I have a jammed thumb and a bruised palm, do I need to seek medical attention?

Yes. The bruising is from blood that can be the result of a muscle, ligament or bone injury. A thorough medical evaluation (that will likely include x-rays) will determine whether you injured a bone (break/fracture) or soft tissue (ligament sprain or muscle tear) or both.
Yes. Jammed thumb with bruising could mean a serious injury. Go see your dr. Or a specialist.