The nervous system is controlled by a collection of neurons that transmit electric signals through the organism. These signals respond to internal and external stimuli and regulate many involuntary physiological functions. The autonomic nervous system regulates involuntary behaviors, such as heart rate, breathing, or pupil size through the action of neuroendocrine substances that modulate the biological processes. These physiological processes allow to express the internal state while interacting with others. This manuscript presents an artificial neuroendocrine model for regulating and expressing the involuntary physiological functions emulated in the Mini social robot. This model employs the robot's perception and simulated biological clock to generate neuroendocrine responses using simulated neuroendocrine substances to control the robot's autonomic processes of heart rate, pupil size, breathing rate, blinking rate, and locomotor activity. The primary contribution of this work is to provide biological modeling to replicate the evolution and effects of neuroendocrine substances on the regulation of autonomic processes and demonstrate how to express them in social robots using their actuators to improve their responsiveness and naturalness. These experiments show that the robot's autonomic processes can maintain proper evolution during long periods, while exhibiting circadian rhythms and responding to unexpected environmental changes.