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Renal Medicine (BDS1-BDS2) > Kidney Tubular Function > Flashcards

Kidney Tubular Function Flashcards

1
Q

How much filtrate is reabsorbed by the kidneys?

A

99%

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2
Q

What part of the nephron is responsible for re-absorption of filtrate?

A

Renal tubule

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3
Q

Describe the role of reabsorbtion by the renal tubule.

A

Reabsorbs and conserves molecules that the body wants to keep (that are important to us). Allows the conc. of molecules to be kept within a narrow range Allows fine-tuning of urine composition

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4
Q

What is reabsorbed by the kidney?

A

-Water and nutrients (glucose, AA’s) -Waste products (urea, creatinine) -Molecules needed for cellular processes (Na+, Cl-, Ca2+, K+, bicarbonate)

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5
Q

What waste product do we reabsorb more of?

A

Urea (creatinine is freely filtered but very little reabsorbed)

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6
Q

What makes up the renal tubule?

A

-Proximal convoluted tube -Loop of Henle -Distal convoluted tube -Collecting duct

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7
Q

What is the function of the proximal convoluted tube?

A

Major site of re-absorption and some secretion

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8
Q

What is the function of the loop of henle?

A

Counter-current multiplier to primarily reabsorb sodium and water

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9
Q

What is the function of the distal convoluting tube?

A

Re-absorption and secretion (fine-tune urine)

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10
Q

What is the function of the collecting duct?

A

Collect urine

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11
Q

What is the meaning of reabsorption in kidney tubules?

A

the movement of molecules from the renal filtrate in the tubule lumen through the tubule wall and into the blood

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12
Q

What is the meaning of secretion in tubular kidney function?

A

The active movement of molecules from the blood and into the tubule lumen to form part of the urine

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13
Q

Where in the kidneys is Na+ reabsorbed?

A

-65% in proximal convoluted tubule -25% in ascending loop of Henle -8% in distal convoluted tubule

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14
Q

What percent of Na+ is reabsorbed by the kidneys?

A

-98%

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15
Q

How much of the energy used by the kidney is used to reabsorb sodium?

A

80% of total energy used by kidney

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16
Q

What is the major site of absorption?

A

The proximal convoluted tubule

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17
Q

How much filtrate is reabsorbed in the proximal convoluted tubule?

A

up to 2/3rds

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18
Q

Describe the filtrate that enters the proximal convoluted tubule.

A

It is an early form of urine containing both waste products and nutrients that our body wants to retain

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19
Q

How is the structure of the proximal convoluted tubule designed to enhance its function?

A

-It is convoluted (curved) to maximise surface area in the small space it has -The epithelial cells of the tubule have microvilli to maximise SA -The proximal convoluted tubule is closely associated with peritubular capillaries allowing reabsorption

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20
Q

Why is blood in the peritubular capillaries low in molecules and nutrients?

A

Because they have been passed into the tubular lumen

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21
Q

Describe the conc. gradient in the PCT.

A

There is a high conc. of molecules and nutrients in the tubular lumen and a low conc. in the blood creating a concentration gradient

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22
Q

By what process are molecules and nutrients reabsorbed into the blood?

A

Passive diffusion (is facilitated)

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23
Q

Describe the movement of molecules from the tubular lumen to the peritubular capillaries.

A

Move from a high con. in the tubular lumen through the epithelial cell wall, through the interstitial space and into the peritubular capillary

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24
Q

What is required to facilitate the passive reabsorption in the PCT?

A

Pores or carrier proteins to allow movement through the phospholipid bilayer

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25
Q

How is H2O transported from the tubular lumen?

A

Through aquaporins (pores that allow the free movement of water molecules down a conc. gradient)

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26
Q

How are glucose and amino acids transported through the tubular lumen membrane?

A

Via Na+ co-transporters (get a Na+ plus glucose transporter and a Na+ plus amino acid transporter)

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27
Q

What is required to maintain the movement of amino acids and glucose?

A

A sodium concentration gradient

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28
Q

What percent of the renal filtrate can be reabsorbed by the PCT without any energy expenditure?

