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556 - Physiology & Pathophysiology II > Exam 8 - Tubular Reabsorption & Secretion > Flashcards

Exam 8 - Tubular Reabsorption & Secretion Flashcards

(69 cards)

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1
Q

Filtration rate

A

GFR x Plasma [ ]

Normal GFR = 180 L/day

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2
Q

100% filtered nutrients

A
  • Glucose
  • Bicarb
  • Na
  • Cl (99%)

Others:

  • K (88%)
  • Urea (50%)
  • Creatinine (0%)
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3
Q

Primary active transport mechanisms in reabsorption

A
  • Na/K ATPase (drives O2 consumption)
  • H ATPase
  • H-K ATPase
  • Ca ATPase
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4
Q

Co-transport mechanisms in reabsorption

A
  • Na/glucose
  • Na/amino acids
  • both concentrate in the body…move into body with Na
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5
Q

Counter transport mechanisms in reabsorption

A
  • Na/H

- move H into lumen for excretion…opposite Na

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6
Q

Pinocytosis

A
  • movement of proteins back into body

- protein in urine is bad

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7
Q

Passive mechanisms in reabsorption

A
  • H20

- bulk flow

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8
Q

Na/K ATPase

A
  • Na into interstitial space and K into tubular cells
  • on basolateral side
  • creates -70mV potential in tubular cells
    • drives Na into cell via electrical and [ ] gradient
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9
Q

Na [ ] gradient

A
  • on brush border side (20x rate increase)
  • [ ] and electrical gradients drive Na from lumen into tubular cells
  • Na also pushed in via other co-transporters/counter-transport
  • Na quickly moves with H20 from interstitial into capillary
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10
Q

Glucose reabsorption

A

Luminal:

  • Co-transport with Na
  • SGLT2…90%…early part
  • SGLT1…10%…later part

Basolateral:

  • passively down [ ] gradient
  • GLUT2…early / GLUT1…later
  • Bulk flow moves from interstitial into capillary
  • cell membrane not permeable to glucose
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11
Q

Amino acid reabsorption

A
  • co-transport pump w/ Na on lumen side
  • diffuse out of cell on basolateral side following [ ] gradient
  • moves into capillary via bulk flow
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12
Q

H secretion

A
  • Don’t want to absorb / control pH balance
  • Na/H counter transport on brush border
  • H gets trapped in lumen
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13
Q

Max solute transport

A
  • depends on type of transport
  • Max tubular reabsorption
  • Max secretion
  • Gradient-time transport (Na…although mainly Na/K ATPase)
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14
Q

Max reabsorption of glucose

A
  • in mg/min
  • carrier proteins are saturated
  • glucose filtered load = 125 mg/min
  • glucose Tmax = 375 mg/min
  • at 200 mg/dl…glucose seen in urine
  • why do we see glucose in urine at 200?
  • so many nephrons…all are different…avg is 375
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15
Q

Tmax of plasma proteins

A
  • 30 mg/dl

- not normally that high

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16
Q

Absorption

A

Filtered > excretion

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17
Q

Secretion

A

Filtered < excretion

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18
Q

Creatinine Tmax

A
  • secretion

- 16 mg/dl

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19
Q

PAH Tmax

A
  • 80 mg/min

- secreted

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20
Q

Gradient time transport max

A

Depends on:

  • electrochemical gradient
  • membrane permeability
  • time in tubule (longer time…more transport)
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21
Q

Na Tmax

A
  • not shown… high Na/K pump capacity
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22
Q

Na leak back into lumen

A

Caused by:

  • through tight junctions
  • interstitial [ ] of Na
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23
Q

Na reabsorption in proximal tubule

A
  • [plasma Na] up…[tubule Na] up… reabsorption up
  • drop in tubular flow rate also increase Na absorption
    • MAP down…GFR down…tube flow down…reabsorption up…H2O up… MAP up
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24
Q

