Explanation:

- Bariatric surgery involves procedures that alter the digestive system to help with weight loss.

- These surgeries often reduce the size of the stomach or reroute the small intestine.

- Option 1: Heart - The heart is not directly altered by bariatric surgery, though weight loss can improve heart health.

- Option 2: Lungs - Bariatric surgery does not make changes to the lungs but can enhance breathing by reducing body weight.

- Option 3: Nasal passage - This area is unrelated to bariatric surgery; it focuses on different bodily functions.

- Option 4: Digestive system - Correct, as these surgeries modify stomach and intestinal structure to assist in weight loss.