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I've got kidney disease > Lecture 17 > Flashcards

Lecture 17 Flashcards

1
Q

Glomerular filtration, tubular secretion and reabsorption are ________ intensive processes. Why is this?

A

energy
it might seem wasteful to filter large amounts of substances from the plasma only to reabsorb most of it back again but this allows the body to quickly rid the body of toxic and harmful substances

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2
Q

Describe tubular reabsorption

A
  • as the filtrate passes down the tubule, most is reabsorbed back into the blood (plasma)
  • this is traveling from the lumen on the tubule through the apical membrane through the basolateral membrane into the blood
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3
Q

How is tubular reabsorption achieved?

A

through the action of specific channels and transporters in the membranes of the epithelial cells of the tubule and through the tight junctions of some of the segments of the nephron

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4
Q

What is the epithelium in the proximal tubule and what is the osmolarity of the solution?

A
  • leaky absorptive epithelium

- isosmotic solution

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5
Q

What is the epithelium in the late distal tubule and collecting duct?
What is the osmolarity of the solution?

A
  • tight absorptive epithelia

- hyperosmostic solution

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6
Q

Which parts of the nephron are under hormonal control?

What is this for?

A

late distal tubule and collecting duct

this is for Na+ and H2O reabsorption

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7
Q

How much water is filtered per day?

A

180L

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8
Q

How much water is excreted per day?

A

1.8L

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9
Q

What percentage of water is reabsorbed per day?

A

99%

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10
Q

How much sodium is filtered per day?

A

630g

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11
Q

How much sodium is excreted per day?

A

3.2 g

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12
Q

What percentage of sodium is reabsorbed per day?

A

99.5%

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13
Q

How much glucose is filtered per day?

A

180g

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14
Q

How much glucose is excreted per day?

A

0g

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15
Q

What percentage of glucose is reabsorbed?

A

100%

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16
Q

How much urea is filtered per day?

A

54 g

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17
Q

How much urea is excreted per day?

A

30g

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18
Q

What percentage of urea is reabsorbed?

A

44%

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19
Q

Na+ is reabsorbed along the length of the what?

A

Proximal tubule

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20
Q

Glucose is reabsorbed through which transporters? Where are these located?

A

SGLT1 in the proximal straight tubule and SGLT2 in the proximal convoluted tubule

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21
Q

What is tubular secretion?

A

substances are secreted from the peritubular capillaries to the filtrate

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22
Q

Like glomerular filtration, tubular secretion constitutes a pathway of moving substances from the _____ to the ________ _______

A

blood

tubule lumen

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23
Q

Secretion at the peritubular capillaries enables what to occur?

A

the disposal of substances at a higher rate than just filtration alone

24
Q

What are four things that are secreted during tubular secretion?

A

H+
K+
penicillin
metabolites from pesticides and many substances

25
Q

Which of the following is true?
A. 100% of the filtered urea is reabsorbed by the nephron.
B. Reabsorption is the only renal process that ‘recovers’ filtered substances and water.
C. Secretion is not an energy intensive process.
D. Normally, 95% of the filtered glucose is reabsorbed by your kidneys, unless you are a diabetic.

A

B. Reabsorption is the only renal process that ‘recovers’ filtered substances and water.

26
Q

Define glomerular filtration rate (GFR)?

A

the amount of filtrate produced per unit time

27
Q

What is the normal value for GFR?

A

120mL/min

180L/day

28
Q

What is GFR a useful measure for?

A

renal functioning

29
Q

Define renal clearance

A

the volume of plasma from which a substance is completely cleared by the kidneys per time

30
Q

What do we need to know in order to calculate the renal clearance?

A

the concentration of the substances in the urine and plasma and rate of urine produced

31
Q

What is the equation for the renal clearance?

What do each of the components mean? What are the units?

A 
Cs = Us x V/Ps where
Cs = clearance
Us = concentration of S in the urine (mg/L or mmol/L)
V = volume of urine per unit time (mL/min or L/hour)
Ps = concentration of S in plasma (mg/L or mmol/L)
32
Q

What does the renal clearance equation describe?

A

the rate at which a substance S is cleared by the kidneys and describes the clearance via the kidneys for all substances that can be detected in the plasma and the urine

33
Q

The renal clearance equation can be used to estimate what?

A

the GFR

34
Q

What are the requirements of a substance to be used to use clearance to measure the GFR?

A

it must not

  • be reabsorbed from the tubule
  • not be secreted into the tubule
  • not be metabolised
35
Q

What two substances fit the requirements to use renal clearance to estimate GFR?

A
  • inulin

- creatinine

36
Q

What is inulin?

