In this paper we propose an approach for the enhancement of software requirements specifications by combining human factors and requirements engineering concepts. The approach we propose uses cognitive engineering methods to increase understanding about how professionals perform complex work, taking into account the cognitive effort made by workers. We employed the suggested the approach in the context of a primary health care facility in Brazil to demonstrate that including human factors models improved the understanding of context, decision making and informal knowledge, enhancing software requirements specifications. Our results point out that a richer set of requirements was obtained, increasing the reliability of requirements specifications, enabling the design of better information technology to support work in the primary health care facility.