I always introduce this unit by reading The Magic School Bus in the Human Body. We talk about the importance of maintaining our bodies physically and do a short unit on nutrition if time permits.
Skeleton: label anatomically correct skeleton or paper halloween skeleton with names of bones- scientific and common names. Label the differnt types of joints( fixed, partially moveable, ball & socket, pivot, gliding) on index cards. On each card a joint is described and all bones in that joint are labeled. For example: hinge- a joint that moves back & forth. The elbow is a hinge, using the humerus, radius, ulna. The skeletons made of paper are hung from the ceiling so all people can see the cards or they can be stapled to the walls.
During this unit we also write letters to Skelly, our 6 foot skeleton, and to Skinny Minny, our 3 foot skeleton. For math we measure our bones, then cut them out on bulletin board paper to put together. They may color their bones in pairs the same color, or color all a different color.
Digestion: We read "What Happens to a Hamburger" and discuss the sequence the food goes through to be digested. They discuss each organ so they can describe color, size, and function. Then each child picks out a food to have digested OR they can decide to have themselves digested. They write a book called "Whast Happens to a __________. I encourage humor as well as scientific accuracy. The class may make a class story and put it into big book form.
Circulation: We define vocabulary from parts of the heart, blood cells, vessel types, and diseases. Then we discuss the path of blood through the heart to all body parts. We learn how to take pulse and do a jump rope activity to measure resting, active, and cool-down heart rates. Making a scab with balloons and masking tape shows the class how each blood cell is necessary to repair a wound ( using a huge piece of bulletin board paper we put a few pieces of making tape acrocc a hole cut into the center. Then the kids throw platelets and red cells inot the tape and those that stick make the scab. We then add white cells by throwing the balloons in as well. It shows them up close and personal how cuts heal. Our last activity is to go to the local blood donation center for a tour. Usually i donate platelets so they can see how the machine separates the blood products.
Repsiration: We discuss the organs of the respiratory system, label a diagram of the oxygen/carbon dioxide exchange, and make lungs from pop bottles, straws, and balloons. We test for lung capacity by making a simple spirometer. Sometimes we measure breathing rate by doing a simple running in place activity and record their breaths per minute before and after 2 minutes of running.
I hope this will be helpful to teachers who don't teach science hands-on or for new teachers who need lots of ideas