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Physiology Exam 5 > Renal: Tubular absorption, salt balance > Flashcards

Renal: Tubular absorption, salt balance Flashcards

1
Q

what occures in the proximal tubule?

A
  1. bulk reabsorption

2. majority of tubular secretion

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2
Q

what is secreted from the tubule?

A

organic cations - neurotransmitters

orgainic anions - bile salts, fatty acids, foreign chemicals

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3
Q

what is the purpose of the distal tubule and collecting duct?

A

fine tuning reabsorption and secretion

to match excretion rates to intake or generation rates

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4
Q

what is filtered load?

A

total amount of any nonprotein or nonprotein-bound substance filtered into Bowman’s space

GFR x (substance concentration)

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5
Q

example: filtered load of glucose at a concentration of 1 g/L (180 g/day of glucose in 180 L/day of H2O)

A

GFR = 180 L/day
so
180 L/day x 1 g/L = 180 g/day

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6
Q

how much water is filtered per day? excreted? reabsorbed?

A

a. 180 L/day
b. 1.8 L/day
c. 99 %

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7
Q

how much Na is filtered per day? excreted? reabsorbed?

A

a. 630 g/day
b. 3.2 g/day
c. 99.5 %

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8
Q

how much glucose is filtered per day? excreted? reabsorbed?

A

a. 180 g/day
b. 0
c. 100 %

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9
Q

how much urea is filtered per day? excreted? reabsorbed?

A

a. 54 g/day
b. 30 g/day
c. 44%

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10
Q

what is true of proximal tubular reabsorption?

A

Na and H2O have iso-osmotic reabsorption (concentration stays constant)

HCO3, glucose, lactate are efficient reabsorded

Cl concentration increases, then remains constant thus it is delayed behind Na

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11
Q

General principles of reabsorption?

A
  1. transcellular (tubular epithelial cell) is driven by secondary active transporters
  2. paracellular via the tight junction, between basolateral membrane, driven by concentration gradient
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12
Q

how does transcelluar uptake/transport work?

A

intracellular Na is lower than tubular luminal Na, this forms a pressure gradient across the apical membrane. the tubule cell uses the Na gradient to transport the substance across (i.e. Na-glucose symporter) via active transport.
the substance leaves the cell into the blood via facilitated diffusion

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13
Q

what is true of glucose concentration and flow rate in the kidney?

A
  1. filtration is linear
  2. reabsorption is not linear, it saturates at higher levels
  3. reabsorption is transporter mediated
  4. what isn’t reabsorbed is excreted to urine.
  5. glucose is osmotically active and induces H2O excretion
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14
Q

what is the apporx. ammount of Na in the body?

A

55 grams

90% extracellular 10% intracellular

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15
Q

How is Na taken in? out put?

A

a. foods

b. urine (regulated), sweat, feces

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16
Q 
place the following in the correct order:
collecting tubule
proximal tubule 
bowmans capsule
loop of henle
collecting duct
dital tuble
A

bowmans capsule > proximal tubule > loop of henle > distal tubule > collecting tubule > collecting duct

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17
Q

how is Na reabsorption mediated in the proximal tubule?

A

Na - H exchanger (NHE) (Na in, H out)
Na coupled co-transporters

accounts for 65 %

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18
Q

how is Na reabsorption mediated in the TAL (thick ascending loop)

A

Na/K/Cl cotransport

accounts for 20 %

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19
Q

how is Na reabsorption mediated in the DT (distal tubule)

A

Na/Cl cotransport

accounts for 10 %

20
Q

how is Na reabsorption mediated in the CD (collecting duct)

A

epithelial Na channels

accounts for 8 - 10 %

21
Q

How is Na transport mediated on the basolateral side of the epithelial cell?

A

Na/K-ATPase transporter

22
Q

True or False. The Na+ movement to the tubule cells leads to a downhill transport of Cl and water. They virtually follow Na exclusively via paracellular pathways.

A

False. they follow Na by both transcelluar and paracellular pathways

23
Q

What is Na relation ship to blood pressue?