Na reabsorption in distal tubule

A
  • can show a Tmax
  • minimal back leak…tighter junctions
  • aldosterone increases Tmax for Na in distal
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25
What replaces Na as H2O driving force in later parts
Urea
26
H2O absorption in proximal tubule
- highly permeable - rapid movement...so solute gradient minimal - solvent drag: H2O carries solute with it due to high permeability
27
H2O in loop of Henle (ascending) / early distal
- low permeability | - little movement even though large osmotic gradient
28
H2O in distal / collecting tubules and ducts
- variable permeability...depends on ADH | - no solvent drag...just water can move here
29
Passive Cl reabsorption
Driven by Na reabsorption: - more negative lumen...pushes Cl into cell - more H2O in...makes lumen [Cl] high...drives Cl into cell - Cl also cotransport with Na in lumen side
30
Passive Urea reabsorption
- H2O into cells makes lumen [urea] high - drives urea into cell - happens in collecting duct - only 50% reabsorption
31
% reabsorption in proximal tubule
- 65% of Na and H2O - little less foe Cl...it follows Na and H2O - can be increased or decreased in later parts
32
Proximal tubule structure
- lots of mitochondria for active transport - high SA brush border - transport proteins for co/counter (glucose, AA / H) - lots of Na/K ATPase in basolateral border - isosmotic...Na/H20 absorbed at same rate
33
Early proximal tubule
- majority of reabsorption - co transport of glucose and amino acids - Na carries glucose, bicarb, organics...leaves Cl - increase [Cl] here... 105 to 140
34
Late proximal tubule
- Na drives Cl reabsorption - high [Cl] favors diffusion - small amount through Cl specific channels
35
Proximal tubule volume concentrations
- stays isosmotic due to Na/H2O reabsorption at same rate - creatinine/urea not secreted yet...but [ ] up due to H2O down - total amount does not change - Na/Cl/bicarb/glucose/AA amount all go down
36
Secretion in proximal tubule
Metabolites: -bile salts / oxalate / irate / catecholamines Toxins/Drugs: - penicillin / salicylates - Also PAH...90% removed...used to determine RBF
37
Juxtoglomerular nephrons
- [ ] urine
38
Thin descending loop
- thin epi / no brush border / few mito / minimal metabolic - reabsorption of H2O...high permeable - moderately permeable to solute (H2O carries... no active) - 20% of H2O reabsorption in loop - Ascending part IMPERMEABLE to water
39
Thick ascending loop
- thick epi / lots of mito / high metabolic - reabsorption Na / Cl / K / Ca / bicarb / Mg....25% of load - dilute here...no water reabsorption - Hyposmotic here... 90% Na in...only 85% water in
40
Na reabsorption in thick ascending
- driven by Na/K ATPase in basolateral border (Na out/K in) - 1 Na-2 Cl-1 K co transport into cell from lumen - primary mover of Na at this level - K moves against gradient - Cl and K diffuse out into interstitial via specific channels - Na/H counter transport here as well
41
Loop diuretics
- affect thick ascending loop - block 1-2-1 - Furosemide / Ethacrynic acid / Bumetanide - less Na reabsorption... less water in... less K in - loss of K a problem here
42
Paracellular reabsorption in thick ascending
- Na/K/Mg/Ca - driven by electrochemical gradient through tight junctions - 1-2-1 carrier keeps ISO electric but K leaks back into lumen - cause +8mV in lumen...pushes ions through out of lumen
43
Early distal tubule
- macula dense first part...feedback for GFR/blood flow - macula dense only in juxtaglomerular nephron - second part highly convoluted - solute reabsorbed...H2O NO (diluting segment) - 5% of Na/Cl here - Na/K in basolateral border - Na/Cl co transport into cell - Cl diffuse into interstitial via specific channels - Thiazide diuretics block Na/Cl co transport - reduces H2O reabsorption in later parts - no effect on K [ ]
44
Late distal / collecting tubule
- impermeable to urea - Na reabsorption / K secretion controlled via aldosterone - secrete H ions against 1000:1 gradient - proximal only 4-10:1 - H2O permeability controlled by ADH aka vasopressin
45
Principal cells
