The hospital treated 23 patients following the explosions, five of whom have undergone amputations involving multiple surgeries, said Jeffrey Kalish, Boston Medical’s director of endovascular surgery at a news conference Monday. About half remain at the center, including one in critical condition.

Boston Medical was one of five trauma centers that handled the worst cases following the blasts, which killed three people and injured more than 175 as nails, pellets, wood and other debris exploded from two bombs. The physical and emotional recovery may take many more months, though doctors said they are encouraged by the early progress.

“We have definitely seen every range of emotion this past week,” Kalish said. “For us, we have seen amazing improvements, really great attitudes. We’ve had veterans come in with amputations that have walked through the halls and shown these patients their life isn’t over.”

A week after the attack, 48 people are still hospitalized, according to figures from six Boston hospitals that dealt with most of the seriously injured. At least 14 survivors lost all or part of a limb, including some who had multiple amputations, said the hospitals, which include Brigham & Women’s Hospital, Beth Israel Deaconess Medical Center, Tufts Medical Center, and Massachusetts General Hospital.

Soldiers from the Semper Fi Fund, a veterans group for injured military personnel, came to Boston to meet with about a dozen patients and their families at four different hospitals. They told them about the importance of ­getting active as soon as possible and setting goals. The group said they plan to be back at the end of the week.

The Semper Fi Fund has set up a Boston Marathon fund. The group helps modify the environment of the injured to help them stay mobile and active, as well as providing support in getting prosthetics and services. They also have a team of athletes, including B.J. Ganem, 36, a Marine veteran who lost one of his legs in Iraq in 2004.

“It’s a small club — not a lot of people know what it’s like,” Ganem said. He competes in adventure races and trains using the fitness program CrossFit, known for its emphasis on difficult body weight exercises.

The one critically ill patient at Boston Medical is in the intensive care unit and on a ventilator, said Peter Burke, chief of trauma services. “Do I think he’s going to ­survive? Yes. Do I worry about him? Yes,” Burke said.

Boston Children’s Hospital is caring for two patients, a 7-year-old in critical condition and an 11-year-old who recently left the intensive care unit.

Doctors have been treating internal bleeding, injuries suffered when falling or thrown to the ground from the bomb’s shock wave and embedded debris. Some victims had 40 or more fragments of pellet- and nail-like objects embedded in their bodies.

Patients with amputations have been put into rehabilitation as soon as possible, to help them use walkers and learn basic exercises.