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095. Renal Exam 1 > 9. Renal Transport Mechanisms > Flashcards

9. Renal Transport Mechanisms Flashcards

1
Q

To be reabsorbed a substance must go through transepithelial transport which includes 5 distinct barriers.
1. Leave tubular fluid by crossing luminar membrane of cell
2. pass through the cytosol from one side of the tubular cell to the other (either via trans/paracellular)
3. Cross the apical and basolateral membrane of the tubular cell to enter the interstitial fluid
4 & 5?

A
  1. Diffuse through the interstitial fluid
  2. Penetrate the capillary wall to enter the plasma
    (luminal cell membrane to cytosol to apical and basolateral membrane to interstitial fluid to capillary wall into plasma)
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2
Q

Why bother to filter 180L/day and reabsorb 99% of it? (2)

A
  1. foreign substances are filtered into the tubule but not reabsorbed into the blood (so keeps it out)
  2. Filtering ions and water into the tubule makes regulation simple
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3
Q 
What percentage is reabsorbed in the proximal convoluted tubule?
Glucose
AA
urea
Na
K
Pi
Ca
Mg
H20
A 
glucose:100 %
AA: 100%
Urea: 50%
Na: 65-70%
K,P,Ca: 70%
H2O: 65-70%
Mg: 30%
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4
Q

What is the percentage of phosphate reabsorbed in the proximal straight tubule?

A

15%

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5
Q

What is the percentage of sodium potassium calcium and magnesium reabsorbed in the thick ascending limb?

A

Na: 25%
K: 20%
Ca: 25%
Mg: 60%

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6
Q

What is the key element in the proximal tubule reabsorption in the basolateral membrane?

A

Na/K ATPase pump

All reabsorption of substances use Na/K ATPase

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7
Q

AAs glucose and HCO3 (to counteract acid) all decrease in concentration in the plasma in the PCT while what will increase?

A

Creatinine, Urea, Cl, and Na

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8
Q

Diffusion is when solute goes down it electrochemical gradiets via transcellular (through cell membrane) or paracellular (between cells). Facilitated diffusion is?

A

movement of solute depending on interaction with a specific protein in the membrane

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9
Q

Symport is where two or more solutes are transported in the same direction where antiport is where 2 are going in opposite directions. At least one solute is transported againt?

A

its electrochemical gradient

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10
Q

Na reabsorption is dependent on the Na/KATPase, which lowers intracellular Na and increases intracellular K, which creates what kind of charge?

A

a negative charge with low intracellular sodium concentration which allows Na to move down the gradient into the cell.

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11
Q

A cotransporter is NaCl, NK2Cl, and NaHCO3 in thick ascending loop of henle while a antiporter/ counter trasnporter is like what?

A

NH exchanger

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12
Q

What is the difference between transcellular route and a paracellular route?

A

trasncellular goes through the luminal membrane while paracellular goes in between the cells through tight junctions which are leaky in the PCT and only allow some things to pass

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13
Q

Water can passively transport via para or transcellular while solutes use ______ transcellularly and use ____ paracellularly?

A

solutes use ATP (active transport) transcellularly

solutes use passive paracellular trasnport with no ATP

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14
Q

Sodium reabsorption is almost always active via transcellular route. They are the most abundunt cation in the filtrate and supply what percentage of energy for transport?

A

80% due to their reabsorption

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15
Q

Most of the sodium reabsorption occurs in the PCT through sodium ion leak channels on the apical surface. How much per day is filtered?

A

25,200 about 25,050 is reabsorbed

180L/day of water is reabsorbed

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16
Q

What are the three steps for transporting Na (general)?

A

Sodium diffuses across luminal membrane down gradiet
Sodium transported across membrane against gradient via NaKATPase
Sodium reabsorbed from interstitial fluid to peritubular cap by ultrafiltration oncotic/hydrostatic pressure

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17
Q

The NaH exchanger (NaHE3) is in the apical membrane of the proximal tubule and use one Na from the lumen in exhcange for one hydrogen ion. This is important for?(2)

A
  1. sodium reabsorption

2. Bicarbonate reclamation

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18
Q

There are five main steps for using the antiport NHE to get rid of filtered HCO3.
1. H is secreted/ exchange for one Na into the cell and combines with HCO3 to form H2CO3 (allow b/c ATPase)
2. H2CO3 is converted to CO2 and H20 via carbonic anhydrase (because H2CO3 is impermeable!)
3. CO2 diffuses into the tubule and combines with H2o via carbonic anhydrase (CA) which forms H2CO3 again
4?
5?

