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Physiology Exam 3 > Tubular reabsorption and secretion > Flashcards

Tubular reabsorption and secretion Flashcards

1
Q

In order for a substance to be reabsorbed, where must it be transported?

A
  1. across the tubular epithelial membranes into the renal interstitial fluid
  2. through the peritubular capillary membrane back into the blood
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2
Q

Describe aquaporins (1, 2, and 3)

A

1- widespread; includes the renal tubules
2.- present in the apical membranes of the collecting tubule cells
3-present in the basolateral membranes of the collecting duct tubes

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3
Q

What is the function of ATPases in the nephron cell membrane?

A

-establish ionic gradients

drive reabsorption or secretion of many other solutes

transported via secondary active transport

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4
Q

Define symport

A

moves WITH the NA+ gradient

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5
Q

Define antiport

A

moves AGAINST the Na+ gradient

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6
Q

Define the ENaC channel

A

found in the apical membrane of the nephron cells

closed by amiloride and opened by hormones

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7
Q

What are the channels that are found int he apical membrane of the nephron cells?

A

CTFR (chloride)
potassium
ENaC

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8
Q

What are the primary active transporters that are involved in the nephron?

A

Na/K ATPase
H+ ATPase
H+K+ ATPase
Calcium ATPase

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9
Q

Describe secondary transport in the renal tubule

A

reabsorption of glucose or amino acids by the renal tubule

SGLT2
SGLT1

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10
Q

Define SGLT2

A

reabsorbs 90% of the glucose in the early proximal tubule

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11
Q

Define SGLT1

A

Reabsorbs 10% of glucose in the late proximal tubule

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12
Q

What are the substances that are actively secreted into the renal tubules?

A

Creatinine

Para-aminohippuric acid

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13
Q

Define the transport maximum

A

limit to the rate at which the solute can be transported

due to saturation of the specific transport system

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14
Q

What is the threshold for glucose reabsorption?

  1. transport max for glucose
  2. filtered load for glucose
  3. GFR x plasma glucose
A
  1. 375 mg/min
  2. 125 mg/min
  3. 123 mg/min x 1 mg/ml
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15
Q

What are reasons that some passively reabsorbed substances do not have a transport maximum?

A
  1. rate of diffusion is determined by the electrochemical gradient of the substance
  2. permeability for the substance
  3. time that the fluid containing the substance remains within the tubule
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16
Q

What does the rate of transport depend on?

A
  1. electrochemical gradient

2. time the substance is in the tubule

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17
Q

Define solvent drag

A

osmotic movement of water can also carry other solutes

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18
Q

Describe the proximal tubule in terms of the surfaces

A
  • highly metabolic with large numbers of mitochondria
  • extensive brush borders on luminal surfaces
  • extensive intracellular and basal channels on intestinal surfaces
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19
Q

What does the proximal tubule resorb?

A

65% of filtered sodium, chloride, bicarbonate, and potassium

all filtered glucose and amino acids

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20
Q

What does the proximal tubule secrete?

A

organic acids, bases, and hydrogen ions into the tubular lumen

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21
Q

Describe sodium reabsorption in the first half of the proximal tubule

A

reabsorption is via co-transport along with glucose, amino acids, and other solutes

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22
Q

Describe the sodium reabsorption in the second half of the proximal tubule

A

reabsorption is mainly with chloride ions

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23
Q

Describe the overall sodium transport in the proximal tubule

Na entry
Na pumping out

A

most of the sodium entry is via anti port with H+

Na+ is pumped out of the cell via the Na+ K+ ATPase pump

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24
Q

What is the electrical gradient in the cytoplasm and the tubular lumen respectively?

A

-70 mV and -3 mV

25
Q

What is the concentration gradient of the cytoplasm and the tubular lumen?

