1 00:00:01,920 --> 00:00:06,480 Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey 2 00:00:06,519 --> 00:00:09,080 Speaker 1: brain Stuff, I'm more in vocal Bomb and today's episode 3 00:00:09,119 --> 00:00:12,320 Speaker 1: is another classic from our former host, Christian Sader. This 4 00:00:12,360 --> 00:00:14,880 Speaker 1: one addresses one of those science things that we hear 5 00:00:14,920 --> 00:00:18,319 Speaker 1: all the time, and we wondered whether it's true. Does 6 00:00:18,360 --> 00:00:24,200 Speaker 1: the human body really replace itself every seven years? Hey, 7 00:00:24,239 --> 00:00:28,200 Speaker 1: brain Stuff, it's Christian Sager. Today's question does your body 8 00:00:28,440 --> 00:00:33,159 Speaker 1: really replace itself every seven years? The short answer is no, 9 00:00:33,560 --> 00:00:37,000 Speaker 1: But don't worry. This isn't a case of Chicanerius researchers 10 00:00:37,040 --> 00:00:40,280 Speaker 1: pulling the wool of shoddy science over your eyes. Your 11 00:00:40,320 --> 00:00:45,800 Speaker 1: body mostly replaces itself every seven to fifteen years. Some 12 00:00:45,920 --> 00:00:49,120 Speaker 1: bits are never replaced. Others, like the lining of your 13 00:00:49,159 --> 00:00:53,960 Speaker 1: stomach and intestines, are renewed much faster due to constant 14 00:00:53,960 --> 00:00:57,560 Speaker 1: wear and tear from the process of digestion. These cells 15 00:00:57,640 --> 00:01:01,800 Speaker 1: have an average lifespan of just five days. Yes, the 16 00:01:01,960 --> 00:01:05,920 Speaker 1: organs that work the hardest have the fastest change over. 17 00:01:06,280 --> 00:01:09,520 Speaker 1: You get a whole new skin every two to four weeks, 18 00:01:09,760 --> 00:01:12,800 Speaker 1: and your red blood cells last less than half a year. 19 00:01:13,160 --> 00:01:16,360 Speaker 1: That's not bad considering that they're route through your circulatory 20 00:01:16,520 --> 00:01:20,880 Speaker 1: system is about a thousand miles. The average American car 21 00:01:21,000 --> 00:01:24,840 Speaker 1: doesn't even travel that far, and your liver renews itself 22 00:01:24,920 --> 00:01:28,119 Speaker 1: at least once every couple of years. As the human 23 00:01:28,280 --> 00:01:33,160 Speaker 1: bodies detoxifier, it goes through a lot. Other tissues take 24 00:01:33,280 --> 00:01:37,160 Speaker 1: longer to completely replenish themselves, like your bones. For instance. 25 00:01:37,560 --> 00:01:42,280 Speaker 1: Skeletal cells die and new ones grow constantly, but the 26 00:01:42,360 --> 00:01:47,720 Speaker 1: complete process takes about ten years, and the process slows 27 00:01:47,760 --> 00:01:50,920 Speaker 1: down as we get older, which is why our bones 28 00:01:51,080 --> 00:01:55,120 Speaker 1: tend to get weaker as we age. And like I said, 29 00:01:55,280 --> 00:01:58,280 Speaker 1: some parts of your body stay with you for life. 30 00:01:58,760 --> 00:02:02,040 Speaker 1: The cells of the ner lens of your eye formed 31 00:02:02,040 --> 00:02:05,280 Speaker 1: when you were just an embryo. Your tooth enamel wears 32 00:02:05,360 --> 00:02:09,520 Speaker 1: down with use, never to return, and evidence indicates that 33 00:02:09,600 --> 00:02:13,880 Speaker 1: you can't regrow the neurons of your cerebral cortex. It's 34 00:02:13,960 --> 00:02:18,760 Speaker 1: loss can lead to diseases like dementia. Luckily, other parts 35 00:02:18,760 --> 00:02:22,280 Speaker 1: of your brain do regenerate, like the hippocampus, which helps 36 00:02:22,360 --> 00:02:26,400 Speaker 1: us create memories, and the olive factory bulb, which helps 37 00:02:26,480 --> 00:02:29,840 Speaker 1: us smell. So how do we know all this? Well, 38 00:02:30,120 --> 00:02:33,520 Speaker 1: it turns out it's thanks to our old pal nuclear 39 00:02:33,560 --> 00:02:38,240 Speaker 1: weapons testing high fives for radioactive stuff being released into 40 00:02:38,320 --> 00:02:42,880 Speaker 1: the atmosphere no really above ground. Nuclear detonations during World 41 00:02:42,880 --> 00:02:47,320 Speaker 1: War Two and the Cold War spiked Earth's air supply 42 00:02:47,600 --> 00:02:52,040 Speaker 1: with extra carbon fourteen. It's been declining back toward the 43 00:02:52,120 --> 00:02:55,800 Speaker 1: norm at a predictable rate since the nineteen sixties, which 44 00:02:55,840 --> 00:02:58,360 Speaker 1: means that you can use the amount of it present 45 00:02:58,440 --> 00:03:02,280 Speaker 1: in any given tissue, sayful, to determine when those cells 46 00:03:02,280 --> 00:03:13,639 Speaker 1: were born. More carbon fourteen means older cells. Today's episode 47 00:03:13,680 --> 00:03:16,720 Speaker 1: was written by me and produced by Tyler Clain. Brain 48 00:03:16,760 --> 00:03:18,960 Speaker 1: Stuff is production of I Heart Radios How Stuff Works. 49 00:03:19,240 --> 00:03:21,360 Speaker 1: For more in this and lots of other replenishing topics, 50 00:03:21,480 --> 00:03:24,040 Speaker 1: visit our home Planet has to Works dot com and 51 00:03:24,240 --> 00:03:26,560 Speaker 1: for more podcasts for my heart Radio, visit the iHeart 52 00:03:26,600 --> 00:03:29,240 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 53 00:03:29,280 --> 00:03:29,959 Speaker 1: favorite shows.