Whenever she hears the helicopter, Umm Abdu tenses, collects her medical kit and runs through the lanes of Old Aleppo to the only working hospital in her neighbourhood.

It is a familiar routine: the thump of the rotor blades, the boom of the explosion from the barrel bomb released by the Syrian government troops far above, followed by Umm Abdu’s scramble towards the four-storey building that will receive the inevitable human carnage.

Not that the hospital is safe. Most large buildings around it have been obliterated by the same half-tonne bombs, leading those who work, live and die within its iodine-stained walls to believe that they are the real targets.

“Hell is never far away,” she says, resting on a gurney in what makes for a trauma area. She is the only woman on the floor, a black-clad figure working alongside three exhausted young men in green gowns to treat most of Aleppo’s victims of war.

Umm Abdu stands out for another reason: the steel pistol she holsters to her back when stitching or bandaging patients using the skills that echo her pre-war career as a wedding dressmaker. “Getting justice from this war has become a personal jihad for me,” she admits. “I can’t work without it [the gun] any more.”

Everyone who remains in the eastern half of this battered city has a story of deprivation and loss. And most, like 40-year-old Umm Abdu, have found ways to cope with life in a wasteland, where existence inches on but life has stopped. “I’ve used the weapons,” she says. “And then I’ve treated the people who were injured.”

The contradiction seems lost, or maybe even no longer relevant, in a conflict where death often comes from the skies. Barrel bombs, the Syrian war’s most savage weapon, are also its most indiscriminate killer.

Slowly, methodically, they have tipped the tide in the favour of the regime, which continues to edge around Aleppo’s north-eastern flank as its bombs erode the city of civilians, fighters, and hope.

Syrian boys play in the rubble of Aleppo. Photograph: Baraa al-Halabi/AFP/Getty Images

Umm Abdu’s son, Yousef, was killed by a bomb three months ago while travelling on a minibus to work in the only other functional hospital in the city’s east. That attack killed 35 people, and gouged yet another giant hole through an urban landscape now difficult to distinguish among piles of rubble often dozens of metres high.

“That day was the worst of days,” she says, sitting in a darkened room of her home on the edge of Old Aleppo. Her surviving son, Abdullah, sitting next to her, says: “We shared the same bed for 17 years. “We did everything together: we played, we dreamed, we grew. Now he’s gone. What can I say.”

In the small flat she shares with her remaining children, Umm Abdu has placed three teddy bears on her pillow, two Free Syria Army flags and an Islamic flag above her bed, and her gun on her mattress. Her medicines are tucked away nearby.

In the early days of a war that promised hope, but has instead delivered three years of unrestrained brutality and an estimated 200,000 dead, Umm Abdu’s husband was shot dead by a regime sniper.

Eighteen months ago, while trying to retrieve a wounded man from a no-man’s land near her home, she too was almost killed. Snipers bullets ripped through her mouth and thigh. “It was only flesh,” she says. “It’s all working now.”

A rebel fighter holds a position in Aleppo. Photograph: Zein al-Rifai/AFP/Getty Images

Rebel fighters who work alongside Umm Abdu in the city say the fighter-cum-medic is unique. “No one else risks her own life as much,” says a local leader, Abu Juud, who helps provide food for her family. “And no one else saves as many other lives.”

“We owe you a lot,” he tells her. “Aleppo owes you as well.”

Those who have remained in the east of the city – maybe 50,000 of the 1 million or so who once lived here – all speak with disconcerting candour about mothers, brothers, fathers and babies killed during the war.

“My three cousins were executed by Isis,” shrugs a fighter from the Islamic Front, the main opposition group in eastern Aleppo. “They betrayed them at a checkpoint.”

The fighter is sitting in a circle of eight men, all of whom had a similar story that they hadn’t deem worthy to share until asked about it.

“My sister was killed last year in al-Bab [a town near Aleppo],” says another fighter. “So was her son.” He shows photos of the boy stored on his mobile phone: “I loved him a lot.”

Another man says quietly but matter-of-factly: “My mother died in her home. I buried her in five pieces. She said she would rather die here than live on her knees in Turkey.”

A man holds a baby saved from under the rubble after an air strike by regime forces. Photograph: Hosam Katan/Reuters

Unfathomable loss is too evident at the hospital. “Most people who come here are ripped apart when they arrive,” says an Egyptian neurosurgeon who tries daily to repair the most seriously injured. “But I don’t have a working CT scan. Do you know how hard it is to do brain surgery without one?”

Despite this, the surgeon does have some successes. He leads us to a civilian who was shot through the brain a week earlier. “He can speak now,” the doctor says enthusiastically. “Say hello, Mohammed. Wave at me.” The patient wearily lifts his arm as his five-year-old daughter sits mutely on a bed across the room.

Nearby, a 30-year-old woman winces as another doctor sterilises a large gash in her thigh caused by a shell, not a barrel bomb.

Shells drop randomly on Old Aleppo many times each day. Later that afternoon, a deafening blast erupts near a fruit stall. The vendor doesn’t flinch as he hands over his produce; nor does his customer.

Fruit packed into carts – oranges, apples, bananas, watermelons – jut vividly from the grime of Aleppo in early winter; rare shocks of colour against a backdrop of grey. Those who can afford food are not starving, but the city itself – one of the oldest continually inhabited cities in the world – is all but broken.

Why, then, do people stay? “This is where I come from and this is where I will die,” says Ibrahim Khatan, 48, a resident of the Old City, who has remained behind with his seven young children. “Even if they surround us, we will sow potatoes in the fields and eat the chickens,” he says, pointing at a dozen hens and ducks his daughters have just fed by a mosque wall. “No one deserves a world without children. My oldest is 20 years old and my youngest, three months. I can’t take them away.”

Syrian children queue for food aid from a community kitchen in the Myassar district of Aleppo. Photograph: Zein al-Rifai/AFP/Getty Images

Nearby, the Islamic Front maintains a field clinic, where its fighters are treated for wounds sustained in clashes with regime troops around the ancient citadel less than a mile away.

Umm Abdu travels here regularly along the ancient cobblestones slick with recent rains, to tend to a local commander, Abu Assad, who is recovering from a gunshot wound to his thigh.

“Before this war, I was a seamstress making wedding dresses,” she says. “My family are all from here. This place is essential to my identity.”

I ask her what could make her change her mind, and take her surviving son and three daughters, one of whom works at the same hospital, to safety in Turkey. “If they don’t unite,” she says of the various rebel groups battling the regime, “I will kill myself.”

“That’s not true, my sister,” says a startled bystander.

“You’re right,” Umm Abdu replies with a smile – a rare sight in northern Syria. “But they need to bring everything together. We all need to support each other.”

Later that night, the clouds that had kept the helicopters away from Aleppo clear, and the risk of barrel bomb attacks increase. As dawn gives way to daylight, bright yellow ambulances parked near the hospital seem like perfect target indicators for any bomber above. The skies, though, stay empty. Clapped out generators that provide neighbourhood power echo through alleyways. A slight wind blows broken doors against stone walls. Islamic Front fighters move slowly through the heart of the Old City’s streets; some shelter in a giant atrium near a soap factory that a dog-eared sign says is heritage listed.

Their choice of refuge is touted as a hospital for intellectually disabled, built in 1354. “There’s no one crazy here,” one rebel says amid the flotsam and jetsam of endless war. “All the people on the streets – those [civilians] who are still here – they’re the crazy ones.”

Additional reporting: Saalim Rizk