Renal Physiology (Part 2) Flashcards
(170 cards)
1
Q
Which ion is the major cation of the ECF?
A
Na+
2
Q
The reabsorption of Na+ into the ECF after filtration is critically important in maintaining what?
A
- normal ECF volume
- normal blood volume
- normal blood pressure
3
Q
The kidneys ensure that Na+ _____ exactly equals Na+ ____, a matching process called what?
A
intake
excretion
Na+ balance
4
Q
If Na+ excretion is less than Na+ intake, then the person is in _____ Na+ balance.
A
positive
5
Q
What happens if the person is in positive Na+ balance?
A
Extra Na+ is retained, therefore there is ECF volume expansion which causes blood volume and arterial pressure to increase. This may result in edema.
6
Q
If Na+ excretion is greater than Na+ intake, then the person is in _____ Na+ balance.
A
negative
7
Q
What happens if the person is in negative Na+ balance?
A
Excess Na+ is lost from the body, therefore is ECF volume contraction which causes blood volume and arterial pressure to decrease.
8
Q
How can a person have increased Na+ content but normal Na+ concentration?
A
If water content is increased proportionally
9
Q
In nearly all cases, changes in Na+ concentration are caused by what?
A
Changes in body water content
*not Na+ content
10
Q
Excretion of Na+ is __% of the filtered load.
Net reabsorption is __% of the filtered load.
A
1
99
11
Q
Where does the bulk of Na+ reabsorption occur?
A
In the proximal convoluted tubule
12
Q
__% of the filtered load is reabsorbed in the proximal convoluted tubule.
A
67
13
Q
What is water reabsorption linked to in the proximal convoluted tubule?
A
Na+ reabsorption
14
Q
__% of the filtered load is reabsorbed in the thick ascending loop of Henle.
A
25
15
Q
Is the thick ascending loop of Henle permeable to water?
A
no
16
Q
__% of the filtered load is reabsorbed in the terminal portions of the nephron (the distal tubule and the collecting ducts).
A
8
17
Q
__% of the filtered load is reabsorbed in the early distal convoluted tubule.
A
5
18
Q
__% of the filtered load is reabsorbed in the late distal convoluted tubule and collecting ducts. These structures are ultimately responsible for what?
A
3
the fine-tuning of Na+ reabsorption which ensures Na+ balance
19
Q
In which part of the nephron are sites of action of the Na+ regulating hormone aldosterone?
A
the late distal convoluted tubule and collecting ducts
20
Q
As already stated, the entire proximal convoluted tubule reabsorbs 67% of the filtered Na+, it also reabsorbs 67% of the filtered water. This tight coupling between Na+ and water reabsorption is called what?
A
isosmotic reabsorption
21
Q
The proximal tubule is also the site of what?
A
glomerulotubular balance
22
Q
What is the first half of the proximal convoluted tubule called?
A
the early proximal convoluted tubule
23
Q
The early proximal convoluted tubule performs the ______ priority reabsorptive work
A
highest
24
Q
In the early proximal convoluted tubule, what are the most essential solutes that are reabsorbed?
A
- glucose
- amino acids
- bicarbonate
25
What are the 2 mechanisms by which solutes are reabsorbed into the proximal convoluted tubule?
- cotransport
| - countertransport
26
What are the 5 cotransport mechanisms in the proximal convoluted tubule?
1) Na+ - glucose (SGLT)
2) Na+ - amino acid
3) Na+ - phosphate
4) Na+ - lactate
5) Na+ - citrate
27
Once Na+, glucose, amino acid, phosphate, lactate, and citrate are in the cell how are they extruded from the cell into the blood?
Na+ by way of the Na+ - K+ ATPase
Glucose and the other solutes are extruded by facilitated diffusion
28
What is the only contertransport mechanism in the proximal convoluted tubule?
Na+ - H+ exchange
29
Via the Na+ - H+ exchange system __ is transported into the lumen in exchange for __.
H+
Na+
30
In the early proximal convoluted tubule what anion is reabsorbed with Na+?
bicarbonate
31
Describe how the H+ that is transported into the lumen is converted to HCO3-
H+ combines with filtered HCO3-, converting it to CO2 and water, which then move from the lumen into the cell. Inside the cell, CO2 and water are reconverted to H+ and HCO3-. The H+ is transported again by the Na+ - H+ exchanged and HCO3- is reabsorbed into the blood by facilitated diffusion.
