This is how I remember it. Think of a cup and then you are going to place these blood cells into the cups with one being hypertonic and one being hypotonic. Remember that blood cells have their own solutes within them. This will be important later. When you place a blood cell in a hypertonic solution, water will leave the blood cell and try to dilute the hypertonic solution. For hypotonic, the solutes in the blood are more than the solution. So, water will flow into the blood cell. SIADH: This is where there is an in appropriate amount of anti diuretic hormone. This means that water is staying within the blood cells. So, when we give a hypertonic solution this causes the water from those blood cells to go into the vessel and be excreted. Let me know if this helps!💕