Traditionally, invitations go out six to eight weeks before the wedding -- that gives guests plenty of time to clear their schedules and make travel arrangements if they don't live in town. If it's a destination wedding, give guests more time and send them out three months ahead of time.
The human body is made up of several organ systems that all work together as a unit to make sure the body keeps functioning. There are ten major organ systems in the body, each of which plays a different role in helping the body work. This system is made up of the heart, blood, blood vessels, and lymphatics.
An organ is a group of different kinds of tissues working together to perform a particular activity. The heart is an organ composed of muscle, nervous, connective, and epithelial tissues. An organ system is two or more organs working together to accomplish a particular task. The digestive system, for example, involves the coordinated activities of many organs, including the mouth, stomach, small and large intestines, pancreas, and liver.