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Tubular Reabsorption Flashcards

1
Q

What is reabsorbed in proximal tubule?

A

All FREELY FILTERED substances: Na+, Cl-, K+, Ca2+, HCO3-, H20, glucose, amino acids, vitamins, urea, choline

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2
Q

What is reabsorbed in the descending limb of Loop of Henle?

A

H20

descending limb = concentrating segment bec/ only permeable to water so water LEAVES

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3
Q

What is reabsorbed in the ascending limb of Loop of Henle?

A

Na+, Cl-, K+, Mg2+, Ca2+, NH4+ = all reabsorbed to create concentration gradient

ascending limb = diluting segment = solute LEAVES

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4
Q

Where does ADH act? What’s the mechanism?

A

Collecting duct,
opens up aquaporin channels there,
ultimately this concentrates urine

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5
Q

What is secreted (and most of the time excreted!) in the proximal tubule?

A

H+, NH4+, Toxins, Drugs

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6
Q

What is reabsorbed in the distal tubule?

A

Ca2+, Na+, Cl-, H20

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7
Q

What is secreted (and excreted most of the time!) into distal tubule?

A

H+, K+

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8
Q

What is reabsorbed in the collecting duct?

A

Na+, K+, Cl-, Ca2+, HCO3-, H+, urea, H20

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9
Q

What’s secreted in the collecting duct?

A

K+, H+, NH4+

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10
Q

Where does Aldosterone act?

A

Distal tubule

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11
Q

What controls Aldosterone’s regulation?

A
  • Potassium (K+) High levels = triggers adrenal cortex cells to release aldosterone
  • Blood pressure (low BP) triggers aldosterone
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12
Q

What transporters are found in the proximal tubule? And which side of the membrane are they found on?

A
  1. Na+ glucose symporter on Apical side
  2. MANY Na+-K+ ATPases (on ALL cells in body) on BasoLateral side (3Na+ out, 2K+ in)
  3. Glut2 Transporter pumps out glucose into plasma (basolateral?)
  4. H+ out, Na+ in antiporter (apical)
  5. K+ channels (apical)
  6. Cl-HCO3 Antiporter (basolateral) OR Na (out)-HCO3 (our) Symporter (basolateral)
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13
Q

What is Tmax for glucose?

A

320 mg/min (= filtered load of glucose)

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14
Q

What structure is found in both the proximal tubule and distal tubule?

A

microvilli (for reabsorption!)

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15
Q

Do organic substances (glucose, amino acids, acetate, Krebs cycle intermediates, water-soluble vitamins, lactate, acetoacetate) use 2ndary transport?
What are key characteristics of this transport?

A

YES!

  • Has Tmax
  • specific for stereochemistry (D or L configuration)
  • can be inhibited by drugs, disease
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16
Q

What is the filtered load of Na+ normally?

A

We reabsorb at least 95% of all Na+ we take in daily!!

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17
Q

What transporters are in the Loop of Henle?

A 
Ascending limb = has Na+-K+-2Cl- exchanger (apical membrane), 
Ca2+ channels (apical?)
Ca2+ ATPase (basolateral)
Cl- (basolateral)
K+ channels (apical + basolateral)
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18
Q

What are the 2 types of cells found in the distal tubule?

A 
Principal cells (mainly in latter DT)
Intercalated cells (mainly in medullary collecting ducts)

*also macula densa cells have baroreceptors? so signal renin to secrete angiotensin?

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19
Q

What transporters are in the distal convoluted tubule?

A
  1. Na+/Cl- symporter (Apical membrane)
  2. Ca+ channels (Apical membrane)
  3. Na+ channels (Apical membrane)
  4. K+ channels (Apical membrane)
  5. Na+K+ ATPase (Basolateral membrane)
  6. Cl- channels (Basolateral membrane)
  7. Ca+/3Na+ antiporter (Basolateral membrane)
  8. Ca2+ ATPase (BL)
  9. H+ into lumen/K+ into cell Antiporter (apical)
  10. HCO3 (out of cell into blood) - Cl- Antiporter (basolateral) OR HCO3- Na symporter (BL)
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20
Q

Apical membrane is side of membrane closest to _______ vs. basolateral which is closest to __________?

A 
Apical = closest to lumen of tubule
Basolateral = closest to blood
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21
Q

Where does Aldosterone act and what’s its effect/does it do?

A 
Distal tubule (remember mainly this for class), Collecting Duct
Effect: increases NaCl + H20 reabsorption, K+ Secretion
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22
Q

Where does ADH act?

A 
Collecting ducts (mainly) and distal tubule to reabsorb water
*also proximal tubule to increase NaCl, water reabsorption, SECRETION of H+
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23
Q

Where does PTH act?

A

Proximal tubule, Thick ascending loop of henle, distal tubule by increasing Ca2+ reabsorption, PHOSPHATE SECRETION

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24
Q

Where does ANP/ANF act?

