def exchanges_secretion(cobra_model, solution):
    """Get fluxes of reactions that export metabolites. Only considers
            exchanges

    Parameters
    ----------
    cobra_model : cobra.Model
    solution : cobra.Solution
        Solution of optimized model.

    Returns
    -------
    dictionary
        keys are bigg ids of import reactions, values are fluxes.
    """
    export_list = [rxn for rxn in cobra_model.exchanges if
                   not rxn.products and solution.fluxes[rxn.id] > 0 or
                   not rxn.reactants and solution.fluxes[rxn.id] < 0]
    exports = {}
    for exp in export_list:
        exports[exp.id] = solution.fluxes[exp.id]
    return exports