32
What is the net result of the countertransport cycle in the early proximal convolutes tubule?
reabsorption of filtered HCO3-
33
There is a lumen-_____ potential difference across the cells of the early convoluted tubule, what is this created by?
negative
Na+ - glucose and Na+ - amino acid cotransport
34
What are the 4 modifications made to the glomerular filtrate by the time it reaches the midpoint of the proximal tubule?
1) 100% of the filtered glucose and amino acids have been reabsorbed
2) 85% of the filtered HCO3- has been reabsorbed
3) most of the filtered phosphate, lactate, and citrate have been reabsorbed
4) Na+ is extensively reabsorbed (because it is coupled to each of the above transport mechanisms)
35
Fluid entering the late proximal convoluted tubule has no ____ or _____, little _____, and high ____ concentration.
glucose or amino acids
bicarbonate
Cl-
36
Why is Cl- concentration high in the late proximal convoluted tubule?
because HCO3- has been preferentially reabsorbed in the early proximal convoluted tubule, leaving Cl- behind in the tubular fluid
37
What does the late proximal convoluted tubule primarily reabsorb?
NaCl
38
What is the driving force for NaCl reabsorption?
high tubular Cl- concentration
39
What are the 2 components of NaCl reabsorption?
- cellular
| - paracellular
40
The cellular component of NaCl reabsorption contains 2 exchange mechanisms, what are they?
1) Na+ H+ exchanger
| 2) Cl- formate anion exchanger
41
The combined function of the Na+ H+ and Cl- formate anion exchangers is to do what?
transport NaCl from the lumen into the cell
42
After NaCl is transported from the lumen into the cell what happens?
Na+ is extruded into blood by the Na+ - K+ ATPase
| Cl- moves into blood by diffusion
43
Are the junctions between the cells of the proximal tubule tight?
No, they are permeable to small solutes (such as NaCl) and to water
44
The diffusion of Cl- between cells, from the lumen to blood extablishes a Cl- _____ potential. This makes the lumen ____ with respect to blood.
diffusion
positive
45
Both the cellular and paracellular route what is the net result?
reabsorption of NaCl
46
What type of reabsorption is a hallmark of proximal tubular function? Why is this reabsorption consider equilibrium?
Isosmotic Reabsorption
Solute and water reabsorption are coupled and are proportional to each other
47
In the proximal convoluted tubule does solute follow water reabsorption or does water follow solute reabsorption?
Solute reabsorption is the primary event, and water follows passively
48
Describe the steps involved in Isosmotic Reabsorption
1) Na+ enters the cell across the luminal membrane by way of one of the previously mentioned mechanisms
2) water follows Na+ to maintain isosmolarity
3) Na+ is pumped out of the cell by the Na+ - K+ ATPase
4) water follows Na+ to maintain isosmolarity
5) water and Na+ fill the lateral intracellular space
6) high oncotic pressure of the peritubular blood drives reabsorption of the isosmotic fluid into the peribular capillary
49
What is the major regulatory mechanism of the proximal tubule?
Glomerulotubular balance
50
What does glomerulotubular balance describe?
the balance between filtration in the glomerular and reabsorption in the proximal tubule
51
What does glomerulotubular balance ensure?
that a constant fraction of the filtered load is reabsorbed by the proximal tubule, even if the filtered load increases or decreases
52
This constant fraction is normally maintained at __% of the filtered load
67
53
How does the glomerulus "communicate" with the proximal tubule to maintain constant fractional reabsorption?
