Well, for starters, the blood is like the interstate highway system of delivery and transportation within the body for every cell in your body. So let us start there.
1. Every cell in your body has to have glucose, a simple sugar the cell breaks apart in a process called cellular respiration to create energy for the cells life functions. The blood delivers glucose from the small intestine of the digestive system.
2. Every cell also has to have oxygen for this process of cellular respiration to occur. The blood carries oxygen attached to the heme molecule in the red blood cells to all the cells in your body.
3. Once this process of cellular respiration has occured, carbon dioxide is created as a waste product. The blood picks up this waste product, and carries it to the lungs, where it is exhaled.
4. Water is also created as a waste product by cellular respiration. The blood carries this water to the kidneys where it is recycled back into the system.
5. Some of the water is needed to help excrete waste known as urea, so some of the water carried by the blood is reserved for the urea. Urea combined with water makes urine, which we get rid of in the restroom.
6. The blood carries necessary and vital hormones which are important to specific functions on a daily basis, such as the regulation of blood sugar, and body calcium levels.
7. And last but not least, the blood provides an effective material to keep the most important organ in the whole body busy for a lifetime---the heart. Without the blood, the heart would have no reason to exist.
All these combine together to insure the bodys organ systems work together to provide what we know as homeostasis, or, the body existing in harmony with itself.