PSL301: Water 3 Flashcards
Tubular Function
1
Q
value: normal GFR
A
> 90 mL/min or > 125 L/day
2
Q
value: normal urine volume
A
0.5L - 2 L per day
3
Q
why is there such a big difference between filtered volume and excreted volume?
A
> 99% of water & solutes are reabsorbed by the tubules
4
Q
function of tubules
A
- reabsorb solutes & water
- secrete solutes & water
- maintain homeostasis
5
Q
when everything is normal, intake…
What is this called?
A
intake = secretion
“steady state”
6
Q
steady state
A
intake = secretion
7
Q
when there is a deficit of something, intake…
A
intake > excretion
excretion decreased
8
Q
when there is an excess of something, intake…
A
intake < excretion
excretion increased
9
Q
How does the kidneys maintain homeostasis?
A
adjust how much is reabsorbed & secreted
10
Q
What signals do the tubules receive, and what do they do?
A
- hormones
- nerves
- pH
- electrolyte concentrations
- pressure
signals modify reabsorption / excretion to keep body fluid composition normal
11
Q
Hormone signals to the kidney
A
- vasopressin / ADH
- aldosterone
- ANG II
- PTH
12
Q
purpose of ADH
A
water balance
13
Q
purpose of aldosterone
A
Na & K balance
14
Q
purpose of ANG II
A
Na & acid-base balance
15
Q
purpose of PTH
A
Ca++ & phosphate balance
16
Q
main nephron segments
A
- proximal tubule
- loop of Henle
- distal tubule
- collecting duct
17
Q
the collecting duct is divided into…
A
- cortical collecting duct
2. medulla collecting duct
18
Q
the Loop of Henle is divided into…
A
- Thick descending limb
- descending limb
- ascending limb
- thick ascending limb
19
Q
function of tight junctions at the transporting epithelium
A
- keep cells attached to each other
- prevent movement between adjacent cells (must pass through epithelial cells)
20
Q
The basolateral membrane of the epithelium faces the…
A
ECF / blood stream
21
Q
The apical membrane of the epithelium faces the…
A
lumen of kidney / intestines
22
Q
____ increases absorptive surface area on the __ side of the proximal tubule
A
brush border microvilli
lumen
23
Q
Most of the reabsorption occurs in the…
A
proximal tubule
24
Q
sites of reabsorption
A
- proximal tubule
- loop of Henle
- distal convoluted tubule & collecting duct
25
Glucose is reabsorbed in the...
all glucose is reabsorbed in the proximal tubule
26
How is K homeostasis maintained?
by secretion at the distal convoluted tubule & collecting duct
27
Most solutes & water homeostasis is controlled by the...
| What is the exception?
distal convoluted tubule & collecting duct
Glucose, controlled by proximal tubule
28
What are the things reabsorbed / secreted by the kidneys? (5)
- water
- Na
- K
- glucose
- bicarb
29
How do transporting epithelial cells work?
Polarized, so have different transport proteins on each side. Solutes must pass through different ones to get to other side.
30
the Na/K ATPase is located on which membrane?
basolateral
31
the Na/K ATPase is next to...
peritubular capillary
32
what does the Na/K ATPase do?
pumps 3 Na out of cell
pumps 2 K into cell
- makes cell negative
- make [Na] in cell low
33
the Na/K ATPase has what effect on Na in the lumen?
can enter cell naturally (down electrochemical gradient) @ apical membrane
Na then leaves through Na/K ATPase @ basolateral membrane
34
What is the purpose of Na movement?
Drives the movement of other solutes by cotransporters and antiporters on the apical membrane
35
cotransporters
transport 2 things in the same direction
| - movement of 1 thing down the gradient drives movement of other against the gradient
36
antitransporters
transport 2 things in opposite directions
| - movement of 1 thing down the gradient drives movement of other against the gradient
37
movement of water at the proximal tubule
```
follows Na (moves into capillaries)
- osmotic gradient
```
38
absorption & secretion t the proximal tubule is ___ because of the movement of sodium
passive
39
define: secondary active transport
an ion can move against the gradient by coupling with another that moves down the gradient
40
the Na/glu transporter is a(n)...
cotransporter
41
reabsorption of glucose
1. Na/glu cotransporter moves glucose into cell (where it is high concentration)
2. glucose moves out of cell on basolateral side using GLUT transporter
3. Na/K ATPase pumps Na out of cell to keep intracellular Na low
42
which ions use sodium co-transport as a method to get through cells?
- glucose
- phosphate
- chloride
...
43
how is paracellular transport achieved (at the renal tubules)?
- through tight junctions
- selective
- have pores
- driven by gradients
- only some ions (Na, Cl, Ca, Mg...) can get through
44
diuretic drugs block...
lumenal Na transporters
- increase Na secretion
specific diuretics target specific transporters
45
common target of diuretics
- loop of Henle
- distal convoluted tubule
- collecting duct
46
how does each nephron segment differ?
