Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. <img src="https://upload.wikimedia.org/wikipedia/commons/e/ec/Blutkreislauf.png" height="500"> <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Blausen_0425_Formed_Elements.png/1280px-Blausen_0425_Formed_Elements.png" height="500"> From [Wikidepia](https://en.wikipedia.org/wiki/Blood) under [CC BY-SA 2.5](https://creativecommons.org/licenses/by-sa/2.5/) and [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/) licenses.