A
  • a polysaccharide not metabolised by the body

- not found in the body and must be constantly infused

37
Q

What is creatinine?

A
  • a waste product produced by muscles
  • it is filtered by not reabsorbed
  • small amounts of secretion
  • already in the body so most commonly used clinically
38
Q

Creatinine is filtered freely at the _______ but is not _______, _______ though slightly _________

A

glomerulus
reabsorbed
metabolised
secreted

39
Q

Estimate the GFR by calculating the renal clearance if the
[creatinine]plasma = 7mg/L
urine volume rate = 0.1 L/hr
[creatinine]urine = 525 mg/L

A 
C = U x V / P
525 mg/L x 0.1 L/hr/7mg/L = 7.5 L/hr
= 0.125L/min
= 125 mL/min
= 180 L/day
40
Q

What is the normal GFR and plasma creatinine concentration?

A

GFR: 120mL/min

conc.: 1mg/dL

41
Q

If we only have 1 kidney, what is the GFR and plasma creatinine concentration?

A

GFR: 60mL/min

conc.: 2mg/dL

42
Q

Calculate the GFR from the following data:
[creatinine]plasma = 30 mg/L
urine volume rate = 0.005 L/hr
[creatinine]urine = 400mg/l
What does this tell you about the functioning of this individual’s kidneys?

A

GFR = 0.07L/hr = 1.1 mL/min
= 1.6L/day

the GFR is way too low which means they have renal failure

43
Q

Which of the following statements is FALSE?
A. The typical GFR for a healthy person is 125 ml/min.
B. Renal clearance is the volume of plasma from which a substance is cleared by the kidneys per unit time.
C. GFR is not a useful indicator of renal function.
D. Creatinine is a substance that can be used to determine GFR.

A

C. GFR is not a useful indicator of renal function.

44
Q

Provided we know the GFR and the plasma concentration of a substance, we can calculate what?

A

the daily filtered load

45
Q

What is the equation to calculate the daily filtered load?

A

DFL = GFR x [substance]plasma

46
Q

Calculate the daily filtered load given [glucose]plasma = 1 g / L (5 mmol/L)

A

Filtered load of glucose = 125 mL/min x 1 g/L (5 mmol/L)
= 0.125 L/min x 1 g/L (5 mmol/L)
= 0.125 g/min filtered x 60 min/hr x 24 hr/day
= 180 g/day filtered

47
Q

Calculate the filtered load of Na+ given [Na+]plasma = 150 mmol / L

A

Filtered load Na+ = 180L/day x 150mmol/L

= 27,000 mmol / day

48
Q

Calculate the filtered load of Cl- given [Cl-]plasma = 110 mmol / L

A

Filtered load Cl- =180L/day x 110mmol/L = 19,800 mmol / day

49
Q

How does the kidney handle the filtered load of ions and glucose?

A

through ion transporters and proteins

50
Q

For the most part, the filtrate is reabsorbed as it passes along the length of the _________. This can change in certain situations/states.

A

nephron

51
Q

What is the transport maximum?

A

Mediated reabsorptive transport proteins can saturate. There is a limit to the amount of a substance transported per unit of time. This is the transport maximum

52
Q

Binding sites on transport proteins become saturated when the concentration of the transported substance increases beyond a single limit. What is this limit called?

A

the transport maximum

53
Q

How does the transport maximum of glucose come about?

A

All of the filtered glucose is normally reabsorbed and so normally, there is no glucose in the urine. Glucose is reabsorbed in the proximal tubule across the leaky absorptive epithelia using Na+/glucose transporters. At high [glucose]plasma, the tubular Na+-glucose co-transporters become saturated and can not reabsorb all of the filtered glucose

54
Q

Give an example of when the transport maximum for glucose is reached. What does this result in?

A

[glucose]plasma does not normally exceed 150 mg / 100 ml because it is under strict control by hormone insulin.
In diabetes mellitus there is a lack of control by insulin leading to hyperglycaemia (too much glucose in the blood). This means that [glucose]plasma can exceed 200 mg / 100 ml. Therefore, there is a large increase in the filtered load of glucose. At this [glucose]plasma, tubular Na+-glucose co-transporters become saturated and can not reabsorb all of the filtered glucose.
Glucose appears in urine
= Glucosuria

55
Q

What is the normal tubular transport maximum for glucose?

A

400mg/min and that is all being reabsorbed

56
Q

If we had unfeathered transport overall by just filtration, we would see what?

A

the loss of glucose due to nothing being able to reabsorb

57
Q

When we have diabetes, there is transport maximum of glucose and what happens when this is exceeded?

A

there is excretion of glucose

I've got kidney disease (43 decks)

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