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Flashcards in Water and Sodium Deck (20):
1

Osmolality of most cells?

290

2

High IC electrolytes

potassium (NOT sodium)

3

High EC electrolytes

sodium (NOT potassium)

4

What happens if you give a person intravenous hypertonic saline?

Blood pressure goes up, goes up more than isotonic because blood is more concentrated so water moves into blood from interstitium

5

What happens if you give IV saline?

BP increases, short time effect -> no fluid shift, no change in osmolality

6

What happens if you give intravenous 5% dextrose solution?

No sodium, osmolality is the same so is the same as giving normal saline
Metabolises sugar quickly, so essentiality water remains which is hypotonic

7

Function of the proximal tubule

70% solutes and water reabsorbed
Fluid resorption mostly isosmotic

8

Function of the loop of henle

Makes urine dilute by reabsorbing salt
Descending limb water permeable - salt stays in
Thin ascending limb water impermeable - salt diffuses out
Thick ascending limb reabsorbs Na (NaKCl2)

9

Function of the distal tubule

Active solute reabsorption (Na/K)

10

Function of collecting duct

ADH sensitive
If no ADH – CD is water insensitive hence dilute urine
In presence of ADH – water is reabsorbed

11

3 things needed to make dilute urine

Adequate fluid delivery
Na reabsorption in TAL
impermeable CD for water

12

4 things are needed to make a concentrated urine

Not too much fluid delivery
Na reabsorption in TAL
Normal ADH production,
Normal medullary hypertonicity

13

Hormonal regulation of water

ADH
Renin-angiotensin-aldosterone
ANP

14

ADH actions and mechanism of action

Direct vasoconstrictor
NaCl reabsorption in TAL loop of Henle
Water retention in collecting ducts
Receptor binding activates cAMP which stimulates water channel (aquaporin 2) incorporation into apical membrane

15

ANP actions

Polypeptide released from cardiac myocytes
Increases urinary excretion of Na and water
Inhibits Na resorption by collecting duct
Inhibits renin production and aldosterone secretion

16

How could you lose too much water through your kidneys?

No ADH
Kidney insensitive to ADH
NaKCl2 channel blocked
Other solutes carrying water through the kidney
Alcohol, caffeine
Drugs inhibiting ADH
Excess ANP

17

Clinical features of dehydration

Postural hypotension, tachycardia, low skin turgor, sunken eyes, dry mouth, thirst

18

Biochemical features of dehydration

Serum osmolality high
Serum Na usually high
Serum K / Mg / Ca – high/low or normal
Serum urea high
Hb high

19

Dehydration treatment

Give back the lost fluid
– if true dehydration – water !
– if salt and water – saline!
Get other solutes right too

20

What is DI?

Central (lack of secretion) or nephrogenic (failure to respond) to ADH (AVP)