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Urinary system > Tubular Function > Flashcards

Tubular Function Flashcards

1
Q

Is transcellular or paracellular more tightly regulated?

A

transcellular

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2
Q

What are the 2 types of reasborption and secretion?

A

transcellular and paracellular

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3
Q

Passive transport

A

Can be controlled by membrane proteins

  • lipophilic diffuse straight through
  • hydrophilic may need carriers
  • with carriers the rate plateaus at high substrate concentrations
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4
Q

Active transport

A

Active transport can be:

  • directly coupled to ATP hydrolysis (primary)
  • indirectly coupled to ATP hydrolysis (secondary)
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5
Q

Give an example of primary active transport

A

vitamin and calcium transport

Na+K+ pump

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6
Q

Give an example of secondary active transport

A

Na+/glucose (cotransport)

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7
Q

Can water travel transcellularly and paracellularly, and via what?

A

Yes
paracellular - via tight junctions
transcellular - aquaporins

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8
Q

How are proteins absorbed

A

receptor mediated endocytosis

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9
Q

What is transport maxima?

A

Systems are regulated and so may have a basal and stimulated maxima rate of absorption. However they may also have only one state of reabsorption.

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10
Q

Transport maxima of glucose

A
  • more glucose in the blood means a proportional increase in rate of reabsorption
  • glucose is reabsorbed up to a point when channels are saturated so plateaus
  • up to 15mmol/L of plasma glucose the excretion equals 0 as rate of filtration and reabsorption are the same
  • past that the glucose is excreted in urine e.g. in diabetes
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11
Q

How does secretion occur?

Give example of secreted substances

A

From peritubular capillaries into the tubular lumen

  • occurs via diffusion or transcellular transport
  • most important secreted substances are H+ and K+
  • choline, creatinine (very little) and pencillin are secreted
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12
Q

What is reabsorbed in the PCT?

A

60-70% all solute

  • 100% glucose
  • 65% sodium
  • 90% bicarbonate
  • 60-70% of water
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13
Q

What is reabsorbed in the LoH?

A

25% sodium

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14
Q

What is reabsorbed in the DCT?

A

8% sodium

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15
Q

Histology of the PCT, LoH, DCT and CD?

A

PCT:

  • ciliated
  • lots of mitochondria

LoH descending:
- no cilia, not much mitochondria

LoH ascending:

  • no cilia
  • lots of mitochondria

DCT:

  • cilia
  • some mitochondria

CD:

  • no cilia
  • not much mitochondria
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16
Q

Function of the PCT?

A

70% of all filtrate reabsorbed

  • driven by Na+/K+ ATPase
  • Pump pushes out sodium out basolateral side into capillaries so intracellular sodium is low. Then sodium is drawn in at apical membrane and co-transported with other molecules
  • Sodium reabsorption them indirectly leads to bicarbonate absorption
  • Sodium acts to excrete protons that buffer bicarbonate
  • carbonic anhydrase forms h20 and co2 - co2 taken up into cells and used to remake bicarbonate and secreted into capillaries
17
Q

Function of LoH?

A

descending - water passively reabsorbed

ascending - chloride actively reabsorbed, sodium passively with it and potassium too. Bicarbonate reabsorbed and its impermeable to water.

18
Q

What do loop diuretics do?

A

Block Na+/K+/Cl- transporter

19
Q

DCT function? (proximal part)

A
  • Na+ and Cl- co transporter linked to calcium reasborption
20
Q

DCT function (proximal distal part) and CD?

A
  • fine tuning of the filtrate for homeostasis
  • DCT depends on aldosterone
  • CD depends on aldosterone too and ADH
  • distal part of CD is impermeable to water without ADH
  • both use aldosterone sodium channel, linked soidum channel and pH controlled proton ATP channel
21
Q

Renal tubular acidosis

A

in early proximal tubule the protons leak back into the cell after being pumped into the lumen so the urine becomes alkaloid

22
Q

Bartter syndrome - cause and what can it lead to?

A

Antenatal

  • in ascending limb there is too much electrolyte secretion due to mutation in Na+/K+/Cl- transporter on apical membrane
  • can cause premature birth, polyhydroamnios, hypokalaemia, metabolic alkalosis, renin and aldosterone hyper secretion
23
Q

Fanconi syndrome - cause

A
  • increased excretion of uric acid, phosphate, glucose, bicarbonate and low molecular weight protein
  • disease in proximal tubule
  • AKA renal tubular acidosis: type 1 dent’s disease
  • in receptor mediated endocytosis a proton pump is needed to dissociate protein and receptor but there is a mutation
  • too many protons in endosome so no receptor dissociation
24
Q

Principal cell in DCT

A

important in sodium, potassium and water balance (mediated via na+/k+ pump)

25
Q

Intercalated cell in DCT

A

important in acid base balance (via H ATP pump)

26
Q

How much water is reabsorbed in the PCT, LOH, DCT and CD?

A 
PCT = 60-70%
LoH = 10%
DCT = 10%
CD = variable from less than 1 - 10% excreted
27
Q

What does the Na+K+Cl- transporter do?

A

Apical membrane of thick ascending limb

transports them in then sodium out into interstitial space

Urinary system (12 decks)

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