For one, there is an anti drain back valve which assists in keeping the filter and oil galleries higher than the oil filter full of oil. This greatly assists in ensuring vital lubricating oil is available quickly at start up. Otherwise a good deal of wear would occur at start up whilst waiting for oil to be pumped from the sump, fill the oil filter and finally get up to where it's needed most.
Another structure is the filter by-pass. The filter medium is restrictive to flow. As the filter becomes clogged, or if high viscosity oil is used in cooler climates, it becomes difficult to pump the required volume of oil through the filter. In order to ensure adequate oil flow, the filter medium itself is by-passed when the resistance is high. It may come as a surprise to some that this type of filter is not a full flow filter (fuel filters are). At higher engine speeds and with high volume of flow, most of the oil by-passes the filter medium.
Many thanks to Norm of Traction4 for the following words and pictures.