Part of the oxygen-rich blood containing THC molecules reaches the brain via the aorta. It diffuses through the tiny capillaries between the brain cells.
Only 5 to 20 per cent of all the THC that was contained in the spacecake will eventually produce any effects in the brain. So the ultimate THC concentration in the blood is lower from spacecake than from smoking an equivalent amount of cannabis.
It also takes much more time to feel the effects. The ‘accidents’ that sometimes happen when people eat spacecake are due either to eating too much cake or to excessive cannabis content in the cake.