Wireless Body Area Networks (WBAN) are an important component of medical monitoring systems. A WBAN includes sensing nodes (SNs) and an access point (AP). A SN is an embedded devices that is capable of sensing many vital physiological and biological data such as body temperature, blood pressure and electrocardiogram (ECG), etc. from human body and sending them to the AP using its wireless interface. In this study, a WBAN system that can transmit any physiological signals considering the QoS requirements, is introduced. The proposed system is modeled and simulated using OPNET Modeler software for performance evaluation and uses IEEE 802.15.4 medium access control protocol. The results show that physiological signals from the human body can successfully be transferred with required QoS support by using the WBAN system implemented.