Via changes in the oncotic pressure of the peritubular capillary blood
54
Increases in GFR produce _____ reabsorption in the proximal tubule.
increase
55
Increased reabsorption in the proximal tubule leads to _____ oncotic pressure in the peritubular capillary and _____ reabsorption in the proximal tubule
increased
increased
56
Decreases in GFR produces ______ in the filtration fraction.
decreases
57
Decreases in the filtration fraction lead to ______ oncotic pressure in the peritubular capillary and _____ reabsorption in the proximal tubule
decreased
decreased
58
How can glomerulotubular balance be altered?
by changes in ECF volume
59
ECF volume expansion produces a(n) _____ in fractional reabsorption in the proximal tubule
decrease
60
When ECF volume increases the capillary hydrostatic pressure (Pc) _____. How does this happen?
increases, because the plasma protein concentration is decreased by dilution
61
Increases in capillary hydrostatic pressure results in ______ oncotic pressure in the peritubular capillary
decreased
62
What is the end result of ECF volume expansion?
A portion of fluid that would have been reabsorbed instead leaks back into the lumen of the tubule and is excreted
63
What are the 2 mechanisms the contribute to the increased proximal tubule reabsorption that occurs in ECF volume contraction
- Starling forces
| - Angiotensin II
64
ECF volume contraction produces a(n) _____ in fractional reabsorption in the proximal tubule
increase
65
When ECF volume decreases the capillary hydrostatic pressure (Pc) _____. How does this happen?
decreases, because the plasma protein concentration increases
66
Decreases in capillary hydrostatic pressure results in ______ oncotic pressure in the peritubular capillary
increased
67
The alteration of glomerulotubular balance that occurs with ECF volume contraction is a mechanism for what?
Protection, in which the kidneys try to restore the ECF volume by reabsorbing more solute and water than usual
68
Other than the Starling forces, what is another mechanism that contributes to the increased proximal tubule reabsorption that occurs in ECF volume contraction?
Decreased ECF volume leads to decreased blood volume and arterial pressure that activates the renin-angiotensin-aldosterone system which produces Angiontensin II
69
What does Angiontensin II stimulate?
Na+ - H+ exchange in the proximal tubule, and thereby stimulates reabsorption of Na+, HCO3-, and water
70
What are the 3 segments of the loop of Henle?
- thin descending limb
- thin ascending limb
- thick ascending limb
71
What are the 3 segments of the loop of Henle essential for?
the concentration and dilution of urine via countercurrent multiplication
72
What is the thin descending limb permeable to?
water and small solutes such as NaCl and urea
73
In countercurrent multiplication, water moves ____ and solutes move ____ the thin descending limb
out of
into
74
As fluid flows down the descending limb is becomes progressively ____osmotic
hyperosmotic
75
What is the thin ascending limb permeable to? What is it impermeable to?
Permeable to NaCl
Impermeable to water
76
Describe countercurrent multiplication in the thin ascending limb
Solutes move out without water because it is impermeable
77
As fluid flows up the ascending limb is becomes progressively ____osmotic
hyposmotic
78
The thick ascending limb reabsorbs about __% of the filtered Na+. By what mechanism?
25
load-dependent mechanism
79
Na+ reabsorption in the thick ascending limb is load-dependent, what does this mean?
The more Na+ delivered to the thick ascending limb, the more it reabsorbs
80
The luminal membrane of the thick ascending limb contains what type of cotransporter?
Na+ - K+ - 2Cl- contransporter
3 ion contransporter
81
Describe the net reabsorption of Na+, K+ and Cl- in the thick ascending limb
1) all 3 ions are transported into the cell on the contransporter
2) Na+ is extruded from the cell by the Na+ - K+ ATPase
3) Cl- and K+ diffuse through channels in the basolateral membrane, down their respective electrochemical gradients
82
Does all K+ that enters the cell on the 3-ion contransport leave the cell across the basolateral membrane?
No, a portion of the K+ diffuses back into the lumen
83
What is a consequence of the K+ diffusing back into the lumen?
The contransporter is electrogenic, meaning it brings slightly more negative than positive into the cell
84
The electrogenic property of the Na+ - K+ - 2Cl- contransporter results in a lumen-____ potential difference across the cells of the thick ascending limb
positive
85
The thick ascending limb is the site of action of what type of diuretics?
loop diuretics
86
What do the loop diuretics do?
