Nowadays, the deployment of wireless sensors on patients becomes more and more popular. This promotes researchers and application developers to focus on issues related to Wireless Body Area Networks (WBANs). Applications associated to WBANs include healthcare, personal assistance, and entertainment where sensor nodes collect information and issue them to a central data server. To meet the new requirements of WBANs, the design of an efficient MAC protocol to handle the diversity of data traffic becomes necessary. In this paper, a Priority MAC (PMAC) protocol is introduced where priority is given to life critical traffics. A QoS architecture containing PMAC protocol is proposed and implemented. Simulation results show that our proposed architecture overcomes other architectures based on IEEE 802.15.4 and IEEE 802.15.6 in terms of energy consumption and Packet Delivery Ratio (PDR).