In the Week 4 Renal ‘Murder Mystery’, Professor Craig Harrison died of cerebral (osmotic) oedema (brain swelling) associated with hyponatremia (caused by a combination of SIADH, his diuretic being swapped for desmopressin and ecstasy, and drinking too much water). 

Explain:

1. Why is SIADH associated with hyponatremia?
2. Draw (and label) a diagram that illustrates why hyponatremia leads to brain swelling and upload it below as a pdf (hint – please show the body fluid compartment, intracellular and extracellular fluids). 
3. What could you have given Craig (intravenously) to save his life? Explain your choice.

[maximum 250 words]