In-vivo sensing, diagnosis and treatment of diseases is having a great attention lately. With advanced computational systems, the processing of the biological data as well as the prediction of diagnosis is becoming more promising. However, the implementation of these systems inside the human body has a major challenge: Modeling the communication channel. To overcome this problem, researchers are investigating the main factors that define the characteristics of the communication channel between nano-devices. In this work, a study of the impact of nano-antenna directivity on the electromagnetic propagating wave in the communication channel inside the human body is conducted. Then, these results are compared to the other contributors in the path loss in-vivo that are discussed earlier in literature: Frequency and propagation distance. The simulation results show that the nano-antenna directivity seems to have minor contributions (5-7 dB) on the total path loss inside the human body compared to the communication distance (20-30 dB) and the operating frequency (10-15 dB).