blood transfers nutrients, water, oxygen throughout your bodies cardiovascular system. When you eat the nutrients are removed from your food and through the lining of your large intestine and transported through your veins (to the heart) throughout your brain and importantly to your bones. When your breath the oxygen is also transported throughout your body and most importantly your brain which is why you feel lightheaded when you hold your breath. So the main function is to transport important nutrients and oxygen throughout your body. It is also used to fight off infections. Your blood holds White blood cells that are kinda a regime against viruses that are attacking your cells, your immune system creates white blood cells, so when it is lessened it reduces the white blood cell count causing you to get sick. I hope this helps, have a nice day ^^
