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SUGER > Proximal Convoluted Tubule > Flashcards

Proximal Convoluted Tubule Flashcards

1
Q

Renal blood flow value

A

1250 ml/min

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2
Q

Renal plasma flow value

A

700 ml/min

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3
Q

Urine flow rate value

A

1 ml/min

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4
Q

Glomerular filtration rate value

A

125 ml/min

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5
Q

Proximal tubule function

A

Active reabsorption of multiple solutes
Metabolically active cells- lots of mitochondria

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6
Q

How is a sodium gradient generated by the PCT

A

Na/K ATPases

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7
Q

What is the PCT vulnerable to

A

Hypoxia and toxicity

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8
Q

Solutes reabsorbed in PCT

A

Glucose
Amino acids
Phosphate
Bicarbonate

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9
Q

PCT disorder - glucose

A

Renal glycosuria

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10
Q

PCT disorder - amino acids

A

Aminoacidurias eg cystinuria

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11
Q

PCT disorder - phosphate

A

Hypophosphataemic rickets eg XLH

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12
Q

PCT disorder - bicarbonate

A

Proximal renal tubular acidosis

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13
Q

PCT disorder - multiple solutes

A

Fanconi syndrome

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14
Q

Structure of proximal convoluted tubule

A

Longest and most coiled part of neohron

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15
Q

Lining of PCT

A

Simple cuboidal brush border
Microvilli
High mitochondria density
Palisade arrangement

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16
Q

Blood supply to PCT

A

From efferent arterioles which form peritubular capillaries

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17
Q

What is the PCT vulnerable to

A

Ischaemic injury due to distance from glomerulus

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18
Q

Function of PCT

A

Bulk reabsorption: Na+, Cl-, H20, glucose, amino acids, HCO3-, lactate, phosphate
Secretion of organic ions

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19
Q

Na+ reabsorption in PCT

A

Driven by Na/K ATPase on basolateral membrane

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20
Q

PCT and H2O

A

High permeability so reabsorbed by osmosis

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21
Q

Other molecules and PCT

A

Taken up ny secondary active transport or by passive diffusion across the membrane or through tight junctions

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22
Q

Water reabsorption in PCT

A

Aquaporin 1 channels on apical and basolateral membranes
Due to osmotic gradient- follows Na+
20% of water passes paracellularly via tight junctions
98% of channel proteins located on cell membrane , other 2% synthesised as new and transported

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23
Q

Percentage of water reabsorbed paracellularly via tight junctions in PCT

A

20%

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24
Q

Which channels reabsorb water in PCT

A

Aquaporin 1

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25
Q

Which transporter is involved in glucose reabsorption in the later parts of the PCT

A

SGLT1 (2Na + and 1 glucose)

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26
Q

SGLT1

A

2 Na+ and 1 glucose
Much higher affinity for glucose as lower concentration in later part of PCT

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27
Q

Which transporter is involved in glucose reabsorption in the proximal parts of the PCT

A

SGLT1 (1 Na+ and 1 glucose)

28
Q

SGLT2

A

1 Na+ and 1 glucose
Early part of PCT
Works fast but doesn’t produce same gradients as SGLT1

29
Q

How does glucose pass from PCT cells to blood

A

Passively on basolateral membrane via channels

30
Q

Amino acid reabsorption in PCT

A

Range of amino acid transporters
Co-transported with Na+
Can flow out passively on the basolateral membrane through their own channels

31
Q

Chloride reabsorption in PCT

A

Moves paracellularly
Exchanged for a base on the apical membrane
Formate cycling
Cl- is transported in a NKCC2 channel on basolateral membrane

32
Q

Cl- transporter on basolateral membrane of PCT

A

NKCC2

33
Q

Formate cycling

A

Formate is exchanged for Cl- on the apical membrane
Formate then becomes formic acid which is able to diffuse across the membrane and be reused

34
Q

Protein Endocytosis and degradation in PCT

A

Microvilli have specialised sensors which specifically bind any protein
Endocytosis occurs in endosomes and protein is degraded by lysosomes to produce amino acids

35
Q

Bicarbonate reabsorption in PCT

A

Active process dependent on tubular secretion of H+ (whilst removing Na+ from lumen)
H+ then combines with HCO3- to produce carbonic acid which dissociates into H20 and CO2
CO2 diffuses through the cell membrane as is small and non-polar
H20 is reabsorbed through osmosis via AQP1 channels
Inside cell carbonic acid is reformed and again dissociates to form HCO3- and H+
H+ is then recycled

