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Physiology II > test 9 > Flashcards

test 9 Flashcards

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1
Q

Maintaining Normal Cellular Environment

A

 Extracellular fluid must have a constant CONCENTRATION of electrolytes and other solutes
 Solute concentration & osmolarity determined by:
 Total amount of solute / Volume of extracellular fluid
 Changing extracellular water has significant effect on solute concentration and osmolarity

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2
Q

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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3
Q

If ECF solute concentration increases

A
  • kidneys hold onto

water so ECF volume increases diluting ECF solutes

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4
Q

Assuming normal solute intake and metabolic production

A

 Solute excretion will remain relatively constant each day
 Total amount of solute in ECF will remain relatively constant
 Quantity of water excreted each day adjusted to keep solute concentration of ECF constant
-usually not the total amount of solute that changes, it’s the total amount of water that changes

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5
Q

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

A

 Normal amount of solute is dissolved in less water
 HOLDING ONTO water will spread the total amount of solute over a larger volume of water thus decreasing solute concentration of the ECF

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6
Q

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

A

 Normal amount of solute is dissolved in too much water
 GETTING RID of water will spread the total amount of solute over a smaller volume of water thus increasing solute concentration of the ECF

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7
Q

Posterior pituitary responds to changes in ECF osmolarity by changing 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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8
Q

Quantity of water excreted controlled by [ADH]

A

 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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9
Q

increase in water reabsorption control urine volume and urine solute concentration

A

 Increased water reabsorption means 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
-smallest amount of urine we can produce

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10
Q

decrease in water reabsorption control urine volume and urine solute concentration

A

 Decreased water reabsorption means 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
-most urine we can produce

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11
Q

Excretion of Dilute Urine

A

 Can excrete 20 liters/day with 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
 Drop water reabsorption from 124 mls/min to approximately 111 mls/min

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12
Q

Water Diuresis

A 
 Drink 1 liter of water
 Changes begin to occur within 45 minutes
 Slight increase in solute excretion (because of backflow)
 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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13
Q

Filtrate osmolarity = Plasma osmolarity

A

 ≈ 300 mOsm/L

 To produce dilute urine, solute has to be reabsorbed at a faster rate than water

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14
Q

how to produce dilute urine (3)

A

 Decrease water reabsorption with no change in solute reabsorption (main way)
 Increase solute reabsorption with no change in water reabsorption
 Decrease water reabsorption and increase solute reabsorption

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15
Q

Production of Dilute Urine: Proximal Tubule

A

 Solute & water reabsorbed at same rate

 No change osmolarity

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16
Q

Production of Dilute Urine: Descending Loop

A

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

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17
Q

Production of Dilute Urine: Ascending Loop

A

 Normal sodium, potassium, chloride reabsorption
 No water reabsorbed regardless of [ADH]
 Tubular osmolarity decreases to 100 mOsm/L
 1/3 osmolarity of plasma

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18
Q

Production of Dilute Urine:

Distal Tubule & Collecting Tubules

A

 Variable amount of water reabsorption based on [ADH]
 No ADH – No water reabsorption
 Normal solute reabsorption continues further decreasing tubular osmolarity
 Max dilution of 50 mOsm/Liter

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19
Q

Excretion of Concentrated Urine

A

 Always losing water (breathing, sweat, feces, urine).
 Must be able to concentrate urine when water intake is limited
 Smallest volume of urine excretion is 500 mls/day with maximum concentration of 1200 to 1400 mOsm/Liter
 High antidiuretic hormone concentration
 Reabsorb normal amounts of solute
 Increased water reabsorption in late distal tubule and collecting ducts controlled by [ADH]

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20
Q

Obligatory Urine Volume

A

 Some urine has to be produced each day to excrete the waste products of metabolism and ingested ions
 Urine volume dictated by ability to concentrate the urine
 Normal 70 kg person needs to excrete 600 mOsm of per day
600mOsm/day / 1200mOsm/L = 0.5 L/day
-1200 is max [urine] that we can produce

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21
Q

Drinking Sea Water

A
  • Sea water has a salt content of 3.5%
     3.5 g/100 mls = 35 g/Liter
     35 g/L / 58.5 g/mole = 0.598 mole/Liter x 2 = 1.196 mole/Liter ≈ 1200 mOsm/Liter
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22
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
 (1200 + 600 mOsm) = (1800 mOsm/day / 1200 mOsm/Liter) = 1.5 Liters of urine / day
 Means you are losing 500 mls of volume each day which means you quickly become dehydrated

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23
Q

What Is Needed To Produce Concentrated Urine?

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A

 High concentration of ADH
 Increased water 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

24
Q

Countercurrent Mechanism Made possible by anatomical arrangement of

Study These Flashcards
A

 Loops of Henle
 Especially the loops of the juxtamedullary nephrons that go deep into the renal medulla (25% of total nephrons)
 Corresponding vasa recta capillaries
 Parallel the loops
 Collecting ducts
 Carry urine down through the renal medulla

