Transport Along The Nephron Flashcards
1
Q
Tube,are Rena, epithelial cells exhibit what
A
Membrane polarity
2
Q
What side of the renal epithelial cells face the urine
A
Apical/tubular
3
Q
What side of the renal epithelial cells faces the interstitial and peritubular caps
A
Basal/basolateral
4
Q
How do the two side of renal epithelial cells differ
A
- different transporters/channels
- maintains a cxn gradient for movement of solutes
- inside of cell maintains a low cxn of everything
5
Q
What are the two ways solutes move in the kidneys
A
Paracellular or transcellular
6
Q
Paracellular
A
Solutes move between the cells (filtration in normal caps)
7
Q
Transcellular
A
Solutes move across the cell (transport protein or cx gradient)
8
Q
Active transport
A
Against gradient
Uses ATP
9
Q
Passive transport
A
With gradient and no atp
10
Q
Simple diffusion
A
Due to gradient, also bulk flow (ultrafiltration)
11
Q
Carrier mediated diffusion
A
Needs a carrier protein. Has a Tm
12
Q
How much plasma does the kidney filter every day
A
180L
13
Q
What is the minimum excretion of urine a day
A
0.5L a day
14
Q
How much of what is filtered gets reabsorbeD?
A
Nearly everything. 99%
15
Q
Ability to adjust reabsorption rate to match the filtered load
A
Glomerulotubular balance
If you eat too much salt, after a couple days your kidney will adjust to secrete more sodium
16
Q
What happens when the pressure drops from glomerular to peritubular capillaries
A
Osmotic pressure rises
17
Q
Net filtration from tubule INTO peritubular capillary
A
Starling forces
18
Q
Where are the sealing forces relevant
A
PCT
19
Q
Transport of OTHER solutes from tubule into caps will osmotically pull water along with it (water follows salt)
A
Osmosis
20
Q
What happens to the osmotic pressure of caps if the RBF increases
A
Will not increase as much.
GFR increases, but reabsorption drops
21
Q
Reabsorption of water (via paracellular filtration) will pull solutes along with it (Ca2+ and K+)
A
Solvent drag
22
Q
Most Na+ movement is __________
A
Transcellular (active transport)
23
Q
Reabsorption of Na and its cotransported solutes causes
A
Osmotic gradient. Reabsorbs water
24
Q
What is the osmotic gradient created by reabsorption of Na and its cotransporters important for
A
-DM. Glucose has to be transports in with Na. Lose glucose in urine and increase osmotic pressure and pull out water
25
Something that isn't supposed to be there keeping water in the tubules
Osmotic diuresis
26
What kind of transport on the baslateral membrane
Active transport
27
What is responsible for the active transport on the basolateral membrane
ATPase (3 Na out, 2 K in)
- makes cell have neg charge relative to tubular fluid
- osmotic gradient to pull water
- forms a Na gradient bc apical side has no Na channels (impermeable)
28
What is the established gradient from the active transport at the basolateral membrane used for
Secondary active transport
29
What is Na reabsorbed wit h
Bicarbonate
30
What is required for the reabsorption of bicarbonate
Carbonic anhydrase
- takes H+ and HCO3- and makes water and CO2. Takes the negative HCO3- which cant get across the membrane and turns it to CO2 and H20 so it can get it across
- usually reabsorbed 100% HCO3
31
What is Na cotransported with
Glucose, amino acids, phosphates, lactate
32
Late PCT reabsorption of Na
No more glucose/ amino acids
| -Na now gets cotransported with Cl- through the paracellular route as well as transcellular
33
What else other than CL- does Na get reabsorbed with in the late PCT?
When anions are secreted/exchanged for Cl-
34
What are some anions that are secreted/exchanged for Cl- in late PCT reabsorption
OH-, formate, oxalate, HCO3-
| -binds H+ and neutralizes charge
35
Lack of filtered bicarbonate leads to what
Hyperchormia
36
What happpens to the lumen as CL- is removed and H+ neutralizes the OA_?
Becomes positive
37
Which of the following could explain why untreated diabetic patients have increases urine flow
Increases tubular fluid osmotic pressure
38
What effect would a carbonic anhydrase inhibitor have on urine volume and osmolarity
Increase volume, decrease osmolarity
39
Reabsorption of cations vs reabsorption of anions in the PCT
About equal
| -we reabsorb a lot of Pi- and HCO3- at the expense of Cl-
40
Movement of water vs the movement of sodium in the PCT
Matched
- osmolality doesn't change
- PCT is isomotic bc of high water permeability
41
What helps drive the paracellular reabsorption of cations late in PCT
Slight positive change in tubular fluid
42
What does PCT secrete
Organic anions (-)
- low specificity, high rate
- 100% cleared in one pass
43
What does PCT reabsorbs to excrete organic anions (PAH, penicillin)
A-ketoglutarate
44
Are transporters selective or non selective
Non selective.