They attach to the Cl- binding site of the Na+ - K+ - 2Cl- contransporter which stops the cycle of this 3 ion contransporter
87
Loop diuretics _____ NaCl reabsorption in the thick ascending limb
completely inhibit
88
What is the thick ascending limb called? Why?
the diluting segment, because the solute is reabsorbed, but water remains behind, diluting the tubular fluid
89
The tubular fluid that leaves the thick ascending limb has a _____ Na+ concentration and a ______ osmolarity than blood
lower
lower
90
What constitutes the terminal nephron?
The distal tubule and collecting duct
91
The distal tubule and collecting duct reabsorb _% of the filtered Na+
8
92
The early distal tubule reabsorbs _% of the filtered Na+
5
93
By what mechanism is Na+ reabsorbed into the early distal tubule?
Na+ Cl- cotransporter
94
Describe what happens after Na+ is reabsorbed into the cells of the early distal tubule with Cl-
Na+ is extruded from the cell into the blood by the Na+ - K+ ATPase, and Cl- diffuses out of the cell through Cl- channels in the basolateral membrane
95
How does the Na+ - Cl- cotransporter of the early distal tubule differ from the Na+ - K+ - 2Cl- contransporter of the thick ascending limb?
It transports 2 ions (not 3) so it is electroneutral (not electrogenic)
96
What type of diuretics inhibit the early distal tubule?
Thiazide diuretics
97
How do thiazide diuretics inhibit NaCl reabsorption?
The bind to the Cl- site of the Na+ - Cl- contransporter and prevent it from cycling
98
Is the early distal tubule permeable to water? What does this result in?
no
The tubular fluid is further diluted
99
What is the early distal tubule called?
The cortical diluting segment (because the distal tubules are in the renal cortex)
100
What are the 2 major cell types dispersed along the late distal tubule and collecting duct?
- principal cells
| - alpha-intercalated cells
101
What 3 things are the principal cells involved in?
- Na+ reabsorption
- K+ secretion
- water reabsorption
102
What 2 things are the alpha-intercalated cells involved in?
- K+ reabsorption
| - H+ secretion
103
The late distal tubule and collecting duct reabsorb _% of the filtered Na+
3
104
The mechanism for Na+ reabsorption in the late distal tubule and collecting duct occurs in the _____ cells
principal
105
What is different about the principal cells?
They contain Na+ channels in which the Na+ can diffuse through down its electrochemical gradient, from the lumen into the cell
106
What is the critical role of the late distal tubule and collecting duct?
fine adjustments to Na+ excretion
107
What regulates Na+ reabsorption in the late distal tubule and collecting duct?
hormones, namely aldosterone
108
Aldosterone acts directly on the principal cells to ______ Na+ reabsorption
increase
109
What inhibits Na+ reabsorption by the principal cells?
K+ sparing diuretics
110
What is water permeability of the principal cells controlled by?
ADH
111
When ADH levels are low, the water permeability of the principal cells is ___, and water ____ reabsorbed with NaCl
low
isn't
112
When ADH levels are high, the water permeability of the principal cells is ___, and water ____ reabsorbed with NaCl
high
is
113
What are the 4 renal mechanisms that regulate Na+ excretion?
- sympathetic nerve activity
- atriopeptin (ANP)
- Starling forces in peritubular capillaries
- renin-angiotensin-aldosterone system
114
How do the 4 renal mechanisms adapt to increase Na+ excretion (associated with increased Na+ intake)?
All of which result in what?
- sympathetic nerve activity decreases
- atriopeptin (ANP) increases
- oncotic pressure in the peritubular capillaries decreases
- renin-angiotensin-aldosterone system acticity decreases
*All of which result in decreased Na+ reabsorption in the proximal tubule and collecting ducts
115
How do the 4 renal mechanisms adapt to decrease Na+ excretion (associated with decreased Na+ intake)?
All of which result in what?
- sympathetic nerve activity increases
- atriopeptin (ANP) decreases
- oncotic pressure in the peritubular capillaries increases
- renin-angiotensin-aldosterone system acticity increases
*All of which result in increased Na+ reabsorption in the proximal tubule and collecting ducts
116
What is the maintenance of K+ balance essential for?
the normal function of excitable tissues
117
Where is most of the total body K+ located?
98% is located in the ICF
118
What maintains the large concentration of K+ in the ICF?
