8.12 Salt, Water & Potassium

Question 1

Hyponatriaemia

Answer 1

• low Na in blood serum
• excessive water intake
  1. Low salt
  2. Add lots of water

RF
- less well trained athletes
- long race times
- weight gain during race (because of water gain)
- females, low body mass, younger age

Symptoms
- confusion
- weight gain
- seizures
- resp distress

Prevention
- education (don’t drink too much water)

Question 2

Water compotition in man and women

Answer 2

M: 60%
W: 50%

ICF: 20L (2/3)
⬆️ K
Bigger vol
⬇️pH

ECF: 10L (1/3)
⬆️ Na

Osmolarity is same ICF & ECF: osmotic forces very powerful, cell membrane full of channels (290-300 mOsm/kg)

Question 3

How is osmolarity meassured?

Answer 3

• depression of freezing point
• with solutes: will not freeze at 0
• the more solutes the lower the freezing point (-1)

salt lowers freezing point

Question 4

How does water move across membrane?

Answer 4

• Permeability
• Driving force (concentration difference)

Driving forces:
- concentration
- electrical
- pressure

Question 5

What force is the strongest force?

Answer 5

Osmotic force

Question 6

Why are most of the potassium inside our cells?

Answer 6

Inside of cells are ➖ charged and hold potassium inside

Question 7

Why is most of sodium outside the cell?

Answer 7

The cell membrane has no permeability for sodium; so stays outside

Question 8

What 2 factors determine ICF?

Answer 8

P osmolarity
Concentration of Na (ICF vol)

Question 9

What is ECF determined by?

Answer 9

Na+ content

Question 10

What happens if give pt 1L of pure water?

Answer 10

• dilute blood (water gets into cells)

Question 11

Regulation of Na+

Answer 11

• by kidney

GO ON WITH SLIDE 22

Question 12

What determines the permeability of collecting duct?

Answer 12

ADH

Question 13

Stimuli of ADH

Answer 13

VASOPRESSIN
- physiologic - SLIDE
- non- physiologic - CNS, lung disease, ectopic cancers, drugs, anxiety, pain, nausea

Question 14

How does the body responds to osmolarity (Na concentration) changes?

Answer 14

Via water intake and output
Water, thirst, ADH

Question 15

How does the body responds to ECF volume (Na content) changes?

Answer 15

Sodium intake & output
(Renin-angiotensin-aldosterone)

Question 16

Acute hyponatraemia

Answer 16

• less than 48hrs

**Causes:* acute water overload (hypotonic iv fluids in hospital, ectasy, marathons, psychogenic polydipsia)

Dangers: brain swelling and herniation (coma, seizures, death)

Question 17

Chronic hyponatraemia

Answer 17

• more than 48hrs

Causes
- Na loss ± water gain
- ADH present & prevents water excertion
- hypovolaemia, drugs, CNS, lung disease

Dangers
- osmotic demyelination from too-rapid correction
- serious neurological damage

Question 18

What are the normal values of potassium?

Answer 18

ECF: 4mmol/L (in blood test)
ICF: 150 mmol/L

Question 19

What are the signs of Hyperkaleamia on ECG?

Answer 19

• Tall peaked T waves
• loss of p waves
• widening QRS complexes
• sine waves, ventricular arrythmias, asystole

Question 20

What keeps K inside cells?

Answer 20

• electrical charge ➖
• Na/K ATPase

Question 21

What leads to a negative K balance?

Answer 21

• ⬇️ input
• ⬆️ output

Question 22

How does acidosis cause hyperkalemia?

Answer 22

• Acidosis cause: diabetic acidosis or lactic acidosis (this is normal!!)
  Therefor this statement is not entirely true. Acidosis doesn’t really cause hyperkalemia

Only when body is confronted with abnormal acid; acidosis will cause Hyperkalemia

Therefor depends ON NATURE OF ACID

Question 23

How does the body handle usual dietary K+ load?

Answer 23

• we absorb all the potassium we ate -> that we need to excrete
• K+ parked in Liver -> redistributed to rest of body
• kidney will excrete it slowly over time
• use insulin to push potassium into cells (this is only temporarily)

Question 24

What should you consider if you have pregnant pt with hypokalemia?

Answer 24

Geophasia