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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
Which transporter is involved in glucose reabsorption in the later parts of the PCT
SGLT1 (2Na + and 1 glucose)
26
SGLT1
2 Na+ and 1 glucose Much higher affinity for glucose as lower concentration in later part of PCT
27
Which transporter is involved in glucose reabsorption in the proximal parts of the PCT
SGLT1 (1 Na+ and 1 glucose)
28
SGLT2
1 Na+ and 1 glucose Early part of PCT Works fast but doesn’t produce same gradients as SGLT1
29
How does glucose pass from PCT cells to blood
Passively on basolateral membrane via channels
30
Amino acid reabsorption in PCT
Range of amino acid transporters Co-transported with Na+ Can flow out passively on the basolateral membrane through their own channels
31
Chloride reabsorption in PCT
Moves paracellularly Exchanged for a base on the apical membrane Formate cycling Cl- is transported in a NKCC2 channel on basolateral membrane
32
Cl- transporter on basolateral membrane of PCT
NKCC2
33
Formate cycling
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
Protein Endocytosis and degradation in PCT
Microvilli have specialised sensors which specifically bind any protein Endocytosis occurs in endosomes and protein is degraded by lysosomes to produce amino acids
35
Bicarbonate reabsorption in PCT
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
2 methods of HCO3- transport across basolateral membrane of PCT
HCO3- is co-transported with Na+ into the interstitium and then blood (1Na+ and 3HCO3-) Pumped passively in exchange for an anion
37
Bicarbonate and sodium co-transport on basolateral membrane of PCT
1 Na+ 3 HCO3-
38
Sodium reabsorption in PCT
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
What contributes to osmosis in PCT
Na+, glucose, phosphate reabsorption as removal of solutes from tubular lumen decreases the local osmolarity of the tubular fluid adjacent to the cell
40
What percentage of Na+ is reabsorbed in exchange for protons
80%
41
Tubular reabsorption
Movement from the tubular lumen to peritubular capillaries
42
Tubular secretion
Movement from peritubular capillaries to tubular lumen
43
Glomerulotubular balance
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
Renal plasma flow equation
Clearance x [1/haematocrit]
45
Notional volume equation
[urine concentration x urine flow rate] / plasma concentration
46
Clearance equation
Amount filtered at glomerulus - amount reabsorbed + amount secreted
47
What is inulin
A polysaccharide
48
Inulin clearance
= GFR
49
Paraminohippuric acid
Actively secreted, freely filtered and not reabsorbed - can be used as a measure of renal plasma flow
50
Albumin clearance
0
51
Renal clearance
The notional volume of plasma cleared of a substance in a given time (ml/min)
52
Sodium clearance
Low (freely filtered but lots of reabsorption)
53
Penicillin clearance
Higher than GFR (actively secreted)
54
Urea clearance
High (excreted about 40% of what enters kidneys)
55
Tmax -transport maximum
When binding sites become saturated when the concentration of a substance is too high
56
Glucose Tmax
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
Plasma glucose concentration in a normal person
150 mg/100ml
58
Transport maximum for glucose
Around 400 mg/min- usually when glucose concentration in 350 mg/100ml
59
When does glucose start appearing in urine
When plasma glucose exceeds Tmax 400 mg/min 350 mg/100ml
60
Where are glucose and amino acids reabsorbed in PCT
Taken up very quickly
61
Where is HCO3- reabsorbed in PCT
Concentration reduces slower but it has a much higher initial concentration so it takes more time
62
Where is inulin reabsorbed in PCT
Keeps going up as it is not being reabsorbed and water is (concentration rises)
63
Where is Cl- reabsorbed in PCT
Initially gets left behind but then develops a concentration gradient so is reabsorbed
64
Where is Na+ reabsorbed in PCT
Stays level as it flows osmotically
65
Urine as it enters the loop of Henle
Isotonic
66
Which transporters are on the base-lateral membrane
Na/K ATPase Na/HCO3-
67
What transporters are on the apical membrane
Na/glucose Na/phosphate Na/H ATPase

SUGER (17 decks)

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