- fast and low specificity
- too much of one organic anion can affect the transport of others
- PAH and penicillin (good)
- some other drug interactions can be fatal
45
Why is low dose penicillin coupled with PAH good
Competing for transporters
46
Where does PCT secrete organic cations
Into the tubular fluid
- creatinine, dopamine, epi/NE
- morphine, atropine, etc
Trades for H+
47
Transport maximum
Any transport process that utilizes a transport protein can become saturated
48
What can cause transporter maximum
Too much solute, not enough transporters
49
What is the Tm of the PCT
325mg/min
| Excretion=FL-Tm
50
Where does renal threshold occur
As you are approaching the maximum
- some glucose gets missed as you approach Tm
- play area is where the lines are not linear
51
If plasma glucose is 400mg/dl and GFR is 125ml/min. How much glucose is secreted. Tm for glucose is 325mg/min
Excretion=FL-Tm
FL=Xa*GFR
FL=4mg/ml*125=5001
500-325=175mg/min
52
What can be used as a readout of kidney health
Tm
53
What is the thin descending loop of henle permeabel to
Only water
54
Where does the DTL passes through
Hyperosmotic interstitium (300-1200mOsm)
55
How is water reabsorbed in the DTL
Due to osmotic forces
- volume of tubular fluid decreases
- solutes remain
- osmolarity increases
56
What is another name for the DTL
Tue concentrating segment
57
The ATL and water
It is impermeable to water, no water movement and no volume change
58
What is reabsorbed in the ATL
Some solutes passively, due to slight electrical forces
59
Transport in the ATL
Lost of transport
| -active, passive, paracellular, and transcellular
60
What is another name for the ATL
The diluting segment
61
What helps generate hyperosmotic gradient in tissue
ATL
62
Where is the Na-Cl-K symporter found
ATL
63
What does Lasix block
The Na-Cl-K symporter in the ATL
64
How does the macula densa sense Na+ to adjust GFR
Na-Cl-K symporter in the ATL
65
K+ transport is _______ in response to voltage difference in the ATL at the Na-Cl-K symporter
Paracellular
| -along with other positively charged ions
66
Where is the site of the macula densa and juxtaglomerular apparatus
ATL
- between the ascending loop and the distal tubule
- sense tubular sodium load by measuring transport rate, adjusts GFR accordingly
67
What does the early distal tubule do
Keep dilating tubular fluid
IMPERMEABLE TO WATER
-lots of transport )active, passive, para and trans)
68
Where is the Na-Cl symporter located
Early distal tube
69
What do thiazides block
Na-Cl symporter in the early distal tubule
70
Other than the Na-Cl sympoter, what else is found in the early distal tubules?
Some Na-Cl-K symporters, not a ton
71
Late distal and cortical collecting duct and water
Variable permeable to water
- responds to ADH
- tubular fluid is negative due to ammonium secretion
72
Where is the tubular fluid negative due to ammonium secretion
Late distal and cortical collecting ducts
73
What responds to ADH
Late distal and cortical collecting duct
74
What does the late distal and cortical collecting duct reabsorb?
NaCl and some water isoosmotically
75
What does the late distal and cortical collecting duct secrete?
K= and acid or bicarbonate if needed
76
What is the major site of aldosterone function
Late distal and cortical collecting duct
77
What are the two kinds of cells in the late distal and cortical collecting duct
Principle cells and intercalated cells
78
What are the principle cells of the late distal and cortical collecting duct important for
In the regulation of Na+, Cl-, K+, and water
- lots of active transport
- apical Na+ and K+ channels are present
- Cl- follows Na+
79
What is very sensitive to Na levels in the principle cells of the late distal and cortical collecting duct
Na-K pump
80
What does aldosterone do the principle cells of the late distal and cortical collecting duct
Increases Na-K pump activity
- also opens more apical Na+ channels
- lose K+ to save Na+ and water
81
What blocks aldosterone from binding the principle cells of the late distal and cortical collecting duct
Spironolactone
82
What do the intercalated cells of the late distal and cortical collecting duct do
- regulate H+ and HCO3- secretion/reabsorption
- can affect K_ levels (moves opposite H+)
- cellular function is dependent on presence of H+ in cells
- must have carbonic anhydrase function
83
What do acidotic tubular cells in the late distal and cortical collecting duct do
Pump acid into the urine, bicarbonate into the blood
84
What are the types of intercalated cells in the late distal and cortical collecting duct
Acidotic and alkolotic
85
What do alkalotic cells in the distal and cortical collecting ducts do
Put acid back in blood, pump base (HCO3-) into urine
86
What secretes acid to correct acidosis
Intercalated type A cells (acidotic cells)
87
What secretes base to correct alkalosis?
Intercalated type B cells (Alkalotic cells)
88
What is the final and more critical site of water balance in urine
Medullary collecting ducts
89
Medullary collecting ducts response to ADH
- ADH binds V2 receptors (vospressin 2)
- ADH adds aquaporins 2 (AQP2) to the apical membrane
- allows water to LEAVE tubule in response to osmotic gradient established by loop of henle of juxtamedullary nephrons
- makes concentrated urine
90
If there are no ADH in the medullary collecting ducts
They are impermeable to water, make dilute urine
91
PCT reabsorops ____ of Na and H2O
65%
| -all metabolic substances reabsorbs
92
DTL reabsorbs
20% H2O
93
TLA reabsorbs
25% Na
| -lots of Cl-, K+, Ca2+, bicarbonate, Mg2+ as well
94
Early DTL reabsorbs
5% Na_
95
Late DTL and CD reabsorbs
Less than 10% of Na+ and H2P
| -variable with ADH
