Why do some parts of the human body (example: alveoli of lungs, skin, intestines) are said to cover a big area when stretched out, but can also fit inside a small human body?

Question

Why do some parts of the human body (example: alveoli of lungs, skin, intestines) are said to cover a big area when stretched out, but can also fit inside a small human body?

In: Biology

Answer 1

Imagine getting a ball of yarn and stretching it out end to end, it would cover a very large distance compared to its volume when it’s in ball mode.

Those surfaces you mentioned are very very small and are very folded up inside our bodies and the same logic applies, If you were to unfold it and stretch it out it would cover very large distances.