A

30 mOsm cyto and 140 mOsm luminal

26
Q

Describe the transport of H+ and bicarb in and out of the proximal tubule

A
  • increased H+ in the lumen because of the anti port transport with the Na+
  • H+ binds with the bicarb that is in the lumen and forms carbonic acid (H2CO3)
  • carbonic anhydrase splits into co2 and h20
27
Q

Describe the transport of CO2 and H20 in the cell

A

Enter into the cell and combine to form carbonic acid

dissociates to form bicarb and H+ and then the bicarb can diffuse out and the H+ can be removed via anti port and the H+ATPase

28
Q

Describe the thin descending segment of the loop of henle

A

-highly permeable to water and moderately permeable to most solutes including urea and sodium

reabsorbs 20% of filtered water

29
Q

Describe the thin ascending segment of the loop of henle

A

impermeable to water

30
Q

Describe the thick ascending segment of the loop of henle

A
  • NaK ATPase pump in the basolateral membrane
  • sodium, potassium, and chloride co-transporter
  • slight back leak of K+ into the lumen
31
Q

Describe the sodium potassium and chloride co-transporter

A

Moves 2 Na , 2 chloride, and 1 potassium into the cell

32
Q

What does the movement of he K+ int the lumen cause Mg and Ca to do?

A

diffuse through the tubular lumen through the paracellular space into the interstitial fluid

33
Q

describe the thick ascending segment of the loop of henle

A

impermeable to water

site of action of powerful loop diuretics
-furosemide, ethacrynic acid, bumetanide

34
Q

Describe the distal tubule

A
  • first portion forms the macula densa
  • next protein is highly convoluted and has characteristics that are similar to the thick ascending loop
  • reabsorbs most ions but is impermeable to water and urea

(diluting segment)

35
Q

What are the ions that are pumped in and out of the distal tubule, and how?

A

Na and Cl co-transporter in the luminal membrane

Na k ATPase pump that is present in the basolateral membrane

36
Q

What is the function of the principal cells in the late distal tubule?

A
  • reabsorb sodium and water from the tubular lumen
  • secrete potassium into the tubular lumen
  • uses the NAK pump
  • primary site of K+ sparing diuretics
37
Q

What are the 4 K+ sparing diuretics?

A

spironolactone
eplerenone
amiloride
trimeterene

38
Q

What is the function of the intercalated discs that are present in the late distal tubule?

A
  • reabsorb K+ from the tubular lumen

- secrete H+ into the tubular lumen

39
Q

Describe the medullary collecting duct

A
  • epithelial cells are cuboidal
  • permeability is controlled by ADH
  • permeable to urea
  • capable of secreting H+ against a large concentration gradient
40
Q

What is the source of aldosterone?

A

adrenal cortex

41
Q

What is the function of aldosterone

A

increases sodium reabsorption and stimulates potassium secretion

stimulates the Na K pump one the basolateral side of the cortical collecting tubule membrane

42
Q

What is the site of action of aldosterone?

A

principal cells of the cortical collecting ducts

43
Q

What is the stimulus for secretion of aldosterone?

A
  • increased extracellular potassium

- increased levels of angiotensin 2

44
Q

What occurs in the absence of aldosterone?

A

addison’s disease

marked loss of sodium and accumulation of potassium

45
Q

What occurs with hyper secretion of aldosterone?

A

Conns syndrome

46
Q

What is the function of angiotensin 2?

A
  • increased sodium and water reabsorption

- returns blood pressure and extracellular volume toward normal

47
Q

What are the effects of angiotensin 2?

A
  • stimulate aldosterone secretion
  • constricts efferent arterioles
  • directly stimulates sodium reabsorption in the proximal tubules, loops, distal tubules, and collecting tubules
48
Q

What is the source of ADH

A

posterior pituitary

49
Q

What is the function of ADH?

A

increases water reabsorption

50
Q

What are the effects of ADH?

A

binds to the V2 receptors in the late distal tubules, collecting tubules, and collecting ducts
increases the formation of cAMP

51
Q

What does cAMp do?

A

stimulate the movement of aquaporin 2 proteins to the luminal side of the cell membranes

52
Q

What is the source of ANP?

A

cardial atrial cells in response to dissension

53
Q

What is the function of ANP?

A

inhibits reabsorption of sodium and water

54
Q

What is the source of PTH?

A

parathyroid glands

55
Q

What is the function of the PTh?

A

increases calcium reabsorption

56
Q

What is the renal clearance of a substance?

A

The volume of plasma that is completely cleared of the substance by the kidneys per unit time

57
Q

What is the equation for renal clearance

A

cs X ps = us x v

cs+ clearance rate of the substance
ps= plasma concentration of the substance
us- urine concentration of the substance
v= urine flow

58
Q

Define inulin

A

polysaccharide

not produced in the body

59
Q

What is the equation for a substance that is completely filtered but not reabsorbed or sercreted

A

GFRxPs=UsxV

Physiology Exam 3 (9 decks)

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