A
  1. H2CO3 then spontaneously breaks down and forms H+ HCO3

5. HCO3 goes into interstitial fluid into blood and H+ is RECYCLED and goes back to filtrate to pick up HCO3

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19
Q

More water than Cl- is reabsorbed in the PCT so as you go along, Cl concentration increases. Initially the amount of Cl is 100mmol/L but at the end of the tube…?

A

it is 120mmol/L

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20
Q

Since the concentration on the inside of the tubule is greater than out side, this increases the gradient which allows Cl to move passivley without any energy via?

A

the paracellular pathway down its concentration gradient

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21
Q

Paracellular movement is determined by the presence or absence of tight juntions. In the thin descending limb there is are few tight junctions so water can move freely. However, in the thick ascending limb and collecting duct?

A

the presence of abundunt tight junctions prohibits paracellular water movement

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22
Q

Aquaporins in the cell membranes conduct water while preventing anything else from passing. Aquaporins use TRANSCELLULAR route! Where is aquaporin 1 and aquaporin2 located?

A

AQP1 in the proximal convoluted tubule

AQP2 in collecting duct under control of ADH

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23
Q

The proximal tubule has tight junctions and many aquaporins making it permeable to?

A

water

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24
Q

Thin descending limb is permeable to water due to?

A

aquaporins and loose junctions

25
Q

The ascedning limb of the loop of henle has high tight junctions and ?

A

NO aquaporins so water is impermeable

26
Q

The collecting duct is unique because it has aquaporin II which is activated by?

A

activated by antidiuretic hormone (ADH) which tells it to absorb more fluid and to excrete less

27
Q

The proximal tubule filters about 67% of water, thin descending limb of henle filters about 15%, what about the late distal tubule and collecting duct?

A

under hormonal control (ANP,BNP,AVP-constriction) about 8-17%

28
Q

Glucose is reabsorbed via active transport using sodium (down its gradient) coupled glucose cotransporters (SGLT). What is the different between SGLT 1 and SGLT2?

A

SGLT1 are high affinity low capacity which absorb 10% in the distal PCT (segment 3)
SGLT2 in segment 1 (2) in the first part of PCT, low aff high capacity which absorb 90%

29
Q

Which transporter, SGLT1 or SGLT2 would be most active and productive under low concentrations of glucose?

A

SGLT1 because it is high affinity so will bind at any concentration!

30
Q

Drugs such as Invokana, farxiga, and jardiance all reduce blood glucose levels resulting from less glucose reabsorption via which transport and to try to cure what?

A

Block SGLT2 transporters so glucose will not be reabsorbed and excreted via urine— type 2 diabetes

31
Q

SGLT1 and 2 will absorb glucose until all receptors are full at which this point is called the transport maximum (TmG). What is the TmG and what happens if glucose is over this amount?

A

the max trasnport amount is 375mg/min or 200mg/dL plasma glucose. Anything over will be excreted into urine

32
Q

In the descending loop of henle, h20 is permeable allowing 15% to be absorbed whil solutes like NaCl are?

A

impermeable

33
Q

What happens as you go down the loop of henle?

A

the concentration of the solutes increase because you are continually loosing water but keeping the same amount of solutes

34
Q

The thick and thin ascending loop of henle are impermeable to water (no aquaporins high tight junctions) but Na Cl is (what percent)?

A

permeable, about 35-40% is reabsorbed here

35
Q

At the end of the ascending loop of henle, alot of NaCl is absorbed so what does this do?

A

it lowers the tubular concentration to about 50-75 where as it was 140 at the beginning in the PCT

36
Q

To acheive the amount of Na and Cl reabsorbed Na-K-2Cl cotransporter on apical membrane is used with the help of energy from?

A

Na/K ATPase

37
Q

What do loop diuretics (furosemide) do?

A

inhibit sodium chloride reabsorption by competing for the Cl- binding site on the carrier

38
Q

NK2Cl transporter allows Na, K, and 2 Cl- cross the apical membrane and subsequently what happens?

A

K exits cell via apical channel and Cl leave basolateral side via chloride channel and the Na exits via Na/KATpase

39
Q

The net effect of the NKCL transporter is transepithelial positive voltage which drives movement of cations such as Na Ca and Mg from what to where?

