Naked Science Forum

Life Sciences => Cells, Microbes & Viruses => Topic started by: thedoc on 04/12/2016 00:23:01

Title: If individual cells are dying all the time, how do we say when a whole organism is dead?
Post by: thedoc on 04/12/2016 00:23:01

Anand asked the Naked Scientists:
   I got a question about organisms. When does an organism.. say human being is said to be dead. As far as I know that even after a person is said to be dead, his/her bodily organs (eg. liver) will funtion for few many hours and some of the tissues will be functioning for som time. Also, does the death always depends on the functioning of the brain? Every single minute, the cells from our body dies and new cells gorw. Does it mean we are dying and reborn every minute?
I have too many questions arising on my mind now but i dont know how to organise them at the moment.
Thanks for such a wonderful show (http://www.thenakedscientists.com/HTML/podcasts/)..
Anand
What do you think?

Title: Re: If individual cells are dying all the time, how do we say when a whole organism is dead?
Post by: evan_au on 04/12/2016 03:36:02

The medical definition of death occurs when there is loss of a good blood supply to the brain - through lack of oxygen, heart failure or head injury. The brain is very energy-hungry, and major damage occurs within 4 minutes of the loss of oxygenated blood supply.

If major damage occurs to the brain, the original individual can no longer return. If the brain-stem is damaged, essential functions like breathing and heart rate may no longer be sustainable without machine assistance.

Other tissues are more effective than the brain at reducing metabolism after the loss of oxygen supply, and so many other tissues are still viable for transplant, long after brain death. Their lifetime is often extended by cooling them, which further reduces metabolism.

See: https://en.wikipedia.org/wiki/Legal_death