- in late distal / cortical collecting tubule - reabsorb Na/H2O - secrete K - Na/K ATPase on basolateral drives activity - Na in from lumen via gradient - K out into lumen via gradient
46
Intercalated cells
- reabsorb K - secrete H - H-ATPase on lumen side - H from carbonic anhydrase rxn - bicarb out into capillary via Cl co-transport on basolateral side - Cl out into lumen - CO2 in and out freely on basolateral side
47
K sparing diuretics - Aldosterone antagonists
- competitive at receptor site - block Na/H2O reabsorption and K secretion - Spironolactone - Eplerenone
48
K sparing diuretics - Na channel blockers
- block entry on Na on lumen side - reduces Na movement via Na/K ATPase - which reduces K secretion - Amiloride - Triamterene
49
Collecting duct
- 10% of H2O/Na - determines final [ ] of urine - few mito - H2O permeability controlled via ADH - Urea main driver now...via Urea reabsorption - secretes H ions like collecting tubule
50
Inulin
- neither secreted or reabsorbed - provides indicator of H2O reabsorption - similar to creatinine except creatinine slightly secreted If inulin [ ] = 3...1/3 of water in tubule...2/3 reabsorbed
51
Regulating tubular reabsorption
- glomerulotubular balance - peritubular capillary and interstitial forces - arterial BP - hormones - sympathetic nervous effect (not big effect) (Na absorption up) - some controlled independently
52
Glomerulotubular balance
- increase in reabsorption if increase in tubular load - If GFR up to 150 from 125...proximal will still take 65% of total - maintains Na and volume homeostasis - keep normal flows to distal tubule even if big change in MAP
53
Peritubular capillary and interstitial forces
- Net reabsorption across length of capillary - IN (32o+6) - OUT (13+15o) = 10 IN - Normal rate of reabsorption = 124 ml/min - interstitial #'s only change if disease - reabsorption coefficient = 12.4 mls/min/mmHg
54
Peritubular hydrostatic pressure increase...
- reabsorption down Caused by: - MAP up - resistance of arterioles down
55
Peritubular oncotic pressure increase...
- reabsorption increases Caused by: - plasma protein up - Filtration fraction up Fraction = GFR / RPF
56
Reabsorption coefficient
- affected by permeability and surface area - directly related - if coefficient up...reabsorption up - only changes in diseased states
57
Arterial pressure control
- Increase MAP...slightly less reabsorption of Na/H2O - small increase in cap hydrostatic / increase in interstitial hydrostatic / increase backflow into lumen THEN.... - angio II decreases... less Na reabsorption.. less aldosterone ...less Na reabsorption
58
Aldosterone
- collecting duct/tubule - increase NaCl/H2O absorption - increase K secretion - regulator of K Stimulated by: - increase K - increase angio II ``` Addison's = absence Conn's = excess ```
59
Angio II
- Proximal / Thick / distal / collecting - increase NaCl / H2O reabsorption - increase K secretion - most powerful - stimulated by low BP/volume - affects transport on both borders - very active in proximal
60
ADH / vasopressin
- distal / collecting - increase H2O absorption - made in hypothalamus ... released in post pit - binds with V2 receptors on basolateral - stimulates H2O channels to open on lumen side - absence causes diabetes insipidus...19L urine
61
Atrial natriuretic peptide
- distal / collecting | - decrease NaCl reabsorption
62
PTH
- proximal / thick / distal - increase Ca reabsorption - decrease PO4 reabsorption
63
Clearance formula
Cz x [Pz] = [Uz] x V Clearance/Volume = ml/min [ ] = mg/ml
64
Urine excretion rate
V x Uz
65
Filtration rate
GFR x Pz
66
Measure of GFR
- Inulin...freely filtered...neither secreted/absorbed - We use creatinine...close - excreted slightly more than filtered - plasma [ ] estimation overestimates...so we cancel - 4x levels of creatinine in blood = 1/4 of normal GFR - creatinine normal = <1.5
67
PAH in renal plasma flow
- 90% cleared RPF = PAH clearence / 0.9 RBF = RPF / (1-Hct) or 22% of CO
68
Absorption formula
Filtered - excretion | GFR x Pz) - (V x Uz
69
Secretion formula
Excretion - Filtered | Uz x V) - (GFR x Pz

556 - Physiology & Pathophysiology II (8 decks)

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