Lecture 22: Kidney function II - production of concentrated urine by the kidney Flashcards Preview

1060 Human form and function > Lecture 22: Kidney function II - production of concentrated urine by the kidney > Flashcards

Flashcards in Lecture 22: Kidney function II - production of concentrated urine by the kidney Deck (23):
1

what is osmolality??

Osmolality (mosm/kg): a measure of water concentration.

The higher the solution osmolality the lower the water concentration. 

 

Plasma 285-295 mosm/kg

Urine 50-1400 mosm/kg 

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2

What are the units for osmolality and osmolarity?

Osmolality = mosm/kg

Osmolarity = mosm/L

3

Osmolality in plasma dependent on ??

[Na+] 

Plasma sodium concentration 135-145mmol/l.

Freely filtered at renal corpuscle

Plasma Na+ concentration (mmol/l) X GFR (l/min) = amount filtered 140 x 0.125 = 17.5 mmoles/min

AMOUNT FILTERED: 25,200 mmoles/day
dietary salt intake varies 0.05-25g/day.
WHAT SALT IS INGESTED MUST BE EXCRETED

SO: ingest and therefore excrete 100 mmol sodium per day. 

SO: 100/25,300

Only 0.4% excreted.

99.6% REABSORBED!!! 

4

where does sodium reabsorption occur?

along the tubule of the nephron

it is an active process so it needs ATP

so we know that it happens where there is alot of mitochondria

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5

what is the sodium reabsorption in the loop of henle?

None in descending limb. Passive in thin ascending limb.

Thin descending limb (thin ascending similar) 

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6

Na transport pathways (1) - proximal tubule 

explain

65% of filtered load of NaCl reabsorbed 

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7

Na transport pathways (2) – thick ascending limb 

explain

25% of filtered load of NaCl reabsorbed in thick and thin ascending limb. 

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8

Na transport pathways (4) – collecting duct 

explain

2 cell types:

1) principal cells (Na+ transport)

2) intercalated cells (H+ transport) 

 

5% of filtered load of NaCl reabsorbed 

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9

Na transport pathways (3) – distal tubule 

explain

2-5% of filtered load of NaCl reabsorbed 

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10

what does water reabsorption depend on ??

osmosis
sodium reabsorption

tubule permeability

11

Coupling of Water Reabsorption to Sodium Reabsorption ???

sotonic reabsorption– tight junctions have high water permeability.

Also membrane expression of aquaporin-1 (AQP1) water channels.

Filtrate volume reduced but not osmolarity. 

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12

How are we going to produce a concentrated urine? 

We need to separate Na+ and water reabsorption.

Generate a renal medulla interstitial fluid with high osmolarity to drive water reabsorption. 

 

(both processes occur at the loop of henle)

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13

permeability factors in the ascending limb??

Ascending limb:
Salt reabsorption via Na+:K+:2Cl- cotransporter.

Water stays in tubule. 

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14

permeability in descending limb??

Descending limb picks up salt and loses water

AQP-1 water channels expressed. 

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15

Setting up medullary interstital gradient

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16

MULTIPLICATION OF OSMOLARITY BY THE LOOP OF HENLE 

explain

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17

special ability of vasa recta??

supply blood without washing the gradient away

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18

Counter-current exchange ?

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19

UREA RECYCLING BY KIDNEY ?

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20

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21

Action of anti-diuretic hormone (ADH) on Collecting Duct 

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22

what does concentrated urine depend on ??

Renal medulla interstitial fluid high osmolarity 

Collecting duct

i) pass through concentrated zone.

ii) water permeable (controllable) 

23

Vasa recta supply blood without washing away gradient and take water away from medulla

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