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Hum Physiology II > Tubular transport, lect 4 > Flashcards

Tubular transport, lect 4 Flashcards

1
Q

give equation for filtered load

A

FLx = GFR x Px

  • Px = plasma concentration of X
  • equation gives the amount of material in glomerular filtrate
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2
Q

give equation for excretion rate (mg/min)

A
  • amount of material lost in urine
  • ER = (Ux)(V)
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3
Q

Give equation for transport rates

A
  • amount of material added to (secreted) or removed (reabsorbed) from glomerular filtrate
  • Tx = FL - ER
    • ER: excretion rate
    • if positive: then some material was removed from filtrate by reabsorption
    • if negative: then some material was added to the filtrate by secretion
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4
Q

name the two routes of reabsorption

A
  • paracellular (Between cells)
    • “leaky” epithelium
  • transcellular
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5
Q

transcellular reabsorption must cross what two barriers

A
  • luminal (apical) membrane
  • basolateral membrane
    • diffusion through interstitial fluid and capillary wall is fast
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6
Q

reabsorption of amino acids, glucose, lactate, citrate, phosphate etc. is done via what mechanism

A
  • secondary active transport
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7
Q

2/3 of water is passively reabsorbed and 2/3 of sodium is actively reabsorbed where in the nephron

A

proximal tubule

  • 2/3 is reabsorbed no matter how dehydrated a person is
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8
Q

sodium reabsorption in the distal tubule and collecting tubule is subjected to control by what

A

aldosterone

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9
Q

water reabsorption in the distal and collecting tubule is regulated by

A

ADH

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10
Q

fluid reabsorption is achieved through what mechanism?

A

a high oncotic pressure in the peritubular capillary

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11
Q

sodium enters proximal tubule cells via what transport system

A

via cotransport with organics and by Na+-H+ antiport (NHE)

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12
Q

sodium leaves the proximal tubule cell to enter interstitium via what transport mechanism

A
  • Na+K+ ATPase or via cotransport with HCO3-
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13
Q

sodium potassium ATPase is always located on what side of proximal tubule cell

A

interstitium side (near blood capillary)

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14
Q

angiotensin II influence on Na+ reabsorption in the proximal tubule

A
  • stimulates Na+H+ exchange (NHE) across apical membrane
  • increases Na+ reabsorption and H+ secretion
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15
Q

sympathetic nerve activity on Na+ reabsorption in the proximal tubule

A

stimulates Na+ reabsorption

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16
Q

parathyroid hormone influence on Na+ reabsorption in the proximal tubule

A
  • inhibits Na+-phosphate cotransport
  • increases urinary excretion of phospate
  • relates to calcium homeostasis; parathyroid hormone released when calcium levels in blood are low and function is break down bone to release calcium; bone releases ca2+ and phosphate but don’t want them to meet in blood so parathyroid inhibits reabsorption of phosphate
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17
Q

tubular fluid to plasma concentration (TF/P) = 1

what does this mean

A

reabsorption has been exactly proportional to the reabsorption of water

18
Q

does osmolarity change in tubular fluid to plasma concentration ratio in proximal tubule

A

osmolarity DOES not change

19
Q

tubular fluid to plasma concentration (TF/P) < 1

what does this mean

A

reabsorption of the substance has occurred to a greater extent than water

20
Q

tubular fluid to plasma concentration (TF/P) > 1

what does this mean

A

reabsorption of the substance has been less than water OR there has been net secretion of the substance

21
Q

how is tubular fluid to plasma concentration of inulin (TF/P) used

A

used as marker

  • since inulin is only filtered, its concentration in the tube is solely determined by the movement of water
22
Q

what is tubular maximum (TM)

A

the maximal rate at which renal transport systems can transport a particular solute

  • maximum rate (mg/min) of a solute that can be transported
23
Q

What is tubular maximum (TM) due to

A

due to saturation of membrane transport proteins

24
Q

below tubular maximum (TM), all of the filtered load is

A

reabsorbed

25
Q

above tubular maximum (TM), all of the filtered load is

A

excreted

26
Q

tubular maxima are found primarily in which portion of the nephron

A

proximal tubule

27
Q

how do you find transport maximum on blood X concentration vs rate (mg/min) graph

A

rate when reabsorption levels off

28
Q

In a blood X concentration vs rate (mg/min) graph, what does decreasing the GFR do to the threshold

A

decreasing GFR increasing threshold

  • threshold (x axis point when reabsorption line breaks off from filtered (GFR) line)
29
Q

name some other solutes that have transport maxima

A
  • sugars (fructose, galactose, glucose)
  • amino acids
  • metabolic intermediates (lactate)
  • phosphate ions
  • vitamins
30
Q

Osmotic diuresis

A

is increased urination due to the presence of certain substances in the fluid filtered by the kidneys that cause water to come into the urine

31
Q

what effect does excess unreabsorbed solute (e.g. mannitol) have in the proximal tubule

A
  • manitol: non-reabsorbed carbohydrate can be given IV to induce osmotic diuresis
  • inhibits osmotic water flow from lumen to basolateral spaces
  • causes Na+ back diffusion into lumen of tubule with increased Na+ and water loss in urine
  • osmotic diuresis
32
Q

osmotic diuresis results in a rapid loss of what two substances

A
  • sodium and water -> polyuria
33
Q

name another commonly known disease that causes osmotic diuresis

A

diabetes: when glucose load exceeds TM , there is excess glucose in filtrate

34
Q

tubular secretion occurs via what two routes

A
  • paracellular
  • transcellular
35
Q

the two main transport mechanisms present in tubular secretion seperate what compounds

A
  • one is for organic cations
  • one is for organic anions
  • **very non-specific
36
Q

compounds to be secreted by the kidney are tagged for secretion in the liver via what

A
  • glucuronic acid or sulfate
37
Q

organic anions are secreted in the nephron via what type of transport

A

tertiary active transport

38
Q

how is PAH, an organic anion, secreted across kidney cell

A
  1. PAH is taken up into the cell in exchange for alpha-KG
  2. PAH leaves the cell on the apical side via a PAH-anion antiporter
39
Q

why does elevated plasma levels on one anion inhibit secretion of others?

A

all organic anions compete for the same transporter

  • ex: infusion of PAH inhibits the secretion of Penicillin, extending its life
40
Q

Why does the inulin concetration increases (Tubular fluid/plasma concentration) in the proximal tubule

A

inulin is neither secreted or reabsorbed but water is reabsorbed making the concentration of inulin in the proximal tubule increase

41
Q

Why does the sodium concetration appear not to change (Tubular fluid/plasma concentration) in the proximal tubule even though you know 2/3 is reabsorbed?

A

equal amount of water are being reabsorbed with it

Hum Physiology II (12 decks)

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