Critical illness and sex hormones: response and impact of the hypothalamic–pituitary–gonadal axis

Understanding the hypothalamic–pituitary–gonadal (HPG) axis is essential for grasping human responses under extreme physiological and pathological conditions. The HPG axis regulates reproductive and gonadal hormone activities and significantly impacts the body’s response to acute and chronic illnesses. This review explores the fundamental functions of the HPG axis, modifications under critical conditions, and impacts on disease progression and treatment outcomes. In addition, it examines interactions between sex hormones and biomolecules like cytokines and gastrointestinal microorganisms, highlighting their roles in immune response regulation. Clinically, this knowledge can enhance patient prognoses. The review aims to provide a comprehensive framework, based on existing research, for understanding and applying the functions of the HPG axis in managing critical diseases, thereby broadening clinical applications and guiding future research.