36
Q

2 methods of HCO3- transport across basolateral membrane of PCT

A

HCO3- is co-transported with Na+ into the interstitium and then blood (1Na+ and 3HCO3-)
Pumped passively in exchange for an anion

37
Q

Bicarbonate and sodium co-transport on basolateral membrane of PCT

A

1 Na+
3 HCO3-

38
Q

Sodium reabsorption in PCT

A

Na+ actively transported out of cell via the Na/K ATPase pump on basolateral membrane into the interstitial fluid- lowering intracellular [Na+] generating a concentration gradient
Na+ transported into cell either in exchange for H+ (NaX) or co-transported with glucose, phosphate - secondary active transport
Once in cell, pumped into interstitium by Na/K ATPase or co-transported with HCO3-

39
Q

What contributes to osmosis in PCT

A

Na+, glucose, phosphate reabsorption as removal of solutes from tubular lumen decreases the local osmolarity of the tubular fluid adjacent to the cell

40
Q

What percentage of Na+ is reabsorbed in exchange for protons

A

80%

41
Q

Tubular reabsorption

A

Movement from the tubular lumen to peritubular capillaries

42
Q

Tubular secretion

A

Movement from peritubular capillaries to tubular lumen

43
Q

Glomerulotubular balance

A

More filtered load is matched by more proximal tubule reabsorption
The greater filtration fraction (due to increased load eg high blood volume) will increase the osmotic pressure in the downstream peritubular capillaries resulting in more reabsorption
Efferent arteriolar constriction reduced peritubular capillary hydrostatic oressure

44
Q

Renal plasma flow equation

A

Clearance x [1/haematocrit]

45
Q

Notional volume equation

A

[urine concentration x urine flow rate] / plasma concentration

46
Q

Clearance equation

A

Amount filtered at glomerulus - amount reabsorbed + amount secreted

47
Q

What is inulin

A

A polysaccharide

48
Q

Inulin clearance

A

= GFR

49
Q

Paraminohippuric acid

A

Actively secreted, freely filtered and not reabsorbed - can be used as a measure of renal plasma flow

50
Q

Albumin clearance

A

0

51
Q

Renal clearance

A

The notional volume of plasma cleared of a substance in a given time (ml/min)

52
Q

Sodium clearance

A

Low (freely filtered but lots of reabsorption)

53
Q

Penicillin clearance

A

Higher than GFR (actively secreted)

54
Q

Urea clearance

A

High (excreted about 40% of what enters kidneys)

55
Q

Tmax -transport maximum

A

When binding sites become saturated when the concentration of a substance is too high

56
Q

Glucose Tmax

A

Glucose is freely filtered therefore concentration is the same in filtrate as in plasma
Amount excreted starts at 0 due to SGLT’s high affinity to glucose and reabsorbing the full amount into blood
Amounts being reabsorbed matches that being filtered
Levels will exceed the transport capacity of cells and so the level excreted begins to rise

57
Q

Plasma glucose concentration in a normal person

A

150 mg/100ml

58
Q

Transport maximum for glucose

A

Around 400 mg/min- usually when glucose concentration in 350 mg/100ml

59
Q

When does glucose start appearing in urine

A

When plasma glucose exceeds Tmax
400 mg/min
350 mg/100ml

60
Q

Where are glucose and amino acids reabsorbed in PCT

A

Taken up very quickly

61
Q

Where is HCO3- reabsorbed in PCT

A

Concentration reduces slower but it has a much higher initial concentration so it takes more time

62
Q

Where is inulin reabsorbed in PCT

A

Keeps going up as it is not being reabsorbed and water is (concentration rises)

63
Q

Where is Cl- reabsorbed in PCT

A

Initially gets left behind but then develops a concentration gradient so is reabsorbed

64
Q

Where is Na+ reabsorbed in PCT

A

Stays level as it flows osmotically

65
Q

Urine as it enters the loop of Henle

A

Isotonic

66
Q

Which transporters are on the base-lateral membrane

A

Na/K ATPase
Na/HCO3-

67
Q

What transporters are on the apical membrane

A

Na/glucose
Na/phosphate
Na/H ATPase

SUGER (17 decks)

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