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When we are pricked by a needle, we bleed nevertheless it's so small wound. But when we do mouse anatomy, it doesn't bleed even if we cut their whole abdominal skin. Other student asked about that, professor didn't know exactly but just guessed that mouse skin has no blood vessel. But I think it's wrong. that makes no sense. As my guessing it's because mouse is dead when we do anatomy so there is no enough blood pressure. Mouse have to bleed like ourselve. is this wrong?

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  • $\begingroup$ You are talking about dead mice? $\endgroup$
    – Chris
    Mar 15 at 8:46
  • $\begingroup$ 'because mouse is dead when we do anatomy '. Yes he is. $\endgroup$
    – KaPy3141
    Mar 15 at 12:24
  • $\begingroup$ By the way, Blood-pressure can be negative (smaller that atmospheric) dependent on where you measure it (due to Bernoulli principle). $\endgroup$
    – KaPy3141
    Mar 15 at 15:04
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    $\begingroup$ the fact the mouse is dead is important dead humans don't bleed either. blood starts to coagulate after only a few hours. $\endgroup$
    – John
    Mar 15 at 16:23
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    $\begingroup$ @John: There are two stages to this. Live animals, whether mice or men, bleed because the blood is under pressure. (Considerable pressure, if you've ever had to deal with an arterial wound.) After death, there can be some blood drainage from wounds, under the influence of gravity &c. That stops when the blood coagulates. See e.g. "livor mortis". $\endgroup$
    – jamesqf
    Mar 15 at 17:30
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From personal experience, extracting organs/tissues of over 1000 mice I can give some hints:

Mice blood coagulates quite fast after death. If you need to extract blood, you are under time-pressure and many scientists extract the blood directly after death from the heart using a syringe. If you are not fast, you miss the chance of drawing blood as this can't be done after coagulation. Others cut up the thorax (post mortem) and then directly draw blood with a syringe. I personally never tried this technique but I spectated that mice bleed a bit, directly after death, when opening the thorax, however it's not much.

After drawing all blood from the heart, mice don't bleed, no matter where you cut, potentially because of low blood content remaining. (Un-?) Fortunately, I never had to cut mice that were alive.. so I cannot tell you what would happen if they were alive.

Edit: Also, in theory, the smaller an animal is, the higher becomes the diffusion/volume ratio and surface-tension/volume ratio. This means smaller animals need less active blood circulation and and their blood vessels might have a small diameter, so that most blood would be kept inside by surface tension if these vessels were cut.

Edit due to comment: The extractable blood from mice is around 1.5 ml, and I have seen opening of the thorax within seconds post mortem with minor bleeding. Afterwards, the majority of blood (1.5 ml) was extracted directly from heart with a syringe. As this was post motrem, I cannot exclude the possibility that coagulation of blood in small peripheral vesicles already affected the observation or how heart beating would affect it. I cannot say what would happen in live mice and I am happy that I don't have this knowledge.

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    $\begingroup$ Live mice certainly do bleed, though their total blood volume is only on the order of 2mL. $\endgroup$
    – Bryan Krause
    Mar 15 at 14:31
  • $\begingroup$ I know it's around 1.5 ml, and I have seen opening of the thorax within seconds post mortem with minor bleeding. Afterwards, the majority of blood (1.5 ml) was extracted directly from heart with a syringe. $\endgroup$
    – KaPy3141
    Mar 15 at 14:46
  • $\begingroup$ thank you! this did help! $\endgroup$
    – cavalist
    Mar 15 at 14:47

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