal medulla

45
Q

urea load normally excreted

A

50%

46
Q

excretion rate of urea depends on

A

 Plasmaconcentration  GFR

47
Q

Proximal Tubule urea absorption

A

50%

48
Q

Urea concentration increases as

A

larger percentage of water is reabsorbed

49
Q

Affects of Urea on Medullary Osmolarity

Thin Loop Segments

A

Descending – more water is reabsorbed
 Descending & ascending – secretion of urea into tubule so urea concentration continues to increase slightly
 Facilitated by urea transported UT-A2

50
Q

Affects of Urea on Medullary OsmolarityThick Ascending Loop, Distal Tubule, Cortical and Outer Medullary Collecting Duct

A

 Urea not permeable

 In collecting duct urea concentration rises quickly as large volume of water is reabsorbed

51
Q

Affects of Urea on Medullary Osmolarity

Inner Medullary Collecting Du

A

Urea permeability increases so urea will diffuse out of duct into interstitial space
 Facilitated by urea transporters UT-A1 and UT-A3
 UT-A3 activated by ADH  Water is still being reabsorbed so duct
concentration of urea remains high
 Some of the urea is secreted back into the thin segments of the loop of Henle
 Recirculation of urea (from collecting duct back into the loop of Henle) works to increase concentration of urea in the urine and inner medullary interstitium

52
Q

Vasa Recta & Urine Concentration

 Blood flow to renal medulla needed for

A

metabolic needs of tissue

53
Q

Vasa Recta & Urine Concentration  How meet metabolic needs without washing out concentrated solute???

A

 Medullary blood flow very
low (5% of total renal flow)
 Vasa recta function as countercurrent exchangers

54
Q

Characteristics of Vasa Recta

A

 Start at cortical-medullary boundary  Descend all way through medulla parallel to
medullary loops of Henle
 Highly permeable to solute (except protein)

55
Q

as vasa recta descend through medulla

A

exposed to ever increasing solute concentration of interstitium
 Water follows concentration gradient from blood to interstitium
 Solute follows concentration gradient from interstitium to blood

56
Q

as vasa recta ascend through medulla

A

now exposed to decreasing interstitial solute concentration

 Water now follows gradient into blood  Solute follows gradient out of blood

57
Q

Characteristics of Vasa Recta Carry away the amount of solute and water

A

absorbed FROM the medullary tubules

58
Q

increasing the blood flow through the vasa recta will

A

washout” solute thus reducing the overall solute concentration in the renal medulla

59
Q

what increases BF through vasa recta

A

 Somevasodilators
 Largeincreasesinarterialblood pressure
 Flow through renal medulla affected more than flow through other areas of kidney

60
Q

Affect of Vasa Recta Blood Flow Rate. Decreased medullary osmolarity

A

means less reabsorption of water more urine output

61
Q

Proximal tubule
 65% of filtered electrolytes are reabsorbed along with proportional amount of water
 Filtrate flow goes from

A

125 mls/minute to 44 mls/minute

62
Q

Descending Loop tubular flow

A

25 mls/minute tubular flow. High permeability to water
 Low permeability to sodium, chloride, urea
 Tubular osmolarity matched interstitial osmolarity
 Low levels of ADH
 Urea absorption from collecting duct reduced so interstitial osmolarity also reduced

63
Q

Thin Ascending Loop

A 
No water permeability
 Some reabsorption of sodium, chloride
 Some diffusion of urea into tubule
 Net result – decrease in osmolarity
 No change in tubular flow (25 mls/minute)
Changes in Osmolarity Through Nephron
64
Q

Thick Ascending Loop

A

 No water permeability
 Active reabsorption of sodium, chloride, potassium
 Largeamount reabsorbed
 Tubular osmolarity continues to decrease
 100 to 200 mOsm/L
 No change in tubular flow (25 mls/minute)

65
Q

Changes in Osmolarity Through Nephron

Early Distal Tubule

A

 Diluting segment
 No water permeability
 Active reabsorption of sodium, chloride, potassium
 Largeamount reabsorbed
 Tubular osmolarity continues to decrease
 50 mOsm/L
 No change in tubular flow (25 mls/minute)

66
Q

Changes in Osmolarity Through Nephron

Late Distal Tubule / Cortical Collecting Tubules

A

Osmolarity based on level of ADH
 Urea permeability low so total urea load at this point does not change until medullary collecting ducts
 LOW: Minimal water reabsorption and further decrease in osmolarity (ions still being reabsorbed)
 Tubular flow still around 25 mls/minute
 HIGH: High water reabsorption so osmolarity increases
 Tubular flow drops to 8 mls/minute

67
Q

Changes in Osmolarity Through Nephron

Medullary Collecting Tubules

A

 Osmolarity depends on [ADH] and interstitial osmolarity
 HIGH [ADH]: High water permeability / reabsorption – Solute concentration increases (especially of urea)
 Tubular flow drops to 0.2 mls/minute
 LOW [ADH]: Low water permeability – Solute concentration drops as urea is reabsorbed
 Slight decrease in tubular flow to 20 mls/minute
 Increased flow through vasa recta decreases overall solute concentration of interstitial fluid which decreases water reabsorption
 Not able to concentrate urine to as high a level or reabsorb as much water

68
Q

Kidneys can produce concentrated urine that contains little sodium or chloride even though under normal conditions

A

make up 50 to 60% of interstitial solute at max concentration. Osmolarity of other solutes increase (urea) Dehydration / low sodium intake – stimulate release of angiotensin
II and aldosterone

69
Q

Kidneys can produce large quantities of dilute urine without changing

A

sodium excretion

Changing [ADH] which changes water reabsorption in later segments of nephron without changing sodium reabsorption

70
Q

Obligatory urine volume dictated by

A

max ability to concentrate the urine

Physiology (27 decks)

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