A

Extracellur volume = plasma + interstitial
so plasma volume is related to plasma Na.
this means an increase in plasma Na increases overall plasma volume thus increase B/P. (opposite effect for decrease plasma Na)

24
Q

how is low blood pressure compensated for when blood volume is low due to Na and H2O loss (i.e. diarrhea)?

A
  1. decreased volume = a decrease in MAP
  2. baroreceptors sense the change
  3. this stimulates the sympathetic renal nerve activity
  4. the afferent arteriols are constricted
  5. this causes decrease glomerular filtration pressure
  6. finally, kidney decreases Na and H2O excretion to maintain plasma volume and pressure
25
Q

True or False. In blood pressure compensation the afferent arteriole constriction/dilation alone is responsible for regulating glomerular filtration pressure.

A

False
afferent arteriole constriction/dilation indirectly lowers the pressure AND the low arterial pressue itself directly reduces the net glomerular filtration pressure

26
Q

Which is best for short term regulation of B/P? Long-term regulation?

A

a. short - GFR control

b. long - control of Na reabsorption

27
Q

how is Na reabsorption regulated?

A

renin-angiotensin-aldosteorone signaling

ANP (atrial natriuretic peptide)

28
Q

which 3 structures, other than nephrons, play an important role in long term regulation of Na reabsorption?

A

liver - secretes angiotensinogen
kidneys - secrete renin
adrenal cortex - secretes aldosterone

29
Q

summarize control of Na reabsorption by aldosterone

A

In response to a low blood pressure, the kidney produces renin from juxtaglomerular cells and secretes it to the blood. Renin converts angiotensinogen (produced from the liver) to Ang I, which then becomes Ang II by AEC. Ang II then triggers aldosterone secretion from the adrenal cortex to plasma. Finally, aldosterone stimulates Na+ reabsorption in the kidney

30
Q

True or False. Ang I, ACE, and Renin are always present in the blood.

A

False. Renin is not always present in blood. release into blood depends on blood volume or pressure?

31
Q

What is aldosterone?

A

steroid hormone produced by adrenal cortex

32
Q

what triggers aldosterone’s synthesis and secrection?

A

Ang II

33
Q

What is the function of aldosterone in regulating Na in the cell?

A

upregulates the number and activity of apical (tubular lumen side of cell) Na channels and basolateral (blood vessel side) Na/K-ATPase

34
Q

How does aldosterone effect K in the cell?

A

increase K secrection by by upregulating K channels

35
Q

how does alosterone effect the Na uptake in the CD (collecting duct)?

A

8% reabsorption without aldosterone

10% with

36
Q

what is true of Renin secretion from the juxtaglomerular cells?

A

it is stimulated by
1 increased activity of renal sympathetic nerves,

  1. reduced stretch of intrarenal baroreceptors in the juxtaglomerular cells,

3 reduced salt concentration flowing to macula densa.

37
Q

How is Na reabsorption regulated by ANP?

A

it inhibits Na reabsorption, inhibits aldosterone secrection, premotes afferent artiole dilation thus increase GFR

when blood volume or pressure in high
the stretch in the atria cause the atria to secrete ANP

38
Q

what is result of ANP in regards to urine?

A

natriuresis (high Na levels in urine)

39
Q

true or false. The kidneys can excrete H2O without excreting Na.

A

True via vasopressin (ADH)

40
Q

What triggers the release of Vasopressin/ADH from the posterior pituitary gland?

A

low B/P - reduced firing of barorecptors

high plasma osmolarity (decrease H2O) concentration) – osmorecptors of hypothamalmus are activated

41
Q

How does ADH enhance water uptake?

A

stimulating insertion of water channels aquaporins into the apical membrane of the collecting duct. (increased tubular permeability)

42
Q

What is another role of vasopressin?

A

vasoconstrictor in peripheral circulation

43
Q

what is the ultimate compensatory mechanism in regards to reduced blood volume?

A

ingestion

44
Q

what makes us feel thirsty?

A

reduced blood volume and increased plasma osmolarities effect on the hypothalmus

45
Q

how do barorecptors trigger thirst?

A

Ang II

Physiology Exam 5 (7 decks)

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