Na+ - K+ ATPase
119
The distribution of K+ across cell membranes is called what?
internal K+ balance
120
A shift of K+ out of cells produces an increase in the blood K+ concentration called ______.
hyperkalemia
121
A shift of K+ into cells produces a decrease in the blood K+ concentration called ______.
hypokalemia
122
What 7 things can cause hyperkalemia?
- insulin deficiency
- beta2 adrenergic antagonists
- alpha-adrenergic agonists
- acidosis
- hyperosmolarity
- cell lysis
- exercise
123
What 5 things can cause hypokalemia?
- insulin
- beta2 adrenergic agonists
- alpha-adrenergic antagonists
- lkalosis
- hyperosmolarity
124
The renal mechanisms that allow for urinary excretion of K+ to vary according to dietary K+ intake is called what?
external K+ balance
125
Urinary excretion of K+ is _____ to the dietary K+
equal
126
If excretion of K+ is less than intake, than a person is in _____ K+ balance and ___kalemia can occur
positive
hyperkalemia
127
If excretion of K+ is greater than intake, than a person is in _____ K+ balance and ___kalemia can occur
negative
hypokalemia
128
What are the 4 mechanisms by which K+ excretion is controlled?
- K+ is not bound to plasma proteins and is freely filtered across the glomerular capillaries
- the proximal convoluted tubule reabsorbs about 67% of the filtered K+ as part of the isosmotic fluid reabsorption
- the thick ascending limb reabsorbs an additional 20% of the filtered load of K+
- the distal tubule and collecting ducts are responsible for the adjustments in K+ excretion that occur when dietary K+ caries
129
How do the cells of the distal tubule and collecting duct fine-tune K+ excretion in persons on a low K+ diet?
There is further reabsorption of K+ by the alpha-intercalated cells
130
Describe the process by which K+ is further reabsorbed by the alpha-intercalated cells
The H+ - K+ ATPase pumps H+ from the cell into the lumen and simultaneously pumps K+ from the lumen to into the cell. The K+ then diffuses from the cell into blood via K+ channels
131
How do the cells of the distal tubule and collecting duct fine-tune K+ excretion in persons on a normal or high K+ diet?
K+ is secreted by the principle cells
132
K+ secretion is the net transfer of K+ from ____ into _____
blood
lumen
133
Describe the process by which K+ is excreted by the principal cells
K+ is brought into the cell from the blood by the Na+ - K+ ATPase. K+ then diffuses across the luminal membrane rather than being recycled across the basolateral membrane into the blood because the K+ permeability and the size of the electrochemical gradient for K+ are higher in the luminal membrane
134
What 6 things can cause increased K+ secretion?
- high K+ diet
- hyperaldosteronism
- alkalosis
- thiazide diuretics
- loop diuretics
- luminal anions
135
What 4 things can cause decreased K+ secretion?
- low K+ diet
- hyperaldosteronism
- acidosis
- K+ sparing diuretics
136
__% of calcium is reabsorbed.
99
137
What percentage of Ca2+ GFR is ultrafiltrate?
60%
138
The _____ tubule is the only nephron segement in which Ca2+ reabsorption is not coupled directly to Na+ reabsorption
distal
139
The distal tubule reabsorbs about _% of the filtered load of Ca2+
8
140
Distal Ca2+ reabsorption has its own regulatory hormone, what is it?
PTH
141
In the distal tubule, PTH ______ Ca2+ reabsorption
increases
142
The action of PTH on the distal tubule is called what?
hypocalciuric action
143
Thiazide diuretics ______ Ca2+ reabsorption
increase
*this is different from Na+
144
Body fluid osmolarity is maintained at a value of about ___ mOsm/L by a process called what?
