Doctors at a San Francisco hospital began an unusual series of kidney transplants on Thursday with six living donors providing organs to six patients in a chain that began with a woman described as an altruistic donor unrelated to any of the recipients. The first donor and recipient went into surgery at California Pacific Medical Center at 7:30 a.m., with two more donor-recipient pairs on the schedule for Thursday, then the remaining three pairs on Friday, hospital spokesman Dean Fryer said. The chain of donations began when Zully Broussard, 55, of Sacramento, whose son and husband both died of cancer, offered to donate a kidney to a friend, but the friend ultimately had to use another donor, according to hospital officials.