The Virtual Habitat project (V-HAB) at the Technical University of Munich (TUM) aims to develop a simulation environment for spacecraft life support systems (LSS). The tool is implemented using the object orientated programming (OOP) approach to enable a highly modular structure. This allows engineers to combine different LSS technologies and elements in a straight-forward and exible way and perform dynamic simulations of open-or closed-loop as well as non-regenerative or regenerative LSS. In addition to providing a toolbox that can be used to create physical/chemical systems out of their basic components and biological modules to simulate plants and algae, the environmentally sensitive dynamic model of the human physiology is crucial part of the V-HAB simulation. The V-HAB human model was developed to provide the relevant metabolic inputs and outputs that respectively serve as outputs and inputs for the LSS, and to correlate these interactions to each other. To achieve that goal, it was necessary to enable the human model to react to environmental and operational influences. The V-HAB human not only tracks mass inputs and outputs, but also includes mechanical work and heat produced as a function of its load level and state. However, no prediction of pathological effects is included, as the calculations are based on high-level physiological relationships, not detailed medical issues. But if desired, some illnesses and the reaction to certain off-nominal conditions can be modeled; they just have to be triggered manually. The V-HAB human is broken into five distinct sub-models (layers) of metabolism, respiration, water, digestion, thermal that where developed in recent years. This paper focusses on how the individual layers have been integrated to one comprehensive model. This was done by linking the important interfaces between the layers to each other. Moreover, the model's reaction to exercise and hypoxic/hyperoxic conditions was verified mainly for the metabolic and respiratory layers using experimental data cited in the literature. Also, a description of the newly developed meta-model, which can be used to introduce additional physiological effects, is given.