Symmetry in the Human Body

The June 1999 issue of Scientific American contains a very interesting article about the symmetry of organs in the human body . From outside our body looks symmetric ie our eyes , nose , ears have a left right symmetry.

From inside however , there is a preferred direction of each organ . The

heart is on the left side , the right lung has more lobes than the left .

      The insides  of our bodies have been arranged so as to pack the max amount of stuff in the little space . Even if the organs were flipped ( ie all of them ) the person will still be perfectly healthy.

      There is a rare condition known as Situs Inversus . It occurs in 1 in 10,000 odd cases and the person has all his organs flipped . The heart is on the right side , the liver on the left , stomach on the right . The person is still perfectly fine .

 

      However there are some dangerous conditions too : A condition known as isomerism can make a person have 2 right sides or two left sides of his body . That person may have 2 spleens or no spleen . 2 hearts or no heart .

This is a fatal syndrome and the dude soon dies .

       How does the body know which side is which and when does the arrangement

or organs take place ???

 

      It all starts in the embryo . The embryo in its earliest stages

is perfectly symmetric . Then after some time the symmetry is broken .

THis is during the development of the heart . A protein called

“Sonic Hedgehog” is released and the tube of the heart loops opposite to it .

THIS IS THE CRUCIAL STAGE !!! The tube of the heart loops opposite the

place where this protein is released . After 18 hours this protein is

inactivated . But it has done its job . Told the embryo what the symmetry

of the final dude will be . But this alone does not make a “normal ” dude .

More harmones are required . And the place where they pop up is crucial.

The Sonic Hedgehog and the Nodal harmones have to be on the left side and

the Activin Beta-B has to be on the right side for a normally placed

heart . Researchers then did an experiment . They put some extra

Sonoc Hedgehog and the Nodal on the right side . So both sides have

these harmones . TThe embryo got confused and the placement of the heart

got random !!

 

      The complete article is very interesting and has some interesting

pictures too . The copy of Scientific American is in my cube . Interested

people can come and see it .  

 

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