This image represents bacteria on the surface of an animal organ. To give you an idea of the scale of the image, the cylindrical yellow objects are the bacterial cells. Here’s another hint: the image shows a tiny part of what represents the largest organ of the human body. Now can you guess what it is? Is it the stomach? The heart? The answer may surprise you. It’s the human skin.
The word organ may bring to mind internal organs such as the stomach or heart, but the skin is an organ too. The skin is thin, averaging only 2 mm in thickness, but it covers a large area—about 2 m2 in adults, making it the largest organ of the human body. You will learn more about the skin and how these organs come together to form the human body when you read this chapter.