News flash: The heart produces urine

In an attempt to explain why astronaut Heidemarie Stefanyshyn-Piper fainted during a welcome ceremony, ABC News reported

The heart of an average person on Earth pumps blood throughout the body. But when an astronaut is in space, Levine explained, the blood remains predominantly in their chest cavity. Because of this, he said, the heart tries to get rid of excess blood through urination.

Comments (17)
  1. Baffled says:

    O M F G

  2. Nawak says:

    Maybe urination of blood?

  3. clandivar says:

    Not literally…

    What I think happens is that the heart detects a higher than normal blood pressure due to the accumulation of blood in the chess cavity and triggers the kidneys to release some liquid out of the system. The kidneys are still producing the urine.

  4. tsrblke says:

    I concur.  That’s what I take from this.  Effectively she donated a quart of plasma, just as if she had gone into the Red Cross and given up a quart of plasma (plasma<>Red Blood cells).  Which is a fair amount of plasma (in terms of TOTAL blood volume, roughly 20%.)  While this isn’t a 1:1 ratio (after all she didn’t lose RBCs)  But still.

    What confuses me is why the blood seems to collect in the Chest Cavity.  Blood defies gravity all the time (think legs and head.)  So it sems to me that a lack of gravity would be a good thing.  Of course I suppose gravity may in the end aid blood.

  5. Dean Harding says:

    tsrblke: Actually what happens is that in normal gravity, blood tends to pool in the lower half of your body. But in zero gravity, the opposite happens (because your ciculatory system evolved in the presence of gravity, it has a slight tendency to pump blood UP). So you face and chest get all the blood, while you legs don’t get very much.

  6. Brian says:

    It’s kind of like when you stand on your head.  All the blood rushes up because your body is used to pumping blood in to your head, not out of it.

    It makes you wonder, if you stood on your head for a few months straight, would your body get used to it and then feel weird and dizzy when you stood up normal again?

  7. amish says:

    Hi, Brian

    There is an answer to your question. You won’t just feel dizzy. It is an ancient Chinese way to kill a man simply by giving him a full meal and then forcing him in a head down position for a few hours.

  8. Clint says:

    Actually, you will notice this when you get cold as well.  Your body concentrates blood in your core and there is a procedure to get rid of the excess fluid by urination. That’s why you pee in the pool so much and why scuba divers smell the way they do.

  9. Steve says:

    Stick to Windows 95, Raymond. Human physiology is a different beast.

  10. John Melville, MD says:

    The first commenter is absolutely correct.  When there is too much fluid the heart released Atrial Naturetic Peptide (ANP) which increases urination.

    The reason the blood pools in your chest isn’t gravity, its pressure.  When your chest expands to breathe in, there is negative pressure in your chest, this sucks both air and blood into your chest cavity.  Exhalation, if you are not exercising, is passive and does not involve huge pressure gradients.  (If you happen to make your living by doing physical exams on children, you can hear a really neat double heart sound when they breathe in, its due to this same phenomenon.)

    And to brian, unfortunately the answer is yes, but you don’t even have to stand on your head.  I had the misfortune of spending two weeks of my life either flat or with my head below my feet (trendelenburg’s position) after a mistake during brain surgery left a leak in my spinal cord.  It took me over a week to be able to stand up again without getting dizzy.  (This is also very well documented in medical literature, but the personal experience is a lot more interesting.)

  11. Mr. Peabody says:

    "From 25 to 66 percent of all astronauts cannot stand for 10 minutes following space flight of up to two weeks"

    What kind of silly stat is that?

  12. kbiel says:

    >>What confuses me is why the blood seems to collect in the Chest Cavity.  Blood defies gravity all the time (think legs and head.)

    If you think about it, you answered your own question.  Since the vascular system is designed to return blood to the heart *despite* gravity, when that gravity is absent it becomes all the more efficient at doing its job.

  13. > What kind of silly stat is that?

    That is a "Media Stat".  Like that one that Dave Letterman quoted once… 75% of the people make up 3/4 of the population.

  14. Carrie says:

    My favourite one :

    Almost 50% of the people have intelligence under the average

  15. kbiel says:

    >Almost 50% of the people have intelligence under the average

    That indeed could be news.  50% of people having intelligence above or below the median is just obvious.

  16. Cody says:

    Except that average intelligence is defined by median, not mean.

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