The article considers the need of use different methods of developing critical thinking of medical students to study natural sciences: «Medical and Biological Physics» and «Biophysics with physical methods of analysis». The use of critical thinking by students is a key point in recognizing the superiority of the active thought process over the passive one, when a person only receives ideas or information from someone else. The essence of critical thinking is a detailed mental analysis before further action. This analysis is conducted in the introductory part of the lesson. A step-by-step lesson (introductory part, main and final part) using a workbook developed at the Department of Biological Physics and Medical Informatics of Bukovinian State Medical University is considered, which simplifies students' recollection of existing knowledge and acquisition of new ones. The topic covered in the lesson is «Thermal radiation of bodies. Thermography». This topic is extremely important for the future physician, because currently a medical examination of the body can be conducted not only through clinical laboratory tests, but also using contact cholesterol thermography. The introductory and main parts of the lesson involve working with block diagrams presented in this paper. The final part is the design of the results and the construction of a graph of dependence. It is the final part in the form of a table with the results and the graph of dependence gives the opportunity to really assess the knowledge acquired by medical students. Students receive professional medical education is possible only if the educational process is constantly improved, students are involved in constant independent work, and this is really possible only when a properly constructed lesson arouses interest in the topic of the lesson, the desire to learn and improve.