The are double sheets of peritoneal membrane that suspend the visceral organs and carry nerves

The mesenteries are double sheets of peritoneal membrane that suspend the visceral organs and carry nerves

Thanks to the mesentery the intestines are attached to the posterior abdominal wall. Mesentery is formed by the double fold of peritoneum (double layers of peritoneum) and its roles are to help in storing fat and to allow blood vessels, lymphatics, and nerves to supply the intestines.

the answer is:

carbon dioxide