A

up to 50%

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29
Q

What other process (not passive diffusion) occurs to maximise the amount of filtrate reabsorbed by the PCT?

A

Active transportation of Na+ via sodium potassium pump in the basolateral membrane

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30
Q

Together passive diffusion and active sodium transport can reabsorb up to what percent of renal filtrate?

A

65% (2/3rds)

31
Q

What is the difference between the basolateral membrane and the apical membrane?

A

Apical membrane = membrane between the tubular lumen and the tubular cell wall
Bilateral membrane = membrane between the tubular cell wall and the interstitial space

32
Q

What facilitates the active transport of sodium?

A

Na+/K+ pump on basolateral membrane

33
Q

Describe the movement of molecules via the Na+/K+ pump.

A

3 Na+ moved against conc gradient into interstitial space 2 K+ moved against conc gradient from interstitial space into tubule wall

34
Q

What does the Na+/K+ pump need?

A

1 ATP per 3Na+/2K+

35
Q

How does the movement of Na+ molecules by active transport facilitate the movement of other molecules?

A

-Water follows Na+ due to principles of osmosis -Glucose and AA co-transported with Na+ -Chloride and other -ve ions follow Na+

36
Q

How does co-transportation of glucose and AA lead to their reabsorbtion?

A

-Glucose and AA moved against conc. gradient when co-transported with sodium from tubule lumen to tubule wall -Causes high conc. of nutrients in the tubule wall so they will move down conc. gradient through interstitial space and into blood

37
Q

What type of transport is the co-transportation of glucose and AA with Na+?

A

Secondary active transport (moved against conc. gradient but doesn’t require energy)

38
Q

What percent of nutrients can be reabsorbed by secondary active transport (co-transportation) ?

A

Up to 100%

39
Q

Describe the conc. gradients of Na+ in the process of active transport for reabsorbtion in the proximal convoluted tubule.

A

-high conc. gradient in tubule lumen -low conc. in tubule wall -high in interstitial space -low in pertitubular capillary

40
Q

Describe the osmotic/electrical gradient in the PCT during active transport of Na+.

A

High in tubule lumen and low in peritubular capillary

41
Q

How many -ve ions are reabsorbed in the PCT?

A

up to 2/3rds

42
Q

What happens to the filtrate that remains after re-absorption in the the PCT?

A

It moves into the loop of Henle which employs counter-current multiplication

43
Q

What are the 2 types of nephrons you get? Describe them.

A

Corticle nephrons - most numerous, short loops of Henle that only extend to the medulla
juxtamedullary nephrons - long loops of Henle that extend deep into the medulla (specialised for urine concentration)

44
Q

What can the walls of the loop of henle be divided into? What is this based on?

A

-Thin descending limb -Thin ascending limb -Thick ascending limb
Based on different structural and permeability properties

45
Q

What can the subdivisions of the Loop of Henle walls be termed?

A

Loop rules

46
Q

Describe the permeability properties of the thin descending and thin ascending limb.

A

They are permeable to water but no Na+ re-absorption occurs here

47
Q

Describe the permeability of the thick ascending limb of the loop of Henle.

A

It is not permeable to water due to the absence of aquaporin channels It is permeable to Na+ (it is the site of ACTIVE Na+ re-absorption)

48
Q

What does the thick ascending Loop of Henle pump into the interstitial space and what does this result in?

A

-Actively pumps Na+, Cl- and K+ into the interstitium -The interstitium becomes “salty” ( no water able to leave the thick ascending limb to dilute) which creates an osmotic gradient -This facilitates water reabsorption from the thin limbs

49
Q

What percent of total sodium re-absorption occurs in the loop of Henle?

A

25% - specifically in the ascending loop of H

50
Q

Describe the process of Na+ re-absorption in the thick ascending limb of the Loop of Henle.

A

-Have Na+, Cl- (x2) and K+ pump instead of the glucose and AA co-transporters -This pump works as secondary active transport -Still have the sodium/potassium pump on the basolateral membrane which moves Na+ against its conc gradient. This causes accumulation of Na+ in the interstitial space -leads to passive transport of na+ from interstitial space into the blood

51
Q

What are the Na+, Cl- (x2) and K+ pumps a target of?

