Renal Physiology: salt and water - DeZoysa

Question 1

Approximately how much of a 5L blood volume is plasma?

Answer 1

3L

Question 2

Sodium and potassium concentrations of intracellular and extracellular fluids

Answer 2

Intracellular: K+ high, salt low
Extracellular: salt high, K+ low

Question 3

Osmotic concentration

Answer 3

the measure of the solute concentration
Is the number of Osm of solute per litre of solution
Osmolarity is tightly regulated

Question 4

Plasma osmolarity

Answer 4

Plasma osmolarity is 285-295mOsm/L
Regulated by the balance of salt and water
hyperosmolarity: too much cation and too little water
Hypo: too little cation and too much water

Question 5

Tonicity

Answer 5

what happens to cells in solution
If the cells take up water from a solution then the solution is hypotonic
If the cells lose water to a solution (shrink) then the solution is hypertonic
If no change in cell size is observed then solution is isotonic.

Question 6

What is GFR and how much do our kidneys filter per day?

Answer 6

120ml/min

120ml x 60min x 24 hours = > 170L/day

Question 7

The LoH

Answer 7

Water freely filtered the descending limb and ions filtered out in the ascending limb

Loop diuretics can act in the LoH to induce diuresis

Question 8

Collecting duct

Answer 8

sodium and water reabsorbed, but this is controlled by antidiuretic hormone

Question 9

ADH

Answer 9

Vasopressin
Made in the hypothalamus, secreted in the pituitary
Increased production of BP falls or osmolarity increases
Increases the absorption of water
Increases BP and reduces osmolarity

Question 10

Aldosterone

Answer 10

a mineralocorticoid
acts on the DCT and collecting ducts
Increases sodium reabsorption and K+ excretion.
Stimulated by potassium and angiotensin II

Question 11

Renin- angiotensin

Answer 11

the junta glomerular apparatus senses decreased renal perfusion and secretes renin
Renin increase production of angiotensin

Question 12

Angiotensin II - causes

Answer 12

vasoconstriction
ADH release stimulated
Sodium reabsorption in proximal tubule
Thirst
Lowers GFR by contraction of measngial cells thus reducing the area for glomerular filtration
Also increases GFR by contraction of efferent arteriole
Stimulates release of aldosterone

Question 13

Hypernatremia

Answer 13

impaired thirst / level of consciousness
No access to water
Burns/ diarrhoea / blood loss
Solute diuresis

Question 14

Hypernatremia due to diabetes insipidus

Answer 14

Reduction in the amount or efficacy of ADH
Polyuria and water loss
Dilute urine (<200mOsm/Kg)
Patient cant drink enough water to keep up with losses
Elevated plasma osmolarity, hypernatremia, dehydration

Question 15

Types of DI

Answer 15

central - 50% from traumatic brain injury
Nephrogenic
- problem with aquaporion channels in the kidney
- Partial of complete resistance to ADH

Question 16

Hyponatremia - causes

- what to do?

Answer 16

excessive sodium loss
Excessive water retention
- Check urine osmolarity: if <100mosm/kg = very dilute urine
Consistent with polydipsia/water intoxication
Ddx-Psychotropic drugs
schizophrenia
beer potomania

Question 17

Pseudohyponatremia

Answer 17

check serum osmolarity
if normal the patient has pseudohyponatremia (may be problems with the way the lab is measuring salt, especially if the glucose is really high)

Question 18

hypovolaemic

Answer 18

Dehydrated. Urine sodium <20mmol/L
sodium loss but relatively less water loss
- diarrhoea, vomiting
- bowel obstruction
- Skin losses, burns/ sweating
- urinary loses ( diuretics, addisons disease, ketonuria, osmotic diuresis, RTA)

Question 19

Hypervolaemic

Answer 19

fluid overloaded 
Sodium retention BUT relatively more water retention 
- cirrhosis 
- nephrotic syndrome 
- Heart failure 
- Renal failure

Question 20

Examples of patients with hyponatremia but who are euvolaemic

Answer 20

SIADH (syndrome of innapopriate ADH)
Endocinopathies (Hypothyroid/ low cortisol)
Diuretics
Fluid replacement

Question 21

SIADH

Answer 21

Inappropriate ADH secreted in absence of normal stimuli such as Low BP
Body accumulates too much water (stored in cells so patient doesn’t appear to be overloaded)
Urine osmol: not low, usually greater than 150mosml/Kg
Urine sodium: not low (>20mmol/L)
Plasma osmolarity: low

Question 22

Symptoms of hypoonatremia

Answer 22

depends on how quickly it has developed 
Slow: --> brain adaptation 
- confused, not quite self 
Rapid: cerebral oedema
- confusion, seizures, coma

Question 23

Brain adaptation

Answer 23

water causes cerebral oedema (much less of a problem if it develops slowly)
Over time brain cells adapt
resulting in correction of cerebral oedema

Question 24

Treatment of hyponatremia: rapid versus slow onset

Answer 24

rapid:
- may need more vigorous treatment
- fluid restriction
- normal saline
- 3% (hypertonic) saline in ICU

Slow onset

• Correct gradually
• generally just fluid restriction
• no more than 8mmol/L/day

Question 25

Complications of treatment of hyponatremia

Answer 25

rapid correction - before brain can adapt
Braindehydraiton = central pontine myelinolysis
Compression of myelin sheaths - rapid demyelination (mainly in pons)
- Quadraparesis
- pseudo bulbar palsy
- Lcoked in syndrome
- Irreversible