The pathogenesis of ectopic gastric mucosa is a matter of debate between a congenital-embryological-and an acquired origin-consecutive to a gastroesophageal reflux (GER) like Barrett's esophagus -, the most commonly accepted theory being that these areas are embryological remnants.
Standard size latex filled helium balloons stay afloat for approx 8 - 12 hours, metallic helium filled balloons float for 2-5 days. I have found that a 36 latex helium filled balloon can stay afloat for a number of days due to the thickness of the balloon and the massive quantity of helium.
I'm guessing that the bigger the balloon, the better it will float? Yes - the more weight it will lift off the ground. Note that at high altitudes in Utah and Colorado, some foil balloons won't float; because of the low air pressure above 5500 feet, the buoyant effect of the helium is decreased. Water vapor in the air (humidity) lowers the molecular weight of the air and decreases the buoyant effect of the helium.