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ESA 3 - Urinary System > Control of Volume > Flashcards

Control of Volume Flashcards

1
Q

What are the compartments of extracellular fluid?

A

Blood plasma
Interstitial fluid
Transcellular fluid

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2
Q

Predominant cation in extracellular?

A

Na

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3
Q

Predominant cation in extracellular?

A

K

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4
Q

What does the volume of ECV depend on?

A

Depends on the Na ion contents in that compartment.
If sodium in ECF changes then the volume then changes to keep concentration the same.
This changes the blood pressure.

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5
Q

What would happen if Na ions were allowed to change due to diet?

A

Water in ECF would change
so BP would change
So you get consequences of change in GFR

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6
Q

How much is the recommended intake is NaCl?

A

10.5g

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7
Q

Where do we loose NaCl from?

A

Sweat (0.25g)
Faeces (10.25g)
Urine (10g) -majority!

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8
Q

How move water?

A

Change conc of ions (move osmoles) so water moves by osmosis until osmolarity either side of membrane is equal

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9
Q

How can you change the renal sodium excretion?

A

Changes in the osmotic Pressure and hydrostatic pressure alter the proximal tubule Na reabsorption (and hence water).
Proximal tubule reabsorption is stimulated by RAAS
Principle cells of DCT and CD targets for the hormone aldosterone.

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10
Q

What are pressure natriuresis and diuresis and when do they occur?

A

Pressure natriuresis is increases Na excretion and pressure diuresis is increased water excretion.

These occur together when renal artery BP increases as:

  • Reduction in number of Na-H anti porters and reduced NaKATPase activity
  • Less Na reabsorbed in PCT
  • Less water absorbed
  • Pressure natriuresis and diuresis
  • ECF volume diminished so no rise in BP
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11
Q

What is the role of tight junction?

A

They act as a barrier to prevent the transporters moving from the apical to the basal membrane.

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12
Q

How does water follow Na?

A

Water travels through aquaporins.
AQP1 on PCT
Decending and DCT - none
Collecting duct- AQP2 (one on each surface and changes depending on osmolarity), AQP3,APQ4

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13
Q

How does Na reabsorption occur?

A

Mainly an active process driven by NaKATPase on basolateral membrane.

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14
Q

What different types of Na transporters are present in different places?

A 
PT 
Na-H antiporter
Na-Glucose (symporter)
Na-AA xo-transporter
Na-Pi

LoH
NaKCC (symporter)

Early DCT
NaCl (symporter)

Late DCT and CD
ENaC (Epithelial Na Channels)

There are many more..

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15
Q

How does the concentration of ions change as the distance from Bowmans space increases?

A

Glucose, AA and lactate decrease first as they are moved in S1 segment.
HCO3- decreases next as a lot of it is moved in S1.

Phosphate decreases evenly throughout PCT as it is evenly removed through all three segments of PCT.

Chloride moves last because the moment of all the other ions creates a concentration gradient so that CL- can diffuse paracellularly, requiring no energy.

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16
Q

What transporters are present in the S1 section of PCT, therefore what ions move?

A

Apical membrane: Na-H exchanger and lots of cotransporters (glucose, AA / carboxylic acid, phosphate)

Basolateral: 3Na-2K-ATPase ans NaHCO3-

Aquaporins too.

17
Q

What transporters are present in the S1 section of PCT, therefore what ions move?

A

Basolateral: 3Na-3K-ATPase

Apical: Na-H exchanger, Pacellular Cl- movement and transcellular chloride

There is also a 4mOsmol gradient favouring water uptake from the lumen and aquaporins.

18
Q

What is paracellular transport?

A

Transfer of substances across an epithelium by passing through the intercellular space between the cells.

19
Q

What is transcellular transport?

A

Substances travel through the cell, passing both the apical and basolateral membrane.

20
Q

What percentage of water, glucose, AA and Na+ is reabsorbed in the PCT?

A 
Water = 65%
Glucose = 100%
AA = 100%
Na+ = 67%
21
Q

What are the driving forces for movement of ions in PCT?

A

Osmotic gradient that is established by solute absorption e.g. osmolarity in interstitial spaces increases

Increase in hydrostatic forces in the insterstitium

Increase in the oncotic force in peritubular capillary due to loss of 20% filtrate at glomerulus but cells and proteins left.

22
Q

There is a concentration gradient running from the cortex to the medulla (cortex is isomotic with plasma), what effect does this have on the movement of ions?

A
  • Pulls water out of the descending limb
  • This means that when the filtrate gets to the bottom of descending limb, it is very concentrated
  • As solution travels up the ascending limb, solutes moves out (passively at first then actively) but not water as the thick ascending limb is impermeable.
23
Q

What transporters are used in the thick ascending limb to move ions?

A
  • Firstly, K,Na,2Cl move from lumen to cells with NKCC2.
  • Then, Na moves into insterstitium (blood) via NaKATPase. This also moves K ion into cells
  • K ions diffuse back to lumen via ROMK to keep conc high for NKCC2
  • Cl- also moves into insterstitium

This region uses more energy that any other in the nephron and is particularly sensitive to hypoxia.

24
Q

How do ions move in the early DCT?

A

DCT (early and late) ATs 5-8% of Na and water permeability is low.

NaCl enters across apical membrane via electro-neutral NCC transporter and leaves via NaKATPase.

25
Q

What drugs are sensitive to NCC transporters?

A

Thiazide diuretics

26
Q

How do ions move in the late DCT?

A

NACl enters via NCC and ENaC and leaves via NaKATPase.

ENaC is not electroneutral and difference drives paracellular Cl- ion reuptake.

27
Q

What drugs are sensitive to ENaC?

A

Amiloride transporters

28
Q

How is Ca transported in DCT?

A

Apical Ca transport.

Cytosolic Ca is immediately bound by calbindin which shuttles Ca to basolateral aspect of DCT cell.

Then transported out by NCX

This process is tightly regulated by hormones such as parathyroid hormone and 1,25-dihydroxyvitamin D.

29
Q

What are the two types of cell found in the cortical collection duct?

A

Principle cells and Intercalated cells.

30
Q

What do principle cells do?

A

70% of cells are principle.

  • Reabsorption of Na+ via ENaC on apical membrane. (same as DCT2).
  • No Cl- movement so provides lumen with negative charge which is driving force for Cl- movement paracellularly.
  • Also variable water intake depending on AQPs
31
Q

What do intercalated cells do?

A

There are two different types (A and B)

A-IC = Acid secreting

B-IC = Bicarbonate secreting.

In cortical and outer medullary collecting duct, type As express H+ATPase and HKATPase at apical membrane and ClHCO3 exchanger at basolateral membrane.

ESA 3 - Urinary System (20 decks)

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