A

Diuretic drugs which inhibit the action of the pump - prevents the reabsorption of sodium and hence water (helps control blood pressure)

52
Q

The difference in osmotic gradient between the thin descending limb and the salty interstitial space facilitates the movement of water. What kind of transport is this?

A

Passive (osmosis)

53
Q

What is the difference in osmotic pressure of the filtrate when it moves form the PCT in the cortex to the LofH in the medulla?

A

in cortex it is isotonic with the intersitium (same osmotic pressure) In medulla it is hypotonic with the interstitium (lower osmotic pressure [so will move into interstitium])

54
Q

Why is the process in the Loop of Henle called the Counter-current Multiplication?

A 
Counter-current = Because the filtrate moves in opposite directions through loop of henle (down descending limb and up ascending limb)
Multiplication = Because the deeper you get into the medulla, the osmotic gradient is multiplied
55
Q

What is the ratio of water to sodium at the top of loop of H vs the bottom?

A 
Top = high water to Na+ ratio 
Bottom = low water to Na+ ratio
56
Q

Why is there a higher salt concentration as you get further down the medulla?

A

To maintain water reabsorption

57
Q

What nephrons participate in counter current multiplication?

A

Only juxtamedullary nephrons

58
Q

What part of the peritubular capillaries reabsorbs molecules form the interstitial space around the loop of H?

A

Vasa recta

59
Q

Why is the vasa recta a special portion of the peritubular capillaries?

A

It employs a counter-current exchange system (arterial blood descends into medulla and venous blood ascends out) which maintains the osmotic gradient

60
Q

Describe the flow of blood in the vasa recta?

A

Slow and sluggish

61
Q

What kind of transport is the exchange of water and salt with the vasa recta?

A

the exchange of water and salt with the vasa recta?
Passive - free movement

62
Q

What term describes the concentration of the filtrate entering the distal convoluted tubule relative to the interstitial space here?

A

Hypotonic (water wants to move into the interstitial space)

63
Q

How much sodium can be reabsorbed in the PCT?

A

Up to 8%

64
Q

What is the difference between the reabsorption of water and salts in the PCT and the pervious sections of the kidney?

A

Reabsorption can be regulated here dependent on whether an individual is more hydrated or dehydrated (this keeps the concs of stuff within the narrow limits required)

65
Q

How is the reabsorption controlled in the distal convoluted tubule?

A

Through hormones

66
Q

What hormones control reabsorption in the PCT? What do they do?

A

Anti-diuretic hormone (ADH) = increases water reabsorption
aldosterone = increases Na+ reabsorption
Atrial natriuretic hormone (ANH) = promotes water and Na+ secretion (blocks the action of ADH and aldosterone)

67
Q

The filtrate in the PCT is hypotonic. Why does it not move into the interstitial space in the absence of ADH?

A

Because there are no aquaporin channels present

68
Q

When is ADH released, where is it released from and how does it work?

A

-when the body recognises you are becoming dehydrated (during exercise etc.) -Pituitary gland -Inserts AQP channels to allow water reabsorption in PCT and collecting ducts

69
Q

What kind of urine is produced as a result of the actions of ADH?

A

A smaller volume of concentrated urine

70
Q

Describe the actions of aldosterone and when it is released.

A

-Released due to fluid loss -Causes upregulation of Na+/K+ pump -leads to reabsorption of Na+ and indirectly secreted K+ into urine (has an effect on BP)

71
Q

What kind of urine is produced as a result of the actions of aldosterone?

A

Concentrated urine

72
Q

When, how and where is atrial natriuretic hormone released?

A

-released when there is an increase in fluid volume -increase in fluid volume causes an increase in blood volume and therefore BP. Smooth muscle cells in the heart detect this increased BP and release ANH

73
Q

Describe the action of atrial natriuretic hormone and what kind of urine is produced as a result.

A

-blocks the action of aldosterone and ADH -large volume of dilute urine produced

Renal Medicine (BDS1-BDS2) (2 decks)

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