The artery that ruptured when freestyle skier Sarah Burke fell during a training run is one of the most critical blood vessels in the body, feeding oxygen-rich blood to the brain stem, neurosurgeons say.

Burke, 29, died Thursday of her injuries in the University of Utah Hospital, nine days after the accident at the Park City Mountain Resort.

It’s the brain stem, located at the bottom of the brain and tucked inside the back of the skull, that controls breathing and heart function.

“Basically there are four major blood vessels that bring blood to the brain, and two are at the back of the head, come up from the back,” explained Dr. Michael Cusimano, a neurosurgeon at St. Michael’s Hospital in Toronto.

“They’re called the vertebral arteries because they come through the bones of the neck and then get to the brain,” he said. The two other major arteries, called the carotids, run up the front of the neck.

It was one of her vertebral arteries that Burke tore when she crashed at the training site, causing what’s called a massive intercranial hemorrhage, in which blood poured into her brain.

Doctors say the severe brain injury caused Burke to go into cardiac arrest. In other words, her heart stopped beating and she was no longer breathing on her own, resulting in a lack of oxygen to the brain.

“So right on the scene of this mountain where she was on, where she was training, her heart stopped,” said Cusimano. “And so it was probably that the artery was partly torn and that led to this bleeding that her heart stopped.”

Paramedics at the scene gave Burke CPR and she was transferred to the Utah Hospital emergency department, where she was put on a ventilator, or breathing machine, and a procedure called therapeutic hypothermia was initiated to control swelling of the brain tissues.

“They purposely put her into what’s called hypothermia,” Cusimano said. “When the brain’s been damaged, one of the ways of treating it is by cooling the body, and cooling the brain to protect the brain. So they were hoping to try to protect her brain so that it might show some recovery.”

The next day, surgeons were able to successfully repair her torn vertebral artery, a tricky operation that Ottawa pediatric neurosurgeon Dr. Michael Vassilyadi said demands a lot of skill. “It’s very difficult to do.”

But tests following the operation, including numerous neurological examinations, electrodiagnostic tests and imaging studies, revealed that the skier had sustained grave and irreversible brain damage caused by the lack of oxygen after her cardiac arrest. The condition is called hypoxic ischemic encephalopathy.

“In general, any decreased perfusion (of blood) to the brain can cause what we call ischemia because with the blood you have oxygen,” said Vassilyadi of Children’s Hospital of Eastern Ontario. “You have less blood, less oxygen to the brain. And then you could get a stroke as a result of the decreased oxygenation to the brain.”

Following Burke’s death Thursday, her organs and tissues were donated for transplantation, according to her wishes, said a statement from her publicist.

“I think it’s a tragic thing,” Cusimano said of Burke’s death.

“It happened and it’s one of the risks. I don’t know what else to say. It just tells us how fragile our lives are and how things can change in an instant. What can you say? She probably loved skiing and loved doing the things she was doing.