A

Distal Tubule, Collecting Duct to DECREASE NaCl reabsorption

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25
Which type of pathway do ions use to cross the cell which involves many transporters?
Transcellular pathway!
26
2ndary active transport always relies on a _______ gradient?
Na+ gradient (created by Na+/K+ ATPase)
27
What are the secondary capillaries surrounding the proximal and distal tubule that can take substances directly into the blood stream?
Peritubular capillaries
28
Reabsorption moves solutes from _______ to ______?
tubular fluid/lumen into (cell then to interstitial fluid) then to plasma
29
What happens when a substance hits transport max - it is reabsorbed or secreted?
Reabsorbed! It's only secreted if the # of molecules filtered ABOVE transport max!
30
Which type of nephron has higher Tmax for glucose?
juxtamedullary
31
What is splay?
variability in body, | heterogeneity in nephrons (cortical= so e.g. glucose hits Tmax earlier in urine) vs. (juxtamedullary)
32
What are the 2 types of nephrons?
Cortical (80% of kidney) and juxtamedullary (20% of kidney)
33
What happens when substances filtered go above Tmax? Reabsorption or secretion?
Secretion!
34
Urea, uric acid, breakdown products of hormones, drugs etc. are ______?
secreted and excreted
35
All organic substances are freely filtered - how are they reabsorbed?
by 2ndary active transport so using transporters | =always less than Tmax
36
You can only reabsorb something if it has a __________ transporter in the body?
specific (configuration-specific e.g. D vs. L)
37
Where and how is Na+ reabsorbed?
1. PCT - 65-75% via Na+/Glucose Transporter (run by Na+/K+ ATPase creating gradient) 2. Loop of Henle - 15-20% = via Na+/K+/2Cl- exchanger (Na+, 2Cl- down its conc gradient, K+ up its conc gradient) 3. Distal tubule = 5% 2 ways: a. Na+/Cl- symporter = SIMPLE way! b. Aldosterone (steroid hormone) = complicated way: Na+ reabsorption by increasing Na+/K+ ATPases, Na+ channels, K+ channels to secrete K+ So at least 95% of Na+ filtered is going to be reabsorbed!
38
What's a normal GFR?
100-125 mEq/L
39
What's the normal filtered load of Na+?
25,200 mEq/day (*95% of Na's Filtered Load is reabsorbed)
40
What's the normal concentration of Na+ in the plasma?
140 mEq/L
41
How do we reabsorb Bicarb?
using Na+/H+ Antiporter (only antiporter in PCT!)
42
Are Na+ and Glucose reabsorbed the same way?
Yes! via the Na+/Glucose Symporter (cotransporter) via Na+/K+ creating gradient *so this is 2ndary active transport and TRANSCELLULAR pathway
43
Every time Na+ is reabsorbed, what is also reabsorbed?
H20
44
What's the major anion in the ECF?
Cl-
45
Does Cl- use a Paracellular pathway? How is it reabsorbed?
Yes! | by being dragged along with Na+ to ensure there's NO electrical gradient
46
Do most ions use the transcellular or paracellular pathway?
transcellular
47
Is inulin filtered, reabsorbed and/or secreted?
only filtered
48
Is glucose filtered, reabsorbed and/or secreted?
filtered and reabsorbed
49
How does the Na+/Cl+/K+ exchanger on Ascending limb of loop of henle work?
Na+ = down conc (out so into blood) 2 Cl- = down conc K+ = up conc gradient
50
How do diuretics work?
Work on distal tubule mainly to increase volume of urine (so more Na+ and more water!): 1. Thiazide = Blocks Na+/Cl- channel so prevents reabsorption of Na+ and Cl- so more Na+, H20 so have more Na+ and H20 in urine 2. Amelioride Blocks Na+ channels that aldosterone opens so excrete more Na+ and H20 in urine
51
Is proximal convoluted tubule equally permeable to both water and solutes?
Yes! | That's why its iso-osmotic
52
What's the concentration of filtrate by the time we get to distal tubule?
150 (bec/ lost solute but kept water in thick ascending limb)
53
Under normal conditions, do we have a net absorption or secretion of K+?
Secretion (occurs in distal tubule and collecting duct) | via Distal Tubule Principal cells via Na+/K+ ATPase, Na+ channel and K+ channel
54
Where and how do you reabsorb K+?
1. Proximal tubule by Bulk flow (K+ pulled along) = paracellular 2. LOH by Na+/K+/Cl- Transporter = transcellular & via bulk flow = paracellular
55
What controls K+ secretion?
``` Aldosterone (increases K+ secretion by decreasing K+ plasma levels!) homeostatic control (negative feedback) ```
56
What affects aldosterone regulation?
1. K+ levels | 2. blood volume/blood pressure
57
Most reabsorption of calcium occurs where?
PCT
58
How is Calcium regulated?
``` PCT - we don't know transporters LOH via primary active transport increases Ca2+ channels (apical) and increases Ca2 + ATPases (but NOT 2ndary only PRIMARY active transport) and Distal tubule (same as LOH) ```
59
PTH works mainly on the ____________?
distal tubule
60
Bicarb is mainly reabsorbed where?
PCT

Kidneys (5 decks)

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