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.
The bodies of organisms are organized into functional systemsâcells are organized into tissues, and tissues are organized into organs. Body systems carry out critical functions, such as locomotion, reproduction, digestion, and circulation. Cells are arranged in hierarchical levels of organization. 2  The lowest form of organization is the cell followed by tissues, organs, and organ systems. 3  A tissue is a group of similar cells in an organism working together to perform a particular function (e.g. nerve or muscle tissue).