How is serum sodium concentration measured?
[Na+] = mmol Na+/1L H2O
What is the reference interval for serum sodium concentration?
Generally, hyponatraemia becauses more serious when sodium levels fall below what level?
A low serum sodium concentration can be caused by which two things?
- Low sodium concentration
- High water concentration
What symptoms may be experienced with hyponatraemia?
- Altered conciousness
In which two compartments is water present within the body?
- Extracellular fluid (ECF)
- Intracellular fluid (ICF)
The _____cellular fluid volume is much greater than the _____cellular fluid volume
The intracellular fluid volume is much greater than the extracellular fluid volume
Which fluid compartment contains the vast majority of sodium?
Why is it that the ECF has a far higher sodium content?
Na+/K+ pump activity
Why is it possible to gain or lose a lot of water without suffering from clinical signs?
Gain or loss is spread across a large volume (ICF + ECF)
Effects are therefore "diluted"
Loss of sodium will lead to a loss of what?
How is it possible for the kidneys to regulate water volume in the body?
By either retaining or excreting sodium, water is conserved or lost respectively
How does a low sodium concentration impact the intracellular fluid?
The ECF is reduced but the ICF remains relatively constant
How does an increased H2O concentration impact the ECF and ICF?
They both increase
How is dehydration and hyponatraemia treated?
- IV saline in an emergency
- Oral sodium can also be used
How is oedema and hyponatraemia treated?
The RAAS pathway acts to _________ blood pressure
The RAAS pathway acts to increase blood pressure
Which two key endogenous steroids have mineralocorticoid activity?
Increased mineralocorticoid activity leads to what?
- Sodium retention
- Increased blood pressure
Where does ADH act and what is the result of its action?
What is the name given to the concentrating mechanism within the kidneys which occurs as a result of ADH?
What properties of the descending limb of Henle allow for countercurrent multiplication?
- Highly permeable to water
- Impermeable to NaCl
What properties of the ascending limb of Henle allow for countercurrent multiplication?
- Active excrusion of NaCl into ECF
- Impermeable to water
How is water lost from the descending limb of Henle?
In response to NaCl being pumped into the interstitial fluid from the ascending limb of Henle
Sodium is pumped out from the ascending limb of Henle until what osmolar difference exists between the ascending limb of Henle and descending limb of Henle/interstitial fluid?
Countercurrent multiplication continues until he fluid in the descending limb of Henle reaches a maximally hypertonic value of what?
Name 3 non-osmotic stimuli for ADH release?
- Nausea and vomiting
What are some pathological reasons for an increased sodium loss?
- Adrenal/kidney causes
- Poor absorption in gut
- Skin (e.g. burns)
What are some pathological reasons for an increased water concentration?
- Decreased excretion (e.g. SIADH)
- Increased intake (compulsive water drinking)
Sodium levels may be considered very high at which level?