主语：The increasing number of healthcare jobs
谓语：is attributable to ,directly 副词做状语
the ageing of the population and the expansion of treatments available for medical conditions.并列的两个短语成分做宾语,其中available for medical conditions做定语从句.
整句话的意思：健康护理工作数量增长的直接原因就是人口的老龄化和医疗环境治疗的扩大.