As well as the obvious 'dead' cells such as your hair and nails, there is one area of living cells that doesn't use a direct blood supply.
Asked by: Lucy Haddacks, Norwich
The only living cells in the body that aren't directly served by blood vessels are those of the cornea in the eye. Oxygen and nutrients instead diffuse directly from the tear fluid on the outside and the aqueous humour (the thick watery substance between the lens and the cornea) on the inside, as well as along the nerve fibres that are connected to the cornea.
One of the problems with contact lenses is that they reduce the oxygen supply from the outside. Even with gas-permeable lenses, this can cause corneal neovascularisation, where blood vessels grow into the cornea. This problem is reduced or eliminated by the newest silicone hydrogel lenses. As well as the cornea, other areas of the body that don't have blood vessels include hair, nails, tooth enamel and the outer skin layers.
Read more:
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.
Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.
Subscribe to BBC Science Focus Magazine and try 3 issues for just $9.95
Discover our latest special editions covering a range of fascinating topics from the latest scientific discoveries to the big ideas explained.
Listen to some of the brightest names in science and technology talk about the ideas and breakthroughs shaping our world.
By entering your details, you are agreeing to our terms and conditions and privacy policy. You can unsubscribe at any time.