Questions answered

By Sherry Seethaler

SAN DIEGO UNION TRIBUNE
November 10, 2004

QUESTION: If the great pyramid at Giza could be weighed would it be found to be heavier than every other building in the world?

ANSWER: Modern buildings do not compete with the Great Pyramid at Giza in Egypt in terms of mass. In fact, better materials and design have permitted skyscrapers to become less massive even as they have grown taller. For example, Chicago's Sears Tower weighs 223,000 tons, a total of 142,000 tons less than the Empire State Building, which was built four decades earlier and is 200 feet shorter.

Designers of modern buildings are usually interested in maximizing internal space, and consequently buildings are up to 95 percent air on the inside. On the other hand, the Great Pyramid is nearly solid stone with the exception of two small burial chambers. Most descriptions of the Great Pyramid give its weight as 6 million tons.

However, according to the Guinness Book of Records, the largest pyramid is actually the Quetzalcatl Pyramid in Cholula, Mexico. Its volume is 4.3 million cubic yards compared with 3.27 million cubic yards for the Great Pyramid at Giza.

Unable to find any estimates of the mass of the Quetzalcatl Pyramid, I calculated it from the pyramid's volume and the density of the material it is made from – adobe. My rough calculation puts it at slightly less than the mass of the (granite, basalt, limestone) Great Pyramid at Giza, making the latter the most massive building in the world.

My question concerns stem cells: What type of tissue would be used if stem cells were harvested from an adult?

– Joan Dayton, San Diego

There are stem cells in many adult tissues, including the skin, gut, respiratory tract, liver, muscle and brain, where they play a role in tissue repair and renewal. Not all of these stem cells are amenable to being harvested and transformed into other cell types.

Many studies have employed hematopoietic stem cells, which are found in bone marrow and generate all the types of cells in the blood. They have been used to treat blood disorders for three decades, and under the right conditions they can be coaxed to give rise to many other cell types.

Recently, researchers discovered stem cells in fat and have transformed them into other tissue types. It would be ideal if stem cells from fat prove to be as versatile as those from bone marrow. Liposuction is simpler than removing bone marrow, and even slender people carry a large enough fat supply for their own treatment.

copyright 2004 The San Diego Union Tribune