290
osmoregulation
145
Urine osmolarity can vary from as low as __ mOsm/L to as high as ____ mOsm/L
50 - 1200
146
When urine osmolarity is equal to blood osmolarity it is called ______ urine
isosmotic
147
When urine osmolarity is higher then blood osmolarity it is called ______ urine
hyperosmotic
148
When urine osmolarity is lower then blood osmolarity it is called ______ urine
hyposomotic
149
Describe the sequence of events that occur when a person is deprived of drinking water
1) plasma osmolarity increases
2) osmoreceptors in the anterior hypothalamus are stimulated
3) this stimulates thirst and also secretes ADH from the posterior pituitary
4) ADH circulates to the kidneys where is produces an increase in water permeability of the principal cells of the late distal tubule and collecting duct
5) this results in increased water reabsorption
6) this results in an increased urine osmolarity and urine volume to decrease
7) these mechanisms coupled with drinking behavior decrease plasma osmolarity back toward normal
150
Describe the sequence of events that occur when a person drinks water
1) ingested water dilutes the body fluids and causes a decrease in plasma osmolarity
2) this inhibits osmoreceptors in the anterior hypothalamus
3) this decreases thirst and inhibits the secretion of ADH from the posterior pituitary
4) this causes a decrease in water permeability of the principal cells
5) this results in decreased water reabsorption and the water that is not reabsorbed by these segments is excreted
6) this means urine osmolarity decreases and urine volume increases
7) these mechanisms coupled with inhibition of thirst and suppression of water drinking plasma osmolarity increases back toward normal
151
What is the corticopapillary osmotic gradient?
A gradient of osmolarity in the interstitial fluid of the kidney from the cortex to the papilla
152
The osmolarity of the cortex is approximately ___ mOsm/L.
| The osmolarity at the tip of the papilla is ____ mOsm/L
300
1200
153
What are the 2 processes that contribute to the osmotic gradient?
- countercurrent multiplication
| - urea cycling
154
Countercurrent multiplication is a function of what?
the loops of Henle
155
What is the role of countercurrent multiplication in the formation of the corticopapillary osmotic gradient?
to deposit NaCl in the interstitial fluid of the deeper regions of the kidney
156
Countercurrent multiplication will build up a gradient of osmolarity in the interstitial fluid through a repeating __-step process. What are these steps?
2:
single effect
flow of tubular fluid
157
What does the single effect refer to?
NaCl reabsorption via the Na+ K+ 2Cl- cotransporter in the thick ascending limb of the loop of Henle that
158
As a result of the single effect, the osmolarity of the ascending limb _____ and the osmolarities of the interstitial fluid and descending limb _____.
decreases
increases
159
Describe how osmolarity of the descending limb and interstitial fluid increases during the single effect?
NaCl is reabsorbed out of the ascending limb and deposited in the surrounding interstitial, water is left behind. Fluid in this limb equilibrates with the interstitial fluid
160
Describe the flow of fluid
New fluid with an increased osmolarity from the descending limb is "oushed down" toward the bend of the loop of Henle
161
What happens to the gradient of osmolarity with each passing step?
it multiples it
162
What does the size of the corticopapillary osmotic gradient depend on?
the length of the loop of Henle
163
Describe what happens to urea concentration in the cortical and outer medullary collecting ducts
1) ADH increases water permeability, but it does not increase urea permeability
2) this results in water being reabsorbed from the cortical and outer medullary collecting ducts, but urea remains behind in the tubular fluid
3) this causes urea concentration of the tubular fluid to increase
164
Describe what happens to urea concentration in the inner medullary collecting ducts
1) ADH increases water permeability and it also increases the transporter for facilitated diffusion of urea
2) urea diffuses down its concentration gradient into the interstitial fluid
3) urea that would otherwise been excreted is recycled into the inner medulla, where it is added to the corticpapillary osmotic gradient
165
When ADH levels are high the corticopapillary gradient is _____ than when ADH levels are low.
larger
166
What specialized capillaries participate in countercurrent exchange?
the vasa recta
167
How does countercurrent exchange differ from countercurrent multiplication?
Countercurrent multiplication is an active process that establishes the corticopapillary osmotic gradient, whereas countercurrent exchange is a passive process that helps maintain the gradient
168
Describe the osmolarity of the descending limb, bend, and ascending limb of the vasa recta
Each segment equilibrates with the surrounding interstitial fluid
169
The blood leaving the vasa recta has a slightly _____ osmolarity than the original blood that entered. Explain why...
higher, because some of the solute from the corticopapillary osmotic gradient was picked up and will be carried back to the systemic circulation
170
The mechanisms of countercurrent multiplication and urea cycling continuously replace any solute that may be carried away by blood flow.
True