A

the lumen to the basolateral side

40
Q

When the lumen generates a positive charge in the thick ascending loop of henle, it drives the paracellular absorption of Ca and Mg, and disruption of what will block this transportation?

A

disruption of NaKCl transporter, K+ recycling, or basolateral Cl- channel

41
Q

What is the difference between normal and low potassium diets?

A

DCT cells, principle cells, connecting tubule and cortical collecting duct percent secretion increases in normal and decrease largely in low. Normal 20-150% urineload , 2% load for low potassium

42
Q

Breifly, what is the countercurrent multiplier?

A

Basically the back and forth of water filtering out of the PCT and then NaClK filtering out of the thick loop of henle to make up for the osmolarity different and so forth until there is an osmotic gradient established

43
Q

the distal tubule normally reabsorbs 5 to 8% of NaCl via the_______ which only about 10% of the NaCl and 25% of the water in the tubule remains?

A

NaCl cotransport

44
Q

Like the ascending limb, the distal convoluted tubule is relatively impermeable (early is impermeable, distal is permeable) to water. Where does the NaCl cotransporter get its energy from?

A

NaKATPase

45
Q

NaCL symporter is blocked by thiazide diuretics, which act to increase the excretion of na and cl by inhibiting the Na/Cl symporter in the DCT. Thiazides increase Ca reabsorption via?

A

increasing Na/Ca exchange (which makes thiazides useful to treat calcium subtypes of kidney stones). They also reduce urinary excretion of Ca

46
Q

In the collecting ducts, reabsorption depends on the bodys needs and is regulated by hormones including?

A

aldosterone for Na, ADH for water and PTH for Ca2

47
Q

In the absence of ADH the collecting ducts are impermeable to water. What would cause the adrenal cortex to release aldosterone (which reabsorbs Na) to the blood?

A

decreased blood volume, blood pressure, low extracellular Na or high extracellular K+
(these conditions beside K+ all promote RAAS)

48
Q

Aldosterone targets principal cells of the collecting ducts and cells of the distal portion of the DCT, prodding them to do what?

A

asynthesize and retain more luminal Na and K channels and more basolateral NaKATPase..resulting in an increase in reabsorption and no Na left to be excreted in urine

49
Q

aldosterone is released directly in response to increase in plasma K+ and by?

A

angiotensin II

50
Q

A rise in K + in the blood increases aldosterone and promotes secretion and urinary excretion and elmination of excess K. when there is a decline in plasma K+ concentration it causes?

A

a reduction in aldosterone secretion which will stimulate renal K + secretion

51
Q

**What is important to remember about aldosterone?

A

Increased secretion of aldosterone promotes Na reabsorption and K+ secretion

52
Q

Urea is freely filtered into glomerular filtrate. The proximal tubules reabsorb 5%. DTS and ATS receives urea via diffusion from interstitium of medulla where urea is high concentrations. thick ascending limb, DCT are impermabel to urea. The collecting duct has urea transport protein UT-A which is stimulated by?

A

ADH which consequently increases urea permeability of the IMCD

53
Q

What inhibits the Na-K2Cl co-transporter in thick asending limb loop of henles which decreases Na reabsorption and increases K+ and Cl urine out put?

A

Loop diuretic

54
Q

K+ sparing spironolactone is an aldosterone-dependent potassium sparing diuretic which does what?

A

inhibits Na/K exchange in distal tubule and collecting duct. Promotes K retention and water loss
Hypotensive effect

55
Q

When there is a water deficit, there are high levels of vasopressin which makes the distal and collecting tubules permeable to h2o. what will happen to the concentration in the tubules and the pee?

A

water will be taken out during the end and the concentration of the pee will be very strong but a small volume of H2o since it was all taken out

56
Q

When there is excess water, there will be no vaspressin present (ADH) so the distal and collecting tubules will remain impermable to water. what is the net result?

A

large volume of dilute urine.

57
Q

what is the percentage of reabsorbed sodium calcium magnesium in the distal convoluted tubule?

A

na 5%
calcium 8%
magnesium 5%

58
Q

what is the percentage reabsorbed of sodium in the collecting duct?

A

3%

59
Q

What is the percentage sent to the bladder of potassium, magnesium, phosphate, sodium, calcium?

A 
K 1-100%
magnesium 5%
Pi: 15%
sodium less than 1
calcium less than 1

095. Renal Exam 1 (11 decks)

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