- type of transport protein
- leakiness
- type of hormone receptors present
47
things that will affect leakiness in tubules
- nature of the tight junction
| - presence of channels (e.g. aquaporins)
48
Trend of leakiness at the nephron tubules
Start off very leaky (proximal tubule)
| Get tighter as you go on (collecting duct)
49
proximal tubule is the site of...
most reabsorption (Na, Cl, K, bicarb, water)
50
the most important lumenal Na transport protein at the proximal tubule is...
NHE3 (sodium-hydrogen exchanger)
51
NHE3 works by...
pump Na into the cell
| pump H+ out of the cell
52
Purpose of NHE3
bicarb reabsorption
53
which cotransporters are only found on the proximal tubule?
- glucose
- phosphate
- amino acid
54
the proximal tubule is very leaky -> ____ reabsorption of Na. What does this mean?
isotonic
| [Na] in lumen is the same as [Na] in plasma due to water moving with Na
55
The thick ascending limb reabsorbs ___% of ___
20 - 30%
| filtered Na
56
what is the lumenal transport at the thick ascending limb?
Na/K/2Cl cotransporter (NKCC2)
57
NKCC2 is inhibited by...
furosemide (diuretic)
58
how permeable is the thick ascending limb to water?
not at all
59
fluid leaving the thick ascending limb is ____
hypotonic
| less concentrated than plasma because water in tubule cannot get out
60
What concentrates the medullary interstitium? What is the necessary for?
Add salt without water
Necessary for urine concentration
61
the thick ascending limb has a ___ lumen and a ___ ISF
dilute
| concentrated
62
the distal convoluted tubule reabsorbs ___% of _____
5 - 10%
| filtered Na and water
63
what is the lumenal Na transporter in the distal convoluted tubule?
NCC (sodium chloride cotransporter)
64
NCC is inhibited by which diuretic?
thiazides
65
Which is more potent: thiazides or furosemides? Why?
furosemide.
| thick ascending loop reabsorb more Na than the distal convoluted tubule
66
the distal convoluted tubule is important for...
urine dilution
67
when are thiazides used? furosemides?
furosemides used when you want a lot of Na+ lost in the urine.
thiazides used when you only want a bit more Na+ lost in the urine.
68
the collecting duct reabsorbs ____% of ____
1-3%
| filtered Na
69
reabsorption at the collecting duct depends on...
body's needs
70
what is the lumenal transport protein at the collecting duct?
ENaC (epithelial sodium channel)
71
the collecting duct has receptors for...
- aldosterone
| - vasopressin
72
effect of aldosterone binding to the collecting duct
increase Na reabsorption
- increase amount of Na channels
- open more Na channels
73
effect of ADH binding to the collecting duct
increase water reabsoprtion
| - increase aquaporin2
74
Effect of drugs on the collecting duct
collecting duct has low capacity, so it is easily affected by drugs
75
why is the collecting duct important?
- can generate large [ ] gradients
| - establish final urine composition / concentration
76
the collecting duct is less permeable to ___ than Na. What does this cause?
Cl-
| Causes lumen to be neg, so K+ will be secreted (down charge gradient)
77
the collecting duct is the site of regulation for the secretion of...
- Na
- K
- water
- ammonium
78
ammonium is secreted to regulate...
acid-base balance
79
There are __ transporters for glucose. They are...
2
| in series: proximal and distal
80
Properties of the proximal glucose transporter
- low affinity
| - high capacity
81
Properties of the distal glucose transporter
- high affinity
| - low capacity
82
How does the SGLT protein work?
1. Na+ binds
2. creates a site for glucose
3. glucose binding changes SGLT conformation
4. Na+ released, glucose follows
83
what does "high affinity for glucose" mean?
can transport glucose even if the glucose gradient is very opposing
84
what is the proximal glucose transporter called?
SGLT2
85
what is the distal glucose transporter called?
SGLT1
86
How does SGLT1 have a higher affinity for glucose?
exchanges 2 Na for 1 glucose
| 2 Na creates a higher drive into the cell
87
SGLT2 is located...
S1 segment of the proximal tubule / early proximal tubule
88
SGLT1 is located...
S3 segment of the proximal tubule / late proximal tubule
89
job of SGLT1
remove all glucose from the lumen
90
glucose (in) : glucose (out) ratio for SGLT2
70:1
91
glucose (in) : glucose (out) ratio for SGLT1
5000:1
92
What happens when someone has glucose in the urine with normal blood glucose?
- problem with SGLT2
| - no problem as long as they get enough calories
93
___ can be possible treatment for hyperglycemia and diabetes. What effect might this have?
SGLT2 inhibitor drugs.
- lower blood glucose
- lower weight
94
lumenal Na transport proteins
- Na cotransporters
- Na antiporters
- Na channels
95
___ has no large gradients because of ____
proximal tubule.
| very leaky
96
___ has large gradients because of ____
collecting duct.
| tight
97
Organic solute transporters are all...
proximal
98
water reabsorption is...
passive (osmotic gradient)
99
water reabsorption at the proximal tubule
follows Na isotonically
100
water reabsorption at the collecting duct
dependson the presence of ADH (aquaporin2)
