# If you nick astronauts in space, do they not bleed? **URL:** \ **Category:** Factual Questions\ **Created:** [November 21, 2012, 6:05pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747 "2012-11-21T18:05:27Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [November 21, 2012, 6:05pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/1 "2012-11-21T18:05:27Z")
See subject. I’m talking like a minor food-cutting-type cut on a finger, say. It might have an effect on healing, closure, and consequent infection, wouldn’t it? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 21, 2012, 6:07pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/2 "2012-11-21T18:07:56Z")
Huh? ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [November 21, 2012, 6:11pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/3 "2012-11-21T18:11:00Z")
Do you mean in a vacuum? I think that will be a really cool scene in a movie the way the blood from a tiny nick goes spurting out. ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [November 21, 2012, 6:28pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/4 "2012-11-21T18:28:04Z")
You bleed because the pressure inside your blood vessels, including veins, is higher than the pressure outside your body, so you will still bleed in zero gravity, maybe not as much for a cut to a foot but more for a head wound. The differences could be significant, especially for the feet, where bleeding may be only half as fast with zero-g: > [@](#): > > The average pressure in the major arteries at the heart is approximately 100 mmHg so that the pressure in the arteries at the feet for a standing individual would be 196 mmHg. Using a similar argument we can see that the pressure in major arteries will decrease leading to the head when standing. > > [Blood Pressure](http://c21.phas.ubc.ca/article/blood-pressure) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 21, 2012, 6:30pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/5 "2012-11-21T18:30:41Z")
> [@Leo\_Bloom](#): > > See subject. I’m talking like a minor food-cutting-type cut on a finger, say. > > It might have an effect on healing, closure, and consequent infection, wouldn’t it? Are you under the mistaken impression that gravity is the primary force that compels blood to flow from a cut? It certainly matters - it’s why you hold your arm straight up immediately after donating blood (after they remove the needle), and it’s why you should stand or sit (rather than lying down) if you’ve got a bloody nose - but even in space, your body produces its own blood pressure. Yes, you’ll bleed just fine on the ISS. Edit: ninja’d by **Michael 63129.** ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [November 21, 2012, 8:23pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/6 "2012-11-21T20:23:51Z")
There are different challenges to the circulatory system in space. From [here](http://www.nasa.gov/mission_pages/station/research/cciss_feature.html) “There’s no gravity to pull blood into the lower part of the body. Instead, blood goes to the chest and head, causing astronauts to have puffy faces and bulging blood vessels in their necks.” ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [November 21, 2012, 10:09pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/7 "2012-11-21T22:09:01Z")
There is, of course, plenty of gravity, you just don’t notice it while in orbit. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [November 21, 2012, 11:26pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/8 "2012-11-21T23:26:06Z")
Thanks. Yes, I knew that blood spurts, gushes and otherwise is pumped around and out by pressure. It just occured to me now, however, that a small scab would form \* quicker\* in microgravity, and prevent the issues in OP. The role of surface tension is larger. I just had this image of having to judge the extent of a small cut not by seeing red streaming down a finger, but by having to count droplets. Just thought of a new astronaut question, will post new query… ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [November 21, 2012, 11:42pm UTC](https://boards.straightdope.com/t/if-you-nick-astronauts-in-space-do-they-not-bleed/641747/9 "2012-11-21T23:42:40Z")
> [@Leo\_Bloom](#): > > I’m talking like a minor food-cutting-type cut on a finger, say. What food would they be cutting? It isn’t like they get a sack of raw potatoes delivered, and the guy on KP has to peel them.