Inclusion Criteria:

• * 6-21 years of age
• * Obese and non-obese individuals
• * BMI ≥10th percentile for age (6-20 years of age)
• * BMI ≥18.5 (\>20 years of age)
• * Otherwise healthy; or otherwise healthy with diagnosis of GERD, NAFLD, chronic abdominal pain or obesity, according to report of medical history and/or review of the medical record
• * Receiving or not receiving pantoprazole or lansoprazole for routine medical care
• * MRI Hoop Test Clearance

Exclusion Criteria:

• * Unable or unwilling to give written permission/assent/consent
• * For PO Study Drug: Any anatomic abnormality of the GI tract as defined by history, PE, or radiographic findings, including Bariatric surgery, Nissen fundoplication or equivalent surgery.
• * For IV Study Drug: Any anatomic abnormality of the GI tract as defined by history, PE, or radiographic findings, except Bariatric surgery, Nissen fundoplication or equivalent surgery.
• * For subjects undergoing weight management, treatment in the last 7 days with proton pump inhibitors omeprazole, esomeprazole, dexlansoprazole, or grapefruit juice.
• * For subjects not undergoing weight management, treatment in the last 7 days with medications known to clinically significantly inhibit (e.g., omeprazole, esomeprazole, fluoxetine, fluvoxamine, ketoconazole, ticlopidine, felbamate, trazodone, valproic acid, topiramate) or induce (e.g., phenobarbital, carbamazepine, phenytoin) CYP2C19; and those known at therapeutic doses to significantly inhibit (e.g., erythromycin, clarithromycin, grapefruit juice, verapamil, diltiazem, cimetidine, ketoconazole) or induce (e.g., oxcarbazepine, carbamazepine, phenytoin, phenobarbital, St. John's Wort, rifampin, rifapentine) or CYP3A4 activity in the last 7 days.
• * Unable to have blood drawn for the screening lab tests
• * Unable or unwilling to fast overnight prior to the study session
• * Unable to have blood drawn for the screening lab tests
• * If taking lansoprazole or pantoprazole for clinical purposes, unable or unwilling to abstain from that PPI for 3 days prior to PK visit when the PPI is not the same as the study drug for that PK visit
• * Metal in the body or any foreign bodies that precludes MRI sequencing
• * Claustrophobia
• * Exceeds 500lbs or 227 kg in Body Weight
• * Demonstrated adverse reaction to previous pantoprazole or PPI exposure
• * Impaired hepatic activity as determined by routine liver function testing and defined as values ≥ 5 times the age-specific upper limit of normal (ULN) for AST, ALT, total bilirubin \>2.0mg/dl, alkaline phosphatase ≥ 5 times the age-specific ULN
• * Impaired renal function defined as creatinine ≥ 3 times the age-specific ULN
• * Females of child-bearing age who are pregnant or breast-feeding
• * Any known infection with hepatitis B, C, or human immunodeficiency virus (HIV)