25
Countercurrent Mechanism
 Urine osmolarity cannot exceed 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
26
Creating A Hyperosmotic Renal Medulla
 Must accumulate solute in the medulla  Once solute accumulated, hyperosmolarity is maintained by a balanced inflow/outflow of water and solutes  Out of loop of Henle and collecting tubules / ducts  Into vasa recta capillaries
27
Factors for creating a hyperosmotic renal medulla
 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 matches 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 water
28
Distal Tubule & Collecting Ducts
 Osmolarity of tubular fluid entering distal tubule is LOW  NO water permeability in thick ascending segment  Minimal water permeability in late distal tubule  Collecting duct water permeability depends on ADH concentration
29
High [ADH] in Distal Tubule & Collecting Ducts simple version
- increase permeability so water moves from the tube to the interstitial spaces (creates high osmolarity in the tubule) - immediately pick up by the vasa recta and does not dilute the concentration in the interstitial space - the osmolarity inside the collecting tubule and osmolarity of the interstitial fluid will match because the movement of water is driven by the osmotic gradient
30
HIGH ADH in Distal Tubule & Collecting Ducts
 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
31
Affects of Urea on Medullary Osmolarity
 Urea accounts for 40 to 50% of total osmolarity of inner renal medulla  Normally excrete 50% of filtered urea load  Excretion rate depends on:  Plasma concentration  GFR
32
Affects of Urea on Medullary Osmolarity in the proximal tubule
 50% of filtered load reabsorbed |  Urea concentration increases as larger percentage of water is reabsorbed
33
Affects of Urea on Medullary Osmolarity in the thin loop segements
 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
34
Affects of Urea on Medullary Osmolarity in the Thick Ascending Loop, Distal Tubule, Cortical and Outer Medullary Collecting Duct
 Urea not permeable |  In collecting duct urea concentration rises quickly as large volume of water is reabsorbed
35
Affects of Urea on Medullary Osmolarity in the Inner Medullary Collecting Duct
 Urea permeability increases so urea will diffuse out of duct into interstitial space  Facilitated by urea transporters UT-A1 (constant) and UT-A3 (variable)  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
36
Vasa Recta
- Blood flow to renal medulla needed for metabolic needs of tissue
37
How to meet metabolic needs without washing out concentrated solute???
 Medullary blood flow very low (5% of total renal flow) (over all of the nephrons)  Vasa recta function as countercurrent exchangers
38
Characteristics of Vasa Recta
 start at cortical medullary boundary and descend all way through medulla parallel to medullary loops of Henle  Highly permeable to solute (not proteins)
39
As vasa recta descends through medulla
 As vasa recta descend through medulla they are exposed to ever increasing solute concentration of interstitium  Water follows concentration gradient from blood to interstitium  Solute follows concentration gradient from interstitium to blood
40
As vasa recta ascends through medulla
 As vasa recta ascend through medulla, now exposed to decreasing interstitial solute concentration  Water now follows gradient into blood  Solute follows gradient out of blood  Carry away only the amount of solute and water that is reabsorbed FROM the medullary tubules
41
Affect of Vasa Recta Blood Flow Rate
- Increasing the blood flow through the vasa recta will “washout” solute thus reducing the overall solute concentration in the renal medulla  Decreased medullary osmolarity means less reabsorption of water more urine output
42
A change in Vasa Recta Blood Flow Rate caused by
 Some vasodilators (increase flow)  Large increases in arterial blood pressure  Flow through renal medulla affected more than flow through other areas of kidney
43
Changes in Osmolarity Through Nephron: Proximal tubule
 65% of filtered electrolytes are reabsorbed along with proportional amount of water  Filtrate flow goes from 125 mls/minute to 44 mls/minute
44
Changes in Osmolarity Through Nephron: Descending Loop
 High permeability to water  Low permeability to sodium, chloride, urea  Tubular osmolarity matches interstitial osmolarity  Low levels of ADH  Urea absorption from collecting duct reduced so interstitial osmolarity also reduced  25 mls/minute tubular flow
45
Changes in Osmolarity Through Nephron: Thin Ascending Loop
```  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) ```
46
Changes in Osmolarity Through Nephron: Thick Ascending Loop
 No water permeability  Active reabsorption of sodium, chloride, potassium  Large amount reabsorbed  Tubular osmolarity continues to decrease  100 to 200 mOsm/L  No change in tubular flow (25 mls/minute)
47
Changes in Osmolarity Through Nephron: Early Distal Tubule
 Diluting segment  No water permeability  Active reabsorption of sodium, chloride, potassium  “Large” amount reabsorbed  Tubular osmolarity continues to decrease  50 mOsm/L  No change in tubular flow (25 mls/minute)
48
Changes in Osmolarity Through Nephron: Late Distal Tubule / Cortical Collecting Tubules
 Osmolarity based on level of ADH |  Urea permeability low so total urea load at this point does not change until medullary collecting ducts
49
Changes in Osmolarity Through Nephron: Late Distal Tubule / Cortical Collecting Tubules with LOW [ADH]:
 Minimal water reabsorption and further decrease in osmolarity (ions still being reabsorbed)  Tubular flow still around 25 mls/minute
50
Changes in Osmolarity Through Nephron: Late Distal Tubule / Cortical Collecting Tubules with HIGH [ADH]:
 High water reabsorption so osmolarity increases |  Tubular flow drops to 8 mls/minute
51
Changes in Osmolarity Through Nephron: Medullary Collecting Tubules
 Osmolarity depends on [ADH] and interstitial osmolarity  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
52
Changes in Osmolarity Through Nephron: Medullary Collecting Tubules with HIGH [ADH]:
 High water permeability / reabsorption – Solute concentration increases (especially of urea)  Tubular flow drops to 0.2 mls/minute
53
Changes in Osmolarity Through Nephron: Medullary Collecting Tubules with LOW [ADH]:
 Low water permeability – Solute concentration drops as urea is reabsorbed  Slight decrease in tubular flow to 20 mls/minute
54
Kidneys can produce concentrated urine that contains little sodium or chloride even though under normal conditions sodium and chloride make up 50 to 60% of interstitial solute at max concentration
 Osmolarity of other solutes increase (urea) |  Dehydration / low sodium intake will stimulate release of angiotensin II and aldosterone
55
Kidneys can produce large quantities of dilute urine without changing sodium excretion
 Changing [ADH] which changes water reabsorption in later segments of nephron without changing sodium reabsorption
56
Obligatory urine volume dictated by max ability to concentrate the urine
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Physiology II (20 decks)

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