The goal of this single-centre observational study conducted at the Royal Hospital for Children in Glasgow, Scotland, is to employ a multi-omics approach to investigate the gut-lung axis in health and disease. Part A is a cross-sectional study design investigating the postulated bidirectional link between the gut and lung microbiomes in children suffering from respiratory or gastrointestinal conditions. Children with no GI or respiratory issues attending for orthopaedic care will be used as a benchmark for a healthy gut-lung axis. The main questions we aim to answer are: * What does a healthy gut-lung axis look like? * Do children with respiratory issues show an altered gut microbiome? * Do children with GI issues show an altered lung microbiome? Part B is a longitudinal study design, that aims to assess the effects of biologics on the gut-lung axis by comparing the gut and lung microbiomes in children with asthma at two time-points who are indicated to start biologics therapy (Asthma treatment) or will not receive biologics therapy (asthma control). Participants will provide: * airway samples (to investigate the lung microbiome) * blood samples (to assess inflammatory and metabolic factors which may mediate communication between the two sites) whilst under general anaesthetic for a treatment related to their standard of care * stool samples (to assess gut microbiome) * dietary information (food diary and/or food frequency questionnaire) to assess